PSI - Issue 30

S.P. Yakovleva et al. / Procedia Structural Integrity 30 (2020) 201–208 Yakovleva S. P. t l. / Structural Integrity P ocedia 00 (2020) 0 –0 0

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b

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Fig. 4. The fracture surface of the working blade # 2 ( a ), the pores ( b ) and packaging defects ( c ) in its metal

4. Conclusion The study of the structure of thermally loaded elements (a heat insert, working blades) of power plants operating under severe operating conditions in the North revealed the premature development of unacceptable high temperature degradation which leads to a decrease in the reserve of plasticity, the transition of metal to an accelerated creep stage and thermal-fatigue fracture. High-temperature degradation of the metal structure of a heat insert was occurred in unfavorable morphological changes of the strengthening γ '-phase and the development of recrystallization processes which accelerated the onset of creep and the exhaustion of plasticity, led the embrittlement of metal, the formation of intergranular discontinuities, porosity and subsequent fracture. High-temperature degradation of the working blades metal structure up to the appearance of heat-temperature fatique cracks is observed even in a lock part working in less strict conditions compared to a feather. The depletion of solid solution with intermetallide, the softening of intermetallide particles, and the formation of pores at the boundaries and in the body of a micrograin was revealed. The process of alloy softening and destruction is controlled by the transition from transcrystalline to intergranular fracture. The reasons for the accidents were related to the insufficient level of service properties of materials, as well as to the peculiarities of operation (for example, over temperature, frequent heat changes). It is possible to increase the operating time of working blades made of the studied alloy by applying protective coatings, or by lowering the operating temperature level. The improvement of materials for gas turbine plants of the North requires an adapted optimizing of compositions of the used alloys and technology development in the manufacture of parts taking into account the operating conditions in cryolithozone connected with a high level of loads and considerable amplitudes of their seasonal and daily fluctuations. References BernshteinM.L., Rakhshtadt A.G., 1985. Metalscienceandheat treatment of a steel. Vol.III. Principles of heat treatment. Metallurgy, Moscow, pp. 215. Botvina L.R., 2008. Destruction: Kinetics, Mechanisms, Common Pattern. Nauka, Moscow, pp. 334. DonachieM.J., DonachieS.J., 2002. Superalloys: A Technical Guide. Second. ASM International, USA, pp. 439. Getsov L.B., 2010. Materialsandstrength of gas turbines details parts. Intwobooks. Book 1. Publishing House «Gazoturbinnyetechnologii», Rybinsk, pp. 611. Haessner F.,1978. Recrystallization of metallic materials. Dr. RiedererVerlag, Stuttgart, pp. 296. Kablov Е .N., 2015. InnovationsofFederalStateUnitaryEnterprise «All-RussianResearch Institute of Aviation Materials» State Scientific Center of the RF on the realization of “Strategic areas of development of materials and technologies of their processing for the period of 2030”. J. Aviation materials and technologies 1 (34), 3-33. Kleshev А .S., KorneevaN.N., Vlasova О .N., 1995. Mechanism of softening of heat-resistant nickel alloys subjected to thermomechanical processing during long-term high-temperature tests. J. Metal science andheat treatment of metals 9, 19-21.