The activation and the spreading of deformation in a fully lamellar Ti–47 at.% Al–1 at.% Cr–0.2 at.% Si Alloy

Abstract

The spreading of deformation in a lamellar Ti–47 at.% Al–1 at.% Cr–0.2 at.% Si alloy deformed under compression is studied at 25°C and 600°C. This microstructure is largely dominated by twin-related variants which are separated by either twin interfaces or thin α ₂ slabs. The alloy deforms at both temperatures by ordinary dislocations and twins. Deformation in a particular γ variant and its adjacent twin-related variant involves the same kind of glide system, either ordinary dislocations or twins. This property is found to be true for all twin-related lamellae. The occurrence of this correlated glide is explained by the introduction of the notion of pilot and driven orientations. The lamellar orientation in which the operating glide system is activated on the basis of Schmid factor considerations is termed the pilot orientation. It imposes its deformation system on to the twin-related lamella, called the driven orientation, whose deformation may not involve the slip system most favoured by the applied stress.

Acknowledgements

The authors acknowledge the Indo-French Centre for the Promotion of Advanced Research, New Delhi for sponsoring this project (number 2308-3) and for funding the visit of one of the authors (J.B.S.) to Toulouse, France. The authors wish to thank Dr Shigehisa Naka and Dr Marc Thomas of the Département de Matériaux Métalliques et Procédés, ONERA, for kindly providing the material and Dr Rajeev Kapoor of the Materials Science Division, Bhabha Atomic Research Centre, for his help in carrying out deformation experiments.