All-Russian Institute of Aviation Materials, Moscow, Russia:

E. I. Iakovlev, Leading Engineer, e-mail: y-e-i@yandex.ru

Firstly we carried out the analysis of the qualitative conditions of structure formation in the casting of turbine blades by directional solidification, showing the peculiarities of existing technologies. We also considered the promising areas of turbine blades' directional solidification development techniques. All-Russian Institute of Aviation Materials offered an “alternative mold”, which is a water-cooled container with sliding heat shields over it. The unit is filled with inert gas under pressure of 30–150 mm Hg. The directional solidification techniques start by moving the mold with the melt from the heating zone to the cooling zone through the heat shield. As the thermophysical analysis on the cooling intensity of this process is slightly superior to the Bridgman-Stockbarger method, however, tight-fitting shape of the heat shield allows you to increase the value of the longitudinal component of the temperature gradient vector and the crystallization rate, which improves the quality of castings. A set of jet nozzle spacers with macrostructure high yield was produced by this method. Further development of directional solidification techniques is possible by intensive convective cooling of forms with an inert gas in vacuum. The process of directional solidification gas-cooled castings (Gas Cooling Casting — GCC) was first patented in 1996 by the famous “Howmet” (now “Alcoa Howmet”) for casting of large-size blades and single crystal and aimed structures for aviation and power turbines. The author of this article, along with the specialists of JSC “NPO “Saturn” developed a technique of directional solidification with argon cooling forms (PGO) for the casting of large gas turbine blades. For this purpose, existing unit for the directional solidification Bridgman-Stockbarger method was upgraded and provides more intensive cooling of forms (convection of argon stream blower forms). The new process allows to increase the number of blades in the block and feeding speed, which leads to increased productivity in 1.8–2.0 times and the suppression of structural defects compared to the Bridgman-Stockbarger method.

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