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

S2405-8440(24)13394-4
10.1016/j.heliyon.2024.e37363
e37363
Research Article
Preparation of electroless deposition of NiTiZr(P) quaternary alloy and their properties
Unni Megha
Sudagar J. sudagar.jothi@vitap.ac.in
⁎
Department of Physics, School of Advanced Sciences (SAS), VIT-AP University, Near Vijayawada, Andhra Pradesh, 522 241, India
⁎ Corresponding author. sudagar.jothi@vitap.ac.in
05 9 2024
15 9 2024
05 9 2024
10 17 e3736310 6 2024
29 7 2024
2 9 2024
© 2024 The Authors. Published by Elsevier Ltd.
2024

https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
The exceptional super elasticity and corrosion-resistance of Ni-Ti alloys have attracted a lot of attention and interest lately for a wide range of applications, and complex alloy components could be prepared effectively by different preparation techniques. Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti -Zr(P) binary, ternary, and quaternary alloys were coated on mild steel by electroless deposition which is a method of plating metallic films on a substrate by the reduction of metallic complex ions in solution with the aid of reducing agent from an alkaline bath. The ternary Ni-Ti-Zr(P) alloy is considered to be one of the most promising high-temperature SMAs. SEM, XRD and EDS were used to examine the morphology, phase composition and elemental composition which demonstrate the microstructure of the deposits. The mechanical characteristics of the samples were examined through scratch test and micro hardness analysis and the value increased from 261 HV200 to 405 HV200 and that the coefficient of friction raised significantly from 0.23 to 3.5 owing to the presences of added elements in Ni(P) matrix. Polarization analysis and EIS were tested to evaluate the corrosion properties of coated samples in a non-deaerated 3.5 %wt. (NaCl) solution. The outcomes indicate that as the amount of Ti-Zr elements in the bath raised, the corrosion potential became more positive and the corrosion current density decreased to 14.903 μA/cm2. Furthermore, Ni-Ti-Zr(P) alloy coating strengthens corrosion resistance in comparison to Ni(P).

Keywords

Ni-Ti-Zr(P) alloys
Electrochemical route
Microstructure
Mechanical properties
Polarization technique
Corrosion resistance
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pmc1 Introduction

Electroless nickel (EN) coatings are primarily employed in a variety of technical applications to offer wear and corrosion resistance. The structure and characteristics of the coated sample are known to be influenced via the quantity of phosphorus employed in the Ni(P) matrix. As-plated hardness increases with decreasing phosphorus content in the coating, whereas corrosion resistance improves with increasing phosphorus content in the coating. The inclusion of supplementary hard or lubricating particles, such as silicon nitride (Si3N4), silicon carbide (SiC), polytetrafluoroethylene (PTFE) particles, Titanium oxide (TiO2) and aluminium oxide (Al2O3), may often boost the mechanical characteristics of Ni(P) coatings [[1], [2], [3], [4], [5]].

Applications for this coating method in industrial plating are numerous. Superior hardness, enhanced resistance to corrosion, and uniform coating on asymmetrical structures are a few characteristics of electroless coating. Additionally, non-conductive materials like plastic, glass, ceramics, etc, can be coated using electroless methods [6,7]. The choice of plating conditions and the chemical substances employed have a major impact on the deposition rate, coating efficiency, and other features [8,9]. The electrolyte bath has a very limited lifespan, but the preparation expenditures are substantial. These intricacies therefore influence the ultimate product's cost [10,11].

It is generally accepted that EN composite coatings have far worse corrosion resistance than standard Ni(P) coatings. The deposit's passivity and corrosion resistance may be lowered by the integrated second phase particles found in the EN matrix. Based on this supposition, electroless Ni(P) composite coatings are often not advised for applications needing strong corrosion resistance [12]. Hubbell [13,14], Hussain and Such [15], and Shoeib et al. [16] determined that electroless Ni(P) composite coatings had a reasonable corrosion performance. Using neutral salts spray tests, Hubbell [13,14] investigated the corrosion resistance of EN composite coatings and found that the level of corrosion inhibition they give is equivalent to that of electroless Ni(P) coatings with comparable thickness. Hussain and Such [15] conducted a 16-h copper-accelerated acetic acid salt spray test (CASS test) to evaluate the corrosion resistance of a 25 mm thick electroless Ni(P)-TiO2 composite coating. They claim that microscopic and optical examination performed following the test suggest that the EN composite coating's corrosion resistance is on line with electroless Ni(P) deposition of comparable width. In contrast to Ni(P), Shoeib et al. [16] discovered that incorporating polymer particles like polyacrylamide (PAm) and poly vinyl alcohol (PVA) improved the corrosion susceptibility of EN deposits in simulated sea water over a period of 28 days. It was shown that in a 3 % wt. NaCl, the addition of nanozinc oxide particles to Ni(P) matrix composite deposition [17] led to a slightly improved corrosion resistance. Anodic polarization corrosion tests conducted in a 0.1 M NaCl solution demonstrate that the electroless Ni(P)–ND composite coating exhibits superior corrosion resistance in comparison to a standard Ni(P) coating [18]. Furthermore, research on the corrosion behaviour of Ni(P)–nano SiC composite coatings in a 3 % wt. NaCl [19] observed that the incorporation of nanoparticles improved the corrosion resistance of heat-treated deposits when contrasted with as-plated coatings. On the other hand, compared to coatings that were plated, vacuum heat-treated deposits in the Ni(P)–nanoTiO2 composite coating demonstrated reduced corrosion resistance [20]. The anticorrosion behaviour and passivity were enhanced on comparing the nano-CeO2 co-deposited Ni(P) deposition to plain Ni(P) coatings in an electrolyte of 3 % NaCl + 5 % H2SO4 [21].

