Fundamental Improvement of the High Temperature Properties of ?-TiAl Alloys by Additions of Substitutional and Interstitial Elements – Hi-TiAl

In order to understand the physical hardening processes that occur in the temperature range of 800°C to 900°C, the Austrian-French project team has developed a unique research strategy, which is based on the investigation of well-selected model alloys using a number of complementary structural and mechanical characterization methods. The goal of the submitted proposal is to gain a fundamental understanding of the role of substitutional and interstitial alloying elements on the constituting phases and physical processes activated during deformation and isothermal ageing, which form the microstructure, thus controlling the mechanical properties at high temperatures.
The material will be produced by a powder metallurgical approach, employing spark plasma sintering of pre-alloyed gas atomized powders. The constituting phases of the microstructure will be characterized from macroscopic scale down to atomic scale, using conventional as well as most advanced microscopic and analytical techniques, such as electron microscopy and atom probe tomography. Concurrently, the activation parameters of the deformation mechanisms will be measured through instrumented mechanical tests.

Under progress

To be discussed

Papers

During the last decade intermetallic titanium aluminides, based on the ordered gamma-TiAl phase, have successfully been implemented in advanced eco-friendly jet engines, which have a sustainably positive impact on environment protection, because air traffic alone holds a share of approximately 3.5% of the human-induced climate change. The maximal application temperature of this innovative class of lightweight materials is limited to 700°C. However, for the next generation of aero-engines application temperatures of up to 850°C are required. In order to understand the physical hardening processes that occur in the temperature range of 800°C to 900°C, the Austrian-French project team from the Montanuniversität Leoben (H. Clemens, S. Mayer) and CEMES, Toulouse (A. Couret, J.P. Monchoux), has developed a unique research strategy, which is based on the investigation of well-selected model alloys using a number of complementary characterization methods. The goal of the submitted proposal is to gain a fundamental understanding on the role of substitutional and interstitial alloying elements on the constituting phases and physical processes activated during deformation and isothermal ageing which form the microstructure, thus controlling the mechanical properties at high temperatures. Here, the main attention is focused on the gamma-phase, which is the softest phase in these alloys. As substitutional alloying additions, the heavy elements W and Mo are selected, whereas small elements, such as C and Si, are considered as interstitial elements. Four model TiAl alloys and an unalloyed reference alloy are chosen to answer the following fundamental questions: (a) where are the selected alloying elements distributed in the microstructure and are they migrating during long-term exposition at high temperatures?; (b) what is the influence of the alloying elements on the physical mechanisms, which are active during high temperature deformation as well as static ageing treatments? The material will be produced by a powder metallurgical approach, employing spark plasma sintering of pre-alloyed powders. The constituting phases of the microstructure will be characterized from macroscopic scale down to atomic scale, using conventional as well as most advanced microscopic and analytical techniques, such as electron microscopy and atom probe tomography. In particular, and that is an originality of the project, atom probe tomography and transmission electron microscopy (TEM) at the atomic scale and in situ TEM and in situ high-energy X-ray diffraction at the microscopic scale will be coupled. Concurrently, the activation parameters of the deformation mechanisms will be measured through instrumented mechanical tests. In sum, the proposed project will gain a better understanding of the high temperature mechanisms and of the role of additive alloying elements in advanced multi-phase structural material systems, which will provide the basis of future knowledge-driven alloy design.