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Vol.38, No.11, 1439 ~ 1445, 2000

Title

Improvement of Creep - Fatigue Resistance in IMI 834 Alloy through Microstructural Control

이덕희Duck Hee Lee,남수우Soo Woo Nam,최승주Seung Joo Choe

Abstract

IMI834 was developed to be used for the compressor parts of gas turbine engines. Compressor parts of gas turbine engine are subjected to cyclic and static loading simultaneously at high temperature and can be degraded by creep-fatigue interaction. The effects of microstructure and various superimposed hold times on high temperature low cycle fatigue behavior of IMI834, near-α titanium alloy, were investigated and the damage process under these conditions was also discussed. In both lamellar and bi-modal microstructures, it was found that fatigue lives for 10 to 30 min tensile hold were lower than those in continuous cycle fatigue due to additional creep resulting from stress relaxation during the tensile hold. This can be explained by the gradual change of the damage mechanism from fatigue dominant crack propagation to creep dominant grain boundary failure. It was also observed that in bi-modal structure of IMI834, low primary α volume fraction in the order of 10% leads to better creep-fatigue resistance at 600℃. Apparent activation energy for creep deformation of about 510-580 kJ/㏖ was obtained from the stress relaxation curve and was consistent with results of other near-α titanium alloys. This means that creep deformation during hold time must be controlled by a mechanism different from that in diffusion-controlled behavior.

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