Temperature-dependent yield strength and deformation mechanism of a casting Ni-based superalloy containing low volume-fraction γ′ phase

This study investigates the temperature-dependent yield strength and deformation mechanism of a new casting Ni-based superalloy K4750. This alloy exhibits yield strength anomaly (YSA) at 650-750 degrees C though it contains only low volume-fraction gamma ' phase (22%). Using the interrupted samples after ~1.0% plastic strain, the dominant deformation mechanisms at the initial yielding stage are identified as: (i) (anti-phase boundary)APB-coupled dislocation pairs shearing gamma ' from room temperature to 650 degrees C, (ii) dislocations bypassing gamma ' and creating loops above 650 degrees C, and (iii) dislocations overcome gamma ' by the thermally activated cross-slip and local climb at 850 degrees C. Additionally, with the proceeding of deformation, superlattice stacking faults shearing is active above 750 degrees C, implying that the deformation mechanism changes as the deformation progresses. According to the theoretical calculation, the critical resolved shear stress of Orowan looping decreases faster than APB shearing with the temperature increase, which is in agreement with the observed transition of deformation mechanism. Moreover, the remaining loops hinder the movement of subsequent dislocations, resulting in severe dislocation entanglement and high dislocation density in the heterogeneous slip bands, contributing to YSA. By contrast, dislocations can easily surmount gamma ' phase by cross-slip and climb at 850 degrees C, leading to a rapid degradation of yield strength.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the temperature-dependent yield strength and deformation mechanism of a new casting Ni-based superalloy K4750. The study found that this alloy exhibits yield strength anomaly in the temperature range of 650-750 degrees C. The dominant deformation mechanisms at the initial yielding stage were identified through interrupted samples with approximately 1.0% plastic strain.