CN114659872B - A method for evaluating the yield of single crystal high temperature alloy hollow blade core - Google Patents

Abstract

The invention discloses a method for evaluating core deformability of a single crystal superalloy hollow blade, and belongs to the technical field of single crystal superalloy blade preparation processes. The invention carries out comparative evaluation on the yield of the single crystal superalloy blade core prepared by adopting different material formulas or different processes. The deformation tendency of the core was evaluated while comparing the core deformability. Carrying out high-temperature solution treatment on the single crystal hollow test rod, and comparing the deformability of the blade core by utilizing the area size of recrystallized grains; the comparison of the deformation tendency is achieved by detecting the wall thickness at the local position of the hollow sample. In the preparation of single crystal hollow blades, the method can evaluate the core deformability and compare the deformation tendency of the core, and provides a method for the preference of the usable core.

Description

A method for evaluating the yield of single crystal high temperature alloy hollow blade core

Technical Field

The invention discloses a method for evaluating the yieldability of a single crystal high temperature alloy hollow blade core, which belongs to the technical field of single crystal high temperature alloy blade preparation technology and is used for comparing casting process properties such as the yieldability of cores prepared by using different core materials or core making processes.

Background technique

Turbine blades are one of the most critical parts in aircraft engines. Single crystal high temperature alloys have basically eliminated all grain boundaries and have excellent high temperature properties. They are widely used as materials for aircraft engine turbine blades. The preparation of single crystal high temperature alloy hollow turbine blades has become one of the major key technologies for aircraft engines.

Since there are air cooling channels inside the hollow blades, turbine blades usually need to be cast. During the cooling process after solidification, due to the difference in thermal expansion coefficients between the metal and the ceramic core, as well as the complexity of the internal structure of the blade, the cooling shrinkage of the alloy is hindered by the core, and large casting residual stress is inevitably present inside the alloy.

In order to obtain the best comprehensive mechanical properties, single crystal high temperature alloys usually need to be fully heat treated, that is, the coarse γ' phase and eutectic in the cast state are completely dissolved during the solution heat treatment process to form a single-phase γ phase. Therefore, single crystal high temperature alloys have a strong tendency to recrystallize during heat treatment. Since recrystallization seriously weakens the mechanical properties of single crystal high temperature alloys, recrystallization is a defect that must be avoided during the preparation of single crystal high temperature alloy blades. Casting residual stress exceeding a certain critical range is one of the main reasons for the driving force of recrystallization. The greater the residual stress, the greater the possibility of recrystallization. One of the main reasons for the generation of casting residual stress in single crystal high temperature alloy hollow blades is that the shrinkage of the alloy during solidification and cooling is hindered by the core. Whether the core yields enough determines whether the residual stress generated in the casting is less than the critical range of recrystallization in the inner cavity.

Due to the presence of the core, certain casting residual stresses will inevitably appear in the alloy. However, the core has sufficient yield to ensure that the residual stress in the alloy of the single crystal blade is small enough, so that no internal cavity recrystallization occurs during the heat treatment of the blade, which has significant practical engineering significance. The evaluation of the quality of the core's yield is very important. However, no process method for characterizing the yield of the core of a single crystal high-temperature alloy hollow blade has been retrieved. However, under normal circumstances, an increase in the yield of the core will lead to a decrease in the core strength and an increase in the deformation tendency of the core. In this patent, a method is proposed to evaluate the deformation tendency of the core while comparing the yield of the core, to ensure the selection of a suitable core material formula and a core making process, so that the core has a relatively comprehensive processability that meets the preparation of single crystal hollow blades.

Summary of the invention

The purpose of the present invention is to provide a method for evaluating the yieldability of a core of a single crystal high-temperature alloy hollow blade, and compare the yieldability and deformation tendency of the core for preparing a core of a single crystal high-temperature alloy hollow blade. The method is simple and direct to operate, and has strong operability.

The technical solution of the present invention: A method for evaluating the yieldability of a single crystal high-temperature alloy hollow blade core, using a single crystal high-temperature alloy hollow thin-walled specimen to evaluate and compare the yieldability of cores prepared using different core material formulas or different processes during directional solidification. The inner cavity structure of the blade is complex, and usually large casting residual stresses are generated at the transition between different cavities. The presence of this residual stress can easily lead to recrystallization inside the blade during subsequent heat treatment. The occurrence of internal recrystallization is related to multiple factors, not only to the yieldability of the core itself, but also to factors such as the size of the blade, the wall thickness, and the size of the transition radius. The present invention extracts representative characteristic values for typical blades of single crystal blades of aircraft engines, and compares the dimensional stability of the core while comparing and evaluating the yieldability.

