Deformation twinning in single crystals of a D0 19 compound with an off-stoichiometric composition (Ti–36.5at.%Al)

Abstract

The characteristics of deformation twinning in single crystals of a D0 19 compound Ti 3Al with off-stoichiometric composition (Ti–36.5at.%Al) have been studied in detail by trace analysis and transmission electron microscopy. Deformation twinning is operative only at high temperatures above 1000 °C when the compression axis is parallel to and close to the hexagonal c-axis. All observed deformation twins are assigned to be of the type II and the twinning elements are determined as: K 1 : ‘ { 2 ¯ 12 10 ¯ 3 } ’ , K 2 : { 2 0 2 ¯ 1 ¯ } , η 1 : 〈 5 1 ¯ 4 ¯ 6 ¯ 〉 , η 2 : ‘ 〈 1 ¯ 3 2 ¯ 2 〉 ’ , s = 0.346 . The critical resolved shear stress for the ‘ { 2 ¯ 12 10 ¯ 3 } ’ twin is estimated to be about 50 MPa at 1000 °C and it gradually decreases with increasing temperature. The possible atom movements by the deformation twinning are described and the reasons why twinning of this type occurs only under a limited condition (i.e., off-stoichiometric compositions, high temperatures and compression axis being close to the c-axis) are discussed in the light of the atom movements by the deformation twinning.