Ga. Salishchev et al., Formation of a submicrocrystalline structure in TiAl and Ti3Al intermetallics by hot working, MAT SCI E A, 286(2), 2000, pp. 236-243
A method of producing a submicrocrystalline structure (grain size d < 1 mu
m) in large pieces of hard-to-deform materials like titanium aluminides has
been developed. The method is based on initiation of dynamic recrystalliza
tion (DRX) during hot working, utilizing the decrease in grain size during
DRX which occurs when the hot working temperature decreases or the strain r
ate increases, both leading to an increase in flow stress. In practice, the
method involves continuous grain refinement due to DRX as the working temp
erature decreases. A grain size of 0.1-0.4 mu m was produced with no porosi
ty in TiAl- and Ti3Al-based alloys. Partial disordering was detected in a T
i3Al alloy with a submicrocrystalline (SMC) structure. The grain refinement
hardens the intermetallic alloys at room temperature. In a fully ordered T
i3Al alloy, room temperature ductility increases when the grain size decrea
ses, while ductility of partially disordered Ti3Al and TiAl alloys is close
to zero at room temperature. Materials with SMC structures show superplast
ic properties at temperatures in the range of 600-900 degrees C, i.e. 200-4
00 degrees C below the temperature range for superplasticity in the materia
ls with micron-sized grains. (C) 2000 Elsevier Science S.A. All rights rese
rved.