
==== Front
Heliyon
Heliyon
Heliyon
2405-8440
Elsevier

S2405-8440(24)12030-0
10.1016/j.heliyon.2024.e35999
e35999
Research Article
Synthesis of a novel AlBeSiTiV light weight HEA coating on SS316 using atmospheric plasma spray process
Singh Aman a
Akhil U.V. a
Kishan S.N. a
Anoosa Sree R. a
Radhika N. n_radhika1@cb.amrita.edu
a⁎
Rajeshkumar L. bc
a Department of Mechanical Engineering, Amrita School of Engineering, Coimbatore, Amrita Vishwa Vidyapeetham, India
b Department of Mechnaical Engineering, KPR Institute of Engineering and Technology, Coimbatore, India
c Center for Research, Alliance University, Anekal - Chandapura Road, Bengaluru, 562106, Karnataka, India
⁎ Corresponding author. n_radhika1@cb.amrita.edu
13 8 2024
30 8 2024
13 8 2024
10 16 e359995 12 2023
7 8 2024
7 8 2024
© 2024 The Authors. Published by Elsevier Ltd.
2024

https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
High Entropy Alloys (HEAs) are currently a subject of significant research interest in the fields of materials science and engineering. They are rapidly evolving due to their exceptional properties, and there is considerable focus on expanding their application potential by developing HEA coatings on various substrate materials. This area of study holds promise for advancing technology and innovation in diverse industries. In this study, a novel equiatomic AlBeSiTiV Light Weight HEA was synthesized via mechanical alloying and was sprayed on the substrate SS316 by the thermal spray process. The microstructural characterization revealed that synthesized HEA had a major FCC phase and the average coating thickness was observed to be 150 μm. The average microhardness was measured to be 975 ± 13 HV for the coating which was five times than the substrate. The coated samples' wear resistance was found out using a pin-on-disc apparatus by varying the wear process parameters and Taguchi's L27 Orthogonal Array was used to interpret the parametric influence on wear rate. ANOVA and regression analysis revealed applied load to be the most significant factor followed by distance and velocity. The major wear mechanisms observed were adhesion abrasion and oxidation, and the formation of tribolayer was observed at higher velocity and distance.

Keywords

Light weight high entropy alloy
Mechanical alloying
Mechanical property
Metallurgical characterization
Thermal spray
Tribology
==== Body
pmc1 Introduction

The demand for materials exhibiting high hardness and exceptional wear resistance, especially in elevated-temperature and harsh service environments, has become critical amidst the rapid technological advancements in industries like aerospace, oil and gas, automotive, power generation, mining, construction, and manufacturing. This necessitates the development of advanced alloys and coatings capable of withstanding extreme conditions. For many years, major alloys have typically relied on one or two principal elements. Enhancements in their properties can be achieved in various ways, including the introduction of multiple alloying elements [1]. The formation of complex intermetallic compounds posed challenges in processing and analyzing and was one of the primary reasons for avoiding the use of more than two elements. To overcome these limitations, a new concept of materials termed HEA was proposed in 2004 by Yeh et al. [2]. HEA systems are composed of four or more principal elements, with each at 5–35 at.%, normally with nearly equal atomic percentages. When compared to traditional alloys, HEAs have much higher mixing entropy in liquid state or solid solution state which leads to sluggish diffusion of atoms. HEAs have garnered significant interest in recent years due to their exceptional mechanical, physical, and chemical properties. These materials are known to exhibit exceptional strength, ductility, and toughness at both ambient and elevated temperatures [3]. HEAs also have more drift to form crystal structures with FCC or BCC, which helps in suppressing the formation of some intermetallic compounds. Also, it is easy to form nano-size precipitates and offers excellent thermal stability, good fatigue [4,5], excellent corrosion resistance and fracture resistance [6].

The development of HEAs can be divided into medium-entropy alloys, high entropy fibers, high entropy films, and Light Weight High Entropy Alloys (LWHEAs) [7]. Due to the high demand for an application, LWHEA has become more popular in industrial areas such as aircraft, chemical plants, or in the field of energy due to its properties such as low density (<7 g/cm3), biocompatibility, excellent strength at high-temperatures, creep resistance, and extraordinary corrosion resistance. Although most HEAs form solid solutions, there are cases where a combination of five elements results in an amorphous phase. Nonetheless, such materials can still be classified as high entropy alloys [8]. Few deposition of thin films resulted in formation of FCC phase structure along with few metal oxides. These oxides helped in increasing the micro hardness. Also, resulting to have an excellent mechanical erosion properties and good adhesion strength [9]. Even amorphous crystal structure with few metal oxides can enhance the mechanical properties of the coating produced [10].

There are various routes to synthesize HEA such as gas atomization, vacuum arc melting, mechanical alloying (MA), etc. FeCoNiMnV HEA synthesized by MA was composed of a solid solution of FCC and BCC [11]. AlFeNiTiZn HEA was prepared by MA in which a solid solution of FCC and BCC with a powder crystallite size of 35 nm was obtained [12]. CrMnFeCoMo HEA subjected to MA processing resulted in the formation of a quinary HEA consisting of two BCC solid solutions having lattice parameters of approximately 3.146 ± 0.002 Å and 2.873 ± 0.002 Å, which are similar to the lattice parameters of Mo and Fe, respectively [13]. The various HEAs so formed exhibits improved properties which can be further extended to surface modification processes. Due to the attractive properties of LWHEA, its applications in surface modification have become more promising.

Due to its desirable mechanical characteristics, steel is widely utilized in various industrial sectors, making it a popular option. But when operated in harsh environments, they are prone to corrosion and wear [14]. A study was carried out to examine the wear performance of Stainless Steel 316 (SS316) under different operating conditions. The results revealed that the material undergoes substantial wear, and the maximum wear rate was observed at 16 N and 0.55 m/s [15]. This urges the need for surface modification of steel for applications demanding improved wear resistance [16]. Thus, coating LWHEA can be a better solution to reduce wear without altering its weight by a major fraction. There are various ways for fabricating HEA coating such as laser cladding, electro-spark deposition, magnetron sputtering, sol-gel method, plasma cladding, and thermal spraying.

Laser cladding of NbMoTaWTi HEA on Ti6Al4V (TC4) substrate resulted in an enhancement of the substrate's wear resistance. In comparison to the substrate's wear rate of 3.04 × 10−4 mm3/(N·m), the coating exhibited a significant reduction in wear rate by 121.9 % [17]. An investigation into Ni0.2Co0.6Fe0.2CrSi0.2AlTi0.2 HEA coatings produced through the atmospheric plasma spraying (APS) and high-velocity oxyfuel processes revealed that the APS HEA coating exhibited remarkable hardness (800 HV) and wear resistance [18]. Deposition time plays an important role to have a good elastic modulus and nano hardness. In a study, it was found that elastic modulus and nano hardness increase initially as deposition time increases and slightly decreased as the deposition time was increased [19]. In recent studies it has been found that APS-coated HEAs on substrate showed some good mechanical properties by forming mainly FCC microstructure with few oxides. These oxides are the main factor for improved microhardness [20,21]. FeCoNiCrMn HEA APS coated on SS304 resulted in an improvement of the surface microhardness. The substrate SS304 showed a considerably higher specific wear rate (SWR) in comparison to the coating, which exhibited a significantly lower SWR due to improved wear resistance. It has been recorded that in few case adhesion strength for APS coating was better than HVOF coating [22]. The APS coatings exhibited impressive characteristics such as remarkable adhesion strength, elevated hardness, and exceptional durability against wear [23]. However, extensive studies on the influence and optimization of wear parameters and their correlation with wear rate are still unexplored to date.

Several factors affect the performance of coatings and optimizing them enhances their properties optimally to suit applications [[24], [25], [26]]. Nitride films of (AlCrNbSiTiV)N were produced using direct current (dc) reactive magnetron sputtering. The deposition parameters were optimized using Taguchi analysis, which resulted in improved microhardness (1286 HV) and tribological properties (32.5 % reduction in friction coefficient) [27]. CrAlN coating deposition parameters were optimized to improve the hydrophobicity and wear resistance. The optimized parameters reduced the wear rate by 35.1 % and increased the water contact angle by 54.7 % [28]. The effect of process parameters on the erosion wear resistance of Ni–Al–Ti and Ni–Cr–Ti was analyzed and particle size was observed to be the most significant parameter [29]. Deposition parameters of Ni–Mo/Al composite coatings were optimized, which improved the microhardness by 8.8 % which resulted in enhancement of wear resistance [30].

SS316 is a steel that is widely used in the chemical industry, food processing, pharmaceutical equipment manufacturing, medical instrument fabrication, wastewater treatment, and marine applications. To overcome its wear and abrasion damage in industrial applications, it can be coated using LWHEA without altering its density by a large difference and LWHEA has a good potential to replace other traditional alloy coatings.

