Investigating the Effects of CoMoCrSi Powder Composition and Particle Size, and Annealing Heat Treatment on Microstructure and Mechanical and Tribological Performance of HVOF Sprayed Coatings

Abstract

An investigation was conducted to analyze the mechanical properties, wear behavior, and microstructure of coatings formed by high-velocity oxygen fuel spraying of CoMoCrSi powders. The effects of varying Cr concentration and particle sizes before and after heat treatment at 900 °C for 4 h were studied comparatively. The increase in Cr and Mo elements in the expanse of Co increased the structure's hardness before and after the heat treatment. As this increase was 10% in as-sprayed conditions, annealing raised the increase to 30%. Splat boundaries were the most vulnerable constituents against forces, creating a significant disadvantage in terms of structural integrity and affecting the overall performance. After annealing, the boundary strengths experienced a remarkable four-fold increase and cracks and fractures reduced significantly. The susceptibility of splat boundaries had a detrimental effect on room temperature wear behavior, and increased boundary densities led to a marked reduction in wear performance. Heat treatment induced improvements significantly increased the room temperature wear performance. At elevated temperature, the formation of oxide layers composed of CoMoO₄, Co₃O₄, MoO₃, and Cr₂O₃ overcame the weaknesses of the as-sprayed coating, reducing both the friction coefficient and wear losses. A reduced Co ratio led to the formation of an oxide blend with a higher concentration of Mo and Cr oxides on the surface, further improving the coating's wear behavior.

Graphical Abstract