Effects of preheating and cooling on the crack defects of laser solid formed Rene 104 superalloy parts

Abstract

In this study, laser solid forming technology has been used to fabricate Rene 104 nickel-based superalloy parts, and severe crack problems were found during the laser solid forming process. To solve the crack problems, the effects of preheating and cooling on the microstructure and crack defects of the laser solid forming Rene 104 superalloy were experimentally investigated. The experimental results demonstrated that crack intensity in parts obtained using laser solid forming decreased with the increase in the preheating temperature. However, when the cooling process was not controlled, the parts obtained using laser solid forming would still exhibit severe crack problems even if the preheating temperature was increased to 750 °C. Therefore, instead of natural cooling, a slow cooling strategy was used after the laser solid forming process in the experiments. It was proved that decreasing the cooling rate of the substrate also helped in eliminating the cracks. Using the slow cooling strategy, crack-free Rene 104 superalloy parts could be fabricated at a relatively low preheating temperature. Moreover, it was found that the multiple growth direction of columnar dendrites under high preheating temperature restricted the propagation of cracks. The microsegregation of Al and Ti in the interdendritic regions decreased when the slow cooling strategy was used, leading to improvements in ductility. Aside from the evolution of the microstructure, the relief of thermal stress during the slow cooling process was another important reason for eliminating the cracks.