Effect of Al content on microstructure and mechanical properties of the (FeCoNiV)100-xAlx high-entropy alloys

Abstract

It is well known that face-centered cubic (FCC) high-entropy alloys (HEAs) typically have excellent ductility at room temperature but relatively low strength, which greatly limits their structural applications. To address the strength-ductility trade-off, researchers synthesized a series of (FeCoNiV)100-xAlx (x = 0–20 at. %) HEAs, investigated the effect of alloying Al on microstructure and tensile properties, then analyzed the strengthening mechanism. It was found that the crystalline structure changed from an initial single FCC structure to a duplex FCC plus body-centered cubic (BCC) structure and then to a single BCC structure with increasing Al concentration. After homogenization process, the FCC and BCC phases can be transformed to ordered L12 and B2 phases, respectively. These HEAs with duplex FCC/L12 plus BCC/B2 structure exhibit the potential for excellent mechanical properties, and their properties can be modulated by Al content and heat treatment. The properties can be tuned by both Al content and heat treatment, as the Al content can modulate the BCC phase content and the heat treatment can change the ordered structure. A careful analysis reveals that the solid solubility of Al element in this system was only 3.6 at. %, which has a limited effect on the strength. FCC/L12 bears the main plastic strain and the high tensile strength of the alloy is achieved thanks to the contribution of the BCC/B2 phase to the work-hardening rate of the alloy during the early stages of deformation and the unique work-hardening ability of the L12 phase.