Mechanical Properties and Deformation Mechanisms at High Temperatures in TiAl Alloys

Following the successful implementation of TiAl blades in aero-engines produced by GENERAL ELECTRIC and SAFRAN companies, the aim is now to increase the operating temperature of TiAl alloys, up to 800°C if possible. This requires optimization of the microstructures and chemical compositions of this family of alloys. In this context, the aim of the present work is to provide an in-depth understanding of the mechanical properties and deformation mechanisms of TiAl alloys in the temperature range above 700°C.<br/>Tensile tests were carried out over the entire temperature range, as well as creep tests at 800°C and 200 MPa. The microstructures of the samples were studied using scanning and transmission electron microscopy, as well as X-ray diffraction. The deformation mechanisms were studied by means of in situ deformation experiments and post-mortem analyses of deformed samples, both using transmission electron microscopy. In addition, atom probe tomography analyses were carried out to assess the influence of additive elements.<br/>Deformation is mainly due to ordinary dislocations. Several populations of dislocations are identified. Their Burgers vectors, the plane in which they move and the corresponding deformation mechanisms are determined. It will be shown that these dislocations are capable of gliding or climbing as a function of temperature and stress conditions. Next, the influence of the addition of elements such as tungsten, molybdenum, niobium, carbon and silicon will be studied. Finally, a controlled microstructure will be proposed to obtain optimum mechanical properties.