Features of Structure Formation in High-Chromium Heat-Resistant Alloys with Directed Crystallization
Processy litʹâ, 2019, Tom 137, №5, p.44-55
Keywords:
gas turbine engines, heat resistant alloys, cast blades, directional crystallizationAbstract
Received 03.09.2019
UDK 669.245:513.71
The analysis of the thermo-kinetic conditions for the formation of an oriented structure in cast blades obtained for gas turbine engines (GTE) by the method of directed crystallization of heatresistant nickel-based alloys is presented. These alloys were developed at the PTIMA NAS of Ukraine in conjunction with the GP NPKG «Zorya» −«Mashproekt» (Nikolaev). Blades of such alloys have increased durability, thermal phase-structural stability. New heat-resistant alloys are created on the basis of serial alloys ХН57КВЮТМБРЛ-ВИ (grade СМ88Y) and ХН57КВТЮББЛ (grade ЧС104) by adjusting the chemical composition and alloying them with tantalum and rhenium. It is shown that the formation of the necessary structure and physico-mechanical characteristics in turbine blades is possible only with optimal heat removal from the casting with directed crystallization of the alloys. For this purpose, an ejector device was installed in an industrial foundry unit for additional cooling of forms with argon. Rational modes of intensification of mold cooling were also determined, which made it possible to increase the temperature gradient at the crystallization front of alloys to 170 deg/cm at a mold moving speed of 10−13 mm/min. In the case of moving the mold at a faster rate, the flat crystallization front in the casting is violated and the growth of axes in second-order dendrites is intensified in alloys. As a result, the direction of crystallization of the alloys is disrupted and the sizes of the structural components in them increase, which leads to a decrease in the strength properties of the blades. The optimal temperature-kinetic parameters of the process of directed crystallization of alloyed heat-resistant alloys are determined, which allow one to obtain the specified structure and dispersion of the hardening phases in them, to increase the main operational characteristics of the blades by 15−20 %.
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Copyright (c) 2019 А. В. Нарівський, Ю. Г. Квасницька, І. І. Максюта, О. В. Михнян
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