Microstructure, Erosion Performance, and Wear Resistance of Laser-Claded NiCrBSi-WC Composite Coatings

In this study, the microstructure, erosion performance, and wear resistance of nickel-based overlay coatings, including NiCrBSi, NiCrBSi-30 wt pct WC, and NiCrBSi-60 wt pct WC, produced by laser cladding on a low-carbon steel substrate have been studied and compared. Microstructural examinations were carried out using a scanning electron microscope equipped with EDS microanalysis, and phase identification was performed using X-ray diffraction. The results revealed that the NiCrBSi (no WC) coating primarily consists of γ-Ni phase with an Fcc structure along with some boride phases, while the composite coatings contain metal carbide phases. The microstructure of NiCrBSi exhibited a dendritic phase with interdendritic precipitates. In the composite coatings, partial melting of WC particles during laser cladding led to the formation of a diffusion zone as well as needle-like and block-shaped carbide precipitates. The addition of WC due to the distribution of the hard particles, their partial dissolution, and the formation of secondary hard phases increased the overall hardness of the coatings. Furthermore, raising the content of reinforcement particles from 30 to 60 wt pct WC increased the coating hardness from 1989.6 to 2538.5 HV, while the hardness of the NiCrBSi coating was measured to be 678.9 HV. Erosion resistance of the coatings was evaluated by dry sand erosion testing based on the ASTM G76 standard at two impact angles of 30 and 90 deg and compared with the results of reciprocation wear tests according to ASTM G133 standard; as it was indicated that the addition of hard particles within the coatings improved the wear and erosion resistance of the coatings. NiCrBSi (no WC) coating had a higher erosion resistance at the high-impact angle of 90 deg as compared to the 30 deg impact angle, while the performance of NiCrBSi-WC composite coatings was optimum at the lower impact angle. The erosion in NiCrBSi (no WC) coating occurred through a ductile mechanism, whereas evidences of a brittle failure mechanism were observed for erosion of the composite coatings. Wear rate measurements further confirmed these findings, as the wear rate of NiCrBSi coating [1.465 × 10⁻⁸ mm³/(N m)] significantly decreased with the addition of 30 wt pct WC [5.94 × 10⁻⁹ mm³/(N m)], indicating a 66.24 pct reduction. However, increasing the WC content to 60 wt pct led to significant change in wear rate [6.24 × 10⁻⁹ mm³/(N m), representing only a 5.05 pct rise] compared to the 30 wt pct WC coating. Overal, the results of tribological tests showed that the addition of reinforcement particles within the coatings improves resistance of the coatings in both dry sand erosion and sliding wear testing; with the NiCrBSi-30 wt pct WC composite coating, exhibiting an optimal performance to sliding wear and dry sand erosion at both 30 and 90 deg impact angles.