Effects of grain refinement on the microstructure and tensile behavior of K417G superalloy

The effects of grain refinement on the microstructures and tensile properties of Ni-based cast superalloy K417G were investigated. The results show that grain refinement could refine the microstructure, and increase the proportions of carbides and eutectics distributed at the grain boundary, which changes the tensile fracture mode from transgranular to intergranular. The effects of grain refinement on the tensile properties vary with temperature. At 21 °C, the strength and ductility of K417G superalloy both increase with grain refinement. At 700 °C, as there is grain refining, the yield strength and tensile strength increase whereas the ductility decreases. At 900 °C, the yield strength and tensile strength change little, whereas the ductility decreases as the grain refines. Grain refinement has refined the γ′ phase and narrowed the γ channels so that the resistance of the dislocation movement during tensile deformation is influenced.