Shih-Chin Lee

Effects of temperature of HIP process on characteristics of Inconel 718 superalloy

Abstract The present study focuses on the effects of the temperature of the hot isostatic pressing (HIP) procedure on Inconel 718 superalloy. HIP temperatures used were 1150, 1175, 1180 and 1205°C. HIP pressure was maintained at 1000 bar (98·6 MPa) and the soaking time was 2 h. Both room and high temperature tensile and bending tests were used to evaluate the effects of HIP temperature on Inconel 718 superalloy. Porosity tests and microstructural examination were performed. The results showed that the optimum HIP process temperature for 718 superalloy is 1180°C. Processing at this temperature can significantly reduce porosity and improve the microstructure segregation of Inconel 718 superalloy. Under these conditions, the superalloy showed an 18·28% increase in tensile strength at room temperature, a 7·38% increase at 540°C, and a 3·84% increase at 650°C. The elongation increased by 55·6% at room temperature, 109·71% at 540°C, and 19·91% at 650°C. Finally, the results of three-point bending tests showed that hipping at 1180°C can enhance the bending strength by 39·5% at room temperature and 13·83% at 540°C.

Effects of vacuum sintering temperature on mechanical properties and electric resistance for Cr50–Si50 optical target

Abstract In this study, two kinds of Cr and Si powders were mixed ingredients in set proportions (Cr/Si = 50∶50 in weight percentage), and different vacuum sintering temperatures were used to achieve the optimal densification process. The specimens used in this investigation have common microstructures of hardness, XRD, transverse rupture strength and resistivity of the Cr50–Si50 targets. The microstructure shows that the porosity tends to decrease as sintering temperature increases. Conversely, hardness and transverse rupture strength increase as sintering temperature increases. These results agree with the variation in porosity. Additionally, the resistivity tends to decrease with increasing sintering temperature. It should be correlated with the microstructure of Cr50–Si50 targets, increasing the density of CrSi2 could significantly decrease the resistance. Meanwhile, the resistivity decreases and conductivity increases as the neighbours are closer together, which also results from the decreasing porosity.