Influence of nano-sized WC addition on the microstructure, residual stress, and tribological properties of WC-Co HVAF-sprayed coatings

It has recently been proposed to modify conventional WC-Co coatings with nano-sized particles to improve their properties. Modification of the coatings with nano-sized carbides may provide higher wear resistance or phase composition stability. This work characterized the changes in the residual stresses induced by introducing WC nanoparticles into a WC-Co coating and the resulting change in their sliding wear behavior. A powder mixture consisting of agglomerated and sintered WC-17Co feedstock powder and 5 % nano-sized WC was deposited on a carbon steel substrate using the High Velocity Air Fuel (HVAF) process. Microstructural characterization using scanning electron microscopy and EBSD confirmed that nano-sized WC particles were embedded in the coatings after the spraying process, primarily along the boundaries of the WC-Co lamellae. This resulted in an enhancement of microhardness, indentation fracture toughness, and dry sliding wear resistance, evaluated via ball-on-disk tests against Al2O3 counterparts. Residual stresses in the coatings were also measured by XRD using the sin2 psi method. The normal stress along the torch movement direction decreased significantly when nano-sized WC was added. The addition of nanoparticles also caused a slight decrease in the normal stress perpendicular to the torch movement.