Eigenschaftsoptimiertes Warmumformen einer intermetallischen Titanaluminid-Legierung

The demand of advanced light-weight high-temperature materials with a low density and good specific high-temperature strength for the application in advanced combustion engines leads to the implementation of intermetallic titanium aluminides. These TiAl-based alloys are multi-phase alloys consisting of γ-TiAl, α₂-Ti₃Al and low volume fractions of β_o-TiAl phase. In the present work a new processing route was established which comprises a combination of heat-treatment and hot-forging to improve the mechanical properties. The observed increase in strength can be attributed to a small lamellar spacing within the α₂/γ-colonies. In order to analyze phase fractions and to determine mechanical properties X-ray diffraction measurements, hardness tests as well as tensile and creep tests were conducted.     

In Situ Synchrotron Study of B19 Phase Formation in an Intermetallic γ‐TiAl Alloy

A multitude of phases exists in the binary Ti–Al phase diagram and even greater numbers are formed in structural TiAl alloys, which contain additional alloying elements to improve their properties. In the current study, a Ti–45 Al–3 Mo–0.1 B (in at%) alloy was investigated with respect to the phases occurring in chemical non‐equilibrium. In situ high‐energy X‐ray diffraction experiments enabled to identify a transient phase to be of the B19 type and to determine its temperatures of formation and dissolution.     

Design,Processing, Microstructure,Properties, and Applications of Advanced Intermetallic TiAl Alloys

After almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ‐TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high‐temperature materials are their low density and their good strength and creep properties up to 750 °C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi‐phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo‐mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e., concurrent increase of ductility at room temperature and creep strength at elevated temperature. This review gives a general survey of engineering γ‐TiAl based alloys, but concentrates on β‐solidifying γ‐TiAl based alloys which show excellent hot‐workability and balanced mechanical properties when subjected to adapted heat treatments. The content of this paper comprises alloy design strategies, progress in processing, evolution of microstructure, mechanical properties as well as application‐oriented aspects, but also shows how sophisticated ex situ and in situ methods can be employed to establish phase diagrams and to investigate the evolution of the micro‐ and nanostructure during hot‐working and subsequent heat treatments.