TiAl-based semi-finished products by heat treatment of Ti/Al composite sheets

• Applicant: Professor Dr. Werner Skrotzki
• Subject Area: Metallurgical, Thermal and Thermomechanical Treatment of Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321924573

The processing of titanium aluminides is exceptionally difficult due to their extreme hardness and brittleness at room temperature. Therefore, until today TiAl based semi-finished products and components are rather expensive and hence are used only sporadically. However, the progress expected in the current field of intense research on net shape or at least near net shape processing should lead to a significant reduction of the production costs and hence lead to a more intensive use of the advantageous properties of titanium aluminides, in particular for high temperature applications. The proposed research project addresses the processing of TiAl sheets via reaction annealing of finely layered Ti/Al composite sheets. Their production by accumulative roll bonding has been developed and optimized [1] under the direction of the applicant in a research project called 'High Strength Metallic Composites (HSMetComp)' financed by the Saxon Excellence Initiative ECEMP (European Centre for Emerging Materials and Processes Dresden). The Ti/Al composite sheets have a thickness of 2.5 mm and contain up to 512 Ti/Al phase boundaries. The layer spacing is about 4 µm and can be further reduced to below 400 nm by subsequent cold rolling. During the above mentioned research project, the reaction annealing of Ti/Al multifilamentary wires generated via a related method (accumulated swaging and bundling (ASB)) into a TiAl/Ti3Al-alloy was proven [2]. Furthermore, the feasibility of the transformation of the Ti/Al composite sheets into a TiAl/Ti3Al-alloy has been demonstrated in a preliminary study. The objective of the proposed research project is a comprehensive study of the reaction annealing of Ti/Al composite sheets. To optimize this process, the phase formation at the interfaces as a function of the energy introduced during the processing has to be investigated, as well as the evolution of microstructure, texture and stress state of the materials during the transformation. Furthermore, the mechanical properties of the TiAl sheets after the reaction annealing should be characterized. In addition, it is the aim to investigate the reaction annealing of previously deformed material to demonstrate the suitability of the method for the production of complex near net shape semi-finished parts (e.g., profiles).

• DFG Programme: Research Grants