PLASTIC-DEFORMATION OF SINGLE-CRYSTALS OF A DO(19) COMPOUND WITH AN OFF-STOICHIOMETRIC COMPOSITION (TI-36.5 AT PERCENT AL) AT ROOM-TEMPERATURE

The deformation behaviour of single crystals of a DO19 compound with an off-stoichiometric composition of Ti-36.5at.% Al has been studied at room temperature both in tension and compression. A tensile elongation as large as 250% has been observed for an orientation where prism slip is fully operative, indicating that the compound is soft and quite deformable in single crystalline form for a certain orientation range. Tensile elongation is not sensitive to test environment and decreases with increasing strain rate. This indicates that the present compound is not susceptible to severe environmental embrittlement. For the basal slip orientations, however, failure occurs soon after yielding even in compression due to the formation of deep shear cracks along basal slip planes. Prism slip obeys the Schmid's law and the critical resolved shear stress is considerably smaller than those for basal and pyramidal slip (one-third and one-ninth, respectively). Based on the results obtained, factors causing the brittleness of polycrystalline Ti3Al compounds at ambient temperature and roles of the Ti3Al phase in the deformation behaviour of PST crystals of TiAl are discussed.