The peak value of the internal casting residual stress is closely related to the inner cavity structure of the blade. The sample designed by the present invention can fully reflect the structural characteristics of the blade that cause the casting residual stress, and the sample itself is simple in shape and easy to realize.

The internal cavity of some blades has a shape characteristic of a long hole. In the present invention, a hollow specimen with a triangular cross section with a sharp corner rounded and an aspect ratio of not less than 10 is used to characterize and evaluate the yieldability of the core.

The internal cavity of some blades has a narrow flat plate-like feature. In the present invention, a hollow rectangular cross-section specimen with a ratio of specimen length to the wide side of the rectangular cross-section of not less than 6 and rounded corners is used to characterize and evaluate the yieldability of the core.

The core of the single crystal hollow specimen and the mold of the wax mold are processed and manufactured separately, and the mold is used to ensure the consistency of the specimen size. The target cores are prepared separately, and then the wax molds are pressed with the cores to assemble the hollow specimen molds. When assembling the molds, the cores to be evaluated are combined in the same mold, so that the directional solidification is completed in the same furnace. The positions of different specimens in the mold are the same, ensuring that the casting conditions of different cores are the same during the directional solidification process. After the mold assembly is completed, the shell is prepared, and the single crystal hollow specimen is cast using the target single crystal high-temperature alloy for directional solidification.

After the casting is completed, the mold is cut into individual samples and heat treated using the solution heat treatment system of the cast single crystal high temperature alloy.

In the middle of the specimen length, there is no support and restriction from the core head, which is the position where the maximum deformation accumulates, and the wall thickness deviation of the specimen is generally the largest. On the same cross section, the wall thickness is thicker at some locations and thinner at others. The smaller the deformation tendency of the core, the smaller the difference between thicker and thinner walls.

During the cooling process of the single crystal high temperature alloy hollow specimen after solidification, the alloy is hindered by the core and casting residual stress is generated at the sharp corners of the specimen. The core's yieldability varies depending on the material formula or process for preparing the core. When the core's yieldability is poor, a large casting residual stress is generated in the specimen, which is easy to cause recrystallization during the subsequent solution treatment process. The yieldability of the core can be evaluated by comparing the size of the recrystallized grain area. The yieldability of different cores is evaluated and compared based on whether recrystallization occurs and the size of the recrystallized grain area. The smaller the recrystallized grain area or even no recrystallization occurs, the better the yieldability of the core.

The beneficial effects of the present invention are as follows: the present invention proposes a method for evaluating the yieldability of a core of a single crystal high-temperature alloy hollow blade, and proposes a method for evaluating the deformation tendency of a core while comparing the yieldability of the core for preparing a core of a single crystal high-temperature alloy hollow blade. It ensures that a suitable core material formula and core making process are selected so that the core has relatively comprehensive processability that meets the requirements for preparing a single crystal hollow blade. The method is simple and direct to operate, and has strong operability.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 Long hollow specimen for testing and evaluating single crystal high temperature alloy hollow blades

Figure 2 Flat hollow specimen used to inspect and evaluate single crystal high temperature alloy hollow blades

Detailed ways

A method for evaluating the yieldability of a single crystal high temperature alloy hollow blade core is provided, and the yieldability and deformation tendency of cores prepared by different core materials or core making processes are compared and evaluated simultaneously. For a specific single crystal blade, the available core materials and processes are optimized and compared.

For single crystal blades of aircraft engines, the internal cavity of some blades has the shape characteristics of a long strip. Accordingly, the core forming the cavity is a long strip with a significantly longer length when viewed as a whole. In the present invention, the cross-sectional shape of the cavity of the long single crystal hollow sample is an equilateral triangle with rounded corners. The side length of the triangle is 6 to 8 mm. The rounded radius of the corner is 0.5 to 1 mm, and the length of the hollow sample cavity is 60 to 80 mm. The wall thickness of the sample is 0.8 to 1 mm.

The internal cavity of some blades has a narrow flat plate-like feature. In the present invention, a hollow specimen with a rectangular cross-section and a sharp corner rounding specimen with an aspect ratio of not less than 6 is used to compare and evaluate the yield of the core. Accordingly, the cross-sectional shape of the specimen cavity is a rectangle with a sharp corner rounding. The narrow side of the rectangle is 2 to 3 mm, the wide side of the rectangle is 10 to 12 mm, and the rounding radius of the sharp corner is 0.5 to 1 mm. The length of the specimen cavity is 60 to 80 mm. The wall thickness of the specimen is 0.8 to 1 mm.

