Effect of Chemical Composition Variability on Phase Composition and Structure of Beta-Solidifying TiAl-Alloy in As-Cast Condition

Resumo

The regularities of the effect of the variation in the chemical composition of the new Russian β‑solidifying TiAl-alloy (Ti–44.5 Al–2 V–1 Nb–2 Cr/1 Zr–(0–0.1) Gd, at %) within the chromium content from 1.5 to 2.5 at % (2.0–3.5 wt %) and zirconium from 0.5 to 1.5 at % (1.2–3.5 wt %), as well as the effect of gadolinium microalloying on the phase composition and the structure of ingots, have been studied. The ingots were obtained using double vacuum-arc remelting with the subsequent vacuum-induction melting and pouring of the melt into the steel chill mold at the melting-casting unit with a cold crucible. It is shown that 0.1 at % gadolinium microaddition results in a decrease in the average size of the macro grains from 3000 ± 500 μm to 400 ± 80 μm in the peripheral part of the ingots after the first remelting. It was found that the phase composition of TiAl-alloy compositions with Cr and Zr is represented by three main phases: γ-TiAl, α₂-Ti₃Al, and β-phase. The volume fraction of β-phase does not exceed 2–3% in ingots containing Zr, while it reaches 5–6% in ingots containing Cr. It was revealed that the microstructure of the ingots of all studied chemical compositions has a lamellar morphology. Sprouting of lamellar colonies through the grain boundaries was noted for ingots containing Zr.