Influence of Heat Treatments on the Microstructure of a Multi-Phase Titanium Aluminide Alloy

摘要

Intermetallic titanium alumlnides are employed in aircraft engines and automobile engines because of their low density and excellent high-temperature properties. Today's TiAl-based alloys are multi-phase alloys of a complex structure which mainly consist of γ-TiAl, α_2-Ti_3Al and low fractions of a β_o-TiAl phase. An example of such an alloy is the so-called TNM alloy which exhibit a nominal composition of Ti-43.5AI-4Nb-1 Mo-0.1 B (in at %). In this alloy, solidification takes place via the p-phase, with the consequence of a finegrained and nearly segregation-free microstructure. In spite of that, the cast microstructure also contains coarser grains which can act as crack initiators at room temperature and will reduce the deformation-capability during tensile tests. Within the framework of this paper, heat treatment studies were conducted on a cast and hot isostatically pressed material with the primary aim of a microstructural homogenization in order to reduce the crack-initiating microstructural components and, hence, increase its fracture elongation at room temperature. In further heat treatments, microstructures with balanced mechanical properties were adjusted.