8/20/2023 0 Comments Download Wallgram - Awesome W![]() These in turn allow for tuning of mechanical properties over wide ranges toward the prerequisites of the particular area of operation mainly by the control of morphological parameters, e.g., grain size, colony size and aspect ratio or lamellar interface spacing. The combination of thermo-mechanical processing and multiple heat-treatments, which exploit the occurrence of several elapsing phase transformations, has therefore been extensively investigated with the result of enabling the adjustment of different types of microstructures. Mainly the inherent brittleness-a result of the intermetallic character of all constituent phases-has made processing a challenging task on the path to industrialization. TiAl alloys consist at room and service temperature entirely of ordered, intermetallic phases, predominantly of γ-TiAl (L1 0 structure), α 2-Ti 3Al (D0 19 structure) and β o-TiAl (B2 structure). For details of current progress in alloy design, processing technologies, applications and prospects, the reader is referred to references. ![]() Application examples are cast turbine blades of the low-pressure turbine introduced in the GEnx™ by General Electrics and forged turbine blades used in the low-pressure turbine of the recently inaugurated Geared Turbofan™ engine by Pratt and Whitney. Today, titanium aluminides have become an established material class and sophisticated processing routes are available reflected by an increasing market penetration of TiAl components in both aerospace and automotive industry. Consequently, extensive fundamental research projects in close collaboration with industrial partners have been launched to create the basis for knowledge-based compositional and microstructural design and concomitant feasible manufacturing routes. Incorporation of innovative lightweight components into latest generation propulsion systems results in substantial reductions of greenhouse gases, CO 2 and NO x, as well as fuel consumption. Especially, tight emission reduction targets, triggered by an increasing global ecological awareness, as directed by national and international initiatives and legislation, have become a major driving force in the development of this alloy class. Due to these properties, TiAl alloys are particularly suitable for rotating components of modern propulsion systems, such as turbine blades of aero engines and turbocharger wheels of automotive engines. Intermetallic titanium aluminides belong to the most promising materials to meet today’s most prevalent demands for structural high-temperature materials of combining high strength with low density (next to other important characteristics like high creep and oxidation resistance as well as high modulus and strength retention at elevated temperatures). This review, thus, aims at summarizing scientific works regarding the application of atom probe tomography towards the understanding and further development of intermetallic TiAl alloys. Atom probe tomography (APT) offers unique possibilities of characterizing chemical compositions with a high spatial resolution and has, therefore, been widely used in recent years with the aim of understanding the materials constitution and appearing basic phenomena on the atomic scale and applying these findings to alloy development. Development trends for the improvement of alloying concepts, especially dealing with issues regarding alloying element distribution, nano-scale phase characterization, phase stability, and phase formation mechanisms demand the utilization of high-resolution techniques, mainly due to the multi-phase nature of advanced TiAl alloys. ![]() Particularly, recently developed alloying concepts based on a β-solidification pathway, such as the so-called TNM alloy, which are already incorporated in aircraft engines, have emerged offering the advantage of being processible using near-conventional methods and the option to attain balanced mechanical properties via subsequent heat-treatment. Advanced intermetallic alloys based on the γ-TiAl phase have become widely regarded as most promising candidates to replace heavier Ni-base superalloys as materials for high-temperature structural components, due to their facilitating properties of high creep and oxidation resistance in combination with a low density.
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