Microstructure evolution and mechanical properties of a novel beta γ-TiAl alloy

A new beta gamma TiAl alloy Ti-43Al-4Nb-2Mo-0.5B (at %) was fabricated by ISM method. The as-cast microstructure consisted of fine lamellar colonies and mixtures of small γ and B2 grains around lamellar colony boundaries. By canned hot forging, the cast microstructure was further refined and homogenized. Microstructure evolution during hot forging was characterized by means of SEM, TEM and EBSD in detail. DRX and phase transformation during forging are also discussed; Based on nano-indentation tests, B2 was found much harder than γ and α2 phases. The tensile properties of the forged alloy were investigated and compared with as-cast condition; this forged alloy maintains high tensile strength over 900 MPa up to 750 °C, and tensile superplasticity appears above 800 °C. B2 phase is proved to be detrimental to room-temperature ductility and to reduce tensile strength sharply above 800 °C, mainly because of its hard and brittle nature at low temperature and its soft feature at high temperature.

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► Hot forging further refines the cast microstructure of current beta gamma alloy.
► This forged alloy maintains high tensile strength over 900 MPa up to 750 °C.
► B2 is the hardest phase in TiAl alloy, with nanohardness of 8.5 GPa.
► B2 phase is detrimental to room-temperature ductility of γ-TiAl alloy.