고온 및 응력하에서 니켈기 초내열합금 Rene 80 의 미세조직 변화

The influence of temperature and stress on the microstructural changes has been studied in Ni-base superalloy Rene 80. While some specimens were only thermally exposed, others were exposed under high temperature and stress. An external tensile stress on the specimen has been found to cause the directional coarsening of γ` precipitates which results in morphological change in γ` precipitates. In particular, the degree of morphological change in γ` precipitates was different around the carbides. This indicates that local stress around carbide varies relative to location. Rene 80 exhibited bimodal size distribution of γ` precipitates after standard heat treatment. Consequently, the variation of γ` precipitate size with exposure time was complex as compared with the systems which exhibit with unimodal size distribution. γ` precipitates have been found to obey the diffusion-controlled coarsening, and the activation energy for coarsening was about 65.1 Kcal/mole.