PHASE TRANSFORMATION STUDIES ON INCONEL 625

Abstract

This study deals with the phase transformation/ occurring .011-different ageing time and temperature in Inconel 625, a Nickel base super alloy extensively used for creep resistant application. The primary aim of the work is to understand the ageing behaviour of the alloy within the temperature regime 650-10500 C. Use of Optical Microscopy, X- ray diffraction and Transmission Electron Microscopy was made to identify the different phases formed during ageing It was seen that when ageing was carried out between 650-8500 C, different phases formed depending upon the temperature and time of ageing . At 6500 C, Y" and carbides formed within the matrix and grain boundaries respectively. At 750°C, precipitation of S is perhaps indicated which could be seen only at larger soaking periods. Ageing at 850° C showed the presence of 6 even at shorter soaking periods. TEM studies have been carried out for a detailed crystallographic study on b phase and also for obtaining the morphology of the phase formed. On ageing at 10500 C, the precipitation related transformation more or less ceased. Hardness measurements carried out to a limited extent were helpful in confirming that matrix precipitation occurred on ageing. Implications of the results obtained being examined to identify what more needs to be done, vis -a-vis, the applicability of Inconel 625 for creep resistant applications.