Effect of pre-deformation on transformation pathways in a precipitation-strengthened medium-entropy alloy

초록

Pre-deformation is widely used to modify precipitation behavior in alloys, yet the mechanistic role of dislocations in governing distinct precipitation pathways in medium-entropy alloys (MEAs) remains unclear. Here, we investigate the precipitation behavior of the γ′ and σ phases in a (CoCrNi)94Al3Ti3 alloy with controlled pre-deformation. In-situ synchrotron X-ray diffraction was employed to track phase evolution during thermal exposure. The results show that increased dislocation density accelerates σ precipitation, leading to an earlier onset temperature and a higher volume fraction, consistent with dislocation-assisted classical nucleation of an intermetallic phase with high interfacial energy. In contrast, γ′ precipitation exhibits nearly identical intensity evolution across all pre-deformation conditions, indicating that its continuous transformation pathway is largely insensitive to dislocation density. These results demonstrate that the influence of pre-deformation in MEAs is strongly transformation-pathway dependent, selectively promoting σ precipitation while leaving γ′ precipitation largely unaffected. © 2026 Acta Materialia Inc.

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