Microstructure and mechanical properties of a new β-solidifying γ-TiAl alloy in the temperature range of the brittle-ductile transition

A new β-solidifying γ-TiAl alloy with a composition Ti-44Al-6(Nb, Zr, Hf)-0.15B (at.%) (designated as TNZ γ-alloy) has been recently designed. In contrast to the so called TNM γ-TiAl alloy (Ti-43.5Al-4Nb-1Mo-0.1B, at.%) the new alloy was alloyed with Zr and Hf instead of Mo that reduced the β-stabilization and led to formation of the metastable β(β0) phase instead of the stable one. Nevertheless, the new alloy showed good forgeability even at 950°C. The alloy ingot was subjected to upset forging at T = 950°C followed by heat treatments. The applied processing led to formation of refined duplex type structures with different lamellar spacing almost free of the β(β0) phase. The obtained microstructural conditions were characterized and the tensile and creep tests were performed. The mechanical tests showed that with increasing the lamellar constituent and decreasing the lamellar spacing the creep resistance increased and ductility decreased. The onset of the brittle-ductile transition was always observed at T ≥ 850°C that should be assumed as an advantage of the new alloy. This is why the alloy demonstrated higher creep resistance than the TNM alloy in a similar microstructural condition. The obtained results are discussed from the viewpoint of processability, mechanical properties and oxidation resistance of the new alloy.

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1. Ministry of Science and Higher Education of the Russian Federation - 122011900470-7