In modern gas-turbine units increase of gas working temperature leads to shortening of blade service life. For this reason their repair becomes a priority. Retailoring of single-crystal blade tip by hardfacing is a rather complicated task. In order to select suitable filler material, thermal cycling tests of samples of deposited welds on CMSX-4 alloy with a single-crystal structure have been performed. Evolution of the structure under the conditions of high-temperature cyclic oxidation is considered. Selection of filler material, which ensures high temperature resistance and stability of weld metal structure, was optimized. These requirements are satisfied by Co-Ni-based material, which was earlier tried out and proved to be very good in complex technology of repair of a blade from ZMI-3U alloy. The technology includes airfoil tip retailoring by hardfacing with subsequent deposition on the item surface of a high-temperature metal coating by electron beam deposition to ensure the required service properties of the item. 18 Ref., 4 Tables, 10 Figures.

Оценивали циклическую долговечность теплозащитного покрытия ZrO2-Y2O3 на кобальтовом сплаве PWA 795, применяемом в качестве наплавляемого материала при восстановлении поврежденного торца пера рабочей лопатки наземной ГТД, изготовленной из монокристального сплава CMSX-4. Установлено, что после 300 термоциклов печных циклических испытаний теплозащитное покрытие, нанесенное на материал наплавки, имеет больший запас долговечности, чем покрытие на базовом сплаве. При длительном высокотемпературном воздействии происходит изменение химического состава связующего покрытия NiCoCrAlY в сторону CoNiCrAlY, что вносит положительный эффект в повышение структурной стабильности системы, замедляя таким образом процесс высокотемпературного окисления и деградации теплозащитных покрытий, а скорость роста TGO снижается на 30 % по сравнению с базовым сплавом. Подтверждено положительное влияние микролегирования активным компонентом (гафнием) наплавляемого сплава на улучшение адгезионной прочности TGO и связующего слоя. Библиогр. 20, табл. 2, ил. 12. К л ю ч е в ы е с л о в а : монокристальный сплав; наплавка; теплозащитное покрытие; TGO; зона обезлегирования; микролегирование; подавление волнистости; модифицирование; зернограничное упрочнение

During prolonged operation (thousands of hours) degradation of base material -EI 893 alloy -proceeds in working blades of GTK 10-4 unit under the impact of static and dynamic loads, temperature gradient, fuel combustion products, etc. Structural changes in the basic blade alloy influence the changes of its mechanical properties, compared to metal in initial state, namely, increase of ultimate strength, yield limit, hardness values and lowering of ductility characteristics take place and, therefore, also lowering of their creep resistance and high-cycle fatigue. For this reason, extension of service life of expensive items in turbine hot section is an extremely important task, which is solved by integrated restoration of initial structure and mechanical properties of EI 893 alloy. The objective of this work was studying GTE material state after operational aging on seven working blades (from sets with different operating lives), determination of their repairability and selection of modes of recovery heat treatment. It was found that during long operation periods at the temperature of 630-670 ºC an essential change of structural-phase state of base material proceeds in the working blades, which is manifested in dissolution, coagulation and non-uniform distribution of strengthening phase in matrix solution volume and carbide precipitation on subgrain boundaries within the grains and on grain boundaries, and formation of carbides of a more complex composition. It was established that optimum base structure with sufficient hardness and microhardness forms at two-step recovery heat treatment, namely, a certain reduction of difference in grain dimensions (mainly, 2-4 grain size point), reduction of density and dimensions of stable carbide phases in intergranular interlayers, and uniform and regular distribution of disperse strengthening phase. Structure recovery after recovery heat treatment leads to improvement of ductile characteristics (δ = 33.2-35.6 %) and, consequently, also of fatigue resistance at admissible values of strength and fracture toughness, that, on the whole, ensures the serviceability of reconditioned items. 16 Ref., 5 Tables, 10 Figures. K e y w o r d s :high-pressure turbine (HPT), low-pressure turbine (LPT), recovery heat treatment (RHT), hardness, microhardness, ultimate strength, yield limit, ductility, fracture energy, deposited weld, heat-affected zone * Carbon content measured by the method of burning a sample in oxygen environment.

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