Achieving dislocation-precipitation strengthening synergy in additively manufactured medium-entropy alloy via cyclic deep cryogenic strategy

Abstract

A problem has recently been highlighted in the additively manufactured (AMed) L1₂-strengthened high/medium-entropy alloys (H/MEAs), where the dislocation strengthening effect will be severely weakened due to the inevitable dislocation recovery that occurs during the aging process. To address this, a cyclic deep cryogenic strategy (CDCS) towards the dislocation-precipitation strengthening synergy is proposed. Besides dislocations, this strategy can introduce dense intersecting stacking faults, thus effectively enhancing the thermal stability of dislocations during aging due to the pinning effect of Lomer-Cottrell locking. The existence of these high-density defects further ensures the uniform precipitation of L1₂ phase. Significantly, the CDCS causes a substantial ⁓ 40% increase in the yield strength of the (CoCrNi)₉₄Al₃Ti₃ MEA sample without compromising the ductility, in which the contribution of dislocation strengthening is doubled. This work provides a pathway for obtaining high-performance AMed H/MEAs, especially L1₂-strengthened H/MEAs.