Temperature Dependence of Deformation Transitions and Anomalous Strengthening in a Novel Ni-based Superalloy

A novel Ni-based superalloy developed as a candidate for turbine-disk application above 800 ℃ was systematically investigated. Uniaxial tensile tests from room temperature (RT) to 850 ℃, combined with microstructural characterization, were used to examine the temperature dependent evolution of the dislocation-mediated deformation modes, namely antiphase boundary (APB) coupled shearing, stacking fault (SF) and microtwin (MT) shearing, and Orowan bypassing. The alloy achieved an ultimate tensile strength (UTS) of 1800 MPa with 15.75% elongation (EL) at RT, and retained a UTS of 941.5 MPa with 11.75% EL at 850 ℃. The dominant deformation mechanisms transitioned from antiphase boundary (APB) coupled dislocation shearing at RT to stacking fault (SF)/microtwin (MT) shearing at intermediate temperatures, and ultimately to Orowan bypassing coupled with dislocation climb at high temperatures. Although this sequence was consistent with previous studies, the present alloy showed several notable microstructural features. Metastable 9R structures, rarely reported in conventional superalloys, were observed at RT, and Lomer-Cottrell (L-C) locks were observed within γ′ precipitates at 815 ℃. The anomalous strengthening peak at 650 ℃ was found to arise from a temperature driven transition from localized planar dislocation glide to extensive SF shearing of γ′ precipitates. These findings expand the current understanding of dislocation mediated deformation mechanisms across a wide temperature range.