Academic literature on the topic 'Ni-P/Ni-W-P Coatings'

The present paper considers the comparative study of tribological characteristics of various electroless alloy coatings viz. Ni-P, Ni-P-W and Ni-P-Cu. The tribological behavior of these coatings depends on various parameters like load, speed, lubricant, chemical compositions and heat treatment temperature to a great extent. One of the main effects of heat treatment on these coatings is phosphide precipitation, which makes them suitable for anti-wear applications. The property of binary Ni-P can be further improved by depositing third particles electrolessly. The phase structure of the coatings depends on the amount of phosphorous and heat treatment temperature. The tribological behavior of heat treated samples reveals that Ni-P-W deposit shows higher coefficient of friction and lowest wear among these three types coatings. Very high tungsten concentration retard the phosphide precipitation, thus low concentration of tungsten and low heat treatment temperature produce better coating. In case of Ni-P-Cu, medium concentration of copper and medium heat treatment temperature produces better coating.

The Ni-Me-P alloy coatings containing metal as alloying component (Me = Co, W) in a Ni-P amorphous matrix, were potentiostatically electrodeposited onto a polycrystalline Cu substrate. Deposition potential was established based on polarization curves of electrodeposition of Ni-Co-P, Ni-W-P and Ni-P alloy coatings. SEM, EDS, XRD and X-ray microanalysis methods, were applied for chemical and physical characterization of the obtained coatings. Linear analysis of Ni, Co and W distribution in the microregions of the appropriate alloy coating revealed that surface distribution of these elements is homogeneous what is due to a molecular mixing of the amorphous nickel matrix with the alloying components. It was found that the Ni-Co-P and Ni-W-P coatings have the amorphous structure like the Ni-P deposit and alloying components as Co or W are built-in into the appropriate coating in the amorphous form. The mechanism of the induced codeposition of these ternary Ni-Me-P coatings, has been discussed.

The hardness, wear rates, phase structure and morphologies of DC(direct current) and PC(pulse current )electrodeposited Ni-W-P-SiC, RE-Ni-W-P-SiC, RE-Ni-W-P-SiC-MoS2 and RENi- W-P-SiC-PTFE composite coatings are studied. The results indicate that the hardness of pulse composite coatings is higher than that of DC composite coatings, but the hardness of RE-Ni-W-PSiC- PTFE composite coating is lower. The hardness of the four kinds of composite coatings increases with the rise of heat treatment temperature and reaches the highest value at 400°C, thereafter, the hardness begins to decrease. The hardness of RE-Ni-W-P-SiC composite coating is the highest when duty cycle is at 0.6 and 0.8 and pulse frequency is at 50Hz and the hardness of RE-Ni-W-P-SiC composite coatings at 0.8 is higher than that at 0.6; the wear rates of Ni-W-P-SiC, RE-Ni-W-P-SiC, and RE-Ni-W-P-SiC-PTFE pulse composite coatings are lower than that of DC composite coatings and the wear rates of RE-Ni-W-P-SiC-MoS2 and RE-Ni-W-P-SiC-PTFE composite coatings are the lowest. Ni-W-P-SiC and RE-Ni-W-P-SiC pulse composite coatings are amorphous, and RE-Ni-W-P-SiC-MoS2 pulse composite coating is mixture, but the RE-Ni-W-PSiC- PTFE composite coating is crystal as–deposited. The crystalline grain size of PC composite coatings is smaller than that of DC composite coatings, and the addition of rare earth into the coatings can make crystalline grains become fine, all kinds of grains in the coatings distribute equably and there are not cracks on the surface and in the sections.

The paper presents results of research concerning the evaluation of corrosion resistance of heat-treated alloy coatings (Zn-Ni-W/320°C and Zn-Ni-P-W/320°C). The surface morphology and phase composition of the obtained coatings were determined. Electrochemical corrosion resistance was studied in 5% NaCl solution. On the basis of these studies it was found that the corrosion resistance of Zn-Ni-P-W/320°C coating is higher than Zn-Ni-W/320°C coating.

