Zirconium-Mediated Modifications in SHS Shear Deformed TiAl(Nb,Mo)B Alloys: A Study of Phase Evolution and Mechanical Response

This work systematically examines the effect of zirconium additions on the phase transition behavior and microstructural evolution of TiAl(Nb,Mo)B systems subjected to shear deformation under unconstrained self-propagating high-temperature synthesis (SHS). The study further evaluates the direct correlation between Zr doping levels, microstructural arrangements, and the resulting mechanical behavior of the densified compacts. The experiments focused on a precursor powder blend with the nominal composition of 51.85Ti–43Al–4Nb–1Mo–0.15B (at %) supplemented with 1–3 at % of zirconium. The results demonstrate that introducing Zr during SHS processing promotes the precipitation of a secondary Al2Zr intermetallic compound, which selectively segregates at the boundaries of the lamellar γ and α2 colonies. This alloying strategy yields a pronounced enhancement in room-temperature improved crack resistance under contact/indentation conditions and structural damage tolerance. These mechanical enhancements are associated with a synergistic effect, phase transformations, and the precipitation of an Al2Zr phase, whose volume fraction is governed by the initial Zr concentration. We assumed that the resulting microstructure effectively impedes macrocrack advancement through multi-directional branching and interfacial energy dissipation, thereby effectively preventing brittle failure under indentation loads up to 100 N at room temperature.