CN102166643B - Method for preventing monocrystal blades from having mixed crystal defects - Google Patents

Abstract

The invention relates to the field of directional solidification of alloys, in particular to a method for preventing miscellaneous crystal defects in single-crystal blades, which is characterized in that: in the process of preparing investment casting mold shells for the production of single-crystal blades, ceramic fiber insulation blocks are planted Into the formwork at the edge of the blade where the single crystal blade is prone to miscellaneous crystal defects, the ceramic fiber insulation block is prefabricated into a U shape by the high temperature resistant ceramic fiber module according to the shape of the formwork at the edge of the blade, and can The U-shaped inner cavity of the ceramic fiber insulation block includes all the mold shells at the edge board. The present invention utilizes the characteristics of extremely low thermal conductivity of the ceramic fiber insulation block to reasonably control the liquidus temperature T _L -isotherm form when the solidification front reaches the edge plate of the single crystal blade when the alloy solidifies at the edge plate of the single crystal blade, so that the edge When the plate is close to the directionally solidified heat shield area, the heat is mainly exported through the main body of the single crystal blade, which avoids spontaneous nucleation at the edge plate, thereby ensuring the smooth growth of the single crystal.

Description

A Method for Preventing Miscellaneous Crystal Defects in Single Crystal Blades

technical field

The invention relates to the field of directional solidification of alloys, in particular to a method for preventing miscellaneous crystal defects in single crystal blades.

Background technique

With its unique characteristics of small size, light weight, high power, quick start, and less auxiliary equipment, gas turbines have first been widely used in the field of aero-engines. In order to improve the functions and efficiency of aero-engines, people have successfully used high-temperature alloys to direct The solidification technology makes the turbine blades into a single crystal form, which increases the high-temperature working life of the blades dozens of times. With the continuous advancement of gas turbine technology, gas turbines that were originally only used in the aviation field have been used in electric power, transportation, ships, and tanks. Petroleum, chemical, municipal, textile and many other fields have been widely used. In the past 30 years, the efficiency of industrial gas turbines has been greatly improved by applying the single crystal blade technology of aero-engines to the blade manufacturing of large-scale industrial gas turbines; due to the industrial The size of gas turbine blades is much larger than that of aviation blades, making the production of single crystal castings extremely difficult. Currently, one of the main problems encountered in the production of single crystal turbine blades with complex shapes by directional solidification technology is the formation of miscellaneous crystals. Due to the sudden change in the cross-sectional area of the casting in the direction of vertical heat flow in the blade edge plate, it is easy to nucleate and grow new grains. Since the grain boundary strengthening elements are removed from the single crystal alloy, the grain boundaries of these miscellaneous crystals will become the weak link of the single crystal blade, and become the source of cracks during use, which will eventually lead to the fracture of the blade. Through various technical methods, single crystal castings can be improved The temperature distribution during directional solidification and the prevention of local miscellaneous crystals are important technologies for the preparation of single crystal blades.

Chinese patent CN101537484A discloses a method that can effectively improve the temperature distribution in the solidification process of single crystal castings, specifically: after the first or second ceramic shell is formed on the surface of the melting (wax) mold, the heat conductor is made of shell-making ceramics The slurry is bonded to the parts where thermal barriers are likely to occur during the process of casting solidification and heat transfer to the outside. The thermal conductor is graphite or SiC; according to the same preparation method as the usual precision casting mold shell, carry out coating and sanding, and after sanding, place the The sand accumulation at the outer end of the heat conductor is wiped off and then sintered. By implanting a heat conductor, the invention can dissipate the heat at the inner corner A of the blade shroud in time, so that it can be cooled rapidly to below the liquidus temperature. The single crystal of the blade itself The growth can quickly enter the leaf crown and expand to the outer edge B, avoiding the generation of miscellaneous crystals here due to long-term overcooling.

Contents of the invention

The purpose of the present invention is to provide a method for preventing miscellaneous crystal defects in single crystal blades. Using the present invention in the preparation process of single crystal blades can significantly improve the horizontal temperature distribution uniformity of the edge plate of single crystal blades in the vicinity of the heat shield. The probability of miscellaneous crystal defects is greatly reduced, thereby significantly improving the yield of single crystal blades.

The invention relates to a method for preventing miscellaneous crystal defects in single crystal blades, which is characterized in that: in the process of preparing investment casting mold shells for the production of single crystal blades, ceramic fiber insulation blocks are implanted into single crystal blades, which are prone to occurrence Miscellaneous crystal defects in the formwork at the blade edge.

The ceramic fiber insulation block is prefabricated into a U-shape by a high-temperature-resistant ceramic fiber module with a thermal conductivity of less than 0.4 W/(mK) at 1250°C according to the shape of the mold shell at the edge of the blade, and can make the U-shaped The mold cavity contains all the formwork at the edge plate.

