In-situ neutron diffraction study of the strengthening mechanism and deformation behavior of cellular structure in high-entropy alloys by additive manufacturing

Abstract

Additively manufacturing alloys by a selective laser melting (SLM) usually generates large temperature gradients and rapidly cooling, which enables a refined microstructure, an elemental segregation and high-density dislocations network to achieve an excellent strength-ductility synergy. In this study, the SLM fabricates FeCoNiAlTi high-entropy alloys (HEAs) with a cellular structure composed of high-density dislocations network and elemental segregation, which results in a noteworthy combination of a yield strength and a significant uniform plastic elongation. Strengthening mechanism and deformation behavior of SLM-prepared FeCoNiAlTi HEAs are investigated by a transmission electron microscopy in combination with an in-situ neutron diffraction technique. The results demonstrate that the high strength is mainly derived from cellular structure strengthening, which accounted for over 64 % of the yield strength. The cellular structure's capability to alleviate severe stress concentrations can facilitate deformation homogenization, and break a strength-ductility trade-off. This study provides essential insights into the underlying mechanisms governing the strength and ductility of additively manufactured HEAs.