The thermodynamic and mechanical properties of Earth-abundant metal ternary boride Mo2(Fe,Mn)B2 solid solutions for impact- and wear-resistant alloys

Abstract

The tetragonal ternary borides Mo₂MB₂ (M = Fe, Mn) and their solid solutions are promising candidates for tungsten-free wear-resistant alloys. In this study, we investigated the thermodynamic, mechanical, vibrational, structural, and electronic properties of Mo₂MB₂ compounds and their solid solutions using density functional theory (DFT) calculations. To model Mo₂(Fe_1−xMn_x)B₂ as disordered substitutional solid solutions, we employed the DFT-based virtual crystal approximation (VCA) and the cluster expansion (CE) approaches. The calculation results showed that both Mo₂MB₂ compounds are mechanically and thermodynamically stable, exhibiting similar features in terms of electronic structure and chemical bonding types. The temperature–dependent interaction parameter for the Mo₂(Fe_1−xMn_x)B₂ phase in the compound energy formalism (CEF) notation was accessed using a combination of the ATAT and the Thermo-Calc software. To experimentally validate the calculated thermodynamic parameters, an isopleth was constructed by intersecting the Fe–Mn–Mo–B–C alloy system within suitable concentration ranges for hardfacing alloy development, and the key alloys were analyzed to compare their phase composition and constitution with the calculation results. The Vickers hardness (H_V) of the Mo₂(Fe_1−xMn_x)B₂ solid solutions was determined as an average value from different models, including elastic constants calculated using DFT. Both VCA and CE approaches showed an HV increase from 22.9 to 24.7 GPa within the composition range of Mo₂(Fe_0.75Mn_0.25)B₂ to Mo₂(Fe_0.25Mn_0.75)B₂. Based on the calculated properties, Mo₂(Fe,Mn)B₂ solutions can serve as a reinforcement phase in high-manganese hardfacing Fe-based alloys.