Evaluation of microstructural, mechanical, and tribological characteristics of Ni-B-W-SiC electroless composite coatings involving multi-pass scratch test

Abstract

A comprehensive study on the fabrication and characteristics of electroless Ni-B-W-SiC composite coating is presented. The role of tungsten in NiB matrix in improving mechanical and tribological performances is well-known. Here, the composite is formed with the incorporation of silicon carbide in Ni-B-W alloy matrix and is systematically investigated in reference to two electroless binary (NiB) and ternary (Ni-B-W) alloy coatings and Ni-B-SiC composite deposited in similar route. All coated specimens are characterized with SEM, EDS, XRD, ICP-AES, and HRTEM analyses in order to draw conclusions in comparative studies concerning morphological features, compositions, and phase structures. These coatings are also subjected to heat treatment at 450 °C for further observations. Raman spectroscopy is used to confirm the presence of SiC particles in coatings' matrix. Tribological evaluations based on results obtained from multi-pass scratch tests provided insights into characteristics evolved in the developed electroless coatings. Silicon carbide reinforcements in electroless alloy matrices (NiB, and Ni-B-W) show noticeable enhancements in microhardness, fracture toughness, and scratch resistance and those further improve on heat treatment due to the formation of harder nickel boride (Ni3B, and Ni2B) phases within crystalline coatings' matrices. Heat-treated Ni-B-W-SiC coating evolved as characteristically superior in terms of average microhardness (1141 HV0.1) and is closely followed by heat-treated Ni-B-SiC, Ni-B-W, and NiB coatings. Under different load values, heat-treated Ni-B-W-SiC composite coating exhibits higher values of scratch hardness and fracture toughness lying within a range of 10.59–10.92GPa and 4.60–4.99 MPam0.5, respectively. These values are significantly higher than all as-plated alloy and composite coatings studied here. Frictional characteristics of all developed coatings are evaluated through both progressive and multi-pass scratch tests by observing failure mechanisms observed on scratch tracks. In this study, heat-treated Ni-B-W-SiC composite coating evolved as superior in terms of mechanical and tribological characteristics.