Nickel-titanium (Ni-Ti) alloys possessing identical atomic ratios are highly favoured as shape memory alloys (SMAs) due to their exceptional characteristics, including remarkable shape memory properties, super elasticity, resistance to corrosion and wear, biocompatibility, and fatigue resistance [22,23]. Unfortunately, binary Ni-Ti alloys have low transformation temperatures-typically less than 100 °C [[22], [23], [24]] which makes them unsuitable for high-temperature SMA actuators used by the aerospace, automotive, industrial, and energy exploration sectors. As a result, its use in extreme temperatures is severely constrained [25]. Research indicates the potential for elevating the martensitic transition temperature (Ms) of Ni-Ti SMAs by introducing a third alloying element, predominantly from group IVB and VIII elements such as Pt, Hf, Zr, Au, and Pd [26]. Hafnium and zirconium are considered as more economical than platinum and gold which are precious metals. The ternary Ni-Ti-Zr alloy is regarded as one of the most promising high-temperature SMAs. It has a transition temperature that can be adjusted by varying the Zr percentage, which is substantially greater than that of the Ni-Ti alloy, in addition to inheriting many of the good features of the binary Ni-Ti alloys [27]. Additionally, the prior work demonstrated the driven fatigue characteristics and exceptional thermomechanical behaviour [28,29] of the high temperature shape memory alloy Ni-Ti-Zr. Because of its distinct metallurgical and chemical properties, producing Ni-Ti-based alloys is fraught with difficulties. First, because of its high chemical reactivity, titanium has a significant propensity to with O2 to produce oxide particles like TiO2 and Ti4Ni2O [30,31]. Second, the alloy's chemical structure has a significant impact on both its performance and characteristics. During the manufacturing process, any unequal dispersion of components, precipitation, and diffusion might have a significant impact on the martensitic transformation [26]. We have attempted for the first time to achieve these Ni-Ti-Zr based alloy by electroless route. As far as we know, there have been no reported or published works on the electroless method for producing Ni-Ti-Zr(P) based alloy coatings. We believe that this alloy coating could contribute to the development of cost-effective shape memory alloy devices in the market in the near future. We focus mainly on automobile, aerospace industry where in variety of steels used. To begin with we started with mild steel which is more convenient for industrial application. If this research comes up with good result we will focus on other automobile steels. Most researchers have focused on investigating the corrosion performance of electroless nickel composite coatings with increased phosphorus content in NaCl solution, utilizing techniques like immersion or potentiodynamic polarization. Considering the exceptional mechanical properties of these coatings, there is a curiosity to investigate the electrochemical performance of electroless Ni(P) coatings. This study seeks to assess the mechanical, electrochemical, and Electrochemical Impedance Spectroscopy (EIS) properties of these newly developed quaternary alloy coatings utilizing microhardness, scratch, and potentiodynamic polarization techniques.

2 Materials and methods

2.1 Preparation technique

Being the substrate, mild steel from rod stock was utilized. Table 1 shows the chemical compositions of low carbon steel that can be utilized as a substrate. It will eventually become ⁓0.9 mm in diameter and 20 mm height and 10 mm width. Ultimately, the substrates underwent disc polishing and grinding to achieve a smooth surface. SiC paper was used to polish the substrates up to 2500 grit. It is important to make sure the substrate is pure before beginning the coating process. Thus, in order to achieve an effective coating, pre-treatment is crucial. Cleansing in acetone, immersing in ethanol for 2 min, soaking in 10 vol.-% sulfuric acid for 1 min, and finally submerging in an electroless bath that has been prepared are the pre-treatment steps. Each stage was finished with a distilled water rinse. Table 2 displays the electroless bath composition and plating requirements and the volume of plating solution for each sample is 150 ml. 3-(N, N-Dimethyl myristyl-ammonio) propane sulfonate zwitterionic surfactant (C14-SB) which possessed both positive and negative charges was used in the electroless alloy coating process. Zwitteronic surfactant reduce the contact angle the leads to good wettability of alloy coating A magnetic stirrer is used to improve the thickness and uniformity of the sample. The electrolyte's temperature was kept constant at 85 °C (±2 °C). The ideal pH and time for deposition are obtained through trial-and-error method.Table 1 Chemical composition of substrate in weight percentage.

Table 1C/wt -%	Mn/wt -%	Si/wt -%	P/wt -%	S/wt -%	Fe/wt -%	
0.2	0.61	0.34	0.06	0.06	Bal.	

Table 2 Electroless Bath parameters.

Table 2Chemicals	g L−1/Range	g L−1/Range	g L−1/Range	g L−1/Range	
Ni-Ti-Zr(P)	Ni-Zr(P)	Ni-Ti(P)	Ni(P)	
Titanium chloride (metal ion)	10	–	15	–	
Zirconium chloride (metal ion)	10	15	–	–	
Nickel chloride (metal ion)	10	15	15	30	
Sodium hypophosphate (reducing agent)	40	40	40	40	
Tri-sodium citrate (stabilizer)	25	25	25	25	
Ammonium chloride (complexing agent)	100	100	100	100	
Lactic acid (stabilizer)	5	5	5	5	
Zwitterionic surfactant (adhesion agent)	0–0.03	0–0.03	0–0.03	0–0.03	
Temperature	85 °C (±2 °C)	85 °C (±2 °C)	85 °C (±2 °C)	85 °C (±2 °C)	
pH	8–9	8–9	8–9	8–9	
Time	1Hr	1Hr	1Hr	1Hr	

Weight gain during the deposition process is used to express the electroless Ni–Ti–Zr alloy deposition rate. The sample that was deposited was dried and weighed. Consequently, the following equation may be used to represent the deposition rate:T=w×104dA

where ‘T’ represents the thickness of the coating in millimetres (mm), ‘w’ denotes the weight gain in grams (g), ‘d’ stands for the density of the deposit in grams per cubic centimetre (g/cm³), and A represents the surface area of deposition in square centimetres (cm2).

