Anomalous temperature dependence of yield strength and deformation mechanisms in chemically complex intermetallic alloy

An ordered L1₂ structure-dominated chemically complex intermetallic alloy (CCIMA) was developed based on a Ni-Co-Cr-Al-Mo-Ti-Ta-Nb-B system. Its phase structure, mechanical behaviors, and underlying deformation mechanisms were investigated systematically at room and elevated temperatures. The CCIMA yields at a strength of 758 ± 2 MPa at room temperature, maintaining a pronounced work-hardening rate of ∼4530 ± 10 MPa throughout the entire deformation, which achieves an ultimate strength of ∼1490 ± 12 MPa attributing to the formation of anti-phase boundary (APB) together with superlattice intrinsic stacking fault (SISF). A remarkable temperature-dependent anomaly in yield strength is formed at temperatures below about 800 °C, obtaining an increment of strength for nearly 200 MPa relative to that at 20 °C. Such yield strength anomaly (YSA) is caused by the pining of Kear-Wilsdorf (K-W) locks, resulting from thermally-activated superlattice dislocations from the (111) octahedral to (010) cube plane. Furthermore, a transition of dissociation scheme from APB-type at intermediate temperatures to SISF-type at 900 °C is believed to be responsible for the absence of YSA at higher temperatures. A high peak of flow stress towards 800 °C is formed in the CCIMA, signifying a great potential for elevated temperature applications. 

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