The wax mold of the hollow specimen is pressed using different cores to be evaluated, and then the wax mold set of the specimen is assembled. When the mold set is assembled, the position of each specimen in the mold set is the same relative to the mold set shape. The shell is prepared for the wax mold set, and then the single crystal hollow test rod is cast using the specified single crystal high-temperature alloy directional solidification.

When evaluating and testing the yield of different cores, the single crystal hollow specimen castings of directionally solidified castings are completed in the same heat, avoiding the dispersion of test results caused by different cooling processes caused by directional solidification in different heats.

Test the wall thickness of the hollow specimen at the middle of its length, and compare the deformation tendency of the core based on the difference between the minimum and maximum wall thickness values on the same section. The smaller the wall thickness difference, the better the dimensional stability of the core.

The hollow single crystal specimen casting is subjected to high temperature solution treatment. The hollow single crystal specimen casting is prone to recrystallization during the high temperature solution treatment. According to the area of the recrystallized grains on the hollow single crystal specimen, the yieldability of different core materials and/or core preparation process methods to be evaluated is compared and evaluated; if the area of the recrystallized grains appearing in the hollow single crystal specimen is larger, the yieldability of the core material or process method to be evaluated is worse.

Example 1

A method for evaluating the yieldability of a single crystal high temperature alloy hollow blade core is provided, wherein the yieldability and deformation tendency of cores prepared by different core materials or processes for preparing the single crystal high temperature alloy hollow blade are simultaneously evaluated. For a specific single crystal blade, the optional core materials and processes are screened and evaluated.

According to the internal cavity shape characteristics of single crystal blades of aircraft engines, the internal cavity of some blades has the shape characteristics of a long strip. Accordingly, the core forming the cavity is a long strip with a significantly longer length from the overall perspective. The cross-sectional shape of the cavity of the single crystal hollow sample is an equilateral triangle with rounded corners, and the side length of the triangle is 8 mm. The rounded radius of the corner is 0.5 mm, and the length of the hollow sample cavity is 80 mm. The wall thickness of the sample is 0.8 mm

Cores are prepared using powders with different particle size gradations and different sintering processes. Wax molds of hollow specimens are pressed for different cores, and then the specimen wax mold modules are combined. When the modules are combined, the position of each specimen in the module is the same relative to the module shape. A shell is prepared, and then a specified single crystal high-temperature alloy is used for directional solidification casting of single crystal hollow test rods.

When evaluating and testing the yield of different cores, the single crystal hollow specimen castings of directionally solidified castings are completed in the same furnace to avoid the dispersion of test results caused by different cooling processes caused by directional solidification in different furnaces.

Test the wall thickness of the hollow specimen at the middle of its length, and determine the deformation tendency of the core based on the minimum and maximum wall thickness values on the same section. The smaller the wall thickness difference, the better the dimensional stability of the core.

The mold is used to prepare cores of the same shape, and hollow single crystal specimens are prepared by directional solidification castings using the cores to be evaluated, and the hollow single crystal specimen castings are subjected to high-temperature solution treatment. Recrystallization will occur in the hollow single crystal specimen casting during the high-temperature solution treatment. According to the specimen position where the recrystallized grains appear on the hollow single crystal specimen casting and the size of the recrystallized grain area, the yieldability of different core materials to be evaluated and the process methods to be evaluated are compared and tested; if the recrystallized grains appear in the thicker and larger position of the hollow single crystal specimen, the yieldability of the core material or process method to be evaluated is worse; if the area of the recrystallized grains appearing in the hollow single crystal specimen is larger, the yieldability of the core material or process method to be evaluated is worse.

Example 2

A method for evaluating the yieldability of a single crystal high temperature alloy hollow blade core is provided, wherein the yieldability and deformation tendency of cores prepared by different core materials or processes for preparing the single crystal high temperature alloy hollow blade are simultaneously evaluated. For a specific single crystal blade, the optional core materials and processes are screened and evaluated.

According to the inner cavity shape characteristics usually possessed by single crystal blades of aircraft engines, the internal cavity of some blades has a narrow flat plate-like feature. In the present invention, a hollow specimen with a rectangular cross section and a sharp corner rounding specimen with an aspect ratio of 6 is used to verify the yield of the core. Accordingly, the cross-sectional shape of the specimen cavity is a rectangle with a sharp corner rounding. The width of the rectangle is 3 mm, the length of the rectangle is 12 mm, and the rounding radius of the sharp corner is 1 mm. The length of the specimen cavity is 60 mm. The wall thickness of the specimen is 1 mm.