Based on the review, thermal spray-coated LWHEA over steel created the impetus to evaluate the property enhancement to suit demanding applications. The alloy system was carefully chosen for its specific benefits: Aluminium reduces density, increases strength, and improves oxidation resistance while promoting a BCC structure. Beryllium, with its low atomic weight and high melting point, enhances specific strength and stability at high temperatures, making it ideal for lightweight applications in automotive and defense industries. Silicon aids in oxidation resistance and stabilizes the BCC structure, while also improving solid solution strengthening and reducing stacking fault energy. Titanium provides high specific strength and ductility, ensuring excellent performance at elevated temperatures. Vanadium contributes to high-temperature performance, reduced density, increased strength, hardness, and wear resistance. Together, these elements create a high-performance alloy suitable for demanding applications. In this work, a novel equimolar LWHEA AlBeSiTiV is synthesized by MA and coated on the SS316 substrate. The microstructure of the synthesized HEA and produced coating is analyzed using Field Emission- Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), and X-Ray Diffraction (XRD). In addition, the mechanical and tribological properties of the coating were analyzed and the Taguchi method, as well as Analysis of Variance (ANOVA), was used to study the influence of wear parameters to optimize the tribological performance.

2 Materials and methods

2.1 HEA synthesis

The decisive consideration while choosing the elements constituting the HEA was to attain improved mechanical properties while having reduced weight, thus the elemental combination of AlBeSiTiV was chosen. The thermodynamic stability of the system can be assessed using the Gibbs free energy of the mixture (ΔGmix) (Equation (1))(1) ΔGmix=ΔHmix−TΔSmix

Configurational entropy (ΔSconf) plays a major factor in deciding whether an alloy is a HEA (Equation (2)).(2) ΔSconf=−R∑i=1nxMilnxMi

where n is the type number of the constituent atoms, xMi is the mole fraction of composition of atom and R = 8.314 J mol−1 K−1 is the gas constant. A maximum ΔSconf occurs in equimolar alloys so that ΔSconf = Rln(n). Generally, HEA satisfies the condition of ΔSconf ≥ 1.5. Also, ΔSconf for an equimolar alloy with n = 5 is 1.61R [31]. In our work 20 atomic wt.% for each element i.e. Al, Be, Si, Ti, and V were taken at it satisfies the condition of ΔSconf ≥ 1.5 to form HEA. Since all the elements present in the system has a density of less than 7g/cc this makes it a LWHEA.

The element Aluminium (Al) was chosen to reduce the density, increase the strength of HEA, decrease plasticity, improves oxidation resistance, and for tailoring the properties [32,33]. Al has a significant effect in producing BCC structure [34]. Due to a low atomic weight of 9 g mol−1 and a relatively high melting point (1287 °C), Beryllium (Be) was chosen. Structural Lightweight components are made in automotive and defense industries with Be alloys due to their better specific strength. They are also used in high-temperature applications [35]. Silicon (Si) has improved oxidation resistance and aid in stabilized BCC formation and can remain as a single-phase BCC structure. It enhances solid solution strengthening and aid in stacking fault energy reduction [36]. The addition of Titanium (Ti) improves mechanical properties as it inherits high specific strength and good ductility. Because of its exceptional structural characteristics, it is utilized to offer sufficient strength and guarantee optimal performance at elevated temperatures [37]. Similarly, the addition of Vanadium (V) leads to the formation of a σ-phase and secondary FCC phase. They are guaranteed to ensure high-temperature performances, reduced density, and improved strength. Also, they enhance the HEA's hardness and ability to withstand wear and tear [38,39]. The HEA was synthesized via MA using a High Energy Planetary Ball Mill with tungsten carbide (WC) balls and vials, the volume of the vials used was 250 ml. The ratio of WC balls and powder was chosen to be 10:1 and stearic acid was used as a process control agent to avoid the agglomeration of powder. The process was carried out at 250 rpm in an Ar atmosphere to avoid oxidation of the powder.

2.2 Coating preparation

AlBeSiTiV HEA coating was produced on the substrate SS316 via “Metco 3 MB Plasma Spray Gun” APS, utilizing 300g of the synthesized HEA. The Molybdenum content present in SS316 results in excellent corrosion resistance properties of the material. So, to increase mechanical and tribological properties, LWHEA coating has been produced on the substrate. The samples, based on the requirement were cut using Wire Electric Discharge Machine followed by sandblasting to increase the surface roughness. The substrate was sandblasted with “MEC Sand Blasting” utilizing alumina sand with process parameters such as air pressure 100–120 kg/cm2, blasting distance 100–300 mm, and blasting angle 60-700. The prepared substrate was then cleaned using compressed air to remove any debris present. Both the substrate and HEA powder were preheated before coating. During APS the temperature increases, and to avoid thermal degradation, the substrate is cooled using air jets. Table 1 shows the spraying parameters of APS.Table 1 Spraying parameters for APS Coating.

Table 1Parameter	Value	
Primary gas (Argon) flow rate, L/min	80	
Secondary gas (Hydrogen) flow rate, L/min	30	
Primary gas (Argon) pressure, psi	120	
Secondary gas (Hydrogen) pressure, psi	100	
Current input, Amperes	500	
Voltage input, Volts	70	
Power feed, grams/minute	40	
Spray distance, mm	110	

2.3 Characterization methods

Microstructural characterization of the synthesized HEA and HEA coating produced was analyzed using ZEISS Gemini SEM 300 Field emission SEM equipped with EDS having an accelerating voltage of 10 kV and XRD utilizing Ultima IV with X-ray energy as Cu-Kα of 1.54 Å wavelength. The scanning range and speed were 1° min−1 and 10°–90°. The HEA coating was further analyzed using Electron backscatter diffraction (EBSD) via FEI 3D Quanta FEG-SEM equipped with EDAX EBSD attachment with 0.5 μm step size before which the samples were electropolished with 20 % perchloric acid and 80 % methanol. The porosity content of the coating was evaluated using Image J software. The microhardness of the substrate and coating was measured using a Mitutoyo Vickers hardness testing machine in accordance with ASTM E384. This involves applying a load of 100 gf for 15 s to create an imprint on the surface using a diamond indenter with a pyramidal shape and square base. The test was conducted on five different locations on the surface and the average value of the hardness was recorded. A pin-on-disc apparatus (Model: TR-20LE-PHM-200) was used to perform the dry sliding wear test. A stationary pin in contact with a rotating disc (EN 32 steel disc) was subjected to an applied load using the device. To conduct the wear experiments, an L27 orthogonal array from Taguchi's Design of Experiments (DOE) was employed. The samples were put through three different loading conditions of 15, 25, and 35N with velocities of 1, 2, and 3 m/s and sliding distances of 500, 1000, and 1500m at room temperature. The weight loss was recorded using an electronic weighing balance, and the wear rate was calculated for three sets of trials. Minitab is a statistical software package used for data analysis, process improvement, and quality control that offers a range of tools for statistical analysis, graphical representation of data, and hypothesis testing was used to analyze the results obtained from the experiment. Finally, the worn surfaces and wear debris were subjected to SEM, Raman spectroscopy and wear profile observations to analyze the wear mechanism of AlBeSiTiV coating. The detailed methodology is depicted in Fig. 1.Fig. 1 Schematic illustration of methodology.

Fig. 1

3 Results and discussion

3.1 Microstructural analysis of powder

Fig. 2a-d represents the microstructures of AlBeSiTiV HEA powders ball milled for 5, 10, 15, and 20hrs respectively. Ball milling for 5 h resulted in the formation of agglomerated particles which were observed to be a lump (Fig. 2a). The continued ball milling for 10, 15 h made the particles to be distinct and homogeneous (Fig. 2b and c). The average particle size of 20h ball-milled AlBeSiTiV HEA powders was found to be 15 μm (Fig. 2d and e). Prolonged ball milling reduced the size of the particle. After ball milling, all the powder particles showed relatively homogeneous sizes and shapes. MA involved a series of impact-induced deformations of the powder particles, including flattening, cold welding, rewelding, and fracture. The initial powder components quickly diffused, and the size of the particles was subsequently refined. Ultimately, a fine-grained powder that was relatively thermodynamically stable was produced. The EDS analysis of mechanically ball-milled AlBeSiTiV HEA powder was carried out. All the primary elements were observed in the EDS results which confirmed the presence of all HEA elements (Fig. 2f). The synthesized AlBeSiTiV HEA powder exhibits a uniform distribution of elements as observed in Fig. 3.Fig. 2 SEM images of ball milled powder at (a)5hrs (b)10 h and (c)15hrs, (d) 20hrs, (e) magnified image of powder morphology of 20hrs ball milled AlBeSiTiV HEA powder and (f)EDS spectra of AlBeSiTiV HEA powder after 20hrs ball milling.

