Segregation engineering assisted cracking inhibition and mechanical-property enhancement of laser additively manufactured Al-bearing CoCrFeNi-based high-entropy alloy

Abstract

Achieving balanced strength-ductility while inhibiting cracking behaviors is a crucial highlight for the laser additively manufactured CoCrFeNi HEAs. Here we designed a [Al-Co₄Fe₄Ni₄]Cr₃ HEA composition using a high-entropy alloying strategy by analyzing the elemental compositions of Fe-based heat-resistant steels and Ni-based superalloys based on a cluster model. The crack-free thin-walled LAM-ed HEAs were acquired by segregation engineering. The results reveal that the cracks are eliminated primarily owing to the inter-dendritic segregation of Ti, Nb, and Zr elements to boost liquid backfilling. Also, the primarily ordered phases along the inter-dendrite deeply affect the tensile properties. Concretely, the Ti-HEA possesses the highest tensile strength (σ_UTS)~ 632 MPa and the best elongation (ε_f)~ 43.1 %. Surprisingly, the brittle Ni₇Zr₂ phases compel the Zr-HEA to show an unsatisfactory ε_f (~12 %). Moreover, the Ti-HEA after direct aging treatment at 650 ℃ for 20 h exhibits high yield strength (σ_0.2)~ 626 MPa, σ_UTS ~ 1100 MPa with sufficient ε_f ~ 20 %, in which the disk-like L1₂ precipitates make significant contributions to the strength increment. The above findings provide a novel paradigm for developing crack-free and high-performance HEAs.