A mold shell local thickness regulation method and system for directional solidification single crystal blade defect control

Abstract

The present application relates to the field of precision casting, and provides a shell local thickness regulation method and system for defect control of directional solidification single crystal blade. The method comprises the following steps: performing defect risk mapping on an original shell structure model to obtain a region to be regulated; performing directional solidification thermal state characterization on the region to be regulated under the original shell thickness condition to obtain solidification thermal state parameters; substituting the solidification thermal state parameters of a loose risk area into a Niyama criterion model to perform loose risk assessment, and calculating a thinning amount of the original shell thickness of the loose risk area according to a critical Niyama criterion value; extracting a main crystal temperature difference of a supercooled heterogeneous crystal risk area from the solidification thermal state parameters, and calculating a thickening amount of the original shell thickness of the supercooled heterogeneous crystal risk area according to a maximum temperature difference of the heterogeneous crystal and critical nucleation supercooling degree of the alloy; and generating a shell local thickness distribution scheme. The present application improves the defect control capability and process stability of the directional solidification process.

Description

Technical Field

[0001] This invention belongs to the field of precision casting technology, and in particular relates to a method and system for controlling the local thickness of the shell for defect control of directional solidification single crystal blades. Background Technology

[0002] Aero-engine and gas turbine blades operate under high temperature, high stress, and complex airflow erosion environments for extended periods, and their metallurgical quality directly impacts engine safety and service life. Advanced turbine blades are typically fabricated using nickel-based superalloy directional solidification or single-crystal solidification processes. By controlling the propulsion direction of the solid-liquid interface, temperature gradient, and solidification rate, dendrites are encouraged to grow along a predetermined crystal orientation, thereby eliminating transverse grain boundaries and improving the blade's creep resistance and thermal fatigue performance. During directional solidification, the ceramic shell not only shapes the molten metal but also serves as a crucial thermal resistance medium influencing local heat transfer conditions within the casting. Its thickness distribution significantly affects the uniformity of local temperature gradients, cooling rates, and solidification time.

[0003] In existing technologies, to control casting defects in directionally solidified single-crystal blades, overall process methods such as adjusting pouring temperature, shell preheating temperature, drawing rate, or external cooling conditions are typically used to intervene in the solidification process. However, these methods are difficult to implement precise thermal resistance control for sensitive areas of local defects in the blades. Overall process adjustments to a certain local area often change the solidification state of other areas simultaneously, and may even induce new structural defects. Furthermore, existing technologies lack an engineering method that can quantitatively back-calculate the local target thickness of the shell based on local solidification thermal state parameters, resulting in insufficient targeted control capabilities for porosity defects and supercooled impurity defects. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of the invention is to provide a method and system for controlling the local thickness of the shell for the directionally solidified single crystal blade defect control.

[0005] This invention provides a method for controlling the local thickness of the shell for defect control in directionally solidified single-crystal blades, comprising: S1: Based on the three-dimensional model of the directionally solidified single crystal blade and historical defect distribution data, the original shell structure model is subjected to defect risk mapping to obtain the region to be controlled; the region to be controlled includes the loose risk region and the supercooled impurity risk region. S2: Characterize the solidification thermal state of the region to be controlled under the original shell thickness conditions to obtain solidification thermal state parameters of multiple regions to be controlled. S3: Substitute the solidification thermal state parameters of the loosening risk zone into the Niyama criterion model to assess the loosening risk and obtain the original Niyama criterion value; calculate the reduction amount of the original shell thickness corresponding to the loosening risk zone based on the ratio of the original Niyama criterion value to the critical Niyama criterion value to obtain the local thinning thickness. S4: Extract the solidification thermal state parameters of the supercooled impurity risk zone by extracting the impurity main crystal temperature difference to obtain the maximum impurity main crystal temperature difference; calculate the increase in the original shell thickness corresponding to the supercooled impurity risk zone based on the ratio of the maximum impurity main crystal temperature difference to the critical nucleation undercooling of the alloy to obtain the local increase in thickness. S5: Combine the local thinning thickness, the local thickening thickness, and the original shell thickness to generate a shell local thickness distribution scheme.

[0006] According to the present invention, a method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades, step S1 further includes: S11: Identify the location of defects in historical castings through defect detection methods to obtain data on the location of porosity defects and impurity defects; S12: Map the location data of the loose defects and the location data of the impurity crystals to the surface of the three-dimensional model of the directional solidified single crystal blade, and further map them to the surface of the original shell structure model to obtain the spatial distribution of the region to be controlled, characterized by spatial distribution.

[0007] According to the present invention, a method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades, step S2 further includes: S21: For the loose risk zone, at least one first feature point is selected in the loose risk zone, and the temperature-time curve of the first feature point and the temperature field distribution of the corresponding neighborhood along the solidification direction are obtained through directional solidification heat transfer simulation. S22: Extract the cooling rate from the temperature-time curve of the first feature point at the solidification feature moment to obtain the local cooling rate; extract the temperature gradient from the temperature field distribution along the local heat flow direction to obtain the local temperature gradient. S23: For the supercooled impurity risk zone, a second feature point is selected at the outer edge of the impurity defect zone, and a third feature point is selected at the inner side of the adjacent main crystal zone. Through directional solidification heat transfer simulation, the temperature-time curves of the second feature point and the temperature-time curves of the third feature point are obtained respectively.

