Deformation-induced internal stresses in multiphase titanium aluminide alloys

Long-range internal back stresses developed during room temperature tensile deformation of titanium aluminide alloys have been determined. Dip tests were implemented during the strain-controlled tensile deformation and the resulting sample deformation was monitored in the relaxation regime of the machine. The internal stress was determined as the critical stress at which the inelastic sample relaxation is reversed, i.e. going from the tensile direction to the compression direction. The investigation involves a wide range of alloy compositions with a corresponding variation in the strength properties. For the alloys investigated, the internal stress is about 80% of the yield stress. The mechanical tests were coupled with electron microscopy examination of the defect structure in order to assess the strain accommodation occurring during deformation. Possible sources for the built up internal stresses are discussed.