Creep anisotropy of a low-cost third generation single crystal superalloy at 760 °C and 1120 °C

Abstract

This research investigated the anisotropy of creep properties of a low-cost third-generation Nickel-based single crystal superalloy under two conditions of 760 °C/800 MPa and 1120 °C/137 MPa. The microstructures and deformation mechanisms of the [011] and [111]-oriented specimens were studied in depth and the determinants of anisotropy were analyzed. The low critical resolved shearing stress and the single activation of the <112> {111} slip system synergistically led to the formation of tremendous continuous stacking faults in the [011]-oriented specimen, which resulted in its extremely poor creep life under condition of intermediate temperature and high stress. In contrast, high critical resolved shearing stress of <112> {111} slip systems led to the formation of a large number of microtwins in the [111]-oriented specimen. The microtwins dispersed in the γʹ phase could well hinder the movement of dislocations and produce a favorable work-hardening effect, which led to the excellent creep life of the [111]-oriented specimens under condition of intermediate temperature and high stress. Under the condition of high temperature and low stress, the deformation mechanism was transformed to the dislocations slipping on the <110> {111} slip system and climbing. At this point, the anisotropy of the two oriented specimens was significantly weakened. Importantly, the creep behavior was compared with that of other SX superalloys, a specific reason for the anisotropy under the condition of intermediate temperature and high stress was proposed. That was [111]-oriented specimens exhibited significant orientation sensitive to forming microtwins, which induced the different creep anisotropy in this low-cost [111]-oriented Nickel-based single crystal alloy.