The Ni-P-W/Al2O3composite coatings were deposited on the surface of sintered NdFeB permanent magnet by electroless plating method. The morphology and the phases of Ni-P-W/Al2O3composite coatings were investigated using scanning electron microscopy and X-ray diffraction respectively. The hardness and the corrosion resistance of the composite coatings were also tested. The results indicated that the composite coatings morphology appears closely nodules morphology, and the microhardness increases linearly with increasing incorporation of Al2O3ratio. Compared with NdFeB magnet and Ni-P-W amorphous alloy coating, the corrosion resistance of the composite coatings was superior to that of the NdFeB magnet and the amorphous alloy coating obviously. However, for the corrosion resistance of Ni-P-W/Al2O3composite coatings with different Al2O3concentration, there is not a linear increase with the Al2O3concentration increasing. The self-corrosion potential of Ni-P-W/Al2O3composite coatings reaches the highest value while increasing incorporation of Al2O3ratio up to 10 g/L.

Corrosion resistance properties, such as porosity, stability in the atmosphere of NaCl mist, and anodic electrochemical activity in a sulfuric acid solution are studied and compared for Ni-W-P and Ni-P coatings obtained by electroless deposition. The studied coatings were obtained from solutions with glycine as the main ligand and contained 10.2 to 15.6 at.% of phosphorus and up to 3.3 at.% of tungsten. It is shown that Ni-W-P coatings with a tungsten content of 2.3 to 3.3 at.% and a thickness of 15 μm have a significantly lower porosity as compared with nickel-phosphorus coatings of the same thickness. Also, significantly better stability of Ni-W-P coatings in a NaCl mist atmosphere was observed, their corrosion damage degree is less than that of Ni-P coatings, and relatively little depends on the duration of exposure in a corrosive environment. Analysis of anodic polarization curves showed an almost similar electrochemical activity upon dissolution of Ni-P and Ni-W-P coatings in sulfuric acid. Both these types of electroless coatings showed a markedly better tendency to anodic dissolution than pure nickel. Taking into account the obtained experimental data, a conclusion is made as to the better protective characteristics of Ni-W-P coatings in comparison with nickel-phosphorus coatings. The main reason of the inferior protective properties of Ni-P coatings is their relatively high porosity.

The Ni-W-P/graphene composite coatings were prepared in the Ni-based electrodepositing solution and graphene oxide mixture, the effect of stirring modes (including no stirring, mechanical stirring or ultrasonic stirring) on the surface quality of the composite coatings was investigated and the optimum formula of the electrodepositing solution of the Ni-W-P/graphene composite coatings was obtained through the orthogonal experiments in 4 factors and 4 levels. It was determined that ultrasonic stirring was the optimum stirring mode during electrodeposition. The Raman spectrum and EDS have shown that there existed graphene, in addition to Ni, W and P in the Ni-W-P/graphene composite coatings. The surface of the Ni-W-P/graphene composite coatings was smooth and the structure was compact. The average microhardness of the Ni-W-P/graphene composite coatings was improved by 26.7% higher than that of the Ni-W-P coatings after the heat treatment of 600°C.

碩士
大葉大學
電機工程學系
101
In this thesis, a block-on-ring tribocorrosion tester was employed to study the corrosion and wear behavior of electrodeposited Ni-W-P alloy in 5% NaCl solution. Under different polarization overpotentials, the effects of coating microstructure on the weight loss and friction coefficient were investigated quantitatively. In corrosion testing, the coating surface started from good corrosion resistant to the initiation of tiny corrosion pits with the increasing polarization potential. Eventually, the growth and interconnection between pitting holes induced cracking and increased the weight loss and surface roughness. For tribocorrosion under the application of very low overpotential, the surface showed trace of wear but no corrosion. Accompanying the raise in overpotential, the area of wear contact as well as the coefficient of friction increased. At high overpotential, pitting holes emerged in addition to the wearing trace on the surface. Finally, the enlargement of the area and depth of pitting holes rendered the initiation of cracking. However, the enlarged pitting holes provided the sites for the inclusion of solution between the coating and the wear block, which assumed the load bearing capability and reduced the area of contact. Subsequently, the coefficient of friction decreased with the increase in overpotential. In quantitative tribocorrosion analysis, Ni-W-P alloy was found to have good wear-corrosion resistance at low overpotentials. Under the application of high overpotential, the synergistic effect between wear and corrosion was the main cause for the quick deterioration of the coating surface. In addition, the wear weight loss increased continuously with the raise in overpotential while the corrosion weight loss remained more or less constant.

