Effect of compositional deviations from stoichiometry on the plastic behaviour of Ti 3Al single crystals

Abstract

Ti 3Al single crystals containing 24.4, 33.0 and 40.0 at.% Al were grown by a floating zone method and deformed in compression at room temperature. The effect of Al content on the slip geometry, yield stress and ductility was investigated. Prism {10 1 0}〈1 2 10〉, basal (0001)〈1 2 10〉 and pyramidal {11 2 1}〈11 26 〉 slips were observed depending on the crystal orientation. The prism slip was more common than the other slip systems and the pyramidal slip was limited to orientations near [0001]. The critical resolved shear stress for the prism and pyramidal slip systems increased with increasing Al content, while the basal slip was not strongly affected by the aluminium content. Ti 3Al crystals could easily be deformed by the prism slip up to more than 30% strain without any cracks, while deformation by the pyramidal and/or basal slips was accompanied by poor ductility. Brittleness was increasingly noticeable with higher Al content.