Abstract
n order to analyze the cracking and delamination processes of hard coating on ductile substrate under bending load, four-point bending tests were carried out for tool steel specimens with WC-Co cermet coating. The coating was divided by cracks repeatedly with increase in the bending load, and finally the delamination of coating occurred. The interval of cracks at the same nominal stress and those at the delamination ware large when the coating thickness was large. The stress distribution in the coating was analyzed by two-dimensional elastic-plastic finite element method. In addition, the stress distribution in the coating was calculated also by an elastic-plastic stress analysis, which introduced the tensile stress in the coating σx1(x) as follows:
σx1(x)=β{1-cosh(αpx)/cosh(αpL/2)}
where, L is the crack interval, x is distance from the center of divided coating, and αp and β are constants which contain thickness, material's constant of coating and substrate, and nominal bending stress. The cracking process calculated both by the finite element method and the analytical method agree relatively well with the experimental results.
