AN INVESTIGATION OF THE EFFECT OF TEXTURE ON THE HIGH-TEMPERATURE FLOW BEHAVIOR OF AN ORTHORHOMBIC TITANIUM ALUMINIDE ALLOY

The effect of mechanical and crystallographic texture on the flow prop erties of a Ti-21A1-22Nb (at. pct) sheet alloy was determined by condu cting uniaxial tension and plane-strain compression tests at temperatu res between 900 degrees C and 1060 degrees C and strain rates between 10(-4) and 10(-2) s(-1). Despite, the presence of noticeable initial t exture, all of the mechanical properties for a given test temperature and strain rate (i.e., peak stress, total elongation to failure, strai n-rate sensitivity, and normal plastic anisotropy) were essentially id entical irrespective of test direction relative to the rolling directi on of the sheet. The absence of an effect of mechanical texture on pro perties such as ductility was explained by the following: (1) the init ially elongated second-phase particles break up during tension tests p arallel to the rolling direction of the sheet, thereby producing a glo bular morphology similar to that noted in samples taken transverse to the rolling direction; and (2) failure was flow localization, rather t han fracture, controlled. Similarly, the absence of an effect of mecha nical texture on strain-rate: sensitivity (m values), normal plastic a nisotropy (r values), and the ratio of the plane strain to uniaxial fl ow stresses was rationalized on the basis of the dominance of matrix ( dislocation) slip processes within the ordered beta phase (B2) as oppo sed to grain boundary sliding. Aggregate theory predictions supported this conclusion inasmuch as the crystallographic texture components de termined for the B2 phase ((001) [100] and (<(1)over bar 12>) [110]) w ould each produce identical r values and uniaxial and plane-strain flo w stresses in the rolling and transverse directions.