Magnesium and its alloys are extensively used for various industries such as aerospace, automobile and electronics due to their excellent properties such as low density, high strength and stiffness and electromagnetic shielding. However, the wide spread applications of these alloys are limited due to the undesirable properties such as poor corrosion, wear and creep resistance and high chemical reactivity. These alloys are highly susceptible to galvanic corrosion in sea water environment due to their high negative potential (-2.37 V vs SHE). The effective way of preventing corrosion is through the formation of a protective coating, which acts as a barrier between the corrosive medium and the substrate. Many surface modification methods such as electro/ electroless plating, conversion coating, physical and chemical vapour depositions, thermal spray coating etc., are available currently to improve the corrosion resistance of Mg alloys. Of these methods, the electroless nickel plating has gained considerable importance because of its excellent properties such as high hardness, good wear and corrosion resistance. The properties of binary electroless nickel coating have been further improved by the addition of a third element such as cobalt, tungsten, tin and copper etc. It has been reported that the addition of tungsten as the third element in the Ni-P improves the properties such as hardness, wear and corrosion resistance, thermal stability and electrical resistance. Magnesium alloys are categorized as a “difficult to plate metal”, because of their high reactivity in the aqueous solution. They react vigorously with atmospheric oxygen and water, resulting in the formation of the porous oxide/ hydroxide film which does not provide any protection in the corrosive environment. Further, the presence of this oxide film prevents the formation of a good adhesive bond between the coating and the substrate. The surface treatment process for removal of the oxide layer is very much essential before plating the Mg alloy. Currently two processes such as zinc immersion and direct electroless nickel plating are adopted to plate Mg alloys. Etching in a solution of chromate and nitric acid followed by immersion in HF solution to form a conversion film is necessary for direct electroless nickel (EN) plating of Mg alloy. However, strict environmental regulations restrict their usage because of hazardous nature. Expensive palladous activation treatment is a well-known process as a replacement for chromate-HF pretreatments for Mg alloys. It has been reported that EN plating has been carried out over Mg alloys by using conversion coating followed by HF treatment. Formation of an intermediate oxide layer by electrolytic methods is also one of the ways these toxic pretreatments can be avoided. Microarc oxidation (MAO) is an environment friendly surface treatment technique which provides high hardness, better corrosion and wear resistance properties for the Mg alloys. EN coating has been prepared on MAO layer for improving the corrosion resistance. These MAO/EN composite coatings have been prepared using chromic acid and HF pretreatment process. As the replacement for the chromate-HF pretreatment, SnCl2 and PdCl2 sensitization and activation procedures respectively were adopted over MAO layer for the deposition of Ni-P coating. From the above reported literature, it can be inferred that for the activation of inert MAO layer to deposit electroless nickel coating, the hazardous chromate/HF and highly expensive PdCl2 activation processes were followed. Therefore, there is a need for identifying an alternative simple and cost effective pretreatment process for the deposition of electroless nickel. It is well known that borohydride is a strong reducing agent that has been used for the deposition of Ni-B coatings. In the present study, an attempt has been made to utilize borohydride in the pretreatment process for the reduction of Ni2+ ions over the MAO interlayer, which provides the nucleation sites for the deposition of Ni-P coating. Ni-P and Ni-P/Ni-W-P duplex coatings were deposited from stabilizer free carbonate bath on AZ31B Mg alloy to improve the corrosion resistance of the base substrate. The conventional chromate and HF pretreatment processes were followed for the deposition of electroless nickel coating. In order to improve the corrosion resistance of the duplex coating, post treatments such as heat treatment (4 h at 150°C) and chromate passivation were adopted. EDX analysis of AZ31B Mg alloy showed the presence of 2.8 wt.