Thermal fatigue behavior of direct metal deposited H13 tool steel coating on copper alloy substrate

Thermal fatigue performance of direct metal deposited H13 tool steel coating on copper alloy substrate was investigated for high pressure die casting applications. An innovative thermal fatigue test rig was used which is capable of applying cyclic identical energy on the test materials regardless of thermal conductivity property. H13 tool steel was coated on cylindrical copper alloy core material both directly as well as using 316 stainless steel as a buffer layer to evaluate and compare their thermal fatigue properties. Two types of cracks at the surface of both coatings were observed and investigated. The network of small and shallow cracks on the surface was the result of thermal stress while the large catastrophic cracks were believed to be the consequence of thermal stress coupled with the thermal expansion mismatch between the H13 tool steel coating and copper alloy core materials. The H13 tool steel, coated with 316 stainless steel showed much less number of cracks compared to the directly coated H13 tool steel indicating superior thermal fatigue resistance. Moreover the first layer of the directly coated H13 tool steel showed vulnerable behavior under high temperature application showing numerous cracks. Both coatings showed no crack propagation along the interface between coatings and the substrate materials.