The effect of WC-CoCr content on hardness and tribological properties of NiCrBSi coatings fabricated by the HVOF process

Abstract

Although Ni-based alloy composites are commonly used as coatings for the enhancement of tribological properties of structural materials. The achievement of a dense and well-distributed microstructure with high content of reinforcing materials is still a challenge. Herein, we aimed to prepare NiCrBSi/WC-CoCr composite materials with different amounts of WC-CoCr (0–45 wt%) using V-mixer and high-velocity oxy-fuel (HVOF) coatings techniques and evaluated the hardness and tribological properties of the coatings at 500 °C. Particularly, we optimized the distribution of WC-CoCr in NiCrBSi matrix using a set of optimized parameters for mixing and coating processes. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterize the microstructures of the coatings. It was observed that an appropriate balance of hard phase (WC-CoCr splats: 30 wt%) and soft phases (Ni-base alloy: 70 wt%) can lead to a uniform, dense, and well-bonded microstructure resulting in the achievement of high hardness, low wear rate, and friction coefficient. Higher contents of WC-CoCr splat (45 wt%) led to a loosening of the interphase bonding on one hand (due to weak wetting between WC-CoCr splats and uncomplete melting of WC-CoCr splats during coating process), and enhanced oxide formation in the coating owing to alumina insertion (from wearing of alumina balls) on the other hand. Overall, the comparison of the harnesses and friction coefficients obtained in the present work shows how an optimized process could lead to the accomplishment of properties superior to those reported in the works.