Effects of 900°C Long-term Aging on Microstructure and Mechanical Properties of Directionally Solidified Superalloy DZ125

Abstract DZ125 alloy is a kind of the first generation directionally solidified nickel-based superalloy, which has excellent comprehensive properties, and been used as turbine blades materials widely. The effect of 900°C long-term aging for 10000h on the microstructure and mechanical properties of DZ125 alloy was investigated in this paper, to guarantee its service security. The results showed that the size of γ phase increased and its volume fraction decreased with exposure time prolonging, while it cubiodal degree continuously decreases. The width of γ phase channel also increased with aging time. At the same time, some of MC carbides transformed to M23C6 /M6C carbides in the interdendritic and grain boundary region, while fine granular M23C6 and MC carbides were precipitated in the alloy. However, no TCP phase precipitation was observed in DZ125 alloy even after aging at 900°C for 10,000h. The microstructure degradation due to aging at 900°C resulted in the decrease of the DZ125 alloy’s mechanical properties, such as tensile, stress rupture and fatigue properties. With aging time prolonging, the tensile yield strength at room temperature of the alloy decreased gradually, and the creep rupture lives at 760°C/804MPa and 980°C/235 MPa declined significantly, which fell to 25 % and 35 % of the unaged value after 10 000 h of aging respectively. For low-cycle fatigue performance at 800°C, the aged alloy showed a distinctly shorter life than the unaged alloy under the same strain amplitude.