Mechanical twinning in a 45°〈321〉 oriented polysynthetically twinned TiAl crystal at a high strain rate and a high temperature

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Mechanical twinning behaviour in a 45° oriented (the lamellar interface was tilted 45° from the loading axis about the direction in the lamellar interface) polysynthetically twinned crystal deformed in compression at a strain rate of 3000s−1 and a temperature of 800°C was characterized. (111)[112] parallel twinning was observed to be the dominant deformation mode in domains [III] and [IV] where the transmission electron microscopy foil normals were close to [101] and [110] respectively. Cross-twinning of the (111)[112], (111)[112] and (111)[112) variants in the remaining domains was found to be a complementary deformation mode to accommodate deformation. The mechanical twin propagation stress was found to be less than 150 MPa at 30003−1 and 800°C in TiAl. Mechanical twin propagation was found to respond to the global sample stress state and thus the crystal yield and flow stresses. When mechanical twinning was the dominant deformation mode in a domain, it was observed to obey Schmid's law.