[0008] According to the present invention, a method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades, step S3 further includes: S31: Using the local temperature gradient and the local cooling rate, calculate according to the Niyama criterion relationship to obtain the original Niyama criterion value; S32: Compare the original Niyama criterion value with the critical Niyama criterion value calibrated based on historical alloy casting data; when the original Niyama criterion value is less than the critical Niyama criterion value, use the square ratio of the original Niyama criterion value to the critical Niyama criterion value as the thermal resistance reduction coefficient to calculate the reduction of the original shell thickness and obtain the local thinning thickness; when the original Niyama criterion value is greater than or equal to the critical Niyama criterion value, it is determined that the porosity risk area does not need to be locally thinned.

[0009] According to the present invention, a method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades, step S32 further includes: The local thinning thickness is compared with the preset minimum allowable thickness; when the local thinning thickness is less than the minimum allowable thickness, the minimum allowable thickness is used as the actual design thickness of the loosening risk zone; when the local thinning thickness is greater than or equal to the minimum allowable thickness, the local thinning thickness is used as the actual design thickness of the loosening risk zone.

[0010] According to the present invention, a method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades, step S4 further includes: S41: Perform time-by-time difference calculation on the temperature-time curve of the second feature point and the temperature-time curve of the third feature point, and take the maximum difference during the solidification process to obtain the maximum temperature difference of the impurity main crystal. S42: Compare the maximum temperature difference of the main impurity crystal with the critical nucleation undercooling of the alloy; when the maximum temperature difference of the main impurity crystal is greater than the critical nucleation undercooling of the alloy, use the ratio of the maximum temperature difference of the main impurity crystal to the critical nucleation undercooling of the alloy as the thermal resistance amplification factor to amplify the original shell thickness and obtain the local thickening thickness; when the maximum temperature difference of the main impurity crystal is less than or equal to the critical nucleation undercooling of the alloy, it is determined that the undercooled impurity risk area does not need to be locally thickened.

[0011] According to the present invention, a method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades, step S5 further includes: S51: Integrate and arrange the actual design thickness of the loose risk area, the local thickening thickness, and the original shell thickness of the non-controlled area, and set a thickness transition area between each thickness difference area to generate a shell local thickness distribution scheme. S52: When the local thinning area corresponding to the loose risk area is a continuous large-area thinning area, the continuous large-area thinning area is divided into multiple discrete thinning windows, and the original shell thickness area or thickness transition area is retained between two adjacent discrete thinning windows; the multiple discrete thinning windows are arranged in an array, strip, grid or along the extension direction of the loose risk area.

[0012] According to the present invention, a method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades, the method further includes the following step after S52: S53: After preparing a locally thickness-adjustable shell according to the local thickness distribution scheme, the shell thickness of the local thinning area, the local thickening area and the thickness transition area is measured to obtain the measured thickness of each area. S54: Compare the measured thickness with the design thickness corresponding to the local thickness distribution scheme of the shell. When the deviation exceeds the preset allowable range, perform local repair or local recoating on the local thickness control shell.

[0013] According to the present invention, a method for controlling the local thickness of the shell for defect control in directional solidification single crystal blades is provided. The preparation of the local thinning region includes: local placement of wax sheet for shielding, local mechanical polishing after shell preparation, and local sandblasting for thinning after shell preparation. The preparation of the local thickening region includes: local application of backing slurry, local application of shell layer of the same material system, and local addition of backing layer structure of the same material system. The preparation of both the local thinning region and the local thickening region is carried out without changing the original shell material system.

[0014] The present invention also provides a shell local thickness control system for defect control in directionally solidified single-crystal blades, for executing a shell local thickness control method for defect control in directionally solidified single-crystal blades as described in any of the above claims, comprising: Mapping module: used to perform defect risk mapping on the original shell structure model based on the three-dimensional model of the directionally solidified single crystal blade and historical defect distribution data, to obtain the region to be controlled; the region to be controlled includes the loose risk region and the supercooled impurity risk region; Characterization module: used to characterize the solidification thermal state of the region to be controlled under the original shell thickness conditions, and obtain solidification thermal state parameters of multiple regions to be controlled; The first assessment module is used to substitute the solidification thermal state parameters of the loosening risk zone into the Niyama criterion model to assess the loosening risk and obtain the original Niyama criterion value; based on the ratio of the original Niyama criterion value to the critical Niyama criterion value, the original shell thickness corresponding to the loosening risk zone is calculated to obtain the local thinning thickness. The second evaluation module is used to extract the temperature difference between the main crystal and the main crystal of the supercooled impurity crystal from the solidification thermal state parameters of the supercooled impurity crystal risk zone, and obtain the maximum temperature difference between the main crystal and the main crystal. Based on the ratio of the maximum temperature difference between the main crystal and the critical nucleation undercooling of the alloy, the module calculates the increase in the original shell thickness corresponding to the supercooled impurity crystal risk zone, and obtains the local increase in thickness. Output module: used to combine the local thinning thickness, the local thickening thickness and the original shell thickness to generate a local thickness distribution scheme for the shell.

