Mechanical twinning was studied in a specimen in which the lamellar interface was tilted by 45º away from the loading axis, about the <¯321> direction, in the lamellar interface. The polysynthetically twinned crystal was deformed in compression, at a strain rate of 3000/s, at a temperature of 800C. It was observed that (111)[11¯2] parallel twinning was the predominant deformation mode in domains III and IV, where the transmission electron microscopy foil normals were close to [10¯1] and [1¯10], respectively. Cross-twinning of the (¯111)[¯11¯2], (1¯11)[1¯1¯2] and (11¯1)[112) variants in the remaining domains was found to be a complementary mode of deformation accommodation. The mechanical twin propagation stress was found to be less than 150MPa at 3000/s and 800C. Mechanical twin propagation was found to respond to the overall sample stress-state, and therefore to the crystal yield and flow stresses. When mechanical twinning was the predominant deformation mode in a domain, it obeyed Schmid's law.

Mechanical Twinning in a 45º <¯321> Oriented Polysynthetically Twinned TiAl Crystal at a High Strain-Rate and a High Temperature Z.Jin, G.T.Gray, M.Yamaguchi: Philosophical Magazine A, 1998, 78[1], 239-53