Solving the problem of solidification cracking during additive manufacturing of CrMnFeCoNi high-entropy alloys through addition of Cr3C2 particles to enhance microstructure and properties
Xintian Wang, Zhiyong Ji, Robert O. Ritchie, I.V. Okulov, J. Eckert, Chunlei Qiu
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.