C-18 Ni基超合金Inconel^[○!R] Alloy 706のクリープおよびクリープ疲労特性に及ぼす環境の影響(材料,一般講演)

概要

論文の詳細を見る
Gas turbine rotor parts are designed to meet the demands of normal operation for the specified life. However, in the course of service, distress may accumulate based on the operation of the specific plants. Few fleet leader machines with non-shot-peened wheels made of Ni-base superalloy Inconel^[○!R] 706 were found to contain cracks in the first stage turbine wheels. These were inter-granular cracking and observed to be highly stressed and damage sensitive locations with less potential for oxidation, which is thought to occur due to hold-time cracking . To recognize the actual phenomena, creep and creep-fatigue tests were conducted in air and vacuum environments for the materials taken from the actual component. Creep test results showed equivalent creep lives in between the air and the vacuum, and remarkably notch-strengthened, but the fracture modes were completely different. The vacuum test sample showed both surface crack and coalescence of creep voids on the fracture surface, and the latter appearance was dominant. The air-tested sample did not show such creep voids and the surface cracks propagated to fracture. In the creep-fatigue tests, no notch-strengthened phenomenon was observed in the air-tested condition even if heavy grain boundary oxidation was not observed. Grain boundary deterioration was thought to occur at stress concentrated area beneath the notch.
2011-07-06