Fig. 2

Fig. 3 EDS mapping of 20 h ball milled AlBeSiTiV HEA powder representing HEA elements with corresponding XRD.

Fig. 3

The XRD analysis depicted in Fig. 4 showed that the combination of elemental powders, which were ball milled for 5 h, resulted in the formation of a mixture of FCC and BCC structures. The h k l indices (101), (110), (220), (200), (112) indicated that the compound consisted of mostly BCC and a minor amount of FCC (Fig. 4a). When the ball milling was continued for 10 h, the major structure formed was FCC, with a smaller amount of BCC (Fig. 4b) having h k l indices (111), (200), (101), (220), (311). After 15 h of ball milling, a combination of FCC and BCC structures with h k l indices (111), (200), (101), (220) were observed (Fig. 4c). Further ball milling resulted in the formation of a HEA with major lattice parameters (111), (200), (101), (220) with the BCC phase exhibiting a lower intensity (Fig. 4d). The LWHEA obtained had a major FCC and minor BCC structure [40]. Based on the Gibbs free energy formula which states that ΔGmix = ΔHmix - TΔSmix, an increase in the mixing entropy results in a decrease in the free energy available within the system, favoring the formation of a single solid solution.Fig. 4 XRD pattern of powder after (a)5hrs (b)10 h and (c)15hrs and (d) 20hrs ball milling.

Fig. 4

3.2 Analysis of coating microstructure

Fig. 5a depicts the surface morphology of the AlBeSiTiV HEA coating, it was found to be homogeneous with few splats and pores, and it can also be noted that no interlamellar gaps and vertical cracks were found. Fig. 5b shows the EDS spectra of the coating which reveals the elemental constituents of synthesized LWHEA along with oxygen which constitutes oxide formation in the APS process. Fig. 5c shows the cross-sectional microstructure of the AlBeSiTiV coating on the SS316 substrate, it indicates that the substrate is well coated with an approximate thickness of 150 μm. The porosity content of the produced LWHEA coating was observed to be 5.80 % (Fig. 5d) which was comparatively lower than APS coated AlCoCrFeNi and MnCoCrFeNi HEA coatings [41]. Analysis of the XRD spectra of AlBeSiTiV HEA coating (Fig. 5e) revealed that the coating was composed of major FCC and minor BCC with some oxides produced due to APS. The observed hkl indices were (200), (220), and (311) respectively which confirms that the coating has a major FCC, few oxides were produced due to the high temperature of the flame. The oxide peaks correspond to Al2O3 and TiO2 due to the reaction between HEA and oxygen at elevated temperatures. This imparts improved hardness and load-bearing capacity to the alloy resulting in the wear resistance of the alloy coating [[42], [43], [44]].Fig. 5 SEM image of (a) AlBeSiTiV coated surface (b) EDS spectra of coating (c) cross-sectional view of substrate and coating (d) porosity analysis image and (e) XRD pattern of the coated surface.

Fig. 5

Fig. 6 depicts the elemental mapping analysis of the AlBeSiTiV HEA coating. In spite of the contribution of major elements including Al, Be, Si, V, and Ti, a small amount of O is present due to the formation of some oxides during the spraying process and shows a more homogeneous distribution of elements. The oxide content was found to be 7 % which can significantly improve the coating's hardness [45]. The elemental line mapping is depicted in Fig. 7, the substrate revealed the presence of all the alloying elements present in SS316 (Fig. 7a). The cross-sectional mapping reveals the transition from the substrate elements to HEA elements traversing from the substrate to the coating, revealing the HEA elemental presence over the coated region (Fig. 7b). The smooth transition ensures improved metallurgical bonding between the substrate and coating, Fig. 7c reveals the HEA elemental presence across the coating along with the presence of oxides (element O is present).Fig. 6 EDS mapping of the coated surface with XRD.

Fig. 6

Fig. 7 EDS Line mapping of the (a)substrate, (b)Substrate, and coating, (c) Coating.

Fig. 7

EBSD was employed for further microstructure analysis of the coating. Fig. 8a shows the microstructure of the AlBeSiTiV coating, the average grain size was observed to be 14.57 μm (Fig. 8d). Fig. 8b shows the IPF of AlBeSiTiV HEA coating, it was observed to be in FCC phase with an equiaxed grain structure with minor BCC. The inclusion of the Ti element altered the coating layer's grain development pattern, resulting in the formation of equiaxial crystals. This is mostly due to the Ti element's greater atomic radius (0.147 nm) compared to the other alloying elements (Al 0.143 nm, Si 0.132 nm, Be 0.112 nm, and V 0.134 nm), which increases the level of lattice distortion, hinders normal atom diffusion, and restricts the pattern of grain growth. Grain coarsening is prevented by the lattice distortion energy, which is greater than the grain boundary energy [46]. Fig. 8c depicts the phase map of the LWHEA coating revealing the FCC phase to be dominant with minor BCC phase. The misorientation angle distribution for the LWHEA coating could be observed in Fig. 8e. The low-angle grain boundary (1⁰<LAGB> 15⁰) is marked by red color and high angle grain boundary (HAGB>15⁰) is marked by blue color. The result depicts that the AlBeSiTiV LWHEA coating contained a high proportion of HAGB. The increased content of HAGB resulted in micro-level grain refinement promoting equiaxed grains formation.Fig. 8 EBSD results of AlBeSiTiV LWHEA coating: (a,b) inverse pole figure (IPF) map of the coated surface, (c) phase image of coating (d) graphical representation of grain size distribution along with coating microstructure and (e)LAGBs and HAGBs superimposed with histogram for LAGBs and HAGBs.

Fig. 8

The average direction difference between adjacent points is represented by kernel average misorientation (KAM). KAM diagrams, often referred to as local orientation difference diagrams, can be used to indicate the extent of material granular plastic deformation [47,48]. The green color line in KAM mapping (Fig. 9a) of the AlBeSiTiV coating can be interpreted as the dislocation. Due to the Ti element's high atomic radius, there would be significant lattice distortion and some degree of plastic deformation. Grain development in the coated layer was constrained by severe lattice distortion brought on by the Ti element and the quick condensation of the APS coating. As a result, the microstructure would have a lot of dislocations, and the dislocation has a high mobility ratio in the FCC phase, which is easily deformable [46]. As a result, the FCC phase's geometrically required dislocation density in the AlBeSiTiV coating is higher which provides greater resistance for plastic deformation to occur. The Schmid factor diagram for the AlBeSiTiV coating is shown in Fig. 9b. Based on the study by Gussev et al. [49], the Schmid factor for soft grains was larger than 0.4 and less than 0.35 for hard grains. The AlBeSiTiV coating was revealed to have a minor fraction of soft grains as the fraction of hard grains in the produced LWHEA coating was 3.14 times that of AlCoCrFeNi(TiN)x and 1.83 times that of FeCoCrNiMn HEA coatings [46,50]. Slip is principally responsible for the material's plastic deformation, because of the increased concentration of hard grains, the AlBeSiTiV coating layer is less susceptible to plastic deformation [50]. The coating's polar density distribution is depicted in Fig. 9c and d by pole figures (PFs) and IPFs, respectively. HEA coatings feature orientation characteristics in the [0 0 1] direction as shown in the PFs (Fig. 9c). The average pole density was found to be 10.858, which suggests the coating to be highly textured. The strength of the texture is reflected in the IPF's various colors, as seen in Fig. 9d. The LWHEA coating's texture strength was found to be 10.375.Fig. 9 (a)KAM mapping, (b)Schmid factor diagram, (c,d) pole figure and inverse pole figures of AlBeSiTiV coating.

Fig. 9

3.3 Microhardness evaluation

Fig. 10 illustrates the microhardness measured from the interface of the AlBeSiTiV HEA coating/substrate. The mean microhardness of the substrate 316 SS was 172.8 ± 10 HV in the range of (−50 μm to −150 μm). The average thickness recorded for the coating was 150 μm and the mean microhardness was observed to be 975 ± 13 HV. Fig. 10 indicates that the microhardness of the AlBeSiTiV HEA coating was five times that of the substrate. The Microhardness of the coating was enhanced due to various contributing factors, including the specific structure, high mixing entropy, coating composition, oxide stringers, grain boundary density, residual stress, and the overall hard BCC phase percentage. The BCC solid solution phases enhanced by Al and Ti in the coating have a substantial solid solution-strengthening effect. The addition of Al to the BCC solid solution phase is known to have a strong stabilizing effect, leading to lattice constant reduction and a shorter distance between adjacent crystalline planes. This makes it harder for intercrystalline dislocations to slip, increases slip resistance and lattice distortion, encourages the stronger strengthening behavior of the solid solution, and ultimately enhances the hardness [51]. The fabricated AlBeSiTiV HEA coating had improved microhardness compared to that of AlCrFeCoNi and nano ceria doped AlCrFeCoNi coatings by 1.96 and 1.82 times respectively [52].Fig. 10 Cross-sectional microhardness of the substrate and coating.

