Effect of powder morphology on tribological performance of HVAF-sprayed WC-CoCr coatings

Abstract

This study investigates the tribological behavior of WC-CoCr coatings deposited using High-Velocity Air Fuel (HVAF) thermal spraying. Three distinct types of feedstock powders were employed to examine the influence of powder morphology on coating performance: a dense, angular fused-and-crushed powder; a spherical, porous agglomerated-and-sintered powder, and a newly developed powder with intermediate features. All powders had analogous particle size distribution approximately in the range of 7–20 μm. Two coating thicknesses were deposited with each powder (50 μm and 150 μm), additionally aiming to verify the possibility of depositing thin hardmetal coatings. The coatings microstructure was characterized, their hardness and porosity were measured and their tribological properties were evaluated by means of ball-on-disk sliding tests and dry jet erosion tests at various impact angles.

The results demonstrated that powder morphology significantly affects deposition efficiency. The newly developed powder offers notable advantages, such as higher deposition efficiency, which accelerates the spraying process and boosts production productivity, along with reduced sensitivity to parameter variations. In fact, the newly developed powder exhibited more consistent deposition rates across varying process conditions. Coatings derived from the new manufacturing route powder also showed improved cohesion and hardness due to stronger interparticle bonding and peening effects. On the other hand, surface roughness was unaffected by the powder type, and the coatings produced from the three powders had comparable wear resistance under erosion and sliding conditions. Coating thickness, rather than powder morphology, appeared to play a greater role in determining wear performance. The thicker coatings demonstrated superior resistance under both test conditions, due to reduced substrate influence.