[0015] This invention provides a method and system for controlling the local thickness of the shell for defect control in directional solidification single-crystal blades. By establishing a mechanism for identifying the controllable region based on historical defect distribution data and a three-dimensional model coordinate mapping, the spatial positioning of the porosity risk zone and the undercooled impurity risk zone becomes more precise, avoiding the ambiguity in the control zone definition caused by traditional empirical judgment. Secondly, this invention introduces a method for calculating the local thinning thickness for the porosity risk zone, using the square ratio of the original Niyama criterion value to the critical Niyama criterion value as the thermal resistance reduction coefficient. This directly links the thinning amount to the local temperature gradient, cooling rate, and porosity formation criterion, overcoming the limitations of traditionally relying on empirical layers to determine the shell thickness. The resulting local thinning thickness has a clear physical basis and verifiability. Simultaneously, a minimum allowable thickness constraint mechanism is introduced, comprehensively determining the lower limit of the thickness by combining process factors such as the area of ​​the region to be thinned, the local radius of curvature, and the hydrostatic pressure height of the molten metal. This effectively prevents the risk of insufficient local shell strength, cracking, or steel leakage while ensuring defect control. For the risk zone of supercooled impurities, this invention characterizes the maximum temperature difference between the impurity and the main crystal by calculating the time-by-time difference of the temperature-time curves of the outer and inner feature points. The ratio of this difference to the critical undercooling degree of alloy nucleation is used as the thermal resistance amplification factor to calculate the local thickening thickness, making the thickening amount directly correspond to the driving force of undercooled nucleation, with clear physical meaning. For continuous large-area thinning regions, this invention further introduces a discrete thinning window division mechanism, retaining the original thickness area or transition area through array-like, strip-like, or grid-like interval arrangements. This significantly reduces the shell structure risk caused by large-area thinning while maintaining defect control. Furthermore, this invention introduces a closed-loop mechanism for thickness detection and deviation comparison after fabrication, effectively ensuring the implementation quality of local thickness control. The overall method possesses strong engineering feasibility and process stability. Attached Figure Description

[0016] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. It is obvious that the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings.

[0017] Figure 1 This is a schematic flowchart of a method for controlling the local thickness of a shell for defect control in directional solidification single crystal blades, provided by an embodiment of the present invention. Figure 2 This is a schematic diagram of a shell local thickness control system for defect control in directional solidification single crystal blades, provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the temperature-time curve of feature point P and a point 84 mm above it, provided in an embodiment of the present invention. Figure 4 A schematic diagram comparing the temperature-time curves and the maximum temperature difference during solidification between the outer edge of the risk zone of supercooled impurities and the inner edge of the adjacent main crystal, as provided in an embodiment of the present invention. Figure 5 A schematic diagram of the local thickness distribution of the shell in the original thickness region and the locally thickened region provided in an embodiment of the present invention; Figure 6 This is a schematic diagram comparing the loose crown defects before and after improvement by the shell thinning method of the present invention, provided as an embodiment of the present invention. Detailed Implementation

[0018] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0019] Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts disclosed in this invention.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "installed," "connected," and "linked" should be interpreted broadly; for example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0021] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of methods and systems consistent with some aspects of the invention as detailed in the appended claims.

[0022] The embodiments of the present invention are described below with reference to the figures.

[0023] like Figure 1 As shown, the present invention provides a method for controlling the local thickness of the shell for defect control in directionally solidified single-crystal blades, comprising: S1: Based on the three-dimensional model of the directional solidified single crystal blade and historical defect distribution data, the original shell structure model is subjected to defect risk mapping to obtain the region to be controlled; the region to be controlled includes the loose risk region and the supercooled impurity risk region.

[0024] Before executing step S1, the present invention first defines two input objects: a three-dimensional model of a directionally solidified single-crystal blade and a primitive shell structure model. The three-dimensional model is a digital representation of the blade's geometry, including the spatial coordinate information of various parts such as the blade body, crown, edge plate, and tenon. The primitive shell structure model is a digital geometric model of a ceramic shell that matches the three-dimensional model of the blade. The two have a corresponding enclosing relationship in space.

[0025] Step S1 further includes: S11: Identify the location of defects in historical castings through defect detection methods to obtain data on the location of porosity defects and impurity defects.

[0026] In step S11, the present invention conducts defect detection on historical castings that have already been produced. The detection methods include at least one of X-ray inspection, industrial CT inspection, fluorescence inspection, metallographic inspection, or casting dissection inspection. Industrial CT inspection involves performing X-ray tomography on the casting to reconstruct a three-dimensional density distribution image of the casting's interior, identifying areas of abnormal density, i.e., the locations of porosity defects. Fluorescence inspection involves applying a fluorescent penetrating liquid to the casting surface, revealing surface and near-surface cracks or defects under ultraviolet light. Metallographic inspection involves grinding, etching, and microscopic observation of the casting cross-section to directly identify the grain morphology and distribution location of heterogeneous defects. After the above inspections are completed, the present invention summarizes the inspection results of each historical casting, extracting data on the location of porosity defects and heterogeneous defects, with each set of data represented as a set of three-dimensional spatial coordinates of the defects in the casting's solid coordinate system.

