On Healing Mechanism of Cast Porosities in Cast Ni-Based Superalloy by Hot Isostatic Pressing

The purpose of this study is to evaluate the effects of hot isostatic pressing (HIP) on the porosity healing and the microstructure evolution of a cast superalloy K452, which is generally applied for fabrication the vanes with the bigger size. The annihilation degree of the porosity, related to the location and shape of the porosity as well as HIP temperature, were studied by high resolution transmission X-ray tomography (HRTXRT) and finite element method (FEM). Results showed that the most of porosities (over 80%) were eliminated by HIP at 1200 degrees C, in which the porosity located in the thin walled parts and with the loose-flat shape was easy to be healed, and the diameter of remnant porosities was decreased to less than 10 lm. Accordingly, A healing mode of the porosity was established. Furthermore, It was found that the slow cooling rate during HIP would obviously lead gamma' precipitates to coarsen, while the rejuvenation heat-treatment (RHT) after HIP could reduce the dendritic segregation degree and readjust the coarsen gamma' precipitates, which finally improved the mechanical properties of the cast superalloy. The HIPed K452 alloy vanes have been successfully used in a civil gas turbine.