Enhancing tensile properties by dual-precipitates in a CrFeNiVAl complex-concentrated alloy

Abstract

Complex-concentrated alloys (CCAs) have gained significant attention in recent years due to their exceptional combination of high strength and ductility. In this work, a novel Cr18.5Fe21Ni46.3V4.2Al10 (at. %) CCA was designed and prepared. The dual-precipitates microstructures with hard B2 precipitates and coherent L12 nanoprecipitates, which provide a synergic strength-ductility effect, were introduced into a Cr18.5Fe21Ni46.3V4.2Al10 CCA through appropriate thermomechanical processing strategy. By severe cold rolling and one-step annealing of 1 h at 900 °C, the CCA exhibits a yield strength of 920 MPa, a tensile strength of 1230 MPa, and a uniform elongation of 23.8 %. Microstructure analysis revealed that the excellent mechanical properties are primarily due to coherent L12 nanoprecipitates being sheared by abundant stacking faults, which facilitates dislocation gliding and enhances the strain-hardening capability and ductility. However, the hard B2 precipitates have two different deformation mechanisms. On the one hand, the B2 precipitates are bypassed by dislocations, leading to the dislocation pile-ups against the interface between the B2 precipitates and the FCC matrix, which increases the strain hardening capability but induces stress concentrations. On the other hand, the B2 precipitates provide fine grain strengthening by hindering grain growth. Additionally, dual-precipitation phases also interact significantly with other crystal defects, such as dislocations, stacking faults, and nano twins. Our results demonstrate that the dual-precipitates microstructure is an effective strategy to achieve CCAs or other alloys with high strength-ductility balance.