EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

High-entropy alloys (HEAs) push the boundaries of high-stiffness lightweight alloy design through their exceptional chemical diversity. Specifically, refractory HEA compositions have shown great promise as their specific stiffness surpasses that of even the more advanced high-modulus steels. A common occurrence in BCC refractory HEAs is their limited ductility due to the complete or partial transformation of the high-temperature BCC solid solution to the BCC_B2 ordered phase at lower temperatures. As this transformation is associated with the presence of generally beneficial alloying elements in terms of the elastic properties and the density of said alloys it is critical that it is suppressed without altering the chemical composition. In the literature, a series of heat treatments have been suggested to control the formation of the ordered phase and achieve a proper balance between strength and ductility. In this work we investigate this processing pathway to tackle such problems evident in the equiatomic AlTiVCr and AlTiVCr-7.2Si alloys. Furthermore, we apply this processing route on two novel high-modulus HEA compositions. The associated experimental work involved manufacturing four HEAs based on the AlTiVCr system through Vacuum Arc Melting (VAM). The alloys were heat treated at $1200\unicode{xb0}$C for 8h followed by quenching to room temperature and subsequently aged at $700\unicode{xb0}$C for 24h. The samples were characterised through means of Optical, Scanning and Transmission Electron Microscopy (OM, SEM, TEM), X-Ray Diffraction Analysis (XRD), together with elastic properties measurements through Microindentation testing.