Microstructure Evolution of Nickel-based Superalloy GH202 After High Temperature Oxidation from 800 °C to 1100 °C

Microstructure evolution of Ni-based superalloy GH202 after oxidation from 800 degrees C to 1100 degrees C was investigated. The results show that the hardness of GH202 decreases with the increase of oxidation temperature, and the hardness is decreased by 43.5% after oxidation at 1100 degrees C for 100 h. The growth rate of the grains after oxidation at 800 and 900 degrees C is slower and the grains increase slightly at 900 degrees C. The grain size increases significantly after oxidation at 1000 and 1100 degrees C, and many fine grains are annexed to form large grains due to grain boundary migration and elemental diffusion during the recrystallization at high temperatures for above 100 h. The big block carbides (MC) decompose into a large number of carbon atoms which combine with Cr atoms to form a few Cr-rich granular M23C6. After oxidation at 900 degrees C for 150 h, the M23C6 evolves into Ti-rich M6C. With the increase of oxidation temperature, the carbides almost melt into gamma phase. Moreover, the gamma' phase gradually grows up after oxidation at 800, 900 and 1000 degrees C, and it is completely dissolved into the gamma phase after oxidation at 1100 degrees C for 100 h.