Investigation of plastic deformation behavior of a grain-size gradient nickel-based superalloy

In this work, the microstructure and plastic deformation behavior of a grain-size gradient nickel-based superalloy was investigated using experimental and simulation methods. The gradient superalloy mainly consists of the γ matrix, multimode size distribution γ′ phases and dispersed carbides, and its grain size changes continuously from 12μm of fine-grain side to 85μm of coarse-grain side. The microhardness decreases with the increase of grain size. Compared to the specimen with fine-grain and the specimen with coarse-grain, the specimen with the grain-size gradient structure possesses the optimum tensile properties. According to the contribution of strengthening mechanisms to the yield strength, the size and volume fraction of secondary γ′ phases and tertiary γ′ phases should be the main factors affecting the yield strength in the alloy. By establishing the tensile models combined with the DIC experiment of gradient materials at room temperature, it has been found that during deformation, the strain and stress are mainly concentrated in the coarse-grain side. In addition, by increasing the thickness of the transition zone, the strain and stress concentration could be effectively suppressed and the room temperature tensile properties could be improved.