The cores are prepared by using powders with different particle sizes and different sintering processes, and hollow wax molds of the samples are pressed for different cores. Then the wax molds of the samples are assembled, and the positions of each sample in the mold are the same relative to the mold shape. The shell is prepared, and then the single crystal hollow test rod is cast by directional solidification of the specified single crystal high temperature alloy.

When evaluating and testing the yield of different cores, the single crystal hollow specimen castings of directionally solidified castings are completed in the same furnace to avoid the dispersion of test results caused by different cooling processes caused by directional solidification in different furnaces.

Test the wall thickness of the hollow specimen at the middle of its length, and determine the deformation tendency of the core based on the minimum and maximum wall thickness values on the same section. The smaller the wall thickness difference, the better the dimensional stability of the core.

The mold is used to prepare cores of the same shape, and hollow single crystal specimens are respectively prepared by directional solidification castings using the cores to be evaluated, and the hollow single crystal specimen castings are subjected to high-temperature solution treatment. Recrystallization will occur in the hollow single crystal specimen casting during the high-temperature solution treatment. According to the specimen position where the recrystallized grains appear on the hollow single crystal specimen casting and the size of the recrystallized grain area, the compromise of different core materials to be evaluated and the process methods to be evaluated are compared and tested; if the recrystallized grains appear in the thicker and larger position of the hollow single crystal specimen, the compromise of the core material or process method to be evaluated is worse; if the area of the recrystallized grains appearing in the hollow single crystal specimen is larger, the compromise of the core material or process method to be evaluated is worse.

Claims (7)

1. A method for evaluating the core deformability of a single crystal superalloy hollow blade, comprising the steps of: the method comprises the following steps:

1) Designing and processing a single crystal hollow sample mold aiming at a single crystal blade to be prepared;

2) Adopting the die prepared in the step 1) to prepare cores with the same shape for different types of core materials to be evaluated; the method adopts powder with different grain size fractions to prepare cores and different sintering processes to prepare cores, presses wax molds of hollow samples for different types of cores, then combines the wax mold modules of the samples, prepares a shell with the same position of each sample in the module relative to the appearance of the module during the combination of the mold modules, and then adopts specified monocrystal superalloy to directionally solidify and cast a monocrystal hollow test bar;

3) Preparing hollow single crystal samples by using the cores prepared in the step 2), wherein the single crystal hollow samples are in a strip shape, namely the cores forming the cavities are in a strip shape with the length being obviously larger than the cross section size as a whole; the cross section shape of the single crystal hollow sample cavity is an equilateral triangle with sharp corners rounded; the cross section shape of the single crystal hollow sample cavity is a rectangle with a rounded sharp corner; carrying out high-temperature solution treatment on the hollow single crystal test rod;

4) Detecting the wall thickness of the hollow sample at the middle position of the length, and comparing the deformation tendency of the core according to the difference between the minimum wall thickness and the maximum wall thickness on the same section, wherein the smaller the wall thickness difference is, the better the stability of the core material to be evaluated is;

5) And carrying out high-temperature solution treatment on the hollow single crystal sample, and comparing and evaluating the concessibility of the core by adopting different core materials and core preparation process methods according to the area of the recrystallized grains on the hollow single crystal test rod, wherein the greater the area of the recrystallized grains is, the worse the concessibility of the core material or the process method is.

2. The method for evaluating the core deformability of a hollow single crystal superalloy blade according to claim 1, wherein the hollow single crystal sample cavity has an equilateral triangle cross section, a side length of 6-8 mm, and a sharp corner radius of 0.5-1 mm.

3. A method for evaluating the core deformability of a single crystal superalloy hollow blade according to claim 2, wherein the hollow sample cavity is 60-80 mm long.

4. The method for evaluating the core deformability of a hollow single crystal superalloy blade according to claim 1, wherein when the cross section of the hollow single crystal superalloy sample cavity is a sharp-angled rounded rectangle, the narrow side of the rectangle is 2-3 mm, the wide side of the rectangle is 10-12 mm, and the radius of the sharp corner is 0.5-1 mm.

5. The method for evaluating the core deformability of a single crystal superalloy hollow blade according to claim 4, wherein the hollow sample cavity is 60-80 mm long.

6. The method for evaluating the core deformability of a hollow blade of a single crystal superalloy according to claim 5, wherein the core is used for preparing a single crystal hollow sample, and the wall thickness of the sample is 0.8-1 mm.

7. A method for evaluating the core deformability of a single crystal superalloy hollow blade according to claim 1, wherein the directionally solidified single crystal hollow sample castings are completed in the same heat when evaluating and inspecting the deformability of different cores.