Effect of silicon carbide incorporation and heat treatment on tribological properties of electroless Ni-B-W alloy coating

Concentration of reinforcing agents govern various characteristics of electroless composite coatings. In this study, silicon carbide (SiC) particles are incorporated into matrices of electroless ternary Ni-B-W alloy coatings. Addition of variable amounts of SiC into electroless bath solution used for the deposition helped in the fabrication of Ni-B-W-based electroless composite coatings of different compositions. Higher hardness value is noticed in composite coatings fabricated with the 1 g/l concentration of SiC particles in the plating bath. The resultant Ni-B-W-SiC composite coating is then subjected to heat treatment at three different temperatures (250 degrees C, 450 degrees C, and 650 degrees C) to study its effects on microstructural, mechanical and tribological characteristics. Alongside the composite coating, characteristics of Ni-B-W alloy coating are also observed in the same route for comparison. Matrices of as-deposited coatings show short-range order characteristics. Heat treatment at different temperatures affects magnitude of crystallization, degree of dispersion, sizes of precipitates within coatings' matrices differently. Development of various borides, such as Ni3B and Ni2B and several silicides, namely Ni3Si, Ni5Si2, and NiSi within coatings' matrices as a function of heating temperature governs the mechanical and tribological properties of coatings. Cumulative effects of composite coatings fabricated with the 1 g/l concentration of SiC particles in plating solution and heat treated at 450 degrees C evolved superiority in terms of mechanical and tribological properties as compared to other coated specimens in this study. Heat treatment at a higher temperature (650 degrees C) causes degradation in coatings' properties due to the coarsening and coalescence of nickel boride precipitates and grain growth. Moreover, at this temperature, nickel reacts with the SiC particles and produces several nickel silicide phases, namely Ni3Si, Ni5Si2, and NiSi, negatively affecting properties of the composite coatings.