2.2 Characterization methods

Phases of the samples at various compositions were determined using X-ray diffraction analysis (XRD). The Rigaku Miniflex 600, produced by the Japanese company Rigaku Corporation, served as the X-ray diffraction tool for this investigation. The XRD was performed using Cu-Kα radiation with a wavelength of 1.5406 Å. A study with a 2θ range of 10°–90° was conducted, with a scan rate of 5°/min employed. The submitted samples were analyzed for morphology using scanning electron microscopy (SEM). A VEGA 3 SBH machine made in the Czech Republic by TESCAN Brno S.R.O. was used for the SEM. The chemical compositions of the present phases were analyzed utilizing energy-dispersive spectroscopy (EDS) with a solid-state detector (SDD) attachment (EDAX Inc., USA). Optical microscope image of the as prepared samples at magnifications ranges of 50× were done using Microscope Primotech MAT cod., stage A, Tube 300/20 with integrated HD IP Camera 3 MP for Primotech manufactured by CariZeiss Microscopy GmbH. A diamond pyramid was used as an indenter for the Vickers microhardness tester (Wilson Wolpert, Germany), which was used to measure the microhardness of the coating. As per ASTM E 384-11 guidelines, microhardness was assessed on the specimen's surface using loads of 200 gf for 15 s. The final figure for microhardness was stated as the average of three observations taken at various points on the coating. Using a scratch test, the coatings' adhesion to the substrate was investigated to understand the strength of the coating. The term Critical Load (Lc) refers to the load at which failure takes place and the first audible signal is recorded. This load is commonly used to determine the adhesive strength of coating [[32], [33], [34], [35]]. Scratch test was conducted using Scratch tester TR-101-IAS manufactured by DUCOM Instruments Pvt. Ltd. A 200 μm Rockwell diamond indenter was used for the scratch test. This led to the production of scratches with a 5 mm interval between them and an increasing scar breadth. For every specimen, four runs were carried out, and the critical load for each specimen is stated based on the two coinciding values. It is mentioned that for sliding contact applications, a critical load of 22 N with a Rockwell C diamond tip is deemed adequate. Additionally, parameters such as the applied load range and scratch length were carefully chosen. Additionally, the scratch test was directed in compliance with ASTM C 1624–05 standard. During the course of the testing, the computer simultaneously recorded parameters such as the imposed normal load, frictional force, and tangential force. Electrochemical studies on Ni(P) and quaternary alloy coatings were conducted using electrochemical work station (CH Instruments, CHI6112E Electrochemical Analyser). A 1 cm2 exposed mild steel surface served as the test's working electrode, and it had been immersed in a 3.5 wt% (0.6 N) NaCl solution without being deaerated. Platinum wire with a diameter of 1 mm served as the counter electrode, while silver/silver chloride (Ag/AgCl) served as the reference electrode. A frequency response analyzer was used to assess impedance (FRA). The frequency ranges in which the spectrum was captured was 0.001 kHz–100 kHz. The root-mean-square amplitude of the applied alternating voltage was 0.1V/s (scan rate) in the range of −1.35 to 0.7 V in respect to OCP. Nyquist of the impedance data were shown following each experiment. The data plotted are the average of 3 measurement for each sample. A Nyquist plot depicts real (Z) versus imaginary (Z) impedance. The frequency-dependent behaviour of the phase angle can help identify the presence of one or more time constants and obtain comparable circuit characteristics. The collected data were assessed and fitted to curves using the EQUIVCRT tool [36]. Following the Electrochemical Impedance Spectroscopy (EIS) measurements, the system was allowed to reach its open-circuit potential. The upper and lower potential limits for linear sweep voltammetry were established at −1.35V–0.7V relative to the open circuit potential (OCP) once a stable open-circuit potential was achieved. These electrochemical observations were then followed by Tafel plot analysis.

3 Result and discussion

3.1 XRD analysis

The XRD spectra of Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti-Zr(P) are shown in Fig. 1. To calculate the sizes of the crystallites Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti-Zr(P) in the samples, the Debye-Scherrer formula [30] was applied. This formula is written as D = kλ/βcosθ. Here, ‘D’ represents the size of the crystallite, ‘k’ is the constant value of 0.9 for the form factor, ‘λ’ stands for the wavelength of the Cu-Kα radiation (0.15406 nm), ‘β’ denotes the full-width half maximum of the diffraction peak in radians, and ‘θ’ represents the diffraction angle in radians. Bragg's equation, d = nλ/2sinθ, was used to compute the interplanar spacing (d) for the samples. Here, ‘d’ represents the interplanar spacing, ‘n’ indicates the diffraction order, ‘λ’ denotes the wavelength of the X-ray, precisely 1.5406 Å, and ‘θ’ represents the diffraction angle in degrees. The total length of dislocation lines inside a given volume provides a quantitative description of a crystal's dislocation density. Dislocations have a significant impact on a material's characteristics; in particular, a higher dislocation density is directly correlated with a higher hardness level. The formula δ = 1/D2 can be used to calculate the dislocation density, or ‘δ’. The dislocation density is denoted by the symbol ‘δ’ in this discussion, whereas the crystallite size is indicated by the symbol ‘D’. The formula ε = βcosθ/4 may be used to calculate the micro strain (ε). The data for dislocation density, micro strain, interplanar spacing, and FWHM average crystallite size of the generated samples are shown in Table 3.Fig. 1 (a) XRD patterns of Ni(P), Ni-Ti(P), Ni-Zr(P), Ni-Ti-Zr(P).

Fig. 1

Table 3 FWHM, Average grain size, d-spacing, dislocation density and strain of Ni(P) and ternary and quaternary alloy coating calculated using XRD.

Table 3S. No	Samples	2θ (°)	FWHM (°)	Crystallite Size (nm)	d-spacing (Å)	Dislocation density(δ) × 10−3 (nm)−2	Strain(ε) × 10−3	
1	Ni(P)	45.128	2.47	3.477	2.007	82.702	25.978	
2	Ni-Ti(P)	46.28	2.57	3.361	1.960	88.492	26.239	
3	Ni-Zr(P)	46.14	3.34	3.690	1.965	73.438	23.972	
4	Ni-Ti-Zr(P)	44.862	3.96	2.170	2.018	212.296	41.857	

The XRD pattern of electroless Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti-Zr(P) is depicted in Fig. 1. The reflections corresponding to the (111) plane of a face-centered cubic nickel phase are presented, and the grain sizes were determined using the Debye-Scherrer technique. Diffraction peaks may be seen at certain angles (2θ) of 45.12 and 82.69. This identity matches the 1534892 JCPDS card number. The deposits were composed of a single, large peak. The average crystallite size (D) and d spacing for Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti-Zr(P) are as follows: The average crystallite size and d spacing for Ni(P) are 3.47 nm and 2.00 A°, respectively; for Ni-Ti, the average crystallite size and d spacing are 3.36 nm and 1.96 A°, respectively; for Ni-Zr, the average crystallite size and d spacing are 3.69 nm and 1.96 A°, respectively; and for Ni-Ti-Zr, the average crystallite size and d spacing are 2.17 nm and 2.01 A°.

