Microstructural evolution and phase transformation of Ni3Al-based superalloys after thermal exposure

The microstructural evolution and phase transformation behavior of a designed multiphase Ni3Al-based superalloy in as-cast and spray casting states were investigated under thermal exposure at various temperatures. For the exposure temperatures range from 600 degrees C to 900 degrees C, the average size of gamma' precipitates in the dendritic dual (gamma+gamma') areas of the two states alloys increases, and the morphology of y' changes to irregular shapes due to merging of neighboring particles and Ostwald ripening. After thermal exposure at 600 degrees C or 900 degrees C, bulky gamma' precipitates generate in the interdendritic regions of as-cast alloy, and the gamma' envelope develops a curved interface by aggregation. For the spray casting sample, high density of microtwins in gamma' precipitates are 'inherited' from the preceding L1(0)-type martensite phases after thermal exposure at 600 degrees C. However, the gamma' precipitates without any microtwins form after thermal exposure at 900 degrees C.