Titanium strength and aluminium lightness: aviation material of the future is studied in MAI

February 8, 2021
Titanium strength and aluminium lightness: aviation material of the future is studied in MAI
Titanium strength and aluminium lightness: aviation material of the future is studied in MAIIntermetallic alloys based on equiatomic titanium aluminide are materials with great potential for the aerospace industry. The high heat resistance in combination with low density opens up prospects for significant aircraft gas turbine engines weight reduction without compromising their quality characteristics.Elena Lukina, the associate professor of the Department of Materials Science and Material Processing Technology of the Moscow Aviation Institute, candidate of Technical Sciences, told us about the fundamental research, conducted by Russian scientists in the area of development and testing of intermetallic TiAl alloys. Let's begin with the terminology. What are intermetallic and why are they so interesting?Intermetallic compounds are stable compounds consisting of two or more metals often possessing a set of properties that are not typical to each of the components separately. Like pure metals, they can serve as the basis for alloys.Intermetallic TiAl alloys (gamma alloys) are a promising class of heat-resistant materials that, on the one hand, have a unique combination of specific stiffness and strength, and, on the other hand, have high oxidation resistance. Thermal stability and heat resistance, which are the consequence of the very nature of the titanium-aluminium system intermetallic compounds, determine the performance of gamma alloys during operation at temperatures of 700-800 degrees Celsius.Materials with the combination of these characteristics are always in demand in aviation turbine construction. For example, according to General Electric, the use of gamma alloys in a low-pressure turbine of a gas turbine engine might result into the weight efficiency of 100–180 kg, if compared to the construction made of traditional nickel superalloys, with the density twice higher.However, the main disadvantages, limiting the practical application of gamma alloys are their fragility and, as a consequence, low plasticity in a wide temperature range. This disadvantage is not unavoidable, therefore, at present, many researchers worldwide are working on the problem of increasing the plasticity and manufacturability of alloys of this class while maintaining high strength.How long has MAI been studying the intermetallic alloys?From 1987 to 2019, our Department for Materials Science and Materials Processing Technology was headed by Alexander Ilyin, the academician of the Russian Academy of Sciences, who created his scientific school in the field of materials science of titanium alloys. For more than 20 years, at first, he, and now his students, who have already become doctors of science, carried out fundamental research on intermetallic titanium alloys, both for aviation (alpha-2, ortho-alloys) and for medical purposes.Is the research an initiative project?  I work as part of a research team created based on the Russian Research Institute of Aviation Materials (federal state unitary enterprise group “VIAM”). Our young team, that brought together scientists from the Moscow Aviation Institute and VIAM, was created in 2018. Then we formulated approaches to several particular problems within the framework of the abovementioned fundamental scientific problem and took part in one of the annual competitions for grants from the Russian Science Foundation (RSF) under the President's program of research projects implemented by leading scientists, including young scientists. According to the results of the competition, the experts of the Russian Science Foundation assessed our application positively and it turned out to be on the precious list of winners.What does the team study exactly?In our scientific project, the object of research is a new domestic six-component heat-resistant TiAl alloy with variable contents of zirconium, chromium and gadolinium. The density of this alloy does not exceed 4.1 g/cm3. In case of positive test results, it might be considered as an alternative to high-temperature nickel-based alloys with a density of 7.8 g/cm3 and more to increase the weight efficiency during the production of rotor parts of the hot section of promising gas turbine engines.We carry out fundamental research of the structure and the crystallographic texture of the alloy under thermal and thermomechanical effects. The efficiency of various processing modes is estimated by the change of mechanical properties. In particular, our studies of the effect of micro additions of gadolinium, a rare earth element, on the sequence of phase transformations and properties of the new TiAl alloy have demonstrated the possibility of simultaneously increasing its strength and plasticity. The original results were published in 2020 in the foreign magazine of the Intermetallics first quartile, published by Elsevier. This is one of the most authoritative periodicals for intermetallic materials research. Articles are selected based on the results of peer review by leading scientists, which confirms the high assessment of the results obtained. Have you ever worked with other intermetallics?Yes, another area of my scientific interests is related to intermetallic alloys based on titanium nickelise - NiTi. This is a special class of intermetallic materials with a unique shape memory effect and superelasticity, it has both high biological and mechanical compatibility with the bone-cartilaginous structures of the human body.Titanium nickelize may be called a truly international material because research on its medical application is carried out in many countries across the globe. For example, several years ago I trained at Kingston University (UK) and University College London (UCL). Using the results of the research, I defended my dissertation and obtained an international PhD degree. In cooperation with foreign colleagues, I wrote several articles devoted to the study of the regularities of corrosion resistance and tribological behaviour of titanium nickelise in spinal implants. These articles have also been published in the leading magazines of the first quartile (Materials Science & Engineering: C; Spine; The Spine Journal).
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