Solving the problem of solidification cracking during additive manufacturing of CrMnFeCoNi high-entropy alloys through addition of Cr3C2 particles to enhance microstructure and properties

Abstract

In this study, TiAl and Cr3C2 particles were added to a high-entropy CrMnFeCoNi alloy through powder mixing and selective laser melting (SLM) with the aim of acquiring both high SLM processibility and an excellent combination of high strength and ductility with a post-process aging treatment. By only adding 4 at.% TiAl particles into CrMnFeCoNi, a number of cracks were found in as-printed samples for the processing conditions under investigation, promoted by a considerable increase in solidification range and gradient in the late stage of solidification. However, further addition of 2.5 at.% Cr3C2 particles into (CrMnFeCoNi)96(TiAl)4 reduced the solidification range and gradient, allowing to successfully suppress hot cracking. The as-printed (CrMnFeCoNi)96(TiAl)4 samples are characterized by γ grains each containing a group of cells oriented along a similar direction, with the matrix decorated by a small number of nano-sized Al2O3 and σ particles and the cell boundaries with segregated Ti. The addition of Cr3C2 transformed the segregated Ti at the cell boundaries into discrete TiC nanoparticles. On aging at 650 °C, a high density of long-range ordered domains with considerable B2 and σ precipitates formed. Compared to the SLM-processed CrMnFeCoNi, the as-printed (CrMnFeCoNi)96(TiAl)4 displays a reduced 0.2% yield strength and significantly reduced ductility due to the presence of cracks. Conversely, the as-printed (CrMnFeCoNi)96(TiAl)4 + Cr3C2 samples showed a slightly enhanced yield strength and considerably improved UTS. Aging significantly improves both strength properties while maintaining the good ductility. The long-range ordered domains and precipitation clearly are effective in impeding dislocation motion and can be considered to be the prime source of the increased strength of the dual-particle containing alloy.

Keywords

• High-entropy alloys
• Selective laser melting
• Solidification cracking
• Microstructure
• Deformation mechanism