Fig. 10

3.4 Wear analysis of coating

The Taguchi method is generally used for product design and to improve quality, it integrates the quality loss function and experimental design theory to attain a robust optimization of design. When implementing the Taguchi design approach, the utilization of an orthogonal array aids in reducing the total number of experimental runs required. Furthermore, a statistical analysis of the signal-to-noise (S/N) ratio is conducted in conjunction with ANOVA [53]. Since the coating exhibited higher hardness compared to the substrate, the AlBeSiTiV coating was subjected to a wear test and the process parameters that resulted in minimal wear were identified by employing a "smaller-the-better" approach. The results of the wear test are presented in Table 2. Using Taguchi's DOE technique, the process parameters were prioritized based on their influence on the signal-to-noise (S/N) ratio. The ranking of the process parameters was determined by computing the delta value for each parameter, which represents the difference between the peak values, and then arranging them in descending order. The S/N ratio response chart for the HEA is presented in Table 3, with the last row indicating the ranking of the process parameters according to their impact on the S/N ratio.Table 2 Experimental wear results.

Table 2Load (N)	Velocity (m/s)	Distance (m)	Specific wear rate (mm3/Nm)	Standard deviation	S/N ratio (d/B)	
15	1	500	0.00026	7.9E-06	48.01697	
15	2	500	8.47E-05	2.5E-06	57.92529	
15	3	500	7.6E-06	2.3E-07	78.85353	
15	1	1000	0.000383	1.1E-05	44.81934	
15	2	1000	0.000646	1.9E-05	40.27801	
15	3	1000	5.96E-05	1.8E-06	60.97714	
15	1	1500	3.68E-05	1.1E-06	65.16374	
15	2	1500	6.66E-05	2E-06	60.00608	
15	3	1500	0.000041	1.2E-06	64.22956	
25	1	500	0.007631	0.00023	14.38943	
25	2	500	0.007976	0.00024	14.00506	
25	3	500	0.004394	0.00013	19.18368	
25	1	1000	0.004947	0.00015	18.15401	
25	2	1000	0.005224	0.00016	17.68074	
25	3	1000	0.004023	0.00012	19.94916	
25	1	1500	0.004011	0.00012	19.97511	
25	2	1500	0.004201	0.00013	19.57373	
25	3	1500	0.004019	0.00012	19.95988	
35	1	500	0.006576	0.0002	12.75896	
35	2	500	0.006862	0.00021	12.39012	
35	3	500	0.005782	0.00017	13.87727	
35	1	1000	0.00779	0.00023	11.28763	
35	2	1000	0.008592	0.00026	10.43685	
35	3	1000	0.00802	0.00024	11.03464	
35	1	1500	0.00553	0.00017	14.26339	
35	2	1500	0.005898	0.00018	13.70507	
35	3	1500	0.006833	0.0002	12.42676	

Table 3 Response table for S/N ratios.

Table 3Level	Load (N)	Velocity (m/s)	Distance (m)	
1	57.81	27.65	30.16	
2	18.1	27.33	26.07	
3	12.46	33.39	32.14	
Delta	45.34	6.05	6.08	
Rank	1	3	2	

Influence of Processing Parameters on Wear Rate:

Fig. 11a, the mean plot, depicts the wear behavior pattern of the HEA coating observed for each level of chosen wear parameters. On the other hand, Fig. 11b, the S/N ratio plot, illustrates the optimal level of each wear parameter for the HEA coating. This indicates the parametric level that resulted in improved wear resistance. Based on the analysis of the S/N plot, it was determined that the optimal parametric conditions for the HEA coating were L = 15 N, V = 3 m/s, and D = 1500 m, which led to improved wear resistance.Fig. 11 (a) Main effect plot of means, (b) main effects plot of S/N ratio.

Fig. 11

3.4.1 Influence of load on the wear rate

The wear behavior of the AlBeSiTiV HEA coating was analyzed in Fig. 11a, it was observed that the increase in the load applied led to a corresponding increase in the wear rate, while the sliding velocity and distance remained constant. The specific wear rate (SWR) increased from 2.6 × 10−4 N/mm3 at 15N to 6.8 × 10−3N/mm3 at 35N indicating that the higher applied load resulted in increased wear. However, there was a minimal wear rate at a load of 15 N due to reduced contact stresses on the sliding pin. Previous studies have shown that the presence of a hard BCC phase formed due to Al enhances wear resistance by increasing material hardness. The synthesized AlBeSiTiV HEA coating exhibits improved adhesive wear resistance at lower loads. The produced HEA coating provides improved resistance to adhesive wear when compared to AlxCo1.5CrFeNi1.5Tiy, Mo20Ta20W20Nb20V20, and FeCoCrNiMnAlx HEAs [[54], [55], [56]]. However, when the applied load increased from 15 N to 35 N, an increase in contact stress was observed, resulting in plastic deformation and delamination of the pin material upon encountering the sliding disc. Thermal softening caused by an increase in temperature at the pin-sliding disc interface also contributes to accelerated wear of the material. At higher loads, the relatively soft FCC phase of Ti leads to an increased wear rate, these observations are consistent with Archard's law as an increment in the applied load results in a corresponding increment in the wear rate [57]. Similar results were observed for CrVTiNbZr(N) HEA nitride coatings [58].

3.4.2 Influence of velocity on the wear rate

While maintaining a constant applied load and sliding distance, the effect of sliding velocity on wear rate was analyzed (Fig. 11a). The inclusion of Ti, Al, and Si results in the formation of the FCC + BCC phase due to the high entropy effect. This enhances the hardness of the coating, and the weight loss/wear rate was observed to be minimal at low-velocity conditions (1 m/s). As the sliding velocity increases from 1 m/s to 2 m/s, a slight increase in wear rate is observed. The HEA coating experiences minor plastic deformation at 2 m/s because of its extended contact with the counterface. This causes the material to start flaking and cracking, which results in a meager amount of the coating being removed. The wear mechanism is greatly influenced by the origin of cracks and their parallel surface propagation at this parametric condition. Under the surface of the plastically deformed material, the fractures begin, ultimately expanding and connecting to reach the free surface. The accumulation of these fissures results in the material's wear degradation and the final loss of substantial amounts of the coating; thus, an increased wear rate is observed [59]. As the sliding velocity further increases to 3 m/s, the wear rate decreases due to mechanically mixed layer (MML) formation on the surface of the pin. This layer is produced by the mixing of wear debris that is generated. The MML functions as a lubricant, lowering friction and therefore reducing the amount of material that is removed from the alloy coating. The decline in the rate of material removal is largely due to the high sliding velocity, which generates substantial pressure and temperature on the pin-disc interface that results in MML formation. The SWR decreased from 7.6 × 10−3 N/mm3 at 1 m/s to 4 × 10−3N/mm3 at 3 m/s indicating reduced wear rates at elevated velocity due to MML formation. Howev A similar formation of MML was found in CoCrWAlNixAly HEA coating due to the elemental presence of Al. The developed MML had a synergetic relationship with the interface temperature as it was observed that the formation of MML is due to oxide formation at higher temperatures [60].

3.4.3 Influence of distance on wear

The effect of distance on the wear rate was evaluated under constant conditions of applied load and velocity as shown in Fig. 11a. At lower distances, the applied force is only distributed at certain areas of the surfaces. This is due to the transit of individual micro protrusions, resulting in the formation of the true contact area due to the flattening of the micro protrusions. The presence of structural porosity, cracks, oxide stringers, and flaws may be responsible for the reduction in the sliding wear resistance of the HEA coating at smaller sliding distances (500m), similar findings were reported for the AlCrFeCoNi HEA coating [52]. An increase in wear was observed with an increase in the sliding distance. However, this trend was observed only until a sliding distance of 1000 m. A reduction in the contact pressure occurs at both micro and macro-scales with an increase in the sliding distance. This adjustment to the real contact area reduces the wear rate and leads to the formation of wider tracks. Archard's theory states that there is a direct relationship between the sliding distance and the wear rate/volume loss, indicating that the wear rate/volume loss increases with an increase in the sliding distance [61]. As the sliding distance increases, the wear zone undergoes expansion, leading to severe deformation and a corresponding increase in temperature. The gradual increase in temperature causes the material to soften, resulting in surface deformation. Further increase in the sliding distance to 1500m cause a decrease in the wear rate due to the increased contact time between the coated sample and the disc, leading to the formation of MML, which acts as an inhibitor for further deformation. The surface becomes softer and begins to delaminate due to the temperature rise caused by thermal build-up. The SWR decreased from 7.6 × 10−3 N/mm3 at 500m to 4 × 10−3N/mm3 at 1500m indicating reduced wear rates at elevated distances due to MML formation Observations of the worn surface of the coating showed the formation of an MML, which occurred due to the spreading of delaminated pieces on the surface under an external load due to the high ductility of the FCC phase, similar results were observed in CrFeNiNbTi HEA cladding subjected to wear [62].

