Microstructures and tensile properties of a grain-size gradient nickel- based superalloy

This work systematically investigated the microstructure characteristics and tensile mechanical properties of a grain-size gradient nickel-based superalloy. The plastically deformation mechanism and the failure behavior of the gradient superalloy at different temperatures (room temperature, 650 & DEG;C, 750 & DEG;C) were discussed. Results show that the microstructure of nickel-based gradient superalloy is mainly composed of & gamma; matrix phases, & gamma;& PRIME; phases and dispersed carbides. The microstructure of the gradient superalloy exhibits equiaxed grains with a few annealing twinning structures. The average grain size changes uniformly from 94.3 & mu;m of the coarse-grain side to 4.9 & mu;m of the fine-grain side. The room temperature tensile strength of the grain-size gradient superalloy is about 1635 MPa, the yield strength is about 1160 MPa and the elon-gation is around 21%. When testing at 650 & DEG;C, the tensile and yield strength of the specimens declined to 1414 MPa and 1034 MPa, respectively, but the elongation raises to 36%. The strength of the specimens continues to decrease at temperature of 750 & DEG;C, whereas the elongation decreases back to around 21%, exhibiting intermediate temperature brittle phenomenon (ITB). Analysis concludes that the micro-twinning mechanism dominates at 750 & DEG;C in the grain-size gradient nickel-based superalloy. Micro-twins formed by intense interaction of dislocations with & gamma;& PRIME; phases lead to the reduction of ductility at 750 & DEG;C. & COPY; 2023 Elsevier B.V. All rights reserved.