Институт проблем сверхпластичности металлов РАН, ул. Степана Халтурина 39, Уфа, 450001, Россия Использование традиционной сверхпластичности позволяет изготавливать уникальные полые конструкции. Од-ним из самых ярких примеров служит изготовление фирмой Роллс-Ройс полой вентиляторной лопатки из тита-нового сплава Ti-6Al-4V для авиационного двигателя. Однако высокая температура сверхпластической формовки (~927°С) ограничивает широкое промышленное применение сверхпластичности титановых сплавов. Объектом исследования были ультрамелкозернистые листы со средним размером зерен 0,2 мкм из отечественного титано-вого сплава ВТ6 (аналог зарубежного сплава Ti-6Al-4V) со стандартным химическим составом, соответствующим ГОСТ 19807-91. На основе результатов механических испытаний на растяжение и примеров изготовления сверх-пластической формовкой при температурах 550, 600, 650, 700, 750 и 800°C модельных образцов полых конструк-ций из ультрамелкозернистого титанового сплава ВТ6 показаны технологические преимущества использования эффекта низкотемпературной сверхпластичности, которые востребованы производством для совершенствова-ния промышленных технологий на основе сверхпластичности. Низкотемпературная сверхпластичность обеспе-чивает повышенное качество полых изделий, в частности, при изготовлении моделей полой лопатки из сплава ВТ6 и открывает перспективу создания экономически эффективных промышленных технологий изготовления полых конструкций методом сверхпластической формовки из ультрамелкозернистых титановых сплавов типа ВТ6 (ана-логи сплава Ti-6Al-4V). Application of the conventional superplasticity allows producing the unique hollow structures. One remarkable example is the hollow titanium blade of the air engine fan produced by Rolls-Royce. However, high temperature of Ti-6Al-4V titanium alloy processing (~ 927°С) limits wide industrial application of the conventional superplasticity. On the base of experimental data examples of superplastic forming of hollow structures for aerospace application out of ultrafine-grained VT6 (Ti-6Al-4V) titanium alloy by using an effect of low temperature superplasticity are demonstrated. We used twophase VT6 titanium alloy produced in VSMPO-AVISMA Corporation, Verhnyaya Salda, Russia. Investigated VT6 alloy had standard chemical composition according GOST 19807-91. The ultrafine-grained sheets with a mean grain size of about 0,2 μm were processed by multiple step forging and subsequent isothermal rolling. Superplastic forming of ultrafinegrained sheets was performed at temperatures of 550, 600, 650, 700, 750 and 800°C. Trials on superplastic forming within the temperature range of 550-800°C were performed by an original technique using special model parts. Investigated sheets showed good processing properties. The use of the low temperature superplasticity provides high quality of hollow components such as blades. Application of low superplasticity temperature can be a basis for creation of economically efficient superplastic forming technologies for producing hollow structures out of ultra...

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Application of the conventional superplasticity (SP) allows producing the unique hollow structures. One remarkable example is the hollow titanium blade of the air engine fan produced by Rolls-Royce. However, high temperature titanium alloys processing (~ 927 °С) limits wide industrial application of the conventional SP. The solution of the mentioned issue can be found through the application of low-temperature SP. Ti-6Al-4V alloy with ultrafine grain structure at the temperature range of 600 ­ 800 °С has enough ductility resources for the superplastic forming (SPF) of the parts with the complicated shape. The formation of pores in Ti-6Al-4V alloy at uniaxial and biaxial tension at the temperature 600 °С is not observed. The effect of low-temperature SP also allows lowering pressure welding (PW) temperature essentially. Herewith, there is a possibility to produce the hollow parts by the combination of SPF and PW. The main goal is the optimization of the technological scheme and processing temperature. The use of the low-temperature SP provides high quality of hollow components such as blades.

In the manufacture of three-layer corrugated structures made of titanium alloys by diffusion bonding followed by superplastic forming, stop-off materials are used. The use of stop-off material makes it possible to selectively connect sheet blanks with each other and, as a result, get a hollow structure with an internal set of stiffeners in the form of a corrugation. The effect of stop-off materials based on boron nitride and yttrium oxide on the structure and mechanical properties of the titanium alloy Ti-6Al-4V is studied. Special attention is paid to the influence of stop-off materials on the quality of solid-phase joints in a corrugated structure. It is shown that the stop-off material based on yttrium oxide leads to the least degradation of the mechanical properties of the titanium alloy. It is established that the quality of the design depends not only on the composition of the stop-off materials, but also on the procedure of its processing before diffusion bonding of blanks. The composition of stop-off materials as binders includes organic components that contain light elements: nitrogen, carbon, oxygen and hydrogen. The latter are known to be harmful impurities for titanium and its alloys, and their chemical interaction with titanium is sharply intensified at high temperatures. The traditional temperatures of diffusion bonding and superplastic forming of the Ti-6Al-4V alloy are in the range of 900 -950°C. Therefore, it is necessary to control and prevent the process of adsorption of hydrogen, nitrogen, oxygen and carbon atoms on the connected surfaces of titanium blanks, since this can have a noticeable effect on the quality of diffusion joints, will lead to defects, and the fatigue strength of the entire structure already depends on this.