Abstract
The effects of microstructure on the creep behavior in a new developed Ni-Co base superalloy were investigated and two microstructures were obtained by different heat treatments. The results show that the air cooling microstructure, consisting of large spherical γ′ and small spherical γ′, resulted in a slow creep rate and small creep strain. While the slow cooling microstructure, consisting of large flowery γ′ and small spherical γ′, resulted in a fast creep rate and large creep strain. The γ channel and γ′ morphology are two main factors for these differences, the large γ channel and flowery γ′ in the slow cooling microstructure causing the dislocations slip easily in the γ matrix and cut into the γ′ precipitates with low stress.
1 Introduction
The newly developed Ni-Co base superalloy is designed to mainly use in aero engine and the gas turbine disk. The disc rotors in the high pressure compressor accommodate higher temperatures and stresses. Therefore, the alloy must possess the inherent capacity to retain strength and resistance to creep, while the creep resistance is an important performance index for this alloy.
Conclusion
The creep test of the new developed Ni-Co base superalloy after two different heat treatments were conducted at 760 ℃ 630 MPa. The effect of heat treatment on the creep performance was discussed and following conclusions were drawn:
(1) The air cooling microstructure, consisting of large spherical γ' and small spherical γ', resulted in a slow creep rate and small creep strain. While the slow cooling microstructure, consisting of large floweryγ' and small spherical γ', resulted in a fast creep rate and large creep strain.
(2) The γ matrix channel width and the γ' morphology are two main factors for the differences in creep behavior. When the γ channel is large in the slow cooling sample, the dislocations slip and by pass easily, resulting a high creep rate and large creep strain and vice versa for the air cooling sample.
(3) When the γ' grow into flowery morphology, it loss coherency with the γ' matrix. The strengthening from the strain field resulting from the mismatch between γ' and γ matrix is disappeared, dislocation cutting into flowery γ' is more easily than the spherical one.
