Friction and wear properties of WC-Co and Mo-Mo₂C based functionally graded materials

Wear resistant coatings based on functionally graded materials (FGMs) applied on industrial machinery components can reduce weight, increase adhesion strength, decrease internal stresses and improve the resistance against propagation of surface defects. Macroscale FGMs offer a new method of surface engineering to produce tailored tribological properties. In order to fully exploit the FGM concepts, an efficient fabrication with advanced process control assuring the stability of the resulting properties is desirable. The fundamental understanding of wear damage modes of each layer, as well as the development of predictive models for through-thickness behavior can increase the industrial applicability of graded coatings. In the present study, two industrially relevant FGM coatings were investigated: High-velocity-oxygen-fuel (HVOF) deposited WCCo/stainless steel and plasma sprayed Mo-Mo₂C/stainless steel FGMs. For both deposition processes, high degree of automation was achieved and linearly graded coatings were successfully prepared. Sliding friction and abrasive wear responses were evaluated through thickness and damage mechanisms controlling the coefficient of friction and wear rates were described. A correlation between composition, microstructure characteristics and damage modes was established. The enhancement of Mo-Mo₂C coating properties through FGM approach with stainless steel was reported.