MECHANICAL PROPERTIES OF MICROLAYERED Ti-Al MATERIALS IN STATIC AND CYCLICAL LOADING

Abstract

The technique for producing microlayered materials by sintering and rolling a package of alternating titanium and aluminum ribbons at 460 and 770 °C is presented. The initial package thickness was 2.6 mm and the final thickness after hot rolling was 1.8 mm. Then the preform was rolled at room temperature to a thickness of 0.5 mm. The total strain at 20 °C was e = ln1.8/0.5 = 1.3. Ribbons 0.5 mm thick were obtained, but some of them stratified in the middle of their thickness and were tested by static and cyclic bending. X-ray diffraction found that the material produced by heating and rolling at 770 °C contained an hcp titanium phase and a TiAl₃ phase. Structural anisotropy in titanium layers was established. The proportionality limit of the 0.5 mm thick material was 368 MPa. The elasticity characteristics, transmission energy of vibrations, and fatigue resistance of the Ti–TiAl₃ microlayered samples 0.25 mm thick cut along and across the rolling direction were determined. For this purpose, first- and second-mode resonant bending vibrations of cantilevered samples were excited and dependences of the maximum stresses in the samples on machine (electrodynamic shaker) power were found. The destructive fatigue stresses in the samples depending on the number of load cycles were determined as well. Young’s modulus of the samples cut out along the rolling direction was 92 and for the samples cut out across the rolling direction was 100 GPa. The microlayered Ti−TiAl₃ material along the rolling direction is less perfect than across the rolling direction since nondestructive stresses are 11% lower along the rolling direction because of greater energy dissipation in anisotropic crystallographic structure, the relative excitation power of vibrations being the same. The fatigue limits of the test materials based on 10⁷ cycles were 303 MPa for the Ti−Al samples (Т_rol = 460 °С) along the rolling direction, 299 MPa for the Ti−TiAl₃ material along the rolling direction and 481 MPa across the rolling direction.