Fatigue performance of tungsten carbide cobalt (WC-Co) hardmetal materials after shot peening process

In order to increase fatigue life of metal-ceramic composite samples, shot peening process, preferred in aerospace and automotive industry, was applied. In addition to fatigue experiments, material characterization tests were performed. According to surface roughness measurements, Ra and Rz values were increased by 113% and 83%, respectively. An increase of 13% in hardness was obtained at the surface of shot peened samples. The depth of hardened region was found as about 300 mu m. Fatigue experiments revealed an improvement in the fatigue performance of the hardmetal samples owing to shot peening. It was concluded that fatigue life increase was due to hardness increase after shot peening. Strain hardening after shot peeing-induced-plastic deformation was found to be the main hardening mechanism. There was no crystal structure transformation that could be associated with cobalt phase, leading to hardness increase. Fracture surfaces of the samples were examined by SEM. Multi-site cracking was found to trigger fatigue failures. It was also found that tungsten carbide grains were fractured due to shot peening and fatigue testing. Transgranular and intergranular cracking was observed after fatigue experiments. No significant fatigue striations were found as in ductile materials.