Project Details
Projekt
Development of refractory metal-based CCAs with improved mechanical properties
Applicants
Professor Dr.-Ing. Hans Jürgen Christ, since 8/2021; Professor Dr.-Ing. Martin Heilmaier
Subject Area
Metallurgical, Thermal and Thermomechanical Treatment of Materials
Term
since 2017
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 388478770
The objective of the present proposal is to develop new refractory metal-based high temperature materials with a thermal capability beyond that of the state-of-the-art Ni-based superalloys. Single-phase refractory high entropy alloys (RHEA) as well as multi-phase refractory compositionally complex alloys (RCCA) within the alloy system Ta-Nb-Mo-Ti-Cr-Al have intensively been investigated in the first funding period in terms of their crystal structure, microstructure, mechanical properties and high temperature oxidation behavior. The exploration of relevant properties proceeded by combining thermodynamic modeling and detailed experimental characterization. Alloys within the Ta-Mo-Ti-Cr-Al system yield outstanding perspective: Some alloys possess solidus temperatures up to 2100°C whilst showing decent oxidation protection up to 1500°C. More specifically, alloys from the Ta-Mo-Ti sub-system exhibit a single-phase A2 microstructure, adequate strength at elevated temperatures and large (compressive) deformability at room temperature. Ta-Mo-Ti alloys with Al and Cr additions, if being single-phase B2, possess very high strength at elevated but low ductility at moderate temperatures. Some alloys within the system Ta-Mo-Ti-Cr-Al even possess a dual-phase A2-B2 microstructure, which is regarded to be favorable for high temperature applications, akin to two-phase microstructures of Ni-base superalloys. The research activities in the second funding period will focus on the development of alloys based on the system Ta-Mo-Cr-Ti-Al with A2 matrix and large volume fractions of ordered B2 precipitates. A balanced portfolio of ductility at room temperature, creep resistance at elevated temperatures as well as oxidation protectiveness is pursued. In order to achieve these objectives, two main approaches will be followed. Starting from the (known) ductile ternary system Ta-Mo-Ti, which possesses a single-phase A2 microstructure in a wide temperature and compositional range, its high temperature mechanical properties will be tuned by: (i) solid solution strengthening of single-phase A2 RHEA and (ii) formation of homogeneously distributed B2 precipitates in a ductile A2 matrix. The solid solution strengthening will be studied by systematic variation of Ta, Mo and Ti contents as well as addition of Cr and Al in low concentrations to the ternary system Ta-Mo-Ti. Guided by thermodynamic calculations, B2 precipitates within the A2 matrix will be realized by increasing the Al and Cr concentrations in combination with the application of appropriate heat treatments. In addition to thermodynamic modeling, the experimental efforts cover thermal and microstructural analyses, characterization of mechanical properties (compressive, tensile, and creep tests) and ensuing examination of oxidation behavior.
DFG Programme
Priority Programmes
Co-Investigator
Dr.-Ing. Alexander Kauffmann
Ehemalige Antragstellerin
Professorin Dr.-Ing. Bronislava Gorr, until 8/2021