3.5 Analysis of variance

ANOVA is a statistical method that was used to examine the variation between and within groups to determine if there is a meaningful difference in the averages. If the variation between groups is significant, then it can be concluded that the means of the groups are different and that the independent variable has a significant effect on the dependent variable. This method was used to conduct a statistical study, which revealed that the applied load has the most significant impact on the wear rate of the AlBeSiTiV HEA coating. Table 4 summarizes the ANOVA results, indicating that the load applied accounts for 91.57 % of the major influence, followed by the load*distance parameter at 3.88 %, and other factors listed below. The level of influence may vary depending on the material's composition and structure.Table 4 ANOVA results for coating.

Table 4Source	DF	Adj SS	Adj MS	F	P	P%	
Load	2	0.255236	0.127618	675.5	0	91.57	
Velocity	2	0.001418	0.000709	3.75	0.071	0.51	
Distance	2	0.004926	0.002463	13.04	0.003	1.76	
Load*Velocity	4	0.001991	0.000498	2.63	0.114	0.71	
Load*Distance	4	0.010829	0.002707	14.33	0.001	3.88	
Velocity*Distance	4	0.002806	0.000701	3.71	0.054	1.00	
Residual Error	8	0.001511	0.000189			0.54	
Total	26					100	

3.6 Regression analysis

This statistical approach correlates the wear rate-affecting variables, such as load (L), distance (D), and velocity (V), to calculate the wear rate mathematically. The wear rate equation for the HEA is given by:

Wear rate (mm3/m) = −0.0836 + 0.01183 L - 0.0384 V - 0.000066 D + 0.000287 L*V - 0.000001 L*D + 0.000026 V*D.

From this equation, it can be deduced that the applied load affects the wear rate the most. The validation of the regression equation involves confirmation experiments. The confirmation experiments were carried out using randomly selected parametric combinations, which fall within the parametric range for HEA, the findings of the confirmation experiments and a comparison of experimental values with computed values derived from the regression equation model are shown in Table 5.Table 5 Experimental and predicted wear rate of confirmation experiments.

Table 5Exp.no.	Load (N)	Velocity (m/s)	Distance (m)	Exp. wear rate (mm3/m)	Reg. wear rate (mm3/m)	%Error	
1	19	1.1	512	0.074269043	0.0760515	2.40	
2	27	2.1	903	0.133094297	0.1367677	2.76	
3	33	2.8	1365	0.184276377	0.1900258	3.12	

Confirmation experiments conducted on the HEA coating indicate that the wear rate predicted by the regression model differs from the experimental wear rate by a small error percentage, ranging from 2.4 to 3.12 %. This suggests that the mathematical model is appropriate for predicting the dry sliding behavior of the HEA coating since the regression wear rate model and the experimental wear rate are almost the same with minimal error.

The effectiveness of the model created in the study was evaluated using the coefficient of determination (R2) [63]. Ranging from 0 to 1, this value indicates the degree to which the dependent and independent variables fit together. The obtained R2 value of 93.45 % in this study indicates that the model can account for approximately 93.45 % of the total variation, leaving only 7 % unexplained. Furthermore, the model's significance was confirmed by the adjusted R2 value of 91.53 %. The wear rate residual plots are presented in Fig. 12. The linear normal probability plot indicates that the residual errors of the model are normally distributed, and the model's coefficients are significant. The normal probability values were found to be closest to the average line. The versus fits plot showed that the values were closer to the average line. The histogram produced a bell-type distribution. No discernible pattern was observed when evaluating the independence of the data by plotting a graph of the residuals against the run order for a particular wear rate. This is because all the residual values were found to be on or between the levels [64].Fig. 12 Residual plots of wear rate.

Fig. 12

3.7 Worn surface analysis

The worn surfaces of the specimens subjected to wear tests were analyzed to understand the wear mechanisms and to obtain a clear representation of wear morphologies. Furthermore, the corresponding wear debris was collected and subjected to microstructural characterization.

Fig. 13 depicts the SEM images of the worn surface at 15N and 35N, keeping velocity 2 m/s and distance 1000 m constant. It was observed that when a low load of 15N was applied, the worn surface displayed shallow grooves and small pits, as depicted in Fig. 13a, indicating the occurrence of wear mechanisms involving both adhesion and abrasion. The reason behind this can be explained by the relatively small levels of contact stresses generated by the load applied, as well as the obstructive properties of components like Al and Ti. At a high load(35N), flaking was observed at the surface of the material with some cracks which reveal the transformation to greater wear (Fig. 13b). The magnified view in Fig. 13c provides evidence of delamination occurring at a higher load. The main reason for the delamination is the robust interaction between the surface and the applied high pressure, which leads to plastic deformation and an increase in the removal rate. Fig. 14a displays the wear debris collected under high load conditions (35 N), while Fig. 14b illustrates the EDS analysis of the collected debris. The latter reveals the presence of HEA elements, along with Fe, C, and Cr, which can be attributed to the generation of substantial contact stresses from the pin on the disc configuration. These forces caused the material to peel off from the sliding disc, leading to the observed wear debris. The wear surface analysis indicates that the dominant wear mechanisms operating in the APS coating at 15N and 35N were adhesive wear, with abrasive wear. At lower load when pin comes to contact with the rotating disc, the surface asperities of the pin and disc undergoes a minor wear and gets stick with coating surface due to the applied load. But at higher load these adhered asperities get peeled off from the coating surface due to higher pressure resulting in coating degeneration. The formation of deep groves due the generated wear debris as well as flaking/delamination of the surfaces can be observed (Fig. 14c and d) [65,66]. A decrease in the interlamellar bonding ratio between splats within APS coatings can lead to the development of adhesive wear. According to a study, the bonding ratio between flattened splats in thermal sprayed coatings was reported to be lower than one-third [67]. The wear profile of the coating, as depicted in Fig. 13d, shows shallow grooves with a depth of 11.4 μm. However, with an increase in load and excessive abrasion, the groove depth increased to 21.2 μm.Fig. 13 Worn surface micrographs of coated samples at (a)15N, (b)35N, (c) Magnified image at maximum load, (d) wear profile of coating subjected to 15N and 35N respectively.

Fig. 13

Fig. 14 (a) SEM image of wear debris, (b) corresponding EDS at 35 N, (c, d) schematic representation of wear mechanism.

Fig. 14

The SEM images depicted in Fig. 15a–c exhibit the worn surfaces of the sliding pin specifically at 1 m/s, 2 m/s, and 3 m/s respectively. At the initial velocity of 1 m/s, flake formation was observed which is shown in Fig. 15a. At the velocity of 2 m/s spallation was observed with few micro-cracks along with flake formation (Fig. 15b). The elemental presence of Ti contributes to solution strengthening, thereby amplifying the likelihood of brittle fracture. Similarly, the worn surface of the CoCr2.5FeNi2Ti1.5 coating also displayed substantial cracking and flaking resulting from brittle fracture due to external loading [53]. An increase in velocity to 3 m/s formed an oxygen-rich layer or MML, leading to the detection of minor delamination in the presence of metallic oxides. This process caused a decrease in friction at the interface and an increase in wear resistance, as evidenced by Fig. 15c. The oxide-rich wear debris was observed at 3 m/s velocity (Fig. 16a), and the EDS analysis (Fig. 16b) revealed the presence of O, which promotes the formation of metallic oxides with elements like Al, Ti, and V. The surface of the coated samples experiences a high density of dislocation, causing micro-cracks to accumulate. These micro-cracks then extend into cracks and fractures, leading to delamination. Additionally, with the gradual increase in sliding velocity, heat generation at the pin-counter face increases, facilitating the formation of an oxide-rich tribo-layer on the contact surface [68]. This tribo-layer effectively reduces the rate of material loss. EDS analysis confirms that the presence of Fe and O along with HEA elemental composition, enhances the formation of metallic oxides to enhance the formation of MML. This hard layer insulates the contact surface between the disc and the sample which reduces the wear rate.Fig. 15 Worn surface micrographs of coated samples at (a)1 m/s, (b)2 m/s, (c) 3 m/s.

Fig. 15

Fig. 16 (a) SEM image of wear debris and (b) corresponding EDS at 3 m/s.

