Fabrication of Bulk Al-Ti-V-Cr-Si Low-Density High-Entropy Alloy Solid Solution by Shock Solidification

The shock-compression method enables dense solidification at relatively low temperatures, and fabrication of bulk material is possible without thermal alteration of the nonequilibrium phases. A metastable phase of an equiatomic Al-Ti-V-Cr-Si high-entropy alloy was prepared by mechanical alloying, and the obtained alloy was solidified by shock-compression to retain the metastable phase of AlTiVCrSi. The bulk form composed of a metastable body-centered cubic (BCC) solid solution was attained after shock solidification at a pressure of 11 GPa. However, when shock stresses of 21 GPa and 31 GPa were applied, the intermetallic compounds (Ti, V)(5)Si-3 and Al-8(V, Cr)(5) were formed in addition to the BCC phase. The formation of these intermetallic compounds during shock compression was consistent with thermodynamical predictions and empirical parameters for phase prediction. The bulk AlTiVCrSi samples shock-solidified at 11 GPa and 21 GPa exhibited Vickers hardness values greater than 1000 HV, whereas that for the sample shock-solidified at 31 GPa was similar to 400 HV. The decrease in hardness was attributed mainly to the formation of a large number of cracks.