Effect of phase transformation on tensile behavior of Co-Cr-Mo alloy fabricated by electron-beam melting

High temperature tensile property and phase transformation of Co-28Cr-6Mo-0.23C-0.17N alloy rods fabricated by electron-beam melting (EBM) with cylinder axes along build direction was investigated. Single-crystal like γ-fcc grain structure can be obtained by EBM. Although constituent phase varied along the build direction in the as-EBM-built rod, from single ε-hcp phase in the bottom to single γ-fcc phase in the top, γ-fcc phase can be kept in a wide range of build height, i.e. about 40 mm from the top finishing plane. ε-hcp grains in the bottom of the rods obtained in the EBM process mostly had preferential orientations. The rods can be transformed into single ε-hcp phase by the aging treatment at 800 °C for 24 h, and ε-hcp phase in the top of the rods obtained by aging heat treatment exhibited diffusion transformation. The yield strength and ultimate tensile strength (UTS) of the top part was higher than that of the bottom part, though the plastic elongation of the top part was a little lower than that of the bottom part.