% of Al and 1.2 wt. % Zn with the balance of Mg for AZ31B Mg alloy. After the chromic acid and HF treatment, the magnesium content was reduced from 90.0 wt % to 54.9 wt%, which could be due to the incorporation of chromium on the surface layer. The surface showed about 17.8 wt. % of F. The alloy exhibited the roughness of about 0.29± 0.01µm after mechanical polishing. The roughness value was significantly changed after the chromic acid treatment processes. The maximum roughness of about 1.28±0.06 µm was obtained after the HF activation. XPS analysis confirmed the existence of chromium in +3 oxidation state after the chromic acid treatment. The Ni-P coating thickness of about 25 microns was obtained in 1 h and 15 min. In the case of duplex coatings, Ni-P plating was done for 45 min. to obtain approx. 17 microns thickness and Ni-W-P plating was done for 1.15 h to obtain a thickness of approx. 10 microns, resulting in a total thickness of 25 ± 5 microns. Ni–P coating exhibited nodular morphology with porosity. The size of these cluster nodules were of about 10 µm in diameter. On the other hand, the duplex coating exhibited a less nodular, dense and smooth appearance. From the compositional analysis it was found that Ni–P coating contained about 6 wt. % P. In the case of duplex coating, the P content was reduced to 3 wt % due to the incorporation of about 2 wt% of tungsten. In corrosion studies, the potentiodynamic polarization data obtained for bare Ni-P coating in 0.15 M NaCl solution exhibited a higher current of about 218 μA/cm2 as compared to the substrate due to the porosity of the coating. However, the Ni-P/Ni-W-P duplex showed 55 times improvement in corrosion resistance, vis-a-vis Ni-P due to the dense nature of the coating. The corrosion resistance of the coatings increased in the following order: Ni-P < bare alloy < duplex < duplex-passivated < duplex-heat treated passivated. In EIS study, the Nyquist plot obtained for the bare substrate and Ni–P coating showed the presence of inductance behavior at the lower frequency region due to the adsorption of electroactive species over the substrate through the porous oxide layer. However, the passivated and duplex passivated coatings exhibited only capacitive behavior due to their compact nature. From the above, it can be concluded that, direct deposition of Ni-P coating over the chosen Mg alloy using chromic acid and HF pretreatment process resulted in porous morphology, which affected the corrosion resistance of the coating. As an alternative strategy, the microarc oxidation conversion coating was developed on Mg alloy and characterized. The MAO coating was developed using silicate electrolyte at three different current densities (0.026, 0.046 and 0.067 A/cm2) for about 15 min. With respect to the MAO coating, an increase in the current density increased the pore diameter and decreased the pore density. The surface of the coating became coarser and rough. The cross-sectional morphology of the coating showed two district layers namely the dense and thin inner layer and a porous thick outer layer. The thickness of the coating increased with increase in current density. MAO coating prepared at an intermediate current density of 0.046 A/cm2 exhibited a higher thickness of about 12 µm and a further increase in current density showed a decrease in thickness, due to the greater rate of dissolution of Mg, relative to the rate of deposition. The surface roughness of the MAO coatings also increased with increase in current density. The Ra value increased from 1.39±0.06 to 3.52±0.17 µm with increase in current density. XRD peaks obtained for the Mg substrates corresponded predominately to magnesium. However, the coated specimens showed the presence of peaks corresponding to Mg2SiO4 along with Mg and MgO. The corrosion measurements for the bare substrate and MAO coatings were carried out in 3.5% NaCl medium (0.6 M). Based on potentiodynamic polarization studies, the MAO coating prepared at 0.046 A/cm2 exhibited a lower corrosion current density with a higher Rp value, which was about five orders of magnitude higher than