Effect of Nb addition on the microstructure of Ni–12Mo–7Cr based superalloy

Abstract The effects of Nb addition on the microstructures of Ni–12Mo–7Cr based superalloy have been systematically investigated in this study. If no Nb addition, the granular and thin rod-like M2C carbides distribute in the matrix and at the grain boundaries. In the alloy with 1 wt % Nb, the needle-like Mo-riched MC carbides and the granular Nb-containing M2C carbides form in the matrix and at the grain boundaries respectively. The needle-like MC carbides were found to grow along the {1 0 0} planes of the matrix and possess a cube-on-cube orientation relationship (OR) with the matrix. In the case of the alloy with 4 wt % Nb, the thick rod-like NbC carbides with few other metal elements were found to form in the matrix, which grow along the {1 1 1} planes and possess a twin-like OR with the matrix with a small-angle deviation. Based on the interface energy analyses, the morphology differences between MC and NbC carbides were found to result from their different ORs and interface structures.