Novel Reduced-Activation TiVCrFe Based High Entropy Alloys

The conditions inside next-generation nuclear reactors are likely to be extreme. High-performance materials will be required, and there is still great scope for developing new and improved alloys. High-entropy alloys (HEAs) are potential candidates, and it is likely that such alloys will need to be based around low-activation elements that tend to form body-centred cubic structures. Whilst there have been a number of investigations assessing the capability of CALPHAD databases to predict the phases formed in face-centred cubic HEAs, their applicability to less studied systems is not well known. Here, two low-activation HEAs are produced; TiVCrMnFe and Si0.1TiVCr0.5Fe, and their microstructures assessed and compared to CALPHAD predictions. The microstructures of both alloys comprised a C14 Laves phase and a B2 phase following casting, and a C14 Laves phase and a BCC solid solution (A2) phase following holding at 1200˚C, with high proportions of both constituent phases found in each case. It was found experimentally that the Laves phases in both alloys were quaternary intermetallics of Fe, V, Cr and Ti, with Fe, V and Cr likely disordered across the Fe site. These observations were compared with predictions made using four CALPHAD databases. The accuracy of the predictions varied markedly between the databases. It was found that the Laves phase was underpredicted, often severely, by the databases that did not account for the quinary nature of phase. Removing Ti from TiVCrMnFe resulted in an equiatomic VCrMnFe alloy that formed a single BCC phase at 1200˚C.