[0027] S12: Map the location data of the loose defects and the location data of the impurity crystals to the surface of the three-dimensional model of the directional solidified single crystal blade, and further map them to the surface of the original shell structure model to obtain the spatial distribution of the region to be controlled, characterized by spatial distribution.

[0028] In step S12, the present invention maps the location data of loose defects and the location data of impurity defects obtained in step S11 to the surface of the three-dimensional model of the blade. Specifically, based on the rigid body transformation relationship (including translation vectors and rotation matrices) between the coordinate system of the historical casting entity and the coordinate system of the three-dimensional model of the blade, the spatial coordinates of the defect locations are transformed one by one to the coordinate system of the three-dimensional model of the blade, and the transformed coordinates are projected to the nearest surface point of the three-dimensional model of the blade to obtain the distribution position of the defects on the surface of the three-dimensional model of the blade. Since the three-dimensional model of the blade and the original shell structure model have a fixed enveloping correspondence in space, the present invention further projects the above-mentioned defect positions on the blade surface outward along the shell normal direction to the inner surface of the original shell structure model, completing the secondary coordinate mapping from the blade surface to the shell surface, and finally obtaining the spatial distribution of loose defects and impurity defects on the surface of the original shell structure model.

[0029] After obtaining the spatial distribution of the original shell structure model surface, this invention uses this spatial distribution as a basis to delineate the areas on the shell surface where loose defects are concentrated as loose risk zones, and the areas where heteromorphic defects are concentrated as supercooled heteromorphic risk zones. Together, these two areas constitute the regions to be controlled. Spatially, the regions to be controlled correspond to at least one of the following: thick blade section, sill section, crown section, tenon section, abrupt section, transition section between blade and sill, and transition section between blade and crown.

[0030] S2: The solidification thermal state of the region to be controlled is characterized under the original shell thickness conditions to obtain solidification thermal state parameters of multiple regions to be controlled.

[0031] In step S2, the present invention uses the original shell thickness as a boundary condition to simulate the heat transfer of the directional solidification process, and extracts the solidification thermal state parameters of each region to be controlled from the simulation results. The input data for the directional solidification heat transfer simulation include: casting alloy thermophysical parameters (specific heat capacity, thermal conductivity, density as a function of temperature), pouring temperature, shell preheating temperature, drawing rate, furnace temperature field distribution, original shell thickness, shell equivalent thermal conductivity, and module arrangement. The above parameters together constitute the complete boundary conditions for the heat transfer simulation. Under these conditions, the entire directional solidification process is numerically solved to obtain the temperature field time series data of each position of the blade and shell throughout the entire solidification time history.

[0032] Step S2 further includes: S21: For the loose risk zone, at least one first feature point is selected within the loose risk zone, and the temperature-time curve of the first feature point and the temperature field distribution of the corresponding neighborhood along the solidification direction are obtained through directional solidification heat transfer simulation.

[0033] In step S21, for the loosening risk zone, the present invention selects at least one first feature point within this zone. The selection principle for the first feature point is the location with the most concentrated historical defect distribution, the most complex geometry, or the largest cross-sectional thickness. Subsequently, the present invention extracts the complete data sequence of the temperature change of the first feature point over time during the entire solidification process from the temperature field time series data of the heat transfer simulation, obtaining the temperature-time curve of the first feature point; at the same time, it extracts the temperature value sequence of several sampling points along the solidification direction (i.e., the main heat flow direction) in the neighborhood of the first feature point at the same solidification moment, obtaining the temperature field distribution of that neighborhood.

[0034] In step S21, the reliability of the directional solidification heat transfer simulation depends on the accuracy of the heat transfer boundary conditions. Therefore, this invention also uses actual temperature measurement data to calibrate the simulation model. Specifically, this invention arranges thermocouple temperature measuring elements on the original shell or experimental shell corresponding to the first feature point and its neighborhood. During the directional solidification process, temperature-time data of each temperature measuring point are continuously collected to obtain the measured temperature-time curve.

[0035] Subsequently, the measured temperature-time curves were compared with the initial heat transfer simulation results at each moment. The difference between the simulated and measured values ​​at each temperature measurement point at each moment was calculated. This difference was used as the error signal to repeatedly adjust the heat transfer boundary condition parameters in the simulation model (including the radiation heat transfer coefficient between the shell and the furnace, and the convective heat transfer coefficient between the shell and the cooling plate) until the deviation between the simulated temperature-time curves and the measured temperature-time curves at each temperature measurement point converged to within the preset error tolerance throughout the entire solidification time process.

[0036] Finally, the heat transfer simulation was rerun with the calibrated heat transfer boundary conditions. The temperature-time curve of the first feature point and its neighborhood temperature field distribution were extracted from the simulation results for subsequent extraction of cooling rate and temperature gradient.

