Enhancing plasticity in laser additive manufactured high-entropy alloys: The combined effect of thermal cycle induced dissolution and twinning

Breaking the trade-off between strength and ductility and pursuing stronger and more ductile metal materials has been a long-standing dream for scientists. Interestingly, even for the same material, different manufacturing methods can lead to significantly different performance. In this study, we utilized different laser additive manufacturing techniques (laser direct energy deposition (LDED), and laser powder bed fusion (LPBF)) to fabricate FeCoCrNiMo_0.5 high-entropy alloy (HEA). Through microstructural analysis, we discovered a novel thermal cycling-induced dissolution (TCID) mechanism. By controlling the cooling rate post thermal cycling, we achieved the dissolution of precipitate phases and increased the Mo content within the matrix. Based on this phenomenon and supported by theoretical calculations, we revealed a reduction in stacking fault energy (SFE), which gave rise to a twinning-induced plasticity (TWIP) mechanism. This led to a dramatical increase in plasticity (LDED: 1.6 %, LPBF: 17.7 %) in the LPBF alloy, while maintaining similar strength (LDED: 784.9 MPa, LPBF: 840.89 MPa). This study provides guidance for designing metals structures with balanced strength and plasticity.