Intermetallic materials based on titanium aluminides have attracted wide-spread attention for potential use in high temperature applications because of their outstanding properties including high specific strength, good creep and corrosion resistance. However their applications have been limited by low ductility, so that generally hot working can only be accomplished at temperatures above 1000-1200^oC. A reduction in the temperature range in which the alloys are superplastic would be commercially attractive. This can be achieved through microstructure refinement to a submicron grain size.
In the present work formation of submicrocrystalline (SMC) structure in different TiAl (L1₀ superlattice) and Ti₃Al (DO₁₉) based alloys during hot working and their mechanical properties were studied. A method of production of a SMC structure (d<1 μm) in massive work-pieces based on initiation of dynamic recrystallization during hot working has been developed. The method involves continuous grain refinement due to dynamic recrystallization at a decreasing deformation temperature. A microstructure with a grain size of 0.1 to 0.4 μm and no porosity was produced in different TiAl and Ti₃Al based alloys. Partial disordering was detected in a Ti₃Al alloy with the SMC structure. The grain refinement hardened the intermetallic alloys at room temperature (RT). In a fully ordered Ti₃Al alloy RT ductility increased when the grain size decreased, while the ductility of a partially disordered SMC Ti₃Al and TiAl alloys was close to zero. Low temperature superplasticity (SP) of intermetallic alloys was studied. The effect of grain size, chemistry, phase composition, temperature and strain rate on elongation, flow stress and strain rate sensitivity were investigated. Low-temperature SP behavior was compared with high-temperature SP. As an example of practical application it will be shown the pack rolling for production of sheets with SMC structure from TiAl₂Nb based alloy.

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