Abstract: Microstructure of the IC21 single crystal alloy at as-cast state, after heat treatment and after different thermal processes were observed by optical microscope(OM) and scanning electron microscopy(SEM).The high-temperature tensile and enduring properties of the alloy at as-cast, heat treated and various thermal processes treated state were tested. The effects of heat treatment and thermal process on microstructure evolution and mechanical properties of the IC21 alloy were studied. The results show that the as-cast alloy is dendritic growth and consisted of γ′ phase, γ phase, bulky γ′ in the interdendritic regions and NiMo phase. The size of γ′ phase in the dendrite region is larger than that in the interdendritic region. The alloy is not complete solid solution after 1315 ℃/6 h/argon cooling and two aging treatment, and the γ′ phase in the dendrite is not completely dissolved. There are still coarse γ′ phases between dendrites. The high temperature rupture properties of the alloy are obviously improved. The γ′ phase grows up obviously and the cubic degree decreases slightly after thermal process. After thermal process, the size difference of γ′ phase between dendrites and interdendrites decreases, and needle phase precipitates. Compared with the heat treatment state, the endurance life of the alloy is slightly reduced, but the tensile strength is improved.

Key words: IC21 alloy, heat treatment, thermal process, microstructure, properties