Variations in the elastic properties and lattice parameters of Mo–Ti and Mo–Cr BCC solid solutions, as estimated by DFT calculations

This study evaluated the changes in the elastic properties and lattice parameters of Mo–Ti and Mo–Cr binary BCC solid solutions (BCC_sss) using density functional theory (DFT) calculations. The Mo–Ti and Mo–Cr BCC_sss are the key phases in ultra-high-temperature MoSiBTiC alloys. The elastic constants of Mo–Ti decreased with increasing Ti content. However, the elastic constants of Mo–Cr exhibit high values irrespective of Cr content. The elastic constants of both of the BCC_sss were affected by the number of valence electrons. The lattice parameters showed a strong relationship between the atomic arrangement in Mo–Ti and Mo–Cr. Both Ti and Cr energetically preferred the third-nearest-neighbor pairs in the BCC structure. The second-nearest-neighbor pairs were also relatively stable in Mo–Cr. These atomic arrangements and differences in electronegativity affected the atomic volumes of Mo, Ti, and Cr. The lattice parameters of Mo–Ti and Mo–Cr deviated from Vegard's law, mainly because of the atomic volume changes of Mo, Ti, and Cr. The results of this study provide useful ideas for designing Mo–Ti or Mo–Cr BCC_sss.