TIALMET - Surface modification of gamma-TiAl alloys and its influence on mechanical properties and phenomena under high temperature conditions

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The aim of the project is to obtain new and detailed knowledge about the influence of surface modifications on microstructure, oxidation resistance and mechanical properties of gamma-titanium aluminides. Within the project several surface modifications will be developed in close coop-eration by the partners, (i) deposition of protective AlSi and TiAlCrY coatings by two different methods, chemical vapor deposition (CVD) and physical vapor deposition (PVD), (ii) an additional surface modification by pre-oxidation under varying partial pressures of oxygen to foster the formation of a stable and TiO2-free protective scale (alpha-alumina), and (iii) shot peen-ing to introduce compressive stresses into the surfaces to improve the mechanical (fatigue) properties of the TiAl alloy. One novelty of the project is the deposition of AlSi coatings by CVD and PVD and its applica-tion as bond coats for TBCs. The ability of AlSi as well as TiAlCrY coatings to form a slow-growing and stable alpha-alumina scale on gamma-TiAl alloys creates a potential for their application in TBC systems where bonding and compatibility between the 7YSZ topcoat and bond coat is of great importance. However, data on interfacial phenomena and their evolution in such TBC systems, and the influence of these protective coatings on mechanical properties of the base alloy are missing. Fundamental analyses of surface modifications such as pre-oxidation relying on the growth of a protective alumina scale under various environmental conditions as well as mechanical treatments by shot peening will lead to modified surfaces with improved properties, evaluated by new techniques such as determination of the brittle to ductile transition with drastically reduced sample numbers.The project aims to give for the first time systematic results on the influence of surface modi-fications on the oxidation and fatigue properties of TiAl at different temperatures. Moreover, introduction of compressive stresses targets to improve the fatigue life, which was never tried before for coatings on gamma-TiAl alloys. All goals can only be achieved by close collaboration between the Polish and German partners, since the sub-tasks, surface modification methods used, and tests rely on the work from each other and could not be performed without this international collaboration.