Effect of Thermal Exposure on Microstructure and Properties of Cr-12Nb-4.4Ni Alloy

The Cr-12Nb-4.4 Ni alloy, prepared by mechanical alloying and hot pressing, was thermally exposed at 1200 degrees C for 30, 50 and 100 h. Then, the microstructure and properties of the thermally exposed Cr-12Nb-4.4Ni alloy were studied. The results show that the phase constituent is stable during the thermal exposure process. It consists of Cr solid solution (Cr-ss) and NbCr2, and Ni is mainly presented in NbCr2. The grain size of Cr increases with the increase of thermal exposure time, while the grain size of NbCr2 particle has no obvious change. The NbCr2 structure becomes loose due to the replacement of Cr by Ni. The increase of compressive stress in the phase interface of Cr/NbCr2 promotes the emergence of dislocations in Cr matrix and the increase of stacking fault/twinning fault in NbCr2 particles. With the thermal exposure time increasing, the compressive strength, yield strength and plastic strain of the Cr-12Nb-4.4Ni alloy decrease slightly while the alloy still remains relatively high room temperature strength and good plastic during the thermal exposure process. After thermal exposure for 100 h, the compressive strength, yield strength and plastic strain are 2170 MPa, 1406 MPa and 9.5%, respectively. The Cr-12Nb-4.4Ni alloy can keep good fracture toughness after thermal exposure for 100 h.