the bare substrate, due to the dense nature of the coating. In EIS study, MAO coatings were fitted with the two time constants equivalent circuit containing outer porous layer and inner barrier layer. The barrier layer resistance values were higher than that of porous layer resistance, which indicated that the resistance offered by barrier layer was higher than the porous layer. The total resistance value obtained for the coating prepared at 0.046 A/cm2 were higher compared to the other coatings, which attested to its better corrosion resistance. The electrochemical noise measurement was carried out for longer immersion durations upto 336 h in 3.5% NaCl solution. The noise resistance value obtained for the base Mg alloy was about 100 Ω at 1h immersion, whereas for the MAO coating prepared at 0.04 A/cm2 a maximum value of about 34.8 MΩ was achieved and it was retained even after 96 h of immersion. Mott–Schottky analysis showed that the oxide layer on magnesium substrate acted as a n-type semiconductor, whereas the MAO coatings exhibited p-type semiconductor behavior. The MAO coating obtained at an intermediate current density showed a higher acceptor density and the flat band potential, which resulted in the better performance of the coating in corrosive environment. In another set of investigations, the Ni-P and Ni-P/Ni-W-P coatings were deposited on AZ31B Mg alloy with MAO coating as an interlayer. The MAO layer was activated by a simple borohydride pretreatment process. During the pretreatment process, the MAO coating was subjected to mild alkali treatment, immersion in the Ni-P plating solution and finally immersion in borohydride solution. During each pretreatment step, the sample was characterized for their surface morphology and composition. The surface morphology showed the distribution of spherical particles over the surface of MAO coating after immersion in the Ni-P plating solution. EDX analysis showed the presence of 2.4 wt. % of Ni, which confirmed that Ni ions were adsorbed over the surface of the MAO coating during the pretreatment process. XPS analysis carried out after immersion in the Ni-P plating solution indicated that Ni existed in +2 oxidation state. The surface became smooth and uniform with flake- like morphology after the borohydride treatment, which indicated that the surface was etched by the borohydride solution. EDX analysis showed the presence of 1.8 wt.% of Ni after borohydride reduction. XPS analysis confirmed the reduction of nickel to the zero oxidation state. Additionally, MAO/Ni-P and MAO/Ni-P/Ni-W-P duplex coatings were developed on MAO coating after a simple borohydride pretreatment. Ni-P and duplex coatings showed uniform and dense nodular morphology without any defects, which clearly indicated that the borohydride treatment provided a uniform and homogeneous active surface for the deposition of electroless nickel based coatings. Borohydride pretreatment process resulted in excellent bonding between MAO/Ni-P layers in the cross section. Based on potentiodynamic polarization studies, the corrosion current values obtained for MAO/ Ni-P and MAO/Ni-P/Ni-W-P duplex coatings were about 1.44 and 1.42 µA/cm2, respectively. The coating showed about 97 times improvement in corrosion resistance compared to the bare substrate, attesting to the dense nature of the coating. In EIS study, the single time constant equivalent circuit was used for fitting the spectra, which pertained to the coating /electrolyte interface. The single time constant could be attributed to the pore-free dense, uniform coatings developed over the MAO interlayer. For the MAO/Ni-P and MAO/Ni-P-Ni-W-P duplex coatings, the charge transfer resistance of about 15 and 11 kΩcm2 were obtained for duplex and Ni-P coatings, which reinforce the better corrosion protective ability of the coating. The above investigation confirms that MAO coatings have good corrosion resistance in the aggressive chloride medium. Consequently, they can serve as an ideal interlayer for the deposition of the electroless nickel coating. Even if the electroless nickel coating is found to fail in harsh environments, the MAO interlayer can protect the base substrate due to its higher corrosion resistance. It is also noteworthy that the borohydride treatment provides better adhesion between the MAO/Ni-P interlayer.

