한국주조공학회

Directionally solidified CM247LC superalloy was exposed to high temperatures of 750ºC, 850ºC, and 950ºC for up to 10,000 hours to observe the microstructural evolution in this material. To evaluate variations in the mechanical properties, creep tests were conducted at 950ºC and 250MPa. The size and morphology of the γ' phase remained mostly unchanged after exposure at 750ºC, while at 850ºC, the γ' phase developed into a more spherical shape. At 950ºC, γ' coarsened rapidly, exhibiting distinct morphological differences compared with those at and below 850ºC. Fine γ precipitates within the coarse γ' phase of the γ-γ' eutectic microstructure were observed only in the specimen exposed to a temperature of 750ºC, attributable to compositional differences in γ' depending on the temperature. After thermal exposure, the decomposition of MC carbides resulted in the formation of M23C6 near the γ-γ' eutectic, while both M23C6 and M6C carbides were observed at the grain boundaries. Additionally, needle-like M6C was found inside the grains. Creep test results at 950ºC/250MPa showed that the higher exposure temperature, the higher creep rate, and the shorter rupture time. Notably, in the specimen exposed to 950ºC for 10,000 hours, γ' rafting was not observed after the creep test, in contrast to the other specimens.

Directionally solidified Ni-based superalloy, CM247LC, Thermal exposure and Creep property.