The variation in the diffraction peak can be seen from the graph. On addition of elements into nickel, the peak intensity first broadens with titanium and it becomes more wider on adding zirconium to the nickel matrix. On adding titanium and zirconium simultaneously to the nickel, the peak intensity has increased. It can be seen that the crystal size decreased with the increase of the added elements to Nickel. The FWHM and height of (1 1 1) peak increased with the increase of the added elements, except some fluctuation in the height of peak. The comprehensive analysis showed that the crystallization quality of the sample was deteriorated gradually with the increase of added concentration.

3.2 Optical surface images

The surface morphology of the coated samples was examined using the optical microscope image (Fig. 2). They are compact, non-uniform in size, and show mild agglomeration. The morphological pictures of the quaternary alloy coating make it evident that the elements agglomerate in the coatings due to an excessive concentration of alloying elements in the bath. The morphology of the coating has the most impact on the capacitive behaviour of the coatings. The coatings that are as-deposited [37] and obtained for these deposits are nodular.Fig. 2 Optical surface images of (a) Ni(P); (b) Ni-Ti(P); (c) Ni-Zr(P); (d) Ni-Ti-Zr(P).

Fig. 2

3.3 Morphological analysis and chemical composition

Using the SEM at various magnifications, the surface morphology of Ni(P) and Ni-Ti-Zr(P) was investigated (Fig. 3(a, b, c) & (d, e, f)). The granular and bubbled like structure in the coating are seen in Fig. 3(a) and (d). The microscale cauliflower-shaped clusters of ultrafine nodules are visible due to the deposit surface morphology. They exhibit moderate agglomeration, have non-uniform in size, compact, and lack any observable defects or porosity. In the absence of Ti-Zr element addition Fig. 3(a), the coating matrix has comparatively larger grains and alloying elements than it does with element addition. The surface morphology of Ni(P) and Ni-Ti-Zr(P), respectively, shows a change from a smooth nodular appearance to a non-smooth surface, as shown in Fig. 3(a) and (d). The effect of the extra element on surface morphology has also been investigated in preliminary studies on electroless Ni(P) deposits. It is clear from the mapping of the quaternary alloy coating that an excessive concentration of alloying components in the bath causes the elements to accumulate in the coatings Fig. 4(c) and (d). Furthermore, after adding Ti-Zr, the coating's phosphorus concentration (not shown) dropped dramatically from 11.16 to 5.74 wt%. Moreover, a smoother and flatter surface is produced by the transition from crystalline phase to amorphous plus nanocrystalline phase. It is stated that their structures are smoother and more amorphous than those of high phosphorus. The thickness of the samples was measured to be 19.95, 14.162, 20.676, and 17.285 μm for Ni(P), Ni-Ti(P), Ni-Zr(P) and Ni-Ti-Zr(P) respectively (see Fig. 5).Fig. 3 SEM images of (a), (b) & (c) Ni(P) at different magnification and (d), (e) & (f) Ni-Ti-Zr(P) at different magnification.

Fig. 3

Fig. 4 EDS spectra of (a) Ni(P), (b) Ni-Ti-Zr(P), (c) elemental mapping of Ni(P), (d) Ni-Ti-Zr(P).

Fig. 4

Fig. 5 Microhardness of the coated samples at two different load.

Fig. 5

Additionally, we determined the elemental composition of the Ni(P) and Ni-Ti-Zr(P) samples by EDS analysis. Fig. 4 displays the EDS spectra of the same samples. The EDS spectra of the samples show that the Ni and P components are present in the Ni(P) sample Fig. 4(a). The absence of additional peaks in the spectrum suggests that there are no contaminants present. The strong and persistent presence of Ni and P is shown by the clear and prominent peaks in the EDS spectra of the Ni-Ti-Zr samples Fig. 4(b). In addition to that, it also confirms the presence of Ti and Zr. The existence of the indicated elements is also verified by the elemental mapping of the samples Ni(P) and Ni-Ti-Zr(P).

3.4 Microhardness

Microhardness tests were performed on substrates coated with Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti-Zr(P). The microhardness value obtained from the binary Ni(P) deposit are 298.5 HV200 and The deposit which has Ni-Ti(P), Ni-Zr(P), Ni-Ti-Zr(P) produced 261 HV200, 282 HV200 and 405 HV200 respectively. The standard deviation is 1.471 HV200, 3.894 HV200, 1.870 HV200 and 2.160 HV200 respectively. The integration of alloying elements into the nickel matrix is responsible for the increased hardness of the Ni-Ti-Zr(P) quaternary alloy coating when compared to Ni(P), Ni-Ti(P), and Ni-Zr(P). The higher hardness of the Ni-Ti-Zr(P) quaternary alloy coating over Ni(P), Ni-Ti(P), and Ni-Zr(P) is caused by the incorporation of added elements into the nickel matrix. Heavy metal (Zr) were introduced between the nickel matrix to withstand the load/force on the substrate, resulting in high microhardness.

The dispersion-strengthening and grain-filling effects of the increased Ti-Zr elements integration in the nickel matrix are what cause the hardness to rise. Alloying elements prevent the dislocation movement while nickel carries the load. Strengthening is attained as element control the metal matrix deformation by nanomechanical restraint (Orowan mechanism) [38]. The increased adsorption on the cathode surface caused by the larger dispersion of Ti-Zr elements in the nickel matrix raises the nucleation rate, inhibits grain development, and reduces the grain size of the deposit. The grain refinement also impedes the dislocation motion, which results in the increase of microhardness of the quaternary alloy coating coatings (Hall-Petch relation). Furthermore, there was higher resistance to plastic deformation because of the distribution of alloying element in the deposit [39].

