초록 열기/닫기 버튼
The effects of a heat treatment on the carbide formation behavior and mechanical properties of the cobalt-based superalloy X-45 were investigated here. Coarse primary carbides formed in the interdendritic region in the as-cast specimen, along with the pre- cipitation of fine secondary carbides in the vicinity of the primary carbides. Most of the carbides formed in the interdendritic region were dissolved into the matrix by a solution treatment at 1274oC. Solutionizing at 1150oC led to the dissolution of some carbides at the grain boundaries, though this also caused the precipitation of fine carbides in the vicinity of coarse primary carbides. A solution treatment followed by an aging treatment at 927oC led to the precipitation of fine secondary carbides in the interdendritic region. Very fine carbides were precipitated in the dendritic region by an aging heat treatment at 927oC and 982oC without a solution treat- ment. The hardness value of the alloy solutionized at 1150oC was somewhat higher than that in the as-cast condition; however, var- ious aging treatments did not strongly influence the hardness value. The specimens as-cast and aged at 927oC showed the highest hardness values, though they were not significantly affected by the aging time. The specimens aged only at 982oC showed out- standing tensile and creep properties. Thermal exposure at high temperatures for 8000 hours led to the precipitation of carbide at the center of the dendrite region and an improvement of the creep rupture lifetimes.
