Development of fine-grained structure in Ni-Cr-W based superalloy and its effect on the mechanical properties

Ni-Cr-W based superalloys with different grain size have been prepared by specifically designed melt treatment technologies. The effect of grain refinement on the macrostructures, microstructures, morphology of precipitates, mechanical properties and the appearance of fracture in Ni-Cr-W based superalloy was investigated. The results showed that the grain refinement decreased the amounts of carbides and eutectics at the grain boundary, and made their distribution more uniform. Moreover, the above series of results changed the tensile fracture mode from transgranular to intergranular. The yield strength, tensile strength and elongation of Ni-Cr-W based superalloy are increased by grain refinement from room temperature (RT) to 900 °C, but this increase tendency gradually decreased with temperature increasing. In addition, an embedded serration was observed in stress-strain curve between 450 and 600 °C in Ni-Cr-W based superalloy. Compression tests were also conducted at RT, 550 and 900 °C, the stripe width of the compression specimen surface becomes small with grain refinement (from 10 µm to 5 µm). With the temperatures raising from room RT to 550 °C, the dislocation images of fine-grained specimen change from nanometer-scale dislocation lines to stacking faults.