Electroless Ni-B Coatings Research Articles

Effect of Different Pretreatments and Heat Treatment on Wear Properties of Electroless Ni-B Coatings on 7075-T6 Aluminum Alloy

The effect of various pretreatments on wear behavior of electroless nickel - boron (ENi-B) deposits obtained from a thallium free bath of nickel chloride as source of nickel is presented in this paper. For any quality coating pretreatment is required. The adhesion of coating significantly depends on the pretreatment. Hence in the present investigations five different pretreatments such as zincate (Zn), Ni strike 1 (Ni 1) and Ni strike 2 (Ni 2), absorbed hypophosphite layer (AHL) and Palladium strike (PD) were given to the substrate prior to the ENi-B coating and their corresponding wear properties were examined. The quality of coatings with and without heat treatments was estimated by pin on disc wear test method as per ASTM G99 standard. The surface morphology of the coated samples were examined by scanning electron microscope (SEM). The structural characterization of the coated samples was examined by X- ray diffraction (XRD) technique. The results obtained indicated that the wear resistance of the ENi-B deposits were significantly influenced by the pretreatment conditions. Among the five different pretreatments, AHL provided better adhesion of coatings over the aluminum alloy. The quality of pretreatments with respect to wear and coefficient of friction are rated as follows: AHL > PD > Ni 2 > Zn > Ni 1. AHL pretreatment significantly improved the wear resistance and decreased the average coefficient of friction. Further to know the influence of heat treatment on wear behaviour of coated samples, the samples were heated at 400° C. It was found that heat treatment improved the wear resistance from ∼ 30μm to ∼ -70μm. After heat treatment the average coefficient of friction of AHL samples decreased from 0.079 to 0.009. The complete experimental results and analysis are reported in main paper.

Research on Micro-Structure of Electroless Ni-B Coatings

By means of X-ray diffractometry (XRD) and transmission electron microscope (TEM), the micro-structure of 5 different Ni–B alloy coatings prepared by electroless plating with Potassium borohydride content ranging from 0.2 to approximately 1.4g/L was studied The influence of the KBH4 content in the coatings on their micro-structure was also investigated. It has been found that Ni–B alloy coatings showed amorphous sytuctue with XRD while with TEM it showed a combination of amorphous and nanocrystalline structure. It was further revealed that the amorphous structure increased with increasing KBH4 content, which means that Ni-B alloy coating prepared with increasing KBH4 content undergoes a transition process as follows: nanocrystalline → crystalline → amorphous structure. Results indicated that the micro-structure of Ni-B alloy coatings should be studied by both methods of XRD and TEM.

The Study of Electroless Ni-B Coating on 45 Steel

In order to improve the corrosion resistance and the hardness of the 45 steel, under comparison tests, the electroless Ni-B was prepared on the 45 steel. We made a contrast test to get the optimal formula. The coating under the optimal formula was characterized by Scanning Electron Microscopy(SEM), Energy Dispersive Spectrometer(EDS), metallurgical microscope and salt spray cabinet. The experimental results showed that the electroless Ni-B coating on 45 steel was low boron coating, with high hardness, and the hardness of the coating could catch HV524; the thickness of the coating was 16μm.

Influence of Process Parameters on Microhardness of Electroless Ni-B Coatings

Electroless Ni-B coatings have found large applications due to their high hardness and wear resistance. The present paper tries to investigate the influence of coating process parameters on the microhardness of electroless Ni-B coating with the help of Taguchi analysis. Four parameters, namely, bath temperature, concentration of reducing agent, concentration of nickel source, and annealing temperature, are considered and fitted into an [Formula: see text] orthogonal array to find out the optimized condition for improved hardness of the coating. The optimized condition is found to yield about 19% improvement in hardness of the coating compared to the initial condition. The significance of the process parameters and their interactions on the hardness of Ni-B coating is studied with the help of analysis of variance, which revealed that annealing temperature and concentration of reducing agent have significant influence over the hardness characteristics of electroless Ni-B coating. The compositional, microstructural, and phase structure analyses are conducted with the help of energy-dispersive X-ray analysis, scanning electron microscope, and X-ray diffraction analyzer, respectively.

Formation of Electroless Ni-B Coating on Boron Carbide Particles for Composite Processing

The present investigation is on formation of a uniform coating of Ni-B coating on the surface of B4C particle by electroless technique by varying process parameters and pH of the coating bath. The coating characteristics observed on majority of pH conditions on activated particles were mesh-like and at higher pH 12 the coated surface characteristics changes to patch like morphology. At lower alkaline condition there was not enough time for co-deposition to occur and the co-deposits appeared along with the coated particles. The studies with varying pH showed that pH 8 gives uniform coating of the entire particles surface with Ni-B and above which higher amount of co-deposited particles of Ni-B is also observed.

Roughness Optimization of Electroless Ni-B Coatings Using Taguchi Method

In this paper, the authors present an experimental study of roughness characteristics of electroless Ni-B coatings and optimization of the coating process parameters based on L27 Taguchi orthogonal design. Three coating process parameters are considered viz. bath temperature, reducing agent concentration, and nickel source concentration. It is observed that concentration of reducing agent together with bath temperature play a vital role in controlling the roughness characteristics of the coatings. The analysis yields the optimum coating parameter combination for minimum roughness. A reduction of about 15% is observed in roughness at the optimal condition compared to the initial condition. The microstructure, composition, and the phase content of the coating are also studied with the help of scanning electron microscopes energy dispersive X-ray analysis, and X-ray diffraction analysis, respectively.

