Simulated single crystal turbine blade composite control seeding technique

Abstract

The application discloses a kind of based on simulation single crystal turbine blade composite control crystal introduction method, belong to single crystal investment casting field, to solve the problem that the cross section size mutation causes thermal barrier zone overheating, rim plate corner undercooling and induces macroscopic heterogeneous crystal defect in the transition zone of blade body to rim plate.The method comprises: determining that rim plate A corner and B corner are heterogeneous nucleation position by Procast software CAFE module;In Visual Viewer, slice analysis rim plate from B point begins to solidify, and finally advances to blade body along corner advancing and solidification sequence;Combining nucleation position and solidification sequence, square crystal introduction strip with cross section area of 10 mm square is added;In Visual Mesh, set the overall shell thickness of blade body to 6 mm, the shell thickness of thermal barrier zone to 4.5 mm, and determine the shell thickness of rim plate corner to 10 mm by 8 mm, 9 mm, 10 mm, 11 mm simulation screening;Finally, compare the rim plate solidification nephogram, temperature field and grain orientation before and after composite control.The method can slow down the solidification rate of rim plate corner, reduce the degree of corner undercooling, improve the hindrance of thermal barrier zone to the transverse expansion of main grain, and inhibit the rim plate heterogeneous crystal and optimize the grain orientation by the composite control of fixed-point crystal introduction, heat dissipation enhancement of thermal barrier zone and fixed-point heat preservation of rim plate corner.

Description

Technical Field

[0001] This invention relates to directional solidification and single crystal preparation technology, and is a method for simulating and guiding single crystal growth through sophisticated simulation. Background Technology

[0002] In the production of single-crystal directionally solidified turbine blades, defects such as significant crystal orientation deviations and impurities are prone to occur. Due to extremely poor heat dissipation conditions at the transition zone between the blade and the spar, the melt in this area remains superheated for a prolonged period, forming a nearly closed thermal barrier. This prevents the single crystals from directly extending laterally towards the adjacent spar, causing the temperature of the molten metal at the spar's edges to continuously decrease. During this complex three-dimensional dendritic growth process, the liquid at the solidification interface front is often in a supercooled state with a negative temperature gradient, making it highly susceptible to impurities. These impurities severely damage the integrity of the single crystals, significantly degrading the material's mechanical properties.

[0003] Currently, two main methods are used to control casting defects in single-crystal turbine blades during factory production. One is to reduce the pulling rate, but this significantly reduces production efficiency; the other is to add seed bars to guide selected single crystals from the blade body to the rim plate, which also conducts heat to the rim plate, reducing edge undercooling and thus promoting the expansion of single crystals from the blade body to the rim plate. Although adding seed bars to regulate the single crystal growth process is widely used, it has been found that the method of adding seed bars to the rim plate is still based on trial and error and relies on experience, and has failed to improve the overheating state in the thermal barrier region. Therefore, this method provides a simulation-based composite seeding control technique for blade single crystal preparation from the perspective of fixed-point heat dissipation + fixed-point heat preservation, to suppress impurities and optimize grain orientation. Summary of the Invention

[0004] To address the issues of significant crystal orientation deviation and impurities during the production of single-crystal directionally solidified turbine blades, a method of fixed-point heat dissipation and fixed-point heat preservation is proposed. This method, based on the nucleation location in simulation, controls the temperature field at abrupt changes in cross-sectional dimensions, improves the overheating state in the thermal barrier zone, and plays a role in suppressing impurities and optimizing grain orientation.

[0005] The technical solution of this invention to achieve the appeal objective includes the following steps:

[0006] Step 1

[0007] The temperature field of a certain type of blade after directional solidification was obtained by Procast simulation. The temperature field was then imported into the CAFE module of Procast software to determine the nucleation location of heterocrystals on its edge plate.

[0008] Step 2

[0009] In Visual Viewer, slices of the blade edge plate are analyzed to determine the solidification process, revealing the solidification sequence and related patterns at the edge plate corners.

[0010] Step 3

[0011] Based on the nucleation location of heterocrystals in the rim plate and the solidification sequence of the rim plate edges, crystal-guiding strips are added at fixed points in the blade CAD model, and the height of the lower end of the crystal-guiding strips in the blade crystal-guiding section is increased, with the cross-section designed as rectangular or circular.

[0012] Step 4

[0013] In Visual Mesh, increase the thickness of the edge shell at the blade corners and decrease the thickness of the shell in the transition zone (thermal barrier zone) between the blade and the edge plate. The specific steps are as follows:

[0014] [1] Set the overall thickness of the blade shell.