3.5 Scratch test

On the basis of the results shown in Fig. 6, Fig. 7, the effect of extra elements in the Ni(P) matrix on the deposit adhesive behaviour is investigated. A scratch test was performed on the alloy coated surfaces of Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti-Zr(P) as shown in optical microscopy images in Fig. 6. The experimental data for the substrates with the greatest weight % of Ti-Zr elements in the coating were analyzed to obtain these concentration values. A change in the interfacial properties of the substrate and deposit surfaces has a direct impact on the compound property of adhesion. Fig. 7 shows the characteristics of the rate of force applied to the coated specimens in relation to the scratch's overall length and coefficient of friction. In the scratch test (Fig. 6), no radial or linear fractures were seen in any of the four specimens. This demonstrates the coatings' efficient adhesion because of the strong attraction forces that exist between the layers. All of the coatings' friction coefficients rise linearly with test load, as shown in Fig. 7(a–d). However, the coating with the Ni-Zr(P) matrix exhibits a significantly smaller increase. However, in the Ni-Ti-Zr(P) situation, the coefficient of friction is rather significantly larger compared to the Ni(P) and Ni-Zr(P) matrices. Apart from adhesion, coefficient of friction provides information regarding the wear resistance of the coated samples. Increasing the friction coefficient increases the wear rate also [40]. Altogether, the Ni-Ti-Zr(P) being the high coefficient of friction (COF) with good adhesion property and high wear resistance property compared to Ni(P), Ni-Ti(P), Ni-Zr(P) while Ni-Ti(P) being the low COF with low adhesion and wear resistance properties compared to others. Moreover, the normal load applied to the samples are 22 N and the total scratch length of each sample are 7 mm.Fig. 6 Morphology of scratch pattern (a) Ni(P); (b) Ni-Ti(P); (c)Ni-Zr(P); (d) Ni-Ti-Zr(P).

Fig. 6

Fig. 7 Scratch profile of deposits (a) Ni(P); (b) Ni-Ti(P); (c)Ni-Zr(P); (d) Ni-Ti-Zr(P).

Fig. 7

3.6 Electrochemical analysis

3.6.1 Polarization studies

The potentiodynamic polarization curves produced for the Ni(P), ternary and quaternary alloy coatings as plated in a non-deaerated 3.5 %wt. (NaCl) solution are shown in Fig. 8. Linear Tafel regions were obtained for Tafel experiments conducted immediately after immersion of the sample in the electrolyte and also freshly prepared samples were used to avoid passivation. By giving up some of the coating's characteristics, the surface is shielded. The application of Ni-Ti-Zr(P) and the presence of P, according to the results, have improved the corrosion behaviour. When compared to the mild steel substrate, the corrosion potential of the Ni-Ti-Zr(P) electroless coating on mild steel shifts to a higher positive potential and the corrosion current decreases. As the concentration of elements in the coating increases, the corrosion current decreases to 14.903 μA, representing the lowest corrosion current among all examined concentrations. However, with the increase in alloying element both agglomeration and the rise in solution viscosity lead to a decrease in the amount of Ti-Zr and phosphorous within the coating, resulting in a decrease in the corrosion current. The deposition of alloying element within the coating impedes the growth of corrosion cavities, thereby enhancing the coating's resistance to corrosion.Fig. 8 Potentiodynamic polarization curves in 3.5 % wt. NaCl solution for Ni(P), Ni-Ti(P), Ni-Zr(P), and Ni-Ti-Zr(P).

Fig. 8

All of the coatings produced anodic and cathodic branches that are essentially identical, suggesting a common corrosion procedure. The Tafel extrapolation technique was used to obtain the values of the corrosion potential (Ecorr), corrosion current density (Icorr), and polarization resistance (Rp) for each coating. These data are shown in Table 4. With the exception of Ni-Ti-Zr(P) which has higher resistance polarization than the other alloy coatings, the polarization behaviour for electroless plain Ni(P) binary and ternary alloy coatings evidently demonstrate there is no greater variation in corrosion behaviour. It is possible to determine that the Ni–Ti–Zr(P) quaternary alloy coatings exhibit a higher increase in corrosion resistance by comparing the Icorr and Rp values. Likewise, quaternary alloy coatings surpassed simple Ni(P) coatings in terms of polarization resistance (Rp). The effective metallic area that is susceptible to corrosion may be used as an explanation for the quaternary alloy coatings' larger increase in corrosion performance.Table 4 Corrosion characteristics of Ni(P) and ternary and quaternary alloy coatings by polarization method.

Table 4Coatings	Ecorr (mV)	Icorr (μA/cm2)	βa (mv/decade)	βc (mv/decade)	Corrosion Rate(mpy)	(mm year−1)	RP(Ωcm2)	
Mild steel	−1039.51	478.071	396.9	314.5	13.87	0.3522	0.1595	
Ni(P)	−834.243	24.316	153.8	290.1	0.57	0.0144	1.7972	
Ni-Ti(P)	−748.967	75.741	194.0	610.6	1.75	0.0444	0.8525	
Ni-Zr(P)	−757.318	68.256	171.7	644.4	1.62	0.0411	0.8642	
Ni-Ti-Zr(P)	−903.162	14.903	169.8	186.1	0.31	0.0078	2.5903	

