Grain Growth Behavior of Inconel 625 Superalloy

The grain growth (GG) behavior of Inconel 625 superalloy was studied in the temperature range of 900-1250 °C and holding time range of 10-80 min. Microstructures of the alloy were characterized by optical metallography, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Grains grew obviously with either increasing temperature or extending holding time at temperatures above 1050 °C. However, at temperatures lower than 1050 °C, the GG was sluggish due to the pinning effect of carbide particles on grain boundary (GB). Threshold temperature for transition from mixed grain structure to uniform one was considered to be around 1100 °C. Once the temperatures surpassed 1200 °C, an instant increase in the grain size occurred showing no dependence on holding time. TEM analysis showed that the dominant second phase formed heterogeneously on the GB was M6C, which significantly impeded grain growth. On the basis of experimental data, the mathematical model of GG was established, which can describe GG behavior of Inconel 625 alloy during solution treatment (ST) at 1100-1250 °C. The activation energy for GG of Inconel 625 alloy was 207. 3 kJ, which suggested that the GG of Inconel 625 alloy was controlled by the process of GB diffusion.