碩士
國立臺北科技大學
製造科技研究所
101
The main purpose of this study is to investigate the effects of various process parameters electrodeposited Ni-W-P alloy on the surface treatment using. The modified Watts bath consisted of nickel sulfate, phosphorous acid and Sodium tungstate solution. The Alpha-Step profilometer, FESEM, XRD were employed for observation and analysis of material microstructure in order to determine the critical factor which inference the coating hardness, such as element content and microstructure of the coating. The experimental results showed that coating hardness, heat-resistant, wear resistance and corrosion resistance is better than nickel, Ni-W alloy and Ni-P alloy. Increasing current density had obvious effect on the coating tungsten content. The hardness of the coating was increased, but the electroplated efficiency was lower, and the roughness of increased the coating surface. The phosphorus content in coating became higher with the raise in the added amount phosphorous acid, which electroplated efficiency was lower. The use of pulse plating increased tungsten content in coating, and reduced internal stress and improved electroplated efficiency. In addition raising the pH value in solution caused increases in internal stress, the coating surface cracks, and lowered electroplated efficiency. With annealing at appropriate temperature, the Ni-W-P alloy coating hardness reached 900~1100HV, which increased the wear resistance, and became a potential candidate for replacing hard chromium coating.

博士
國立清華大學
材料科學工程學系
91
Electroless nickel (EN) deposit is frequently employed for many industrial applications due to its various excellent properties. The electroless Ni-P deposit can be strengthened by the precipitation of Ni-P compounds after heat treatment. Nevertheless, the hardness of Ni-P films degrades with excessive annealing. It is thus critical to increase the crystallization temperature so that the Ni-P deposit can withstand sufficient or even superior hardness at elevated temperatures. To enhance the thermal stability, the addition of a third element in the Ni-P coating to form a ternary Ni-P-based coating is put into practice. It is found that thermal stability of electroless Ni-P-W deposit can be enhanced by the co-deposition of W as compared to binary electroless Ni-P films. The ternary Ni-P-W alloy coating is also fabricated by rf magnetron sputtering technique with dual targets of Ni-P/Cu and pure W. A fixed P/Ni ratio and linear W content dependence on input power is revealed in the ternary Ni-P-W coating, indicating a well control in composition of the coating through sputtering technique. Thermal stability analysis shows that the introduction of W in the Ni-P coating by co-sputtering retards the Ni3P precipitation and retains the strengthening effect to a higher temperature of 550°C. Microstructure evolution indicates that all coatings in the as-deposited state show amorphous structure. The precipitation of Ni3P accompanied with W dissoluted Ni matrix is revealed to be the final product of the phase transformation in Ni-P-W coatings after thermal treatment. Results in microhardness test show that the surface hardness can be engineered by the controlling the composition and microstructure in the Ni-P-W coating. After heat treatment, the coating is strengthened by the precipitation of Ni-P compounds and solutioning of W in the crystallized Ni matrix. Quantitative analysis for the strengthening effect of the Ni-P-W coatings is performed based on Ni-P compound precipitation and Ni(W) matrix ratio. Both electroless Ni78.4P18.3W3.3 and sputtered Ni80.0P15.3W4.7 coatings exhibit a hardness around 1600 HK due to Ni3P precipitation and W solutioning hardening in Ni matrix to a W/Ni(W) ratio of approximately 12at.% after heat treatment. A higher microhardness of 1790 HK is measured in the sputtered Ni76.7P15.9W7.4 coating. Through quantitative analysis, the effect of strengthening in Ni-P-W ternary coatings under heat treatment can be clearly demonstrated. From surface analysis, the nodular nature of the electroless coatings is responsible for the rougher surface profile as compared to the sputtered coatings. With the co-sputtering of W, the early stage Ni-P compounds is suppressed, according to X-ray and surface morphology analysis. After heat treatment, the surface morphology and roughness of both electroless and sputtered Ni-P-W films remain identical to those in the as-deposited state, indicating a stable surface characteristic under thermal treatment.