3.6.2 Electrochemical impedance studies

Fig. 9 shows the impedance spectra (Nyquist plost) obtained for as-plated electroless plain Ni(P) and ternary and quaternary alloy coatings in 3.5 wt% NaCl solution at their respective open-circuit potentials. A half semicircle was observed in the nyquist plots produced for ternary and quaternary alloy coatings as well as plain Ni(P). The charge control reaction and corrosion process of these coatings are represented by all curves, which have been drawn in a singular half semi-circular in the frequency range of 100 kHz to 0.001 Hz and have a constant time (τ = Qdl Rct). The half semicircles have different diameters but similar shapes. The semicircle's diameter determines the coating's resistance to corrosion. The impedance spectra are fitted using the analogous circuit shown in Fig. 10. The analogous circuit constructed for these deposits shows two-time constants, or two capacitive responses. The equivalent circuit has components that are similar to the solution resistance (Rs), double layer capacitance (Qdl), coating capacitance (Qcoat), charge transfer resistance (Rct), and coating resistance (Rcoat). At the high frequency end, the measured impedance would be close to Rs, and at the low frequency end, it would be close to the sum of Rs, Rcoat, and Rct. The related circuit description for low P ternary and quaternary alloy coatings is R(QR)(QR). The used electrical equivalent circuit was satisfied since the chi-squared (χ2) values used to assess the quality of fitting were found to be match with 10−3. The impedance parameters are obtained by fitting the data and are shown in Table 5. For these coatings, the Rct value ranges from 0.5604 to 589.4 Ω cm2, while the Rcoat value varies from 258.9 to 1536 Ω cm2. A somewhat higher Rct value than that of the plain Ni(P) (45.87 Ω cm2) coatings was found for the quaternary alloy coatings (Ni-Ti-Zr(P) 589.4 Ω cm2). This suggests enhanced corrosion resistance. One possible explanation is that the elements are embedded in the coating of quaternary alloys, reducing the effective metallic surface area exposed to the corrosive media. Corrosion resistance in the quaternary alloy coatings has improved noticeably. The capacitive behaviour of the coatings can be ascribed to Qcoat and Qdl. The double layer capacitance reveals the polarity and charge concentration at the electrode/electrolyte contact. The constant phase element (CPE) is substituted for the capacitance to provide a better match. The impedance of CPE is evaluated by the following relationship [41].ZCPE=[Q(jω)n]−1

where Q represents the magnitude of the CPE, j = √−1, n is a deviation constant and ω being the angular frequency. A pure resistance yields n = 0 and a pure capacitance (ideal capacitor) yields n = 1. The variation from perfect dielectric behaviour is explained by CPE, which is connected to surface inhomogeneity. It should be mentioned that Q represents constant phase element in the EQUIVCRT software [42]. For the binary, ternary, and quaternary alloy coatings, the Qcoat value was found to be between 3.684E-5-29.12E-5 (S. secn). The range of ncoat values found for these coatings, 0.81881–0.9977, represents the coatings' roughness. The Qdl value for these coatings is around 0.0005139–0.004175 (S. secn). The morphology of coatings is the main element controlling their capacitive behaviour. The as-deposited coatings [37] generated for these deposits show nodules. These nodules are the cause of the increased Qcoat levels. The inclusion of Ti–Zr components to the Ni(P) matrix has resulted in an increase in nodule size when compared to a basic Ni–P deposit. Consequently, the Qcoat value of quaternary alloy coatings has gone raised.Fig. 9 Changes in the Nyquist curve in 3.5 %wt. NaCl solution according to the number of elements in the coating with fitted curve.

Fig. 9

Fig. 10 The equivalent electric circuit of Ni(P) and ternary and quaternary alloy Coatings.

Fig. 10

Table 5 Corrosion characteristics of Ni(P) and ternary and quaternary alloy coatings by EIS method.

Table 5Coatings	Rs (Ω cm2)	Qcoat−Y0 (S. secn)	nc	Rcoat (Ω cm2)	Qdl − Y0 (S. secn)	Rct (Ωcm2)	χ2(10−3)	
Ni(P)	8.199	29.1E-5	0.9977	258.9	0.002228	45.87	0.7	
Ni-Ti(P)	6.318	12.7E-5	0.8185	1010	0.0005139	0.5604	1.9	
Ni-Zr(P)	2.971	3.68E-5	0.8181	743.6	0.004175	21.99	1.6	
Ni-Ti-Zr(P)	7.404	8.41E-5	0.9939	1536	0.001045	589.4	0.4	

After the potentiodynamic polarization test the corroded samples were subjected to Optical microscope analysis to find out any pit formation in the deposit and the presence of any corrosion products. Fig. 11, Fig. 12 gives the corroded regions of low phosphorus Ni(P) and Ni-Ti-Zr(P) coatings at 20 μm magnifications. The presence of corrosion products of the same deposit is shown at red identification in Fig. 11. From Fig. 11 it is evident that a large number of small nodules are present at the corroded area which are absent in Fig. 12. According to the literature these nodules are surrounded by a wide and big nodule and the presence of iron could not be found. Similarly, even in the outer region no iron could be noticed [43]. According to the study ‘Fe’ element containing regions are more in the case of low P electroless plain Ni(P) coating compared to low P electroless Ni–Ti-Zr(P) coating and it could be due to not only the effective metallic area available for corrosive solution to attack but also the alloying element resistance to corrosive environment. Hence, Ni-Ti-Zr(P) coatings exhibited an improvement in the corrosion resistance in 3.5 % NaCl medium. The corrosion current density values obtained from potentiodynamic polarization and Rct values obtained from the EIS studies for both the coatings also confirms the above observations made.Fig. 11 Ni(P) before and after corrosion.

Fig. 11

Fig. 12 Ni-Ti-Zr(P) before and after corrosion.

Fig. 12

4 Conclusion

A new type of alloy coating (Ni-Ti-Zr(P)) was successfully developed through electroless route, and this research finds a stepping stone to the development of low-cost shape memory alloy devices which can be developed through further optimisation methods (future scope). The following conclusions were derived.➢ Using XRD analysis, it was determined that face-centered cubic nickel was present in every sample. The FWHM and height of (1 1 1) peak increased with the increase of the added elements, except some fluctuation in the height of peak. The comprehensive analysis showed that the crystallization quality of the sample was deteriorated gradually with the increase of added concentration.

➢ The findings of the SEM analysis show that the surface morphology of Ni(P) deposits changes from a smooth state to a non-smooth state when Ti-Zr is present because less nickel elements are deposited on the deposit surface. EDS analysis verifies that all of the additional components are present on the coatings. It is clear from the mapping of the quaternary alloy coating that an excessive concentration of alloying components in the bath causes the elements to accumulate in the coatings.

