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As a strong β-stabilizing alloying element, Mo has gained importance for intermetallic β/γ-TiAl alloys. In general, TiAl alloys containing a significant volume fraction of the disordered body-centered cubic β-phase exhibit improved processing characteristics during hot-working. To increase the understanding of the alloying effect of Mo, a model alloy with the chemical composition Ti-44Al-7Mo-0.1B (in at.%) was investigated. In this work, the microstructural evolution after individual heat-treatment steps was studied by means of scanning as well as conventional and in-situ transmission electron microscopy. Additionally, macro-hardness and nanoindentation measurements were conducted to study the change in hardness due to grain refinement and solid-solution hardening. The variation of the observed macro- and nano-hardness corresponds well with the microstructural evolution. The obtained grain refinement effect leads to a significant increase in the macro-hardness, whereas the increase in the average nano-hardness of the individual phases is related to solid-solution hardening.

Nb-V additions clearly affected the precipitation state, respective phase transformations and final microstructure, and in turn, resulting mechanical properties of an intercritically annealed transformation induced plasticity sheet steel. As the precipitation hardening played a limited role in the overall strengthening, the grain refinement was the prevailing strengthening mechanism associated with the addition of the Nb-V microalloying to a basic TRIP780 composition. In addition to this, the microstructural changes, resulting from the addition of microalloying, lowered the stability of retained austenite, which decreased the elongation of the steel. Nevertheless, using this microalloying concept, an exceptional product of R m xA 80 exceeding 16 000 MPa % could be achieved.