Temperature and Strain-Dependence of Tensile Behavior of a High-Cr CoNi-Based Single-Crystal Superalloy
摘要
To further understand the anomalous yielding behavior of γ′-strengthened Co-based superalloys, the tensile properties of a high-Cr CoNi-based single-crystal superalloy were investigated within the temperature range from room temperature to 1000 °C. The alloy exhibited a yield strength anomaly (YSA) from 650 °C to 760 °C, and the flow stress decreased with increasing temperature up to 1000 °C. Moreover, the YSA was enhanced due to work-hardening or softening processes as the plastic strain increased. At the peak temperature (760 °C), the initial plastic deformation behavior was characterized by continuous work hardening. The initial work-hardening behavior at the low plastic strain was mainly ascribed to the Kear–Wilsdorf locks induced by the antiphase boundary (APB)-coupled dislocation pairs shearing the γ′ precipitates. In comparison, dislocation accumulations in the γ matrix and stacking fault (SF) interactions in γ′ precipitates were responsible for the subsequent work-hardening process. Above the peak temperature (950 °C), the initial plastic deformation behavior was dominated by a work-softening stage at low plastic strain, followed by a work-hardening stage with increasing plastic strain. The thermally activated bypassing of γ′ precipitates via dislocation gliding/climbing reduced the deformation resistance and accounted for the work-softening stage. As plastic deformation proceeded, the subsequent work-hardening process was governed by the increasing dislocation entanglements in the γ matrix and complex interactions among the SFs, APBs and other APB-related configurations in γ′ precipitates. This work is meaningful for understanding the deformation mechanism of γ′-strengthened Co-based superalloys and improving their tensile performance.