➢ In comparison with Ni(P) coating, the deposit's microhardness increased from 261 VHN200 to 405 VHN200, favouring greater wear resistance without affecting the deposit's structural integrity.

➢ Improved adhesion of the coatings was achieved due to the quaternary alloy coatings with Ni-Ti-Zr(P) having a substantially greater scratch resistance than coatings developed with Ni(P) alone. Ni-Ti-Zr(P) has excellent wear resistance and a strong adhesion property because of its high coefficient of friction.

➢ The optical pictures of the deposits revealed that there was some agglomeration in a few isolated spots, but overall, the second phase elements were equally blended throughout the thickness.

➢ Potentiodynamic polarization studies showed that, in comparison to plain Ni(P) deposits, low phosphorus quaternary alloy coatings exhibited higher polarization resistance values, comparatively lower corrosion current density and lower corrosion rate. Two-time constant behaviour was noted for both quaternary alloy and plain Ni(P) coatings based on EIS investigations; this behaviour may have resulted from the greater nodular morphology. Comparing quaternary alloy coatings to plain Ni(P) deposits, the coatings' increased corrosion resistance was shown by higher charge transfer resistance (Rct) values.

Data access statement

All relevant data are within the paper and its Supporting Information files.

CRediT authorship contribution statement

Megha Unni: Writing – original draft, Validation, Software, Methodology, Formal analysis, Data curation, Conceptualization. J. Sudagar: Writing – review & editing, Validation, Supervision, Resources, Project administration, Investigation, Funding acquisition, Formal analysis, Conceptualization.

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.

Acknowledgment

The Vice-Chancellor of VIT-AP and the Chancellor of the VIT groups are especially appreciated by the authors for granting permission to publish this article. Furthermore, acknowledgment is given to the RGEMS project (VIT-AP/SpoRIC/RGEMS/2023-24/010 ), and Open access fund, VIT-AP University, India.
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References

