TEMPERATURE DEPENDENCES OF THE MECHANICAL PROPERTIES OF MICROLAYER Ti/TiAl₃ COMPOSITES UNDER CYCLIC LOADING

Abstract

Three microlayer Ti/TiAl₃ materials of starting Ti–Al composition produced by reaction sintering and rolling of packets consisting of alternating titanium and aluminum strips of different thickness at 600, 700, and 770 °C were studied. Young’s modulus of the materials at longitudinal vibrations and room temperature was determined at a frequency of about 45 kHz and that at bending vibrations and high temperatures ranging from 20 to 820 °C at resonant bending vibrations with a frequency one hundred times lower. The dependences of the elastic modulus E of the microlayer materials on testing temperature have slopes in the range between the slopes of similar curves for titanium and the well-known VT25U alloy. Heating and holding of Ti/TiAl₃ at 700 °C resulted in a material with stable E values, which are noticeably higher than that of the VT25U alloy at temperatures up to 700 °C. The dependences of stresses in the samples on the relative power of the installation were determined at constant test temperatures of 650 and 700 °C of the microlayer Ti/TiAl₃ and VT25U materials. A much larger amount of mechanical vibration energy is dissipated in the microlayer materials in comparison with the known heat-resistant VT25U material. The difference in the mechanisms of fatigue resistance of the microlayer and isotropic materials at high temperatures is due not only to the difference in their temperature dependences of Young’s modulus at the level of atomic interaction but also mainly due to the difference in temperature dependences of cyclic deformations associated with the action of dislocations at the level of micro- and macrostructure. A fatigue crack is shown to delaminate the material structure in the middle of the intermetallic layers.