Fig. 16

The morphology of the worn surface of the samples at sliding distances of 500 m, 1000 m, and 1500 m is shown in Fig. 17. At 500 m sliding distance; flakes formation and minor delamination were observed (Fig. 17a). With an increase in sliding distance, a few micro-cracks formed along with spallation (Fig. 17b). But at a higher sliding distance of 1500m, MML formation was observed, due to the formation of the oxygen-rich layer as observed in Fig. 17c. Fig. 17 (d) illustrates the Raman spectra of oxides and the oxide film found within the wear scar. Based on Raman spectroscopy analysis, elements in the AlBeSiTiV system undergo oxidation reactions with oxygen, forming their respective oxides. The primary oxides formed are Al2O3, SiO2, TiO2 and Fe3O4. Notably, the presence of Al2O3 and SiO2 contributes to enhancing the surface hardness and tribological characteristics of the material [69]. The presence of Fe₃O₄ is attributed to the material from the pin-on-disc test, which adhered to the coated surface during the wear test. This contributes to improved wear resistance, reducing the wear rate and enhancing the durability of the coated surface [70]. During friction, Ti undergo tribochemical reactions, resulting in the formation of a protective tribofilm on the contact surfaces. This tribofilm helps minimize wear by preventing direct metal-to-metal contact [71,72]. The oxide layer formed during the wear test is notably thicker, facilitating the detection of oxide signals in the Raman spectrum. The wear debris analysis also revealed the presence of oxide rich regions (Fig. 18a), which is confirmed through the presence of Fe, O, Cr and HEA elements from EDS analysis (Fig. 18b). Few cracks and pores on the coating surface promotes the diffusion of oxygen which enhances the formation of tribolayer (Fig. 18c), similar results were observed for AlCoCrFeNiTi HEA coating [73]. Tribolayer formation at 1500m sliding distance significantly reduced the wear rate, since the sliding distance is the most significant factor after load, the wear debris was subjected to elemental mapping, Fig. 19 shows the elemental mapping for wear debris at 1500 m which confirms the presence of elements O, Fe, and C with HEA elements forming oxide debris.Fig. 17 Worn surface micrographs of coated samples at (a)500m, (b)1000m, (c) 1500m, (d) Raman spectra of oxide layer developed.

Fig. 17

Fig. 18 (a) SEM image of wear debris, (b) corresponding EDS at 1500m, (c) schematic representation of MML formation.

Fig. 18

Fig. 19 Elemental mapping of wear debris at 1500m.

Fig. 19

The high-entropy effect offers several benefits that enhance the wear resistance of HEAs. These benefits include solid solution strengthening, microstructural stability, high hardness, and notable wear resistance. Solid solution strengthening from the high-entropy effect increases the hardness and yield stress of the alloy, making HEAs more resistant to wear and erosion [74,75]. Additionally, the high-entropy effect contributes to microstructural stability, which prevents rapid degradation during wear and is essential for maintaining the wear resistance of HEAs [74,75].

4 Conclusion

AlBeSiTiV LWHEA was synthesized via MA and coated on SS316 by APS. The synthesized HEA as well as fabricated HEA coating was subjected to metallurgical characterization. The HEA-coated SS316 was evaluated for its mechanical and tribological performance and the corresponding wear mechanism was analyzed.• AlBeSiTiV LWHEA was synthesized after ball-milling the feedstock powders for 20 h. Based on the microstructural characterization, it was determined that the shape of the HEA powder was irregular, and the average particle size was measured to be 15 μm. The XRD results suggested that the HEA synthesized consisted mainly of the FCC phase with a minor occurrence of the BCC phase.

• The microstructural analysis of APS-coated HEA revealed that the surface was homogeneous with few pores and had a thickness of 150 μm. The EDS analysis and elemental mapping revealed the surface to have few oxides due to the high temperature of the plasma flame.

• The XRD analysis revealed the coating had a major FCC phase with a BCC phase. EBSD analysis was conducted to identify the grain size, orientation, and corresponding KAM and Schmid factor values was analyzed. The coating was subjected to a microhardness test and the average microhardness was observed to be 975HV.

• The tribological analysis revealed that the fundamental mechanisms responsible for wear were adhesion, abrasion, and oxidation. Taguchi's analysis and ANOVA revealed that load is the most significant factor followed by distance and velocity in influencing wear rate. The regression equation was validated by confirmation experiments which revealed that the results vary by a minor fraction.

• Upon subjecting the worn surface and wear debris to SEM and EDS analysis the occurrence of MML was observed at greater distances and velocities, leading to a decrease in the rate of wear. The synthesized LWHEA has wide applications including the field of aircraft, railways, defense, energy sector, etc. where improved wear resistance is required.

Compliance with ethical standards

Disclosure of potential conflicts of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Research involving human participants and/or animals

This article does not contain any studies with human participants or animals performed by any of the authors.

Ethical statement

Authors state that the research was conducted according to ethical standards.

Data availability statement

Data included in the article.

CRediT authorship contribution statement

Aman Singh: Writing – original draft, Visualization, Validation, Investigation, Formal analysis, Data curation, Conceptualization. U.V. Akhil: Writing – original draft, Visualization, Project administration, Methodology, Investigation, Conceptualization. S.N. Kishan: Writing – original draft, Investigation, Formal analysis, Data curation, Conceptualization. R. Anoosa Sree: Writing – original draft, Investigation, Formal analysis, Data curation, Conceptualization. N. Radhika: Writing – review & editing, Supervision, Methodology, Conceptualization. L. Rajeshkumar: Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.L. Rajeshkumar is the Associate Section Editor in Materials Science section. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
==== Refs
References

