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MATERIALS SCIENCE
ArticleName Prospective ways of development of directional solidification techniques for turbine blades manufacturing. Part 1
DOI 10.17580/tsm.2017.05.11
ArticleAuthor Iakovlev E. I.
ArticleAuthorData

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

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

Abstract

The first part of this paper shows the analysis of the conditions of qualitative structure formation in the turbine blades casting by directional solidification techniques. The main method to obtain the single crystal and directionally solidified turbine blades in Western Europe and the US is the Bridgman – Stockbarger technique, when liquation defects, significantly reducing the blades performance, arise due to the low temperature pressure and low-speed solidification of large castings. In attempts to increase the solidification rate by raising the pulling speed, increase ratio of the transverse and longitudinal vector components of the temperature gradient on the front liquidus occurs, leading to a shift in liquidus front cooling zone and causing harmful spurious crystals in the blades with directional and single crystal structures. One way of cooling rate increase during directional solidification is to raise the heat transfer coefficient on the shapes' outer surface. Liquid metal cooling technique in the melt aluminum was realized in 1975 on VIAM’s pilot unit. Currently Russia accumulated sufficiently large industrial experience using the aluminum casting baths for 200 mm blades with directional and single crystal structures, where liquation defects are excluded due to low cooling rate during solidification. The VIAM specialists developed the technological processes for the production of single crystal blades of aircraft turbines with macrostructure yield ratio over 80%. However, there is a number of technological issues in the casting of large rotor blades of advanced groundbased gas turbines. Due to the increased residence time in the casting mold with a cooler and a large hydrostatic pressure, the coolant shell mold cracking occurs and causes parts faulty. The analysis of recently conducted research of new methods for the preparation of large single-crystal blades and designed structures will be shown in the second part of this paper.

keywords Directional solidification processes, Bridgman-Stockbarger technique, liquid mechanical cooling, turbine blades, heat convection coefficient, single-crystal and directed structures
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