The present chapter aims to determine optimal tribo-testing condition for minimum coefficient of friction and wear depth of electroless Ni-P, Ni-P-W and Ni-P-Cu coatings under lubrication using grey relational analysis. Electroless Ni-P, Ni-P-W and Ni-P-Cu coatings are deposited on AISI 1040 steel substrates. They are heat treated at suitable temperatures to improve their hardness. Coating characterization is done using scanning electron microscope, energy dispersive X-Ray analysis and X-Ray diffraction techniques. Typical nodulated surface morphology is observed in the scanning electron micrographs of all the three coatings. Phase transformation on heat treating the deposits is captured through the use of X-Ray diffraction technique. Vicker's microhardness of the coatings in their as-deposited and heat treated condition is determined. Ni-P-W coatings are seen to exhibit the highest microhardness. Friction and wear tests under lubricated condition are carried out following Taguchi's experimental design principle. Finally, the predominating wear mechanism of the coatings is discussed.

Ni-Cu-P-W coating was deposited by electroless method on mild steel substrate to study the crystallization and tribological behavior at different annealing temperatures. Energy dispersive x-ray (EDX) analysis, scanning electron microscopy (SEM), x-ray diffraction (XRD), and differential scanning calorimeter (DSC) were used to study the composition, surface morphology, phase behavior, and thermal behavior of the coating, respectively. Tribological study was conducted using Pin-on-Disc tribotester. EDX analysis confirms the presence of Ni, Cu, P, and W in the deposit. SEM image shows the surface is dense, smooth, and without any observable nodule. Some of the samples were heat treated to 300°C, 500°C, and 700°C for 1 hour to observe the crystallographic change by XRD. One sharp crystalline peak of Ni (111) is present in all condition, but the intensity increases rapidly with the heat treatment temperature. The phase transition temperature of this quaternary coating analyzed by DSC was 431.8°C.

Chemically deposited nickel coatings possess superior tribological properties such as high hardness, good wear, and corrosion resistance. The quest for improved tribological performance has led to the design and selection of newer variants of these coatings. The present chapter deals with the development of Ni-P-W coating on mild steel substrate and the improvement of tribological characteristics through modification of the coating process parameters. Three coating process parameters, concentration of nickel source, concentration of reducing agent, and concentration of tungsten source along with the annealing temperature, are optimized for minimum friction and wear of the coating. Friction and wear tests are carried out in a multi-tribotester using block on roller configuration under dry conditions. Taguchi-based grey relational analysis is employed for the optimization of this multiple response problem using L27 orthogonal array. Analysis of variance shows that the concentration of nickel source, the interaction between nickel source concentration, and reducing agent concentration, and also the interaction between nickel source concentration and tungsten source concentration have significant influence in controlling the friction and wear behavior of chemically deposited Ni-P-W coating. It is observed that wear mechanism is a mild adhesive in nature. The structural morphology, composition, and phase structure of the coating are studied with the help of Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray analysis (EDX), and X-Ray Diffraction analysis (XRD), respectively.

In this study we consider copper sample as a substrate under which the Electroless Ni-W-P coatings were established and successfully deposited. The three factor was taken into consideration, i.e. concentration of the Nickel Sulphate, Sodium Hypophosphite and Sodium Tungstate Dihydrate. Central Composite Design modelling was done with the help of total 20 runs that were conducted in the design, with mass deposition per unit area as the response parameter. The optimized sample was evaluated from the Design of Experiments based on Central Composite design. From where we examined the individual levels of the coatings, ANOVA, Examination of Normal Plot of Residual, Predicted and Actual plot and Second order 3-D and Contour plot showing interaction for Response Surface Mass Deposition per Unit Area.It was found that the optimized as-coated value for mass deposition per unit area has the significant process parameters, the value is linear in nature and it has highest response which is of 134.055×10-4 gm/cm2.