Electroless Ni–B–W coating is deposited on low carbon steel in an alkaline sodium borohydride-reduced electroless bath. The mechanical and tribological properties of such coatings are much necessary to be assessed to carry out application-based studies. The present work focuses mainly on the evaluation of hardness and fracture toughness of electroless Ni–B–W coatings using a scratch tester. Coating's response toward scratching is also studied thoroughly. The characteristic short-range order present in its lattice structure causes the generation of a specific behavioral pattern. Furthermore, a linear sliding wear test is carried out on coatings' surface to analyze the wear behavior at different loading conditions. The specific wear rate is observed to be minimum at a normal load of 22.5 N against Si3N4 counterbody. The patterns of tribological behavior of the coating at different load values are examined from the worn surface morphologies. But before embarking on the scratch and sliding wear tests, the synthesized coatings are characterized under field emission scanning electron microscope and X-ray diffraction in an exhaustive manner. The growth rates with respect to time and the changes in morphological aspects of the coating are also evaluated. The present study establishes electroless Ni–B–W deposits as a suitable option for protecting mechanical components against wear.

Concerns raised about the environmental ramifications of electrodeposited hard chromium (EHC) plating are perhaps the paramount challenge posed to the finishing industries to find a suitable alternative. Electroless Ni-B coatings have attracted much attention due to their superior mechanical and tribological properties; those are enhanced further in electroless Ni-B-W coatings. Electroless Ni-B-W can be a suitable alternative for the replacement of EHC in a variety of engineering applications. In the present study, the changes in morphological features, deposition rates with respect to time, and deposition mechanisms of electroless Ni-B-W coatings are studied thoroughly. After heat treatment, all deposited coatings are characterized thoroughly for the evaluation of their mechanical and tribological characteristics. This is helpful in the comparison of characteristics with properties of industrial EHC coatings. To analyze the coating-substrate adhesion in the electroless depositions, scratch tests with progressive load and repetitions are carried out. Frictional behavior and failure mechanisms at the scratch tracks of all fabricated coatings are also studied through repetitive scratch tests. Heat treatment of electroless Ni-B-W coatings induced significant improvements in mechanical, tribological properties and adhesion behavior. The present study establishes beyond doubt that owing to a specific set of properties, electroless Ni-B-W coatings show tremendous potential to be recommended as a replacement for chrome coatings.

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Electroless deposition process can develop composite coatings superior in mechanical and tribological characteristics. The deposited alloy matrix with the reinforcement of a hard ceramic phase can produce a stronger composite coating, favorable for industrial applications. Fabrication process of Ni-B-W-SiC electroless composite coating on steel substrate by reinforcing silicon carbide (SiC) in ternary Ni-B-W matrix is presented in this report. Characteristics of the developed composite coating are studied in reference to electroless ternary Ni-B-W alloy coating. These ternary alloy and composite coatings are also subjected to heat treatment (450oC, 1 hr) to observe the changes. All coated samples are characterized with FESEM, XRD, ICP-AES, and HRTEM analyses to draw conclusions in comparative studies concerning morphological features, compositions, and phase structures. Cross-sectional and Raman spectroscopic examinations are performed to authenticate the presence of SiC phases in alloy matrix. To get a further insight on the nature, various nanomechanical and tribological properties of these coatings are evaluated and subsequently co-related. Coatings developed with silicon carbide particles present in matrices show remarkable improvements in nano-hardness (H), reduced modulus (Er), yield strength, and fraction of plastic work done. Heat treatment imparts propitious effects on these mechanical properties due to the formation of harder nickel boride (Ni3B, and Ni2B) phases. Heat-treated Ni-B-W-SiC composite subjected to tribological and micro-scratch testing reveals a significant improvement in sliding wear and scratch resistance as compared to those in other coatings.

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