1 ASM ASM handbook Volume 2 - properties and selection: nonferrous alloys and special-purpose materials ASM Metals Handbook 2 1993 1300
2 Yeh J.W. Chen S.K. Lin S.J. Gan J.Y. Chin T.S. Shun T.T. Tsau C.H. Chang S.Y. Nanostructured high-entropy alloys with multiple principal elements: novel alloy design concepts and outcomes Adv. Eng. Mater. 6 2004 299 303 10.1002/ADEM.200300567
3 Zhou Y.J. Zhang Y. Kim T.N. Chen G.L. Microstructure characterizations and strengthening mechanism of multi-principal component AlCoCrFeNiTi0.5 solid solution alloy with excellent mechanical properties Mater. Lett. 62 2008 2673 2676 10.1016/J.MATLET.2008.01.011
4 Hemphill M.A. Yuan T. Wang G.Y. Yeh J.W. Tsai C.W. Chuang A. Liaw P.K. Fatigue behavior of Al0.5CoCrCuFeNi high entropy alloys Acta Mater. 60 2012 5723 5734 10.1016/J.ACTAMAT.2012.06.046
5 Tang Z. Yuan T. Tsai C.W. Yeh J.W. Lundin C.D. Liaw P.K. Fatigue behavior of a wrought Al0.5CoCrCuFeNi two-phase high-entropy alloy Acta Mater. 99 2015 247 258 10.1016/J.ACTAMAT.2015.07.004
6 Gludovatz B. Hohenwarter A. Catoor D. Chang E.H. George E.P. Ritchie R.O. A fracture-resistant high-entropy alloy for cryogenic applications Science 345 2014 1153 1158 10.1126/SCIENCE.1254581 25190791
7 Zhang Y. Li R. New advances in high-entropy alloys Entropy 22 2020 2020 1158 10.3390/E22101158 33286927
8 Feng C.S. Lu T.W. Wang T.L. Lin M.Z. Hou J. Lu W. Liao W.B. A novel high-entropy amorphous thin film with high electrical resistivity and outstanding corrosion resistance Acta Metall. Sin. 34 2021 1537 1545 10.1007/S40195-021-01255-9/FIGURES/4
9 Liao W.B. Wu Z.X. Lu W. He M. Wang T. Guo Z. Huang J. Microstructures and mechanical properties of CoCrFeNiMn high-entropy alloy coatings by detonation spraying Intermetallics 132 2021 107138 10.1016/J.INTERMET.2021.107138
10 Xiao X. Lin M. Xu C. Zhang J. Liao W.B. An efficient approach to develop and screen out high-entropy alloy composition with high performance for biomedical application Surf. Coat. Technol. 478 2024 130504 10.1016/J.SURFCOAT.2024.130504
11 Zhou H. Jiang L. Zhu S. Jia L. Wu A. Zhang X. Structure evolution and electromagnetic-wave absorption performances of multifunctional FeCoNiMnVx high entropy alloys with harsh-environment resistance J. Alloys Compd. 946 2023 169402 10.1016/J.JALLCOM.2023.169402
12 Kalantari H. Khayati G.R. Adeli M. Structure investigation of AlFeNiTiZn nanocrystalline high entropy alloy Vacuum 210 2023 111878 10.1016/J.VACUUM.2023.111878
13 Pradhan P. Shadangi Y. Shivam V. Mukhopadhyay N.K. Powder metallurgical processing of CrMnFeCoMo high entropy alloy: phase evolution, microstructure, thermal stability and mechanical properties J. Alloys Compd. 935 2023 168002 10.1016/J.JALLCOM.2022.168002
14 Akhil U.V. Radhika N. Rajeshkumar L. Sivaswamy G. A comprehensive review on ceramic coating on steel and centrifugal thermite process: applications and future trends Journal of Bio- and Tribo-Corrosion 9 3 2023 1 23 10.1007/S40735-023-00765-6
15 Farias M.C.M. Souza R.M. Sinatora A. Tanaka D.K. The influence of applied load, sliding velocity and martensitic transformation on the unlubricated sliding wear of austenitic stainless steels Wear 263 2007 773 781 10.1016/J.WEAR.2006.12.017
16 Sathish M. Radhika N. Saleh B. A critical review on functionally graded coatings: methods, properties, and challenges Compos. B Eng. 225 2021 109278 10.1016/J.COMPOSITESB.2021.109278
17 Ren Z.Y. Hu Y.L. Tong Y. Cai Z.H. Liu J. Wang H.D. Liao J.Z. Xu S. Li L.K. Wear-resistant NbMoTaWTi high entropy alloy coating prepared by laser cladding on TC4 titanium alloy Tribol. Int. 182 2023 108366 10.1016/J.TRIBOINT.2023.108366
18 Hsu W.L. Murakami H. Yeh J.W. Yeh A.C. Shimoda K. On the study of thermal-sprayed Ni0.2Co0.6Fe0.2CrSi0.2AlTi0.2 HEA overlay coating Surf. Coat. Technol. 316 2017 71 74 10.1016/J.SURFCOAT.2017.02.073
19 Lu T.W. Feng C.S. Wang Z. Liao K.W. Liu Z.Y. Xie Y.Z. Hu J.G. Liao W.B. Microstructures and mechanical properties of CoCrFeNiAl0.3 high-entropy alloy thin films by pulsed laser deposition Appl. Surf. Sci. 494 2019 72 79 10.1016/J.APSUSC.2019.07.186
20 Wu Z.X. He M.J. Feng C.S. Wang T.L. Lin M.Z. Liao W.B. Effects of annealing on the microstructures and wear resistance of CoCrFeNiMn high-entropy alloy coatings J. Therm. Spray Technol. 31 2022 1244 1251 10.1007/S11666-021-01292-X/FIGURES/6
21 Liao W.B. Xu C.H. Wang T.L. Feng C.S. Khan M.A. Yasin G. Oxidation influences on the microstructure and mechanical properties of W–Nb–Mo–Ta–V–O refractory high-entropy alloy films Vacuum 207 2023 111586 10.1016/J.VACUUM.2022.111586
22 Silvello A. Torres Diaz E. Rúa Ramirez E. Garcia Cano I. Microstructural, mechanical and wear properties of atmospheric plasma-sprayed and high-velocity oxy-fuel AlCoCrFeNi equiatomic high-entropy alloys (HEAs) coatings J. Therm. Spray Technol. 32 2023 425 442 10.1007/S11666-022-01520-Y/FIGURES/21
23 Ghadami F. Davoudabadi M.A. Ghadami S. Cyclic oxidation properties of the nanocrystalline AlCrFeCoNi high-entropy alloy coatings applied by the atmospheric plasma spraying technique Coatings 12 2022 2022 372 10.3390/COATINGS12030372
24 Jojith R. Radhika N. Govindaraju M. Reciprocating wear behavioural analysis of heat-treated Aluminium ZrO2/Al7Si0.3Mg functionally graded composite through Taguchi's optimization method Silicon 14 2022 11337 11354 10.1007/S12633-022-01862-W/METRICS
25 Saleh B. Ma A. Fathi R. Radhika N. Yang G. Jiang J. Optimized mechanical properties of magnesium matrix composites using RSM and ANN Mater. Sci. Eng., B 290 2023 116303 10.1016/J.MSEB.2023.116303
26 Arun K.L. Udhayakumar M. Radhika N. A comprehensive review on various ceramic nanomaterial coatings over metallic substrates: applications, challenges and future trends Journal of Bio- and Tribo-Corrosion 9 1 9 2022 1 32 10.1007/S40735-022-00717-6
27 Hsieh T.H. Hsu C.H. Wu C.Y. Kao J.Y. Hsu C.Y. Effects of deposition parameters on the structure and mechanical properties of high-entropy alloy nitride films Curr. Appl. Phys. 18 2018 512 518 10.1016/J.CAP.2018.02.015
28 Sen Yang Y. Cho T.P. Lin J.H. Optimizing hydrophobic and wear-resistant properties of Cr–Al–N coatings Thin Solid Films 544 2013 612 616 10.1016/J.TSF.2012.11.042
29 Singh A. Kumar H. Kumar S. A comparative study of erosion wear performance of thermally sprayed Ni-based composite coatings J. Mater. Eng. Perform. 2023 1 13 10.1007/S11665-023-08041-X/FIGURES/9
30 Mousavi R. Esmailzadeh M. Bahrololoom M.E. Deflorian F. Optimization of Ni–Mo/Al composite coating parameters using Taguchi method Mater. Res. Express 6 2019 056534 10.1088/2053-1591/AB050A
31 Zhang Y. Zuo T.T. Tang Z. Gao M.C. Dahmen K.A. Liaw P.K. Lu Z.P. Microstructures and properties of high-entropy alloys Prog. Mater. Sci. 61 2014 1 93 10.1016/J.PMATSCI.2013.10.001
32 Joseph J. Jarvis T. Wu X. Stanford N. Hodgson P. Fabijanic D.M. Comparative study of the microstructures and mechanical properties of direct laser fabricated and arc-melted AlxCoCrFeNi high entropy alloys Mater. Sci. Eng., A 633 2015 184 193 10.1016/J.MSEA.2015.02.072
33 Borkar T. Gwalani B. Choudhuri D. Mikler C.V. Yannetta C.J. Chen X. Ramanujan R.V. Styles M.J. Gibson M.A. Banerjee R. A combinatorial assessment of AlxCrCuFeNi2 (0 < x < 1.5) complex concentrated alloys: microstructure, microhardness, and magnetic properties Acta Mater. 116 2016 63 76 10.1016/J.ACTAMAT.2016.06.025
34 Stepanov N.D. Yu Yurchenko N. Shaysultanov D.G. Salishchev G.A. Tikhonovsky M.A. Effect of Al on structure and mechanical properties of AlxNbTiVZr (x = 0, 0.5, 1, 1.5) high entropy alloys 31 2015 1184 1193 10.1179/1743284715Y.0000000032
35 Arakawa E.T. Callcott T.A. Chang Y.-C. Beryllium (Be), Handbook of Optical Constants of Solids 1998 421 433 10.1016/B978-0-08-055630-7.50027-4
36 Jin B. Zhang N. Guan S. Zhang Y. Li D. Microstructure and properties of laser re-melting FeCoCrNiAl0.5Six high-entropy alloy coatings Surf. Coat. Technol. 349 2018 867 873 10.1016/J.SURFCOAT.2018.06.032
37 Zhang B. Gao M.C. Zhang Y. Yang S. Guo S.M. Senary refractory high entropy alloy MoNbTaTiVW Mater. Sci. Technol. 31 2015 1207 1213 10.1179/1743284715Y.0000000031
