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

该项目的目的是获得关于表面改性对伽马钛铝化物的微观结构、抗氧化性和机械性能影响的新的和详细的知识。在该项目中，合作伙伴将密切合作开发几种表面改性方法，(I)通过两种不同的方法沉积AlSi和TiAlCrY保护性涂层，即化学气相沉积(CVD)和物理气相沉积(PVD)，(Ii)通过在不同氧分压下预氧化进行额外的表面改性，以促进形成稳定的、不含二氧化钛的保护层(α-氧化铝)，以及(Iii)喷丸处理，向表面引入压应力，以改善TiAl合金的机械(疲劳)性能。该项目的一个新颖之处是用CVD和PVD方法沉积AlSi涂层，并将其用作热障涂层的粘结层。AlSi和TiAlCrY涂层能够在伽马-TiAl合金表面形成缓慢生长且稳定的α-Al_2O_3涂层，这为它们在热障涂层系统中的应用创造了潜力，7YSZ面层和粘结涂层之间的结合和兼容性非常重要。然而，关于这种热障涂层体系中的界面现象及其演变，以及这些保护层对基合金力学性能的影响的数据还缺乏。对表面改性的基本分析，如在各种环境条件下依靠保护性氧化铝氧化膜的生长进行预氧化，以及通过喷丸进行机械处理，将导致表面性能得到改善，通过新技术进行评估，如测定脆性到韧性的转变和急剧减少的样本数。该项目旨在首次给出表面改性对TiAl在不同温度下的氧化和疲劳性能影响的系统结果。此外，压应力的引入旨在提高疲劳寿命，这是以前从未尝试过的伽马-TiAl合金涂层。所有目标只能通过波兰和德国合作伙伴之间的密切合作才能实现，因为子任务、使用的表面改性方法和测试依赖于彼此的工作，如果没有这种国际合作，就无法执行。

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.