Remarkable improvement in tensile strength of a polycrystalline γ-TiAl-based intermetallic alloy by deformation nanotwins

Strengthening of TiAl-based intermetallic alloy is vital for its broader application, however, microstructural refinement through conventional processes is difficult to further strengthen this intermetallic alloy. Although high-density deformation nanotwin is expected to effectively strengthen it, there is still lack of in-depth understanding about the strengthening mechanism of high-density deformation nanotwin in TiAl-based alloy. Herein the microstructures, room-temperature (RT) tensile properties, tensile fracture behavior, and deformation mechanism of the Ti-45.5Al-4Cr-2.5Nb (at.%) master alloy (M. A.) as well as its continuous casting (C. C.) alloy and the heat-treated alloys were systematically investigated. After the C. C. alloy was annealed at 1250 degrees C for 2 h, the volume fraction of (B2+gamma) coupled structures in the original grains reached the minimum, the interlamellar spacing was markedly refined; besides, substantial Shockley partial dislocations and stacking faults were generated in gamma phase. During RT tension, both the dominant deformation mechanisms of the M. A. and C. C. alloy were dislocation slip, while that of the 2 h heat-treated alloy was changed into deformation twinning. Highdensity deformation nanotwins were generated in the gamma phase (especially the gamma lamellae) of the 2 h heattreated alloy, which improved the tensile strength of the M. A. by 79%. High-density deformation nanotwins can further strengthen TiAl-based alloy to a large extent, which is mainly attributed to the fact that their batchto-batch generation in the polycrystalline TiAl-based alloy during tension could considerably relief the stress concentration in addition to effectively improving the work-hardening rate, thus making the work-hardening rate keeping stable.

Automated summary

The microstructural refinement using deformation nanotwins can significantly improve the tensile strength of TiAl-based alloy. The generation of high-density deformation nanotwins can effectively strengthen the material by relieving stress concentration and improving the work-hardening rate during tension, thus keeping the work-hardening rate stable.