Room temperature mechanical behavior of silicon-doped TiAl alloys with grain sizes in the nano- and submicron-range

Abstract

Nano- and submicron-grained intermetallic compounds consisting of γ-TiAl and ξ-Ti 5(Si,Al) 3 were produced by high energy milling and hot isostatic pressing. Owing to the pure and controlled processing conditions, the mechanical properties may be indubitably related to the microstructure. Both yield strength and hardness show a Hall–Petch-type dependence on grain size, resulting in extremely high flow and fracture stresses under compression of up to 3 GPa. With a reduction of grain size, the coefficient of strain hardening as well as the compressive fracture strain decrease and drop to zero for alloys with grain sizes of about 150 nm. Deformation at room temperature is accomplished by dislocation glide and mechanical twinning, with twinning attaining more and more importance as the grain size is further reduced. Diffusion-controlled deformation mechanisms can be ruled out even for intermetallics with crystallite sizes as small as 50 nm. A room temperature ductilization of intermetallic compounds by switching to a nanocrystalline microstructure seems to be rather unlikely.