Tuning the hydride stability of the TiVNb-based alloys by equimolar Cr/Al addition

Body-centered multi-principal element alloys (BCC-MPEAs) based only on hydride-forming elements have low equilibrium plateau pressures during reaction with hydrogen and, consequently, high decomposition temperatures due to the high thermodynamic stability of related hydrides. In this work, we present a strategy to decrease the stability of the final hydrides formed in the BCC TiVNb alloy by simultaneous addition of two non-hydride forming elements, Cr and Al. The (TiVNb)100-x(CrAl)x alloys with x = 10, 20, 30, and 40 at.% crystallize as major BCC solid solutions with dendritic microstructures. Pressure-Composition-Temperature diagrams revealed that the combined addition of Cr and Al thermodynamically destabilizes the dihydride formation for x = 10 and 20 at.%. For higher Cr/Al contents the destabilization is too large to form stable hydrides under maximum 100 bar pressure. The absorption/desorption plateau pressure at room temperature for (TiVNb)80(CrAl)20 alloy are 9 and 0.6 bar, respectively, enabling a reversible capacity of about 0.8 H/M (1.4 wt%) at ambient conditions. The present results provide important insights into the effects of simultaneous Cr and Al additions in BCC-MPEAs and shed light on the design of new alloys with hydrogen absorption and desorption ability at ambient conditions. •A set of alloys of the Ti–V–Nb–Cr–Al system were produced by arc-melting.•The alloys crystallize as major BCC solid solutions with dendritic microstructures.•The combined Cr/Al addition thermodynamically destabilizes the dihydride formation.•The (TiVNb)80(CrAl)20 alloy has a reversible capacity of 0.8 H/M (1.4 wt%) at 25 °C.