Laser-directed energy deposition of a high performance additively manufactured (CoCrNi)₉₄(TiAl)₆ medium-entropy alloy with a novel core-shell structured strengthening phase

Abstract

Additively manufactured (CoCrNi)₉₄(TiAl)₆ medium-entropy alloys (MEAs) were fabricated by laser-directed energy deposition. The strengthening induction mechanism in the additively manufactured (CoCrNi)₉₄(TiAl)₆ MEAs was investigated using electron backscatter diffraction and transmission electron microscopy. The results showed that the addition of TiAl powder led to increases of 29.6% and 43.5% in the ultimate tensile strength (UTS) and yield strength (YS), respectively, at 298 K, and a decrease of 17.1% in the elongation. For the samples tested at 77 k after the addition of the TiAl powder, the UTS and YS improved by 26.6% and 28.0%, respectively, and the elongation increased by 26.3%. The microstructural observation results indicated that the matrix grains changed from initial columnar grains with a uniform growth direction to fine dendrites. Numerous TiO clad Al₂O₃ strengthening nano-precipitates with a novel core–shell structure were found in the additively manufactured (CoCrNi)₉₄(TiAl)₆ MEAs, and both featured a face-centered cubic structure. No crystallographic orientation was observed between the nano-precipitates and the matrix. At 298 K, the dislocation line bypassed the nano-precipitates during the plastic deformation period and Lomer–Cottrell locks appeared near the nano-precipitates, thereby strengthening the additively manufactured (CoCrNi)₉₄(TiAl)₆ MEAs. At 77 K, plastic deformation resulted in the synergistic deformation of the nano-precipitates and matrix, the formation of a large number of dislocations, and a twinning induced plasticity effect, which further increased the strength and plasticity of the additively manufactured (CoCrNi)₉₄(TiAl)₆ MEAs.

More information

Identifiers

ORCID for Dikai Guan: orcid.org/0000-0002-3953-2878

Catalogue record

Export record

Altmetrics