Chemical complexity-changed deformation behavior of NiTi-based B2 low- to high-entropy intermetallic compounds: Atomistic simulations

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Owing to the high chemical complexity and severe lattice distortion but still long-range ordered structure, the deformation behavior and defect activities of high-entropy intermetallic compounds are worth investigations. Hence in this study, the mechanical properties of NiTi-based low- to high-entropy intermetallic compounds were measured from different orientations at different temperatures simply by using nanoindentations, and compared with the structural evolution and defect activities suggested by molecular dynamics simulations. The deformation of the low-entropy intermetallic compound proceeded with regular martensitic transformation, followed by the heterogeneous nucleation of dislocations at the martensite/austenite interface and the subsequent long-distance gliding accompanied with sharp stress drops. With increasing temperature, a more intense shearing events and marked strength reduction were observed. In comparison, with the introduction of constitutional complexity, the martensitic transition was suppressed. Instead, the early homogeneous nucleation at a relatively small activation volume (acquired from indenting displacement bursts) and small-range activities of abundant defects mediated the smooth stress-strain response and uniform plastic deformation of the high-entropy intermetallic compound. At an elevated temperature, a similar deformation mechanism and the same level of strength were retained in the chemically complex alloy.