Effect of Cobalt Fraction Mixing WC Clads on Microstructural Evolution, Crack Formation and Tribological Properties by Laser Cladding

Abstract

In the present work, a ceramic-matrix composite coatings with different weight percentages of Co additive in the WC powders was studied on 45 steel by laser cladding. The effect of cobalt mixture with WC on mechanical properties such as microstructural evolution, hardness, wear and residual stress behavior of the coatings was carried out. The results show that high residual stresses induce significant cracking on 100% WC and that cracking activity is reduced by adding concentrations of 20% Cobalt to WC. Further, the microhardness of the coatings was more than five times higher than that of the substrate. The observation of the microstructural evolution reveals the fracture mechanism is a typical intergranular fracture in the molten zone and the crack propagates through the interior of the unmelted WC at 100% WC. Overall, the additive of high cobalt in WC did not result in a reduction of residual stresses due to less amount of brittle carbide. However, a reduced number of microstructural defects as well as a better wear behavior were obtained for the WC coated layers with suitably added Cobalt alloys.