[0037] S22: Extract the cooling rate from the temperature-time curve of the first feature point at the solidification feature moment to obtain the local cooling rate; extract the temperature gradient from the temperature field distribution along the local heat flow direction to obtain the local temperature gradient.

[0038] In step S22, the present invention extracts the cooling rate at the solidification characteristic moment from the temperature-time curve. Further, the solidification characteristic moment is determined based on the time interval during which the first characteristic point is in the solid-liquid two-phase region, i.e., the characteristic moment within the time interval between the alloy liquidus and solidus lines. At this moment, the present invention performs differential calculation on the temperature-time curve, dividing the temperature difference between adjacent moments by the corresponding time interval to obtain the instantaneous cooling rate at that moment, i.e., the local cooling rate. Subsequently, the present invention performs spatial differential calculation on the temperature field distribution along the solidification direction in the neighborhood of the first characteristic point, dividing the temperature difference between two adjacent sampling points along the solidification direction by the spatial distance between them to obtain the temperature gradient along that direction, i.e., the local temperature gradient.

[0039] In step S22, the expression for the local cooling rate of the present invention is:

[0040] in, The local cooling rate at the first feature point under the original shell thickness condition; Indicates time; The first feature point at time t The temperature at that time; This represents the characteristic moment when the first characteristic point is in the solidification stage.

[0041] The expression for the local temperature gradient is:

[0042] in, The local temperature gradient at the first feature point under the original shell thickness condition; Let be the temperature field function in the neighborhood of the first feature point; The spatial coordinates of the local heat flow direction or the main solidification direction passing through the first feature point; This indicates the amount of temperature change along that direction. This represents the corresponding change in spatial distance, and the ratio of the two is the temperature gradient along the main solidification direction at the first feature point.

[0043] S23: For the supercooled impurity risk zone, a second feature point is selected at the outer edge of the impurity defect zone, and a third feature point is selected at the inner side of the adjacent main crystal zone. Through directional solidification heat transfer simulation, the temperature-time curves of the second feature point and the temperature-time curves of the third feature point are obtained respectively.

[0044] In step S23, for the supercooled impurity risk area, the present invention selects a second feature point at the outer edge of the impurity defect area and a third feature point inside the main crystal area adjacent to the impurity area. The second feature point is located at the outer edge where the shell heats up the most and the temperature drops the fastest, and the third feature point is located inside the main crystal area adjacent to the impurity defect distribution area, representing the solidification temperature level of the main crystal area.

[0045] Subsequently, this invention extracts the temperature-time curves of the second and third feature points from the time series data of the temperature field in the heat transfer simulation during the entire solidification process, respectively, to obtain the outer edge temperature-time curve and the inner side temperature-time curve, which are used for subsequent temperature difference calculation.

[0046] It should be noted that the principle underlying steps S3-S4 of this invention is: without changing the shell material system, the equivalent thermal conductivity of the shell is... Remaining constant, localized shell unit area thermal resistance With local shell thickness Proportional, expressed as:

[0047] in, This represents the thermal resistance per unit area of ​​a localized shell. For localized shell thickness; The equivalent thermal conductivity of the shell is given.

[0048] The ratio of localized shell thermal resistance before and after regulation is defined as the ratio of the thermal resistance per unit area after regulation to that before regulation, expressed as:

[0049] in, The thermal resistance ratio of the localized shell is dimensionless. This represents the thermal resistance per unit area of ​​the original shell. To adjust the localized thermal resistance per unit area of ​​the shell; This represents the original shell thickness. To adjust the local shell thickness after modification. When When the thermal resistance ratio is less than 1, a localized thinning zone is formed; when When the thermal resistance ratio is greater than 1, a localized thickening zone is formed. Based on this, the reduction and thickening amounts of the original shell thickness can be calculated in steps S3 and S4 of the present invention.

[0050] S3: Substitute the solidification thermal state parameters of the loosening risk zone into the Niyama criterion model to assess the loosening risk and obtain the original Niyama criterion value; calculate the reduction amount of the original shell thickness corresponding to the loosening risk zone based on the ratio of the original Niyama criterion value to the critical Niyama criterion value to obtain the local thinning thickness.

[0051] Step S3 further includes: S31: Using the local temperature gradient and the local cooling rate, calculate according to the Niyama criterion relationship to obtain the original Niyama criterion value.

[0052] In step S31, the present invention uses the local temperature gradient and local cooling rate obtained in step S22 as inputs, and performs calculations according to the Niyama criterion to obtain the original Niyama criterion value. The Niyama criterion is a widely used criterion for predicting porosity defects in the casting field. Its physical meaning is that during the solidification and feeding process, the larger the local temperature gradient and the smaller the cooling rate, the stronger the feeding driving force of the molten metal and the lower the risk of porosity defects; conversely, insufficient feeding increases the risk of porosity. The Niyama criterion value is calculated by dividing the local temperature gradient by the square root of the local cooling rate. The larger the value, the better the feeding conditions.

[0053] Specifically, the formula for calculating the original Niyama criterion value is as follows:

[0054] in, The original Niyama criterion value for the porous risk zone under the original shell thickness condition; For local temperature gradients; This represents the local cooling rate.

