Effect of heat treatment on tensile/cOmpressional strengths in U720Li

Abstract

The inner and outer regions of a turbine disks are exposed to service temperatures and the required properties are different. Although the anisotropy of properties in single crystal Ni-base superalloys has been reported, the anisotropy in polycrystalline superalloys has not been reported yet. The purpose of this study is to investigate the effect of heat treatment on the microstructure, the proof strength and the plastic anisotropy in polycrystalline superalloy U720Li. The solution heat treatment was performed at 1100, 1150 and 1170°C. In the as-received billet, it was found that the crystal grains were equiaxial in the inner region and elongated in the outer region. For the specimens heat treated at 1150°C, different crystal grain structures were observed in the inner and outer regions, as the grain growth was only observed in the inner region. The difference in proof stresses between the inner and outer region increased as the solution-heat-treatment temperature was increased. For every heat treatment condition, the proof stress in tension was approximately the same as that in compression. © 2005 The Japan Institute of Metals.