Deposited Ductile-GPa CoCrNi-based FCC medium entropy alloy with continuously precipitation by directed energy deposition-Arc

Abstract

An L1₂-strengthened Co₃₀Cr₁₈Ni₄₂Al₅Ti₅ medium-entropy alloy was fabricated via directed energy deposition (DED)-Arc technique, focusing on investigating the modulation mechanism of the process on L1₂ phase precipitation behavior. The results showed that the high heat input and moderate cooling rate features of DED-Arc process effectively suppressed the discontinuous precipitation (DP) behavior: the coarse columnar crystal structure significantly reduces the number of grain boundaries; moderate cooling rate promotes homogeneous distribution of Al/Ti elements and eliminates grain boundary segregation; This “coarse grain-element homogenization” synergy results in a high-density distribution of the L1₂ phase within the grain through a continuous precipitation (CP) behavior. Directly deposited alloys exhibit gigapascal strength (∼1090 MPa) and high uniform elongation (∼28.4 %). Furthermore, subsequent heat treatment of the deposited alloys confirmed the thermal stability of the continuous L1₂ precipitation, with increased L1₂ phase fraction while maintaining “FCC+L1₂” structure. This work provides guidance for the fabrication of L1₂-strengthened high-entropy alloys and medium-entropy alloys with excellent mechanical properties by additive manufacturing.