The implantation method of the ceramic fiber insulation block is as follows: after the first six or seven layers of the single crystal blade formwork are prepared according to the conventional investment casting process, the U-shaped inner part of the ceramic fiber insulation block is prefabricated according to the outer shape of the formwork at the edge plate. cavity, and make the U-shaped insulation block cover all positions of the edge plate formwork, the thickness of the insulation block is 3-5mm, as shown in Figure 1; then use the shell-making slurry as a binder to bond the ceramic fiber insulation block to the blade The exterior of the fringe formwork; the formwork is then prepared according to conventional processes.

The high-temperature-resistant ceramic fiber module refers to ceramic fibers with a resistance above 1450°C.

The difference between the present invention and the Chinese patent CN101537484A is that the present invention utilizes the characteristics of the extremely low thermal conductivity of the ceramic fiber insulation block to reasonably control the liquid temperature when the solidification front reaches the single crystal blade edge plate when the alloy solidifies at the edge plate of the single crystal blade. The phase line temperature T _L - isotherm shape (Figure 2), so that when the edge plate is close to the directionally solidified heat shield area, the heat is mainly exported through the main body of the single crystal blade, which avoids spontaneous nucleation at the edge plate, thereby ensuring the smooth operation of the single crystal Growth is different from the Chinese patent CN101537484A by implanting a heat conductor with high thermal conductivity.

The invention is simple in operation, does not need to transform directional solidification equipment, significantly suppresses miscellaneous crystal defects, and can greatly increase the yield of single crystal blades.

Description of drawings

Figure 1: Schematic diagram of ceramic fiber insulation block for single crystal blade;

Figure 2: The shape of the liquidus temperature T _L -isotherm when the solidification front reaches the edge plate of the single crystal blade during the directional solidification process, a) When there is a ceramic fiber insulation block, the solidification front T _L -isotherm is relatively straight; b) When there is no ceramic fiber insulation block, a large-scale supercooled area appears at the outer end of the edge plate, which is prone to spontaneous nucleation, resulting in miscellaneous crystal defects;

Fig. 3: Structural diagrams of single crystal blades in Examples and Comparative Examples.

Detailed ways

Example

The present invention is applied to the production of a single crystal blade (Fig. 3). The blade material is superalloy CMSX-4. The raw material of the ceramic fiber insulation block is the SILCASTACK-160 ceramic fiber module produced by SILCA Service- und Vertriebsgesellschaft fuer Daemmstoffe mbH , temperature resistance 1600°C, thermal conductivity 0.31 W/(mK) at 1250°C. In the preparation process of the aluminum oxide formwork for the blade, the first seven layers of the single crystal blade formwork are prepared according to the conventional investment casting process; the U-shaped inner cavity of the insulation block is prefabricated according to the outer shape of the formwork at the edge plate of the blade at this time, and made The insulation block can cover all positions of the edge plate formwork, and the thickness of the insulation block is 3-5mm; then use the shell slurry as the adhesive to bond the insulation block to the outside of the edge plate formwork; after that, the formwork is prepared according to the conventional process , the directional solidification process was carried out according to the conventional process parameters, and a total of 12 blades were produced. After routine tissue inspection, 2 blades had small-volume miscellaneous crystals at the outer end of the edge plate, and the miscellaneous crystal defect rate was 16.7%.

comparative example

According to the same materials, process parameters and production conditions in the above examples, 12 identical blades were produced, but the ceramic fiber insulation block according to the present invention was not used. After routine tissue inspection, 7 blades had miscellaneous crystals at the edge plate. , and most of them are large in volume, among which the miscellaneous crystals of 5 blades grow to the main body of the blade, and the miscellaneous crystal defect rate is 58.3%.

Claims (1)

1. A method for preventing miscellaneous crystal defects in single crystal blades, characterized in that: in the process of preparing an investment casting mold shell for the production of single crystal blades, implanting ceramic fiber insulation blocks into single crystal blades is prone to miscellaneous defects. In the formwork at the edge of the blade with crystal defects, the ceramic fiber insulation block is prefabricated into a U-shape by a high-temperature-resistant ceramic fiber module according to the shape of the mold at the edge of the blade, and can make the U-shape of the ceramic fiber insulation block The inner cavity contains all the formwork at the edge plate; the implantation method of the ceramic fiber insulation block is as follows: after the first six or seven layers of the single crystal blade formwork are prepared according to the conventional investment casting process, according to the position of the edge plate at this time The outer shape of the formwork prefabricates the U-shaped inner cavity of the ceramic fiber insulation block, and enables the U-shaped insulation block to cover all positions of the edge plate formwork. The thickness of the insulation block is 3-5mm, and then the shell slurry is used as a binder to The ceramic fiber insulation block is bonded to the outside of the blade edge plate formwork; then the formwork is prepared according to the conventional process; the high temperature resistant ceramic fiber module refers to the ceramic fiber resistant to 1450°C and above, and the thermal conductivity is less than 0.4 W at 1250°C /(mK) .

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