[0055] In addition, during directional solidification, when the pulling rate When the local cooling rate remains constant and the local solidification front movement velocity is approximately stable, It can be approximated as a local temperature gradient. With pull-out speed The product of, that is This invention substitutes this relationship into the Niyama criterion calculation formula, and the Niyama criterion value can be transformed into:

[0056] in, This is the Niyama criterion value; For local temperature gradients; This represents the directional solidification pulling rate. Therefore, it can be deduced that when the pulling rate... When kept constant, the Niyama criterion value is proportional to the square root of the local temperature gradient.

[0057] Furthermore, under the condition that the shell material system and equivalent thermal conductivity remain unchanged, the local temperature gradient is approximately inversely proportional to the local thermal resistance per unit area of ​​the shell, that is:

[0058] in, To regulate the local temperature gradient; This represents the original local temperature gradient. Therefore, the Niyama criterion values ​​before and after adjustment satisfy:

[0059] Niyama Criterion Value After Seasonal Adjustment Reaching the critical Niyama criterion value Then, squaring both sides of the above equation and rearranging, we obtain the target shell thickness after local thinning:

[0060] in, This refers to the thickness of the shell after thinning. This represents the original shell thickness. The original Niyama criterion value; This is the critical Niyama criterion value.

[0061] S32: Compare the original Niyama criterion value with the critical Niyama criterion value calibrated based on historical alloy casting data; when the original Niyama criterion value is less than the critical Niyama criterion value, use the square ratio of the original Niyama criterion value to the critical Niyama criterion value as the thermal resistance reduction coefficient to calculate the reduction of the original shell thickness and obtain the local thinning thickness; when the original Niyama criterion value is greater than or equal to the critical Niyama criterion value, it is determined that the porosity risk area does not need to be locally thinned.

[0062] In step S32, the present invention compares the original Niyama criterion value obtained in step S31 with the critical Niyama criterion value. The critical Niyama criterion value is determined by the historical casting data and experimental calibration results of the alloy, and represents the minimum Niyama criterion value required for the alloy to avoid porosity defects under specific casting process conditions.

[0063] When the original Niyama criterion value is less than the critical Niyama criterion value, it indicates that the current porosity risk area has insufficient feeding conditions under the original shell thickness. This invention uses the ratio of the square of the original Niyama criterion value to the critical Niyama criterion value as the thermal resistance reduction coefficient. This coefficient is multiplied by the original shell thickness to obtain the local thinning thickness. When the original Niyama criterion value is greater than or equal to the critical Niyama criterion value, it is determined that the porosity risk area does not need to be locally thinned.

[0064] Step S32 further includes: comparing the local thinning thickness with a preset minimum allowable thickness; when the local thinning thickness is less than the minimum allowable thickness, using the minimum allowable thickness as the actual design thickness of the loosening risk area; when the local thinning thickness is greater than or equal to the minimum allowable thickness, using the local thinning thickness as the actual design thickness of the loosening risk area.

[0065] After calculating the local thinning thickness, this invention further compares it with a preset minimum allowable thickness. The minimum allowable thickness is determined based on at least one of the following: the lower limit allowed by the shell-making process, the area of ​​the region to be thinned, the local radius of curvature of the region to be thinned, and the hydrostatic height of the molten metal, and is not less than 50% to 60% of the original shell thickness. When the local thinning thickness is less than the minimum allowable thickness, the minimum allowable thickness is used as the actual design thickness of the porosity risk area; when the local thinning thickness is not less than the minimum allowable thickness, the local thinning thickness is used as the actual design thickness of the porosity risk area, thereby completing the final determination of the shell thickness of the porosity risk area.

[0066] S4: Extract the solidification thermal state parameters of the supercooled heterocrystal risk zone from the heterocrystal main crystal temperature difference to obtain the maximum heterocrystal main crystal temperature difference; calculate the increase in thickness of the original shell corresponding to the supercooled heterocrystal risk zone based on the ratio of the maximum heterocrystal main crystal temperature difference to the critical nucleation undercooling of the alloy to obtain the local increase in thickness.

[0067] The input data in step S4 are the temperature-time curves of the second feature point and the third feature point extracted in step S23. The second feature point is located at the outer edge of the impurity crystal defect region. This position is directly exposed to the heat dissipation environment outside the shell, and the cooling rate is relatively fast, resulting in a relatively low temperature level. The third feature point is located inside the main crystal region adjacent to the impurity crystal defect region. This position is covered and insulated by the shell as a whole, resulting in a longer heat dissipation path and a relatively high temperature level.

[0068] Step S4 further includes: S41: Perform time-by-time difference calculation on the temperature-time curve of the second feature point and the temperature-time curve of the third feature point, and take the maximum difference during the solidification process to obtain the maximum temperature difference of the impurity main crystal.