[0015] [2] The mold shell is thinned in the thermal barrier zone. With the increase in casting wall thickness and heat content in the transition zone between the blade and the rim, and further due to the significant thickening of the mold shell and the deterioration of heat dissipation conditions, a thermal barrier zone forms here. This hinders the lateral expansion of single crystals from the blade to the rim, causing the nucleation and growth of impurity crystals at the rim corners. Therefore, thinning the mold shell in the thermal barrier zone and increasing the mold shell thickness at the corners are key aspects of composite control of crystal growth. Select the specified area mesh node and create a new Shellpatch in Shelling to set the mold shell thickness.

[0016] [3] Thicken the upper and lower surfaces of the flange. Taking advantage of the software's operability, display the blade separately, select all mesh nodes, adjust the Feature Angle (generally 5°-10° in complex curved surfaces) and then invert the selection of the flange part. Finally, thicken the shell and display it in the All Other panel of Shell Options.

[0017] Step 5

[0018] Based on the nucleation location, simulations were conducted using the methods of point-based heat preservation and heat dissipation with crystal guides and variable mold shell thickness to study the temperature field changes at the abrupt change in cross-sectional dimensions before and after the simulation.

[0019] The beneficial effects of this invention are: it avoids the traditional method of adding crystal guides to the edge plate, which is still based on trial and error and relies on experience. It adopts a refined simulation method and controls the temperature field at the point of abrupt change in cross-sectional size by using fixed-point heat dissipation and fixed-point heat preservation based on the nucleation position of impurity crystals in the simulation. This improves the overheating state of the thermal barrier zone and plays a certain role in suppressing impurity crystals and optimizing grain orientation.

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0021] Figure 1 This is a flowchart of the present invention.

[0022] Figure 2 This is a diagram of heteromorphic crystal nucleation in the blade rim.

[0023] Figure 3 This is a solidification cloud map of the blade edge plate over 5200 steps and the final grain orientation map.

[0024] Figure 4 This is a structural diagram showing the position and dimensions of the blade's lead-agent strips.

[0025] Figure 5 Non-uniform mold shell thickness setting diagram

[0026] Figure 6 This is a cloud map showing the solidification time of the corners after setting the non-uniform mold shell thickness.

[0027] Figure 7 This is the solidification contour map and final grain orientation map after adding the seed crystal segment and the thickness of the modified shell, spanning 5200 steps. Detailed Implementation

[0028] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings: These embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and processes are given. However, the scope of protection of the present invention is not limited to the following embodiments.

[0029] Taking a certain type of turbine blade as an example, the specific implementation process of this invention is as follows: Figure 1 As shown:

[0030] Step 1

[0031] The temperature field of a certain type of blade after directional solidification was obtained by Procast simulation, and the temperature field was imported into the CAFE module of Procast software.

[0032] The nucleation sites of the rim plate heterocrystals were determined, and the nucleation sites of the rim plate were approximately at corners A and B.

[0033] Step 2

[0034] In Visual Viewer, slice the blade edge plate, such as... Figure 3 As shown on the left, the solidification process is analyzed to obtain the solidification sequence and related patterns at the edge corners of the rim plate. Details are as follows:

[0035] [1] The rim plate first solidifies from point B, then progresses towards A along the edge, and finally towards the blade body. Based on the grain misalignment diagram, the large wall thickness and heat content of the casting in the transition zone between the blade body and the rim plate, coupled with the significant thickening of the mold shell and the deterioration of heat dissipation conditions, create a thermal barrier zone. This zone hinders the lateral expansion of the blade body's single crystals towards the rim plate, ultimately solidifying in the thermal barrier zone. Figure 3 As shown on the right, macroscopic defects are formed.

[0036] [2] According to the analysis results of step 1, the edge plate also nucleates first near point B, which corresponds to the solidification process cloud map.

[0037] Step 3

[0038] Combining the nucleation location of heterocrystals on the rim plate and the solidification sequence at the rim plate edges, such as Figure 4 As shown, seed bars are added at specific points in the blade CAD model, and the height of the lower end of the seed bars in the seed initiation zone is increased. The cross-section is designed to be rectangular or circular; in this design, it is square with a cross-sectional area of ​​10 mm². 2 .

[0039] Step 4

[0040] In Visual Mesh, select 2D shelling, as shown below. Figure 5 As shown, the thickness of the shroud shell is increased, while the thickness of the shroud shell in the transition zone (thermal barrier zone) between the blade and the shroud is decreased. The specific steps are as follows:

[0041] [1] The overall thickness of the blade shell was set to 6mm.

[0042] [2] The thermal barrier zone shell is thinned. Due to the operability of the software, first locate the blade, add a patch, and use the red box button in Select Contiguous to select the required area. Based on experience, the thickness of the transition area between the blade and the edge plate is reduced to 4.5mm.

