발간논문

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Vol.33, No.3, 421 ~ 428, 1995
Title
The Effect of Creep Deformation on the Microstructures of a Ni - Cr - W - Al - Ti Superalloy KM 1557
도정만Jung Man Doh, 유경근Jung Keun Yoo, 백홍구Hong Koo Baik, 최주Ju Choi, 허성강Sung Kang Hur
Abstract
Creep induced instability of hardening precipitates at the grain boundaries occurs at high temperatures. This paper discusses the effect of tensile creep stress on the microstructural instability of a Ni-Cr-W-Al-Ti superalloy(KM 1557). The tensile creep stress results in the formation of the precipitate free zones(PFZs) of α-W and γ′ near grain boundaries, and PFZs are generally found near grain boundaries inclined to the tensile-stress axis or triple points. These PFZs are not formed at secondary stage, but observed at tertiary stage and in the creep-ruptured specimens. In the TEM observations, it is found that the cutting of γ′ particles by dislocations starts at the secondary stage, and slip lines and bands are formed in the tertiary stage. Many PFZs are observed from the region very close to the fracture surface where severe deformation took place. On the other hand, gage section near the grip of creep specimen in which lightly deformed did not contain PFZs. The area fraction of PFZs is directly proportional to the reduction of area in the creep specimens. These experimental results support that the formation of PFZs is dependent on the plastic deformation.
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