Materials for High-Speed Transport Systems

Titanium aluminides are promising perspective materials which provide a unique combination of physical and mechanical properties for high-speed transport systems, like sport cars, racing cars and high-speed trains. These materials are characterized by good strength at temperatures up to 650 0C (?600 MPa), but poor roomtemperature plasticity (?1-2 %). The latter property limits their commercial applications. The efforts aimed at the improvement of the plasticity of these alloys include both the design of new alloys and new methods of their production. A comparative study of the phase content, structure and the mechanical properties of the different titanium aluminides are presented. We study the influence of the crystallization conditions on the microstructure and mechanical properties of the TiAl- and Ti3Al- based alloys prepared by the special method of pulsed volume pressing (PVP) and the Ti2AlNb-base alloys. The factors responsible for the successful structure of TiAl-alloys with high mechanical properties were found. The cooling rate that varies in the mold with different heat capacities (0.385 cal/g K for copper and 0.12 cal/g K for steel) substantially affects the grain size, the uniformity of its distribution and the lamella thickness. In the Ti3Al-base alloy high rates of cooling allow conserving “soft” plates of ?0 -phase. The mechanical properties and structure of the stable and metastable phases in the Ti2AlNb-base alloys under severe plastic deformation (shear under pressure) were also studied.