Heat shock behavior of permanent die during non-solid near-net forming process

Heat shocks caused by alloy melt and coat spraying are the main reason of die plastic deformation and early fracture. Based on theoretical analysis of heat shock phenomenon, two characteristic parameters of die damage caused by heat shock were proposed, which are heat shock plastic deformation index (HSPI) and heat shock crack index (HSCI). The effect of heat shock on die plastic deformation and fracture behaviors was described quantitatively by these two parameters. HSPI represents approaching of heat shock stress to die yield stress. Plastic deformation will happen on a die if this index reaches 1. HSCI represents approaching of heat shock stress to die tensile strength. Die fracture will happen if this index reaches 1. According to theoretical analysis of heat transfer, theoretical models of HSPI and HSCI were established. It is found that, the smaller the interfacial thermal resistance (ITR) is, the higher the pouring temperature and die temperature are before heat shock, and the greater the HSPI and HSCI are, which can be fitted as exponential curves, linear and cubic curves.