[0069] In step S41, the present invention performs time-by-time difference calculation on the two input temperature-time curves. Specifically, at each discrete moment in the solidification process, the temperature value of the third characteristic point is subtracted from the temperature value of the second characteristic point to obtain the impurity-main crystal temperature difference at that moment. Then, the difference data for all moments throughout the entire solidification time process are iterated, and the maximum value is taken to obtain the maximum impurity-main crystal temperature difference. This maximum temperature difference characterizes the degree of supercooling corresponding to the moment when the temperature difference between the outer edge region and the main crystal region is most significant during solidification, and is a core quantitative indicator for determining whether there is a risk of supercooled nucleation in the outer edge region.

[0070] Specifically, the formula for calculating the maximum temperature difference between the impurity crystal and the host crystal is:

[0071] in, The maximum temperature difference between impurities and main crystals during solidification under the original shell thickness condition; For the second feature point (outer edge point) at time... The temperature at that time; For the third feature point (inner point) at time... The temperature at that time.

[0072] After calculation, the maximum value of the difference at all times during the entire solidification time process is taken to obtain the maximum temperature difference between the impurity crystal and the main crystal.

[0073] Under the condition that the shell material system and equivalent thermal conductivity remain unchanged, the local shell thermal resistance is proportional to the shell thickness. After thickening, the heat dissipation in the outer edge region weakens, and the temperature difference between the impurity crystal and the main crystal decreases with the increase of local thermal resistance. Therefore, after calculating the maximum temperature difference between the impurity crystal and the main crystal, this invention further reduces the temperature difference between the impurity crystal and the main crystal to the critical nucleation undercooling of the alloy. To control the target, a proportional relationship is established between the shell thickness scaling ratio and the temperature difference control target:

[0074] The target shell thickness after local thickening is obtained:

[0075] in, The target shell thickness after local thickening; This represents the original shell thickness. The maximum temperature difference between the impurity crystal and the main crystal under the original shell thickness condition; This represents the critical nucleation undercooling of the alloy.

[0076] S42: Compare the maximum temperature difference of the main impurity crystal with the critical nucleation undercooling of the alloy; when the maximum temperature difference of the main impurity crystal is greater than the critical nucleation undercooling of the alloy, use the ratio of the maximum temperature difference of the main impurity crystal to the critical nucleation undercooling of the alloy as the thermal resistance amplification factor to amplify the original shell thickness and obtain the local thickening thickness; when the maximum temperature difference of the main impurity crystal is less than or equal to the critical nucleation undercooling of the alloy, it is determined that the undercooled impurity risk area does not need to be locally thickened.

[0077] In step S42, the present invention compares the maximum temperature difference between the impurity crystal and the main crystal obtained in step S41 with the critical nucleation undercooling of the alloy. The critical nucleation undercooling of the alloy refers to the minimum undercooling temperature difference required for heterogeneous nucleation of the alloy during solidification. It is obtained by calibration using nucleation undercooling tests and historical casting data of the alloy, and is input as a fixed value. When the maximum temperature difference between the impurity crystal and the main crystal is greater than the critical nucleation undercooling of the alloy, it indicates that the temperature of the outer edge region during solidification is lower than that of the main crystal region to a level sufficient to trigger nucleation. The present invention divides the maximum temperature difference between the impurity crystal and the main crystal by the critical nucleation undercooling of the alloy to obtain a thermal resistance amplification factor. Then, this thermal resistance amplification factor is multiplied by the original shell thickness to obtain the local thickening thickness. When the maximum temperature difference between the impurity crystal and the main crystal is less than or equal to the critical nucleation undercooling of the alloy, it is determined that the undercooled impurity risk area does not meet the undercooling nucleation conditions under the original shell thickness, and no local thickening is required.

[0078] S5: Combine the local thinning thickness, the local thickening thickness, and the original shell thickness to generate a shell local thickness distribution scheme.

[0079] Step S5 further includes: S51: Integrate and arrange the actual design thickness of the loose risk zone, the local thickening thickness, and the original shell thickness of the non-controlled area, and set a thickness transition zone between each thickness difference zone to generate a shell local thickness distribution scheme.

[0080] In step S51, the present invention integrates and arranges the actual designed thickness of the loose risk zone determined in step S32, the local thickening thickness obtained in step S42, and the original shell thickness of the non-controlled area to form a complete thickness distribution data table on the surface of the shell structure model, wherein each region corresponds to a specific target thickness value. When there are adjacent areas of local thinning and non-controlled areas, local thickening and non-controlled areas, and local thinning and local thickening areas, the present invention sets a thickness transition zone between each thickness difference zone. The thickness value of the thickness transition zone is determined by linear interpolation of the design thicknesses on both adjacent sides, gradually changing along the transition direction to avoid abrupt changes in the shell thickness, thereby generating a complete local thickness distribution scheme for the shell.

[0081] S52: When the local thinning area corresponding to the loose risk area is a continuous large-area thinning area, the continuous large-area thinning area is divided into multiple discrete thinning windows, and the original shell thickness area or thickness transition area is retained between two adjacent discrete thinning windows; the multiple discrete thinning windows are arranged in an array, strip, grid or along the extension direction of the loose risk area.

