Effect of Grain Size and Crystal Orientation on Creep Damage Evaluation by Changes of Misorientation in Hastelloy X
Reki TAKAKU, Daizo SAITO and Yomei YOSHIOKA
Abstract:In this study, EBSP (electron backscatter diffraction pattern) method was applied to evaluate changes in misorientation during creep deformation. The tested material was a solid solution strengthened Ni base superalloy, Hastelloy X, and creep tests were conducted at 1123K under the stress of 49MPa. It was confirmed that Kernel Average Misorientation (KAM), which indicates the degree of misorientation in grains, increased with creep on the later period of creep life. And KAM showed a good correlation with creep strain at the strain of larger than about 5%. Analyses of grain size dependence showed smaller grains had larger KAM than larger grains. As the investigation of crystal orientation dependence, KAM changes in grains with <001>, <011> and <111> toward the stress axis were analyzed and compared. The starting point of increase of KAM in <001> grains was the latest among the three directions. KAM was thought to be an effective parameter for the evaluation of local damages on high temperature components such as turbine blades and pressure tubes. Key Words:Misorientation, EBSP, Creep damage evaluation, Life assessment, Crystal orientation, Grain size