[0043] [3] The edges and corners of the upper and lower surfaces of the flange are thickened in sequence according to 8, 9, 10, and 11 mm. Display the blade separately, select all visible mesh nodes, adjust the Feature Angle (generally 5°-10° in complex curved surfaces), cancel the symmetry plane, select the upper and lower shell-less surfaces and the thickened area of ​​the flange mold shell, and finally display the thickened mold shell in the All Other panel of Shell Options. Set the thickness in sequence according to 8, 9, 10, and 11 mm, and all other should be the largest among all patch values;

[0044] [4] Based on the actual shell, the thickness of the mold shell in the green area (where the supercooling is greater) was increased sequentially to 8mm, 9mm, 10mm, and 11mm. The solidification time cloud map was compared, as shown below. Figure 6 As shown, it can be observed that as the regional mold shell thickness increases, the green area first decreases and then increases, and at 10mm there is basically no green area. Therefore, the thickness of the edge plate mold shell is 10mm.

[0045] Step 5

[0046] Based on the above method of using seeding strips and variable shell thickness for point-based heat preservation and heat dissipation according to the nucleation location, the simulation was conducted to study the temperature field and grain orientation changes at the abrupt change in cross-sectional dimensions before and after the simulation.

[0047] According to the principle of impurity crystal formation: if the nucleation supercooling has been reached at the corner of the edge plate before the original dendrite grows from the leaf blade to the edge plate, impurities will be generated at the edge plate. Figure 3 As shown on the right.

[0048] From the simulation results, such as Figure 7 As shown, the comparison is performed at 5200 steps. Figure 3 (Left) and Figure 7 (Left) Solidification cloud diagram of the edge plate shows that, within the same number of steps, the solidification rate of the edge plate corners is slowed down.

[0049] From the simulation results, such as Figure 7 As shown, comparison Figure 3 (Right) and Figure 7 (Right) It was found that the main grain orientation was changed from 20° to 10°, which optimized the grain orientation.

[0050] In summary, this method increases the insulation time at the edge corners of the rim plate, reduces the solidification and cooling rate at the edge corners, makes the temperature field at the abrupt change in the cross-sectional dimensions of the rim plate more stable, reduces the impact of the thermal barrier zone on grain growth, and buys more time for the growth of the main grains in the blade, ultimately yielding the desired result. Figure 7 The grain orientation diagram shown on the right demonstrates the effectiveness of this method.

Claims

1. A simulation-based composite controlled crystal pulling method for single-crystal turbine blades, characterized in that, Includes the following steps: Step 1: Obtain the blade temperature field after directional solidification using Procast simulation, import the temperature field into the CAFE module of Procast software, and determine the nucleation positions of the edge plate heterocrystals, which are corner A and corner B. Step 2: In Visual Viewer, slice the blade edge plate, analyze the solidification process, and determine the solidification sequence of the edge plate corners as follows: the edge plate first solidifies from point B, then moves towards point A along the edge corner, and finally moves towards the blade body. It is also determined that the transition zone between the blade body and the edge plate is the last to solidify and form the thermal barrier zone. Step 3: Based on the nucleation location of the heterocrystals on the rim plate and the solidification sequence of the rim plate edges, add crystal-guiding strips at fixed points in the blade CAD model, and increase the height of the lower end of the crystal-guiding strips in the crystal-guiding section of the blade body. The crystal-guiding strips have a square cross-section and a cross-sectional area of ​​10 mm². Step 4: In Visual Mesh, select 2D Shelling, set the overall shell thickness of the blade to 6mm, add a Shell patch in the transition area between the blade and the fin plate, reduce the shell thickness in the thermal barrier area to 4.5mm, and increase the shell thickness at the corners of the upper and lower surfaces of the fin plate sequentially to 8mm, 9mm, 10mm, and 11mm, comparing the solidification time cloud map. When the area with large supercooling basically disappears, determine the shell thickness at the corners of the fin plate to be 10mm. The thickening of the corners of the upper and lower surfaces of the fin plate includes: displaying the blade separately, selecting all visible mesh nodes, adjusting the Feature Angle to 5°-10°, and unselecting the symmetry plane, the upper and lower shell-free surfaces, and the thickened area of ​​the fin plate shell, so that the thickened shell is displayed in the AllOther panel of Shell Options. Step 5: Perform simulation based on the seeding strips in Step 3 and the shell thickness in Step 4. Compare the solidification cloud diagrams of the edge plate before and after the simulation with the final grain orientation to obtain the composite controlled seeding scheme.

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