38 Senkov O.N. Wilks G.B. Scott J.M. Miracle D.B. Mechanical properties of Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20 refractory high entropy alloys Intermetallics 19 2011 698 706 10.1016/J.INTERMET.2011.01.004
39 Gorsse S. Miracle D.B. Senkov O.N. Mapping the world of complex concentrated alloys Acta Mater. 135 2017 177 187 10.1016/J.ACTAMAT.2017.06.027
40 Zhang M. Zhou X. Yu X. Li J. Synthesis and characterization of refractory TiZrNbWMo high-entropy alloy coating by laser cladding Surf. Coat. Technol. 311 2017 321 329 10.1016/J.SURFCOAT.2017.01.012
41 Ang A.S.M. Berndt C.C. Sesso M.L. Anupam A. S P. Kottada R.S. Murty B.S. Plasma-sprayed high entropy alloys: microstructure and properties of AlCoCrFeNi and MnCoCrFeNi Metall. Mater. Trans. 46 2 46 2014 791 800 10.1007/S11661-014-2644-Z
42 Li T. Liu Y. Liu B. Guo W. Xu L. Microstructure and wear behavior of FeCoCrNiMo0.2 high entropy coatings prepared by air plasma spray and the high velocity oxy-fuel spray processes Coatings 7 2017 2017 151 10.3390/COATINGS7090151
43 Sun Z. Li X. Wang Z. Sun Z. Li X. Wang Z. Microstructure and mechanical properties of low activation Fe-Ti-Cr-V-W multi-principal element alloys JNuM 533 2020 152078 10.1016/J.JNUCMAT.2020.152078
44 Nair R.B. Perumal G. McDonald A. Effect of microstructure on wear and corrosion performance of thermally sprayed AlCoCrFeMo high-entropy alloy coatings Adv. Eng. Mater. 24 2022 2101713 10.1002/ADEM.202101713
45 Meghwal A. Anupam A. Murty B.S. Berndt C.C. Kottada R.S. Ang A.S.M. Thermal spray high-entropy alloy coatings: a review J. Therm. Spray Technol. 29 5 29 2020 857 893 10.1007/S11666-020-01047-0
46 Cui Y. Shen J. Manladan S.M. Geng K. Hu S. Strengthening mechanism in two-phase FeCoCrNiMnAl high entropy alloy coating Appl. Surf. Sci. 530 2020 147205 10.1016/J.APSUSC.2020.147205
47 Li J. Li H. Liang Y. Liu P. Yang L. The microstructure and mechanical properties of multi-strand, composite welding-wire welded joints of high nitrogen austenitic stainless steel Materials 12 2019 2019 2944 10.3390/MA12182944 31514393
48 Krishna S.A. Radhika N. Saleh B. Manivannan S. Microstructural mechanical and corrosion properties of SS304/HEA surface layer produced by Friction Stir Processing J. Alloys Compd. 953 2023 170153 10.1016/J.JALLCOM.2023.170153
49 Gussev M.N. Field K.G. Busby J.T. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels J. Nucl. Mater. 460 2015 139 152 10.1016/J.JNUCMAT.2015.02.008
50 Jin B. Zhang N. Yin S. Strengthening behavior of AlCoCrFeNi(TiN)x high-entropy alloy coatings fabricated by plasma spraying and laser remelting J. Mater. Sci. Technol. 121 2022 163 173 10.1016/J.JMST.2021.12.055
51 Yu T. Wang H. Han K. Zhang B. Microstructure and wear behavior of AlCrTiNbMo high-entropy alloy coating prepared by electron beam cladding on Ti600 substrate Vacuum 199 2022 110928 10.1016/J.VACUUM.2022.110928
52 Ghadami F. Ghadami S. Davoudabadi M.A. Sliding wear behavior of the nanoceria-doped AlCrFeCoNi high-entropy alloy coatings deposited by air plasma spraying technique J. Therm. Spray Technol. 31 2022 1263 1275 10.1007/S11666-022-01354-8/FIGURES/13
53 Hamzaçebi C. Taguchi method as a robust design tool, quality control - intelligent manufacturing, robust design and charts 10.5772/INTECHOPEN.94908 2021
54 Chuang M.H. Tsai M.H. Wang W.R. Lin S.J. Yeh J.W. Microstructure and wear behavior of AlxCo1.5CrFeNi1.5Tiy high-entropy alloys Acta Mater. 59 2011 6308 6317 10.1016/J.ACTAMAT.2011.06.041
55 Poulia A. Georgatis E. Lekatou A. Karantzalis A.E. Microstructure and wear behavior of a refractory high entropy alloy Int. J. Refract. Metals Hard Mater. 57 2016 50 63 10.1016/J.IJRMHM.2016.02.006
56 Lu J.Z. Cao J. Lu H.F. Zhang L.Y. Luo K.Y. Wear properties and microstructural analyses of Fe-based coatings with various WC contents on H13 die steel by laser cladding Surf. Coat. Technol. 369 2019 228 237 10.1016/J.SURFCOAT.2019.04.063
57 Noble N. Radhika N. Sathishkumar M. Saleh B. Characterisation and property evaluation of High Entropy Alloy coating on 316L steel via thermal spray synthesis Tribol. Int. 185 2023 108525 10.1016/J.TRIBOINT.2023.108525
58 Chang Y.Y. Chung C.H. Tribological and mechanical properties of multicomponent CrVTiNbZr(N) coatings Coatings 11 41 2021 11 10.3390/COATINGS11010041
59 Poulia A. Georgatis E. Lekatou A. Karantzalis A.E. Microstructure and wear behavior of a refractory high entropy alloy Int. J. Refract. Metals Hard Mater. 57 2016 50 63 10.1016/J.IJRMHM.2016.02.006
60 Yang X. Li C. Zhang M. Ye Z. Zhang X. Zheng M. Gu J. Li J. Li S. Dry sliding wear behavior of additively manufactured CoCrWNixAly alloys Wear 2022 496 497 10.1016/J.WEAR.2022.204285 204285
61 Lentzaris K. Poulia A. Georgatis E. Lekatou A.G. Karantzalis A.E. Analysis of microstructure and sliding wear behavior of Co1.5CrFeNi1.5Ti0.5 high-entropy alloy J. Mater. Eng. Perform. 27 2018 5177 5186 10.1007/S11665-018-3374-Y/FIGURES/6
62 Zhang T. Liu H. Hao J. Chen P. Yang H. Evaluation of microhardness, tribological properties, and corrosion resistance of CrFeNiNbTi high-entropy alloy coating deposited by laser cladding J. Mater. Eng. Perform. 30 2021 9245 9255 10.1007/S11665-021-06107-2/FIGURES/14
63 Gupta M.K. Sood P.K. Sharma V.S. Machining parameters optimization of titanium alloy using response surface methodology and particle swarm Optimization under Minimum-Quantity Lubrication Environment 31 2016 1671 1682 10.1080/10426914.2015.1117632
64 Saravanan I. Elaya Perumal A. Vettivel S.C. Selvakumar N. Baradeswaran A. Optimizing wear behavior of TiN coated SS 316L against Ti alloy using Response Surface Methodology Mater. Des. 67 2015 469 482 10.1016/J.MATDES.2014.10.051
65 Radhika N. Krishna S.A. Basak A.K. Adediran A.A. Microstructure and tribological behaviour of CoCrCuFeTi high entropy alloy reinforced SS304 through friction stir processing Sci. Rep. 14 1 14 2024 1 14 10.1038/s41598-024-54267-7 38167627
66 Akhil U.V. Radhika N. Ramkumar T. Pramanik A. Effect of graphene on the tribological behavior of Ti6Al6V2Sn/Gn composite produced via microwave sintering International Journal of Lightweight Materials and Manufacture 7 2024 1 13 10.1016/J.IJLMM.2023.10.001
67 Ohmori A. Li C.J. Quantitative characterization of the structure of plasma-sprayed Al2O3 coating by using copper electroplating Thin Solid Films 201 1991 241 252 10.1016/0040-6090(91)90114-D
68 Noble N. Radhika N. Natarajan J. Microstructure and wear behaviour of AlCoCrFeNi-coated SS316L by atmospheric plasma spray process Sci. Technol. Adv. Mater. 2024 10.1080/14686996.2024.2341611
69 A Look at Self-Healing Metal Oxides as a Corrosion Prevention Method, (n.d.). https://www.corrosionpedia.com/a-look-at-self-healing-metal-oxides-as-a-corrosion-prevention-method/2/6795 (accessed May 22, 2024).
70 Bai T. Liu Z. Pei Z. Fang W. Ma Y. Tribological performance studies of waterborne polyurethane coatings with aligned modified graphene oxide@Fe3O4 ACS Omega 6 2021 9243 10.1021/ACSOMEGA.1C00688 33842793
71 Ilie F. Ipate G. Manaila F.C. Tribological properties study of solid lubrication with TiO2 powder particles Materials 15 2022 10.3390/MA15207145
72 Yu H. Chen H. Zheng Z. Qiao D. Feng D. Gong Z. Dong G. Effect of functional groups on tribological properties of lubricants and mechanism investigation Friction 11 2023 911 926 10.1007/S40544-022-0630-9/METRICS
73 Tian L.H. Xiong W. Liu C. Lu S. Fu M. Microstructure and wear behavior of atmospheric plasma-sprayed AlCoCrFeNiTi high-entropy alloy coating J. Mater. Eng. Perform. 25 2016 5513 5521 10.1007/S11665-016-2396-6/FIGURES/11
74 Feng C. Wang X. Yang L. Guo Y. Wang Y. High hardness and wear resistance in AlCrFeNiV high-entropy alloy induced by dual-phase body-centered cubic coupling effects Materials 15 2022 2022 6896 10.3390/MA15196896 36234236
75 Buluc G. Chelariu R. Popescu G. Sârghi M. Carcea I. Study on wear resistance FeNiCrMnAl high entropy alloy - mechanical properties Key Eng. Mater. 750 2017 34 38 10.4028/WWW.SCIENTIFIC.NET/KEM.750.34
