Effect of Mo content on microstructure and stress-rupture properties of a Ni-base single crystal superalloy

The additional 1.5 wt% Mo was added in a Ni-base single crystal (SC) alloy with the composition of Ni-6.5A1-8.0Mo-2.4Cr-6.2Ta-4.9Co-1.5Re-(0.01-0.05)Y (wt%) to study the effect of Mo content on the microstructure and stress-rupture properties. The creep and stress-rupture tests under the conditions of 850 degrees C/500 MPa and 1100 degrees C/130 MPa were conducted, and the microstructure of as-cast, heat treated and stress ruptured specimens were analyzed. It was found that the 1.5 wt% Mo addition enhanced the stress-rupture lives at both intermediate (850 degrees C) and high (1100 degrees C) temperatures. The microstructure analysis showed that adding 1.5 wt% Mo in the basic alloy affected the microstructure dramatically, i.e., the Mo-rich phases formed in the specimens of as-cast and stress-ruptured specimens. It is considered that the improvement of the stress-rupture lives is duo to the strengthening effect of Mo to both gamma and gamma' phases and the decrease of stacking fault energy, diffusion constant and dislocation spacing. The Mo-rich phases precipitated under condition of 1100 degrees C/130 MPa did not affect the creep and stress-rupture properties obviously in the present study. (C) 2016 Chinese Materials Research Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (httplicreati ecommons.org/licen,,es/by-nc-ndf4.0).