1 Muraliraja R. Anthoni Sagaya Selvan R. Mayanglambam Franco Sanjith U. Tamilarasan T.R. Selvakumar A. Sha W. Sudagar J. A review of electroless coatings on non-metals: baths conditions, properties and applications Journal of Alloy and Compounds 960 2023 170723 10.1016/j.jallcom.2023.170723
2 Sudagar Jothi Muraliraja R. Tamilarasan T.R. Udayakumar Sanjith Selvakumar A. ‘Electroless Composite Coatings’, Book Title: Electroless Nickel Plating: Fundamentals To Applications 2019 CRC Press 10.1201/9780429466274 ISBN 978-1-138-60580-0
3 Selvakumar A. Sanjith U. Tamilarasen T.R. Muraliraja R. Sha Wei Sudagar J. A critical review of carbon nanotube-based surface coatings Progress in Physics of Metals 23 1 2022 3 26 10.15407/ufm.23.01.003
4 Tamilarasan T.R. Rajendran R. Rajagopal G. Sudagar J. Effect of surfactants on the coating properties and corrosion behaviour of Ni-P-nano-TiO2 coatings Surf. Coating. Technol. 276 2015 320 326 10.1016/j.surfcoat.2015.07.008
5 Tamilarasan T.R. Rajendran R. Siva Shankar M. Sanjith U. Rajagopal G. Sudagar J. Wear and scratch behavior of electroless Ni-P-nano-TiO2 coatings: effect of surfactants Wear 346–347 2016 148 157 10.1016/j.wear.2015.11.015
6 Sha Wei Wu Xiaomin Keong Kim Ghee Electroless Copper and Nickel-Phosphorus Plating: Processing, Characterisation and Modelling 2011 Elsevier Hardback ISBN: 9781845698089, Paperback ISBN: 9780081014974, eBook ISBN: 9780857090966
7 Liu Bernard Haochih Liao Fang-Yi Chen Jian-Hong Design, fabrication, and characterization of electroless Ni–P alloy films for micro heating devices Thin Solid Films 537 2013 263 268 10.1016/j.tsf.2013.04.136
8 Sudagar Jothi Lian Jianshe Sha Wei Electroless nickel, alloy, composite and nano coatings–A critical review J. Alloys Compd. 571 2013 183 204 10.1016/j.jallcom.2013.03.107
9 Liu Hai-Ping Effect of organic additives on the corrosion resistance properties of electroless nickel deposits Thin Solid Films 516 8 2008 1883 1889 10.1016/j.tsf.2007.10.008
10 Chen B.-H. Effects of surfactants in an electroless nickel-plating bath on the properties of Ni− P alloy deposits Ind. Eng. Chem. Res. 41 11 2002 2668 2678 10.1021/ie0105831
11 Elansezhian R. Ramamoorthy B. Kesavan Nair P. The influence of SDS and CTAB surfactants on the surface morphology and surface topography of electroless Ni–P deposits J. Mater. Process. Technol. 209 1 2009 233 240 10.1016/j.jmatprotec.2008.01.057
12 ASM Handbook Cleaning and finishing Am. Soc. Metals vol. 5 1991 Material Park Ohio ISBN: 978-0-87170-384-2
13 Hubbell F.N. Chemically deposited composites—a new generation of electroless coatings Transactions of the IMF 56 1 1978 65 69 10.1080/00202967.1978.11870455
14 Hubbell Frederick N. Chemically deposited composites--a new generation of electroless coating Plating Surf. Finish. 65 12 1978 58 62 10.1080/00202967.1978.11870455
15 Hussain M.S. Such T.E. Deposition of composite autocatalytic nickel coatings containing particles Surf. Technol. 13 2 1981 119 125 10.1016/0376-4583(81)90052-2
16 Shoeib M.A. Mokhtar S.M. El-Ghaffar M.A.A. Mechanical and corrosion protection properties of electroless nickel-polymer composite coatings Met. Finish. 11 96 1998 58 59 10.1016/S0026-0576(98)80873-8
17 Shibli S.M.A. Jabeera B. Anupama R.I. Incorporation of nano zinc oxide for improvement of electroless nickel plating Appl. Surf. Sci. 253 3 2006 1644 1648 10.1016/j.apsusc.2006.02.063
18 Alirezaei S. Moonirvaghefi S.M. Salehi M. Saatchi A. Kargosha M. Surf Eng. 21 1 2006 60 10.1016/j.wear.2006.10.013
19 Bigdeli Faryad Allahkaram Saeed Reza An investigation on corrosion resistance of as-applied and heat treated Ni–P/nanoSiC coatings Mater. Des. 30 10 2009 4450 4453 10.1016/j.matdes.2009.04.020
20 Novakovic J. Vassiliou P. Vacuum thermal treated electroless NiP–TiO2 composite coatings Electrochim. Acta 54 9 2009 2499 2503 10.1016/j.electacta.2008.12.015
21 Huiming Jin Jiang Shihang Zhang Linnan Structural characterization and corrosive property of Ni-P/CeO2 composite coating J. Rare Earths 27 1 2009 109 113 10.1016/S1002-0721(08)60202-1
22 Yu Lin Microstructures and mechanical properties of NiTi shape memory alloys fabricated by wire arc additive manufacturing J. Alloys Compd. 892 2022 162193 10.1016/j.jallcom.2021.162193
23 Patel Swadhin Kumar A review on NiTi alloys for biomedical applications and their biocompatibility Mater. Today: Proc. 33 2020 5548 5551 10.1016/j.matpr.2020.03.538
24 Feng Bo Effect of laser hatch spacing on the pore defects, phase transformation and properties of selective laser melting fabricated NiTi shape memory alloys Materials Science and Engineering: A 840 2022 142965 10.1016/j.msea.2022.142965
25 Carl Matthew Van Doren Brian Young Marcus L. In situ synchrotron radiation X-ray diffraction study on phase and oxide growth during a high temperature cycle of a NiTi-20 at.% Zr high temperature shape memory alloy Shape Memory and Superelasticity 4 2018 174 185 10.1007/s40830-018-0149-0
26 Pang Jianbo Effect of Ti/Ni and Hf/Zr ratio on the martensitic transformation behavior and shape memory effect of TiNiHfZr alloys Materials Science and Engineering: A 807 2021 140850 10.1016/j.msea.2021.140850
27 McCluskey Patrick J. Precipitation and thermal fatigue in Ni–Ti–Zr shape memory alloy thin films by combinatorial nanocalorimetry Acta Mater. 59 13 2011 5116 5124 10.1016/j.actamat.2011.04.043
28 Karakoc O. Effects of training on the thermomechanical behavior of NiTiHf and NiTiZr high temperature shape memory alloys Materials Science and Engineering: A 794 2020 139857 10.1016/j.msea.2020.139857
29 Karakoc O. Actuation fatigue performance of NiTiZr and comparison to NiTiHf high temperature shape memory alloys Materials Science and Engineering: A 829 2022 142154 10.1016/j.msea.2021.142154
30 Chmielewska Agnieszka Heat treatment of NiTi alloys fabricated using laser powder bed fusion (LPBF) from elementally blended powders Materials 15 9 2022 3304 10.3390/ma15093304 35591638
31 Oshida Yoshiki Tominaga Toshihiko "Nickel-Titanium Materials." Nickel-Titanium Materials 2020 De Gruyter 10.1515/9783110666113
32 Hogmark Sture Jacobson Staffan Larsson Mats Design and evaluation of tribological coatings Wear 246 1–2 2000 20 33 10.1016/S0043-1648(00)00505-6
33 Wu Fan-bean Duh Jenq-gong Scratch behavior and in situ acoustic emission analysis of PVD chromium nitride coatings on mild steel with electroless nickel interlayers Surf. Coating. Technol. 162 1 2003 106 112 10.1016/S0257-8972(02)00562-5
34 Chen Zhong Multi-layered electroless Ni–P coatings on powder-sintered Nd–Fe–B permanent magnet J. Magn. Magn Mater. 302 1 2006 216 222 10.1016/j.jmmm.2005.09.008
35 Vitry Véronique Delaunois Fabienne Dumortier Christian Mechanical properties and scratch test resistance of nickel–boron coated aluminium alloy after heat treatments Surf. Coating. Technol. 202 14 2008 3316 3324 10.1016/j.surfcoat.2007.12.001
36 Boukamp Bernard A. A linear Kronig‐Kramers transform test for immittance data validation J. Electrochem. Soc. 142 6 1995 1885 10.1149/1.2044210
37 Balaraju J.N. Rajam K.S. Preparation and characterization of autocatalytic low phosphorus nickel coatings containing submicron silicon nitride particles J. Alloys Compd. 459 1–2 2008 311 319 10.1016/j.jallcom.2007.04.228
38 Aal A. Abdel Hard and corrosion resistant nanocomposite coating for Al alloy Materials Science and Engineering: A 474 1–2 2008 181 187 10.1016/j.msea.2007.04.058
39 Subakova Ilzira Petukhov Igor Medvedeva Natalia Obtaining of Ni–P–TiO2 composite coatings with TiO2 sol and surfactants and their properties Mater. Manuf. Process. 30 6 2015 766 770 10.1080/10426914.2014.994756
40 Rus Dorin Capitanu Lucian Badita Liliana-Laura A qualitative correlation between friction coefficient and steel surface wear in linear dry sliding contact to polymers with SGF Friction 2 2014 47 57 10.1007/s40544-014-0038-2
41 Ingle Avinash V. Corrosion resistant quaternary Al–Cr–Mo–N coating on type 316L stainless steel bipolar plates for proton exchange membrane fuel cells Int. J. Hydrogen Energy 45 4 2020 3094 3107 10.1016/j.ijhydene.2019.11.119
42 Balaraju J.N. Electrochemical studies on electroless ternary and quaternary Ni–P based alloys Electrochim. Acta 52 3 2006 1064 1074 10.1016/j.electacta.2006.07.001
43 Balaraju J.N. Ezhil Selvi V. Rajam K.S. Electrochemical behavior of low phosphorus electroless Ni–P–Si3N4 composite coatings Mater. Chem. Phys. 120 2–3 2010 546 551
