Coarsening behavior and strengthening mechanisms of L12-Ni3(Al, Ti) precipitates in a (CoCrNi)94Al3Ti3 medium-entropy alloy

초록

L12 precipitate-hardened high-entropy alloys (HEAs) and medium-entropy alloys (MEAs) exhibit outstanding mechanical properties. A comprehensive understanding of L12 precipitate behavior is essential to optimize the mechanical performance of these alloys. In this study, the precipitation behavior and corresponding mechanical properties of a (CoCrNi)94Al3Ti3 MEA were systematically investigated under various aging treatments. Aging at 900 degrees C significantly improved the strength-ductility balance compared to conventional L12-hardened MEAs. In particular, the specimen aged at 900 degrees C for 1 h showed an ultimate tensile strength (UTS) of 1102 MPa, a yield strength (YS) of 632 MPa, and an elongation (EL) of 45.7 %. However, prolonged aging to 48 h resulted in a reduction in strength due to the coarsening of the L12 precipitates. Quantitative analysis of the precipitate strengthening contribution revealed that the variation in strength was governed by distinct precipitate strengthening mechanisms: dislocation shearing and dislocation bypassing mechanisms. These findings provide valuable insights for optimizing aging conditions in L12 precipitate-hardened HEAs and MEAs, facilitating the design of next-generation structural materials.

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