[0082] In step S52, the present invention determines the area of ​​the local thinning area corresponding to the loosening risk area. When the continuous area of ​​the local thinning area exceeds a preset area threshold (i.e., the threshold for determining a large area thinning area, which the present invention sets at 4 cm), the local thinning area is determined. 2 In this invention, instead of uniformly thinning the entire area, the region is divided into multiple discrete thinning windows. The shell thickness of each discrete thinning window is the actual design thickness determined in step S32. A region of original shell thickness or a thickness transition region with a width not less than a preset value is retained between two adjacent discrete thinning windows. The planar arrangement of the multiple discrete thinning windows is selected according to the geometry of the loosening risk area, including array-like, strip-like, grid-like, or spaced-out arrangements along the extension direction of the loosening risk area. These arrangement schemes are also incorporated into the local shell thickness distribution scheme.

[0083] The process after step S52 also includes: S53: After preparing a locally thickness-adjustable shell according to the local thickness distribution scheme, the shell thickness of the locally thinned area, the locally thickened area and the thickness transition area is measured to obtain the actual thickness of each area.

[0084] In step S53, after preparing the shell with local thickness control according to the local thickness distribution scheme, the present invention performs shell thickness detection on the local thinning area, local thickening area, and thickness transition area respectively. The detection methods include at least one of industrial CT detection, ultrasonic thickness measurement, or three-dimensional scanning thickness measurement. Industrial CT detection directly reads the wall thickness value at each location by reconstructing a three-dimensional image of the shell cross-section; ultrasonic thickness measurement calculates the local thickness using the product of the propagation time and sound velocity of ultrasonic waves in the shell material; three-dimensional scanning thickness measurement obtains the measured thickness value at each location by acquiring three-dimensional point clouds of the inner and outer surfaces of the shell, aligning the point clouds of the inner and outer surfaces, and calculating the normal distance point by point. The above detection results are output in the form of measured thickness data for each region.

[0085] S54: Compare the measured thickness with the design thickness corresponding to the local thickness distribution scheme of the shell. When the deviation exceeds the preset allowable range, perform local repair or local recoating on the local thickness control shell.

[0086] In step S54, the present invention calculates the difference between the measured thickness of each region obtained in step S53 and the designed thickness at the corresponding position in the local thickness distribution scheme of the shell, point by point, to obtain the thickness deviation value at each position. Then, the thickness deviation value at each position is compared with a preset allowable deviation range, which is determined by the casting process requirements. For locally thinned areas where the thickness deviation exceeds the preset allowable range, the present invention performs local mechanical grinding or local sandblasting to remove excess material; for locally thickened areas where the thickness deviation exceeds the preset allowable range, the present invention performs local application of backing slurry or local application of a shell layer of the same material system to replenish insufficient material until the measured thickness falls within the allowable deviation range.

[0087] The preparation methods for the locally thinned areas include: locally placing wax sheets for masking, locally mechanically polishing after shell making, and locally sandblasting for thinning after shell making; the preparation methods for the locally thickened areas include: locally applying backing slurry, locally attaching a shell layer of the same material system, and locally adding a backing structure of the same material system; the preparation of both the locally thinned areas and the locally thickened areas is carried out without changing the original shell material system.

[0088] Regarding the preparation of locally thinned and locally thickened areas, the present invention provides methods for preparing locally thinned areas, including: placing wax sheets locally at corresponding positions during shell fabrication to shield these positions from being covered by slurry during shell fabrication, forming thinned areas after dewaxing; or performing localized mechanical grinding on corresponding positions after shell fabrication, controlling the grinding amount to achieve the target thinning thickness; or using localized sandblasting to remove material from corresponding positions, controlling the sandblasting time and intensity to achieve the target thickness. Methods for preparing locally thickened areas include: applying a backing slurry of the same material system as the original shell to corresponding positions after shell fabrication, forming a thickened layer after drying and curing; or locally attaching a pre-fabricated shell layer of the same material system to corresponding positions; or locally adding a backing structure of the same material system to corresponding positions, superimposing it to the target thickening thickness. The above thinning and thickening operations do not introduce any new shell material system, and the equivalent thermal conductivity of the shell remains consistent with the original shell.

[0089] like Figure 2 As shown, the present invention also provides a shell local thickness control system for defect control in directionally solidified single-crystal blades, used to execute a shell local thickness control method for defect control in directionally solidified single-crystal blades as described in any of the above claims, comprising: Mapping module 100: used to perform defect risk mapping on the original shell structure model based on the three-dimensional model of the directional solidified single crystal blade and historical defect distribution data to obtain the region to be controlled; the region to be controlled includes the loose risk region and the supercooled impurity risk region; Characterization module 200: used to characterize the solidification thermal state of the region to be controlled under the original shell thickness conditions, and obtain solidification thermal state parameters of multiple regions to be controlled; First assessment module 300: used to substitute the solidification heat state parameters of the loose risk zone into the Niyama criterion model to assess the loose risk and obtain the original Niyama criterion value; and to calculate the reduction amount of the original shell thickness corresponding to the loose risk zone based on the ratio of the original Niyama criterion value to the critical Niyama criterion value to obtain the local thinning thickness. The second evaluation module 400 is used to extract the temperature difference between the main crystal and the main crystal of the supercooled impurity crystal from