Effect of applied stress on r'-rafting behavior in a Ni-based singlecrystal superalloy:experiments and finite element analysis

The effect of applied tensile stress on the r'-rafting behavior for a Ni-based single-crystal superalloy with more negative misfit was investigated.By conducting interrupted creep tests at high temperature,it indicated that the increase in the applied stress accelerates the r'-rafting(directional coarsening of yr phase).In the early stage of rafting,the r'-cubes start interconnecting at the ends of the parallel-to-applied-stress r'-channel.The distributions of misfit stress,coherent strain and strain energy density of the r/r'phases are then calculated by finite element analysis.The calculation results show that the rafting acceleration is mainly ascribed to the reduced strain energy density in the parallel-to-applied-stress r'-channel that is driven from the couple interaction of external load and misfit stress.Interface dislocation network formation,resulting from the misfit-induced increase in resolved shear stress,also contributes to the r'-rafting.