The effects of deposition parameters on surface morphology and crystallographic orientation of electroless Ni-B coatings

Electroless Ni-B coatings were deposited on AISI 304 stainless steels by electroless deposition method, which was performed for nine different test conditions at various levels of temperature, concentration of NaBH4, concentration of NiCl2, and time, using the Taguchi L9(34) experimental method. The effects of deposition parameters on the crystallographic orientation of electroless Ni-B coatings were investigated using SEM and XRD equipment. SEM analysis revealed that the Ni-B coatings developed six types (pea-like, maize-like, primary nodular, blackberry-like or grapes-like, broccoli-like, and cauliflower-like) of morphological structures depending on the deposition parameters. XRD results also showed that these structures exhibited different levels of amorphous character. The concentration of NaBH4 had the most dominant effect on the morphological and crystallographic development of electroless Ni-B coatings.

Study of Potentiodynamic Polarization Behaviour of Electroless Ni-B Coatings and Optimization using Taguchi Method and Grey Relational Analysis

Electroless nickel coatings are very popular for their corrosion resistant actions. The present article attempts to study the corrosion behaviour of electroless Ni-B coatings by varying the coating parameters viz. bath temperature, reducing agent concentration and nickel source concentration together with the annealing temperature. The electrochemical parameters viz., corrosion potential and corrosion current density are evaluated with the help of potentiodynamic polarization experimentation. Taguchi based Grey analysis is employed in order to optimize this multiple response problem and the optimal combination of parameters for maximum corrosion resistance for Ni-B coatings is presented. Moreover, analysis of variance reveals that bath temperature and concentration of nickel source have significant influence on the corrosion performance of the coating. The microstructure characterization of the coating is also conducted with the help of scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction analysis. The Ni-B coating in general exhibits a nodular structure and turns crystalline with heat treatment. The corroded surface exhibits cracks and black spots which imply the occurrence of localized corrosion.

A parametric investigation of the friction performance of electroless Ni‐B coatings

AbstractFriction performance of electroless Ni‐B coatings sliding against steel is experimentally investigated in this paper. Friction performance is measured in terms of coefficient of friction (COF) for varying tribological testing parameters such as load, speed and time. Taguchi‐based optimisation of the testing parameters is attempted to find the optimal combination of testing parameters for minimum COF. An analysis of variance reveals that all the testing parameters have significant influence on the friction performance of the coating. Also, the interaction between load and speed is found to affect the friction more compared with the rest of the interactions. The coating characterisation is done with the help of scanning electron microscopy (SEM), energy dispersive X‐ray and X‐ray diffraction analysis. It is found that the Ni‐B coating is amorphous in the as‐deposited condition but gradually turns crystalline with heat treatment. The sliding tracks observed with SEM showed that abrasive failure is the predominant wear mechanism. Copyright © 2010 John Wiley & Sons, Ltd.

Effects of Heat-Treatment Processes on the Electroless Ni-B Coating and its Natural Aging Mechanism

SUMMARYA Ni-B coating was prepared with EN using potassium borohydride reducing agent. The as-plated micro-structure of the coating was confirmed from XRD to be a mixture of amorphous and supersaturated solid solution. Three kinds of phase transformation were observed from the DSC curve. Different from the previous works, the formation of Ni4B3 and Ni2B was found during some transformation processes. The key factors which influence the variation of micro-hardness and micro-structure in deposits are the formation, the size and amount of Ni3B, Ni4B3 and Ni2B. Aging of the deposits treated under some heat treatment conditions occurred at room temperature. Changes of micro-hardness indicated aging phenomena evidently. The natural aging phenomena are concerned with various kinds of decomposition of borides, especially with Ni4B3 phase. The extent of natural aging depends on the formation and the quantity of Ni4B3 and Ni2B.

Electrochemical characteristics of hydrogen storage alloys modified by electroless nickel coatings

Multicomponent hydrogen storage alloy with the composition MmNi3.31Mn0.37Al0.28CO0.64 (Mm = misch metal consisting of 24.87% La, 52.56% Ce, 5.57% Pr, 16.86% Nd and 0.14% Sm) was used as a negative electrode material. To improve the performance of the negative electrode, the alloy particles were modified with various electroless Ni-P and Ni-B coatings. Electrochemical properties such as discharge capacity and high-rate dischargeability of the negative electrode were generally improved by the surface modifications. However, in the case of a Ni-P (10 wt % P) coating, the discharge capacity and high-rate dischargeability decreased with increasing thickness, due to the low hydrogen permeability and high electric resistivity of the coating. Consequently, both kinds of coating and their thickness are critical factors in determining the performance of such a negative electrode.

Laser-induced prenucleation of alumina for electroless plating

This paper deals with the deposition of palladium from decomposition of a thin palladium acetate layer on rough and porous alumina ceramic surfaces by irradiating it with a UV excimer laser. The palladium acetate layer was formed from a combination of propyl glycol methyl ether acetate solvent and photoresist, and the undecomposed material was removed with the photoresist remover. The discontinuous palladium cluster film formed by the technique was used as seed for electroless coatings. Different patterns were obtained using point focus as well as projection pattering method and subsequently plated with adhesive layers of electroless Ni-B coatings.

The oxidation of electroless Ni-B and Ni-P coatings in air at 800 to 1000�C

The oxidation of electroless Ni-B coatings in air at 800 to 1000°C has been determined by kinetic, X-ray diffraction, and microscopical methods. Some data have also been obtained on the oxidation of Ni-P coatings, the oxidation of nickel, and the effect of Na2SO4 on the oxidation process. All kinetics followed the parabolic oxidation law and the rate increased in the order spectrographically pure nickel, commercially pure nickel, Ni-B, and Ni-P, with the Ni-P oxidizing approximately 1000 times faster than the spectrographically pure nickel. Fine surface deposits of Na2SO4 greatly increase the oxidation rate of all materials except the Ni-P coatings which appear to be immune to hot-corrosion. The nature of the oxidation processes are discussed.