Misorientation-dependent stress and strain concentration near grain boundaries in Ni-based bi-crystal superalloy

Abstract

Tensile tests at 650℃ and crystal plasticity finite element analysis on CMSX-4 bi-crystal were performed to investigate the effect of grain boundary misorientation angle (GBMA) on the tensile behavior and failure mode. The tensile tests showed that transgranular fracture occurred at the GBMAs of 6.3° and 10.3°, while intergranular fracture occurred at the GBMA of 20.5°. In addition, the stiffness increased and the 0.2% proof stress decreased as the GBMA increased. The result of crystal plasticity finite element analysis indicated that there is a stress singularity along the radial direction due to the differences in deformability of each grain. Furthermore, the element sizes in the radial and hoop directions were determined by examining different element sizes. It is considered that mode mixing loading led to intergranular fracture because the shear stress on the grain boundary increases with increasing GBMA.