Abstract: The development of a Ni-based superalloy that consists of only the γ-solid-solution phase is highly desired for some applications such as high-temperature gas-cooled reactors in power plants. In this study, the temperature dependence of the plastic deformation behavior of Ni-22Cr-8W (at%) alloy was examined for the first time by using a single crystal, focusing on the influence of the short-range order (SRO), especially upon high-temperature deformation behavior. The critical resolved shear stress (CRSS) for (111)[10$\bar{1}$] slip exhibited a rapid decrease as the temperature increased at low temperatures but an almost constant value of ∼45 MPa between 500 and 900 °C. In addition, a slight yield stress anomaly (YSA) was observed, reaching a maximum value at 1000 °C.
To clarify the influence of the SRO on the YSA behavior, the mechanical properties of Ni-8W and Ni-5Re single crystals were also examined. Similar temperature dependence for the CRSS, including the occurrence of slight YSA, was observed for Ni-8W, in which SRO developed. In the Ni-5Re single crystal in which SRO did not significantly develop, however, the CRSS monotonically decreased as the temperature increased. The results suggest that the presence of SRO in a Ni-Cr-W alloy contributes to the strengthening of the alloy not only at low temperatures but also at high temperatures up to ∼1000 °C. The results strongly suggested that the pseudo-PLC effect is related to the origin of YSA appearing in Ni-based γ-solid-solution alloys at high temperatures.

Key words: Ni-based superalloy, Short-range order (SRO), Dislocation, Yield stress anomaly (YSA)