Dual effects of local chemical order on the ductility of body-centered cubic multi-principal element alloys

In recent years, the role of local chemical order (LCO) in the mechanical properties of multi-principal element alloys (MPEAs) has attracted extensive attention. However, the extent of LCO's impact on the ductility of BCC MPEAs and the underlying mechanisms remain elusive. Here we found that introducing LCO into the non-equiatomic TiVZr alloy significantly reduces the uniform elongation, but increases the elongation to fracture. The dual ductility response stems from the alteration in a character of dislocation glide. In fact, whether the uniform elongation increases depends on the degree of recovery of the work-hardening rate caused by dislocation delocalization. Furthermore, the potential microstructural characteristics affecting the capacity for dislocation delocalization in BCC MPEAs with LCOs are discussed from two aspects: the ability of LCO to stall dislocations and the degree of lattice distortion.