Gas turbine blades: preparation of directional solidification Україна

Turbine blade is the core hot end component of gas turbine, its research and development and manufacturing is an important reflection of the development scale and technical level of a country's industry. The recent research progress of gas turbine blade preparation technology is reviewed. Based on the research of the research group, the research progress in the field of directional solidification of gas turbine blades is introduced, and the focus direction is put forward.

Directional solidification technology refers to a technology that establishes a temperature gradient in a certain direction by forced means during the solidification process, so that the solidification proceeds along a certain direction. In the solidification process of a metal, there is a temperature gradient in a specific direction between the solidified part and the unsolidified melt, which causes the metal to solidify in the direction opposite to the heat conduction. By using directional solidification technology, columnar or single crystal with specific orientation can be obtained, and the columnar or single crystal blade can be prepared, and its performance can be significantly improved.

In the late 1960s, Versnyder et al. applied directional solidification technology to the production of superalloys, which better controlled the grain orientation of the solidification structure, eliminated the transverse grain boundaries, and greatly improved the mechanical properties of superalloys. Directional solidification technology after decades of research, developed exothermic powder (EP) method, power down (PD) method, high rate solidification (PD) method, Conventional techniques such as HRS [12] and liquid metal cooling (LMC). At present, the high-speed solidification method and liquid metal cooling method are widely used.

High speed solidification method is a method to make castings move in one direction gradually away from the high temperature region to achieve single direction solidification. This method improves the problem that the temperature gradient decreases gradually in the solidification process. The principle of high-speed solidification method is shown in Figure 1(a). An adiabatic baffle is set at the bottom of the furnace, and a mouth slightly larger than the casting is opened on the baffle. The interior of the furnace is kept heated. During the solidification process of the metal, the shell is slowly pulled down, so that the part of the metal exposed to the outside begins to cool and solidify, while the metal melt located in the furnace is still in a heated state, thus establishing an axial temperature gradient. The high speed solidification method has a high and stable temperature gradient and cooling rate, and can obtain a long columnar crystal and a fine structure, thus greatly improving the mechanical properties of the castings, but the temperature gradient of the method is still insufficient, and casting defects such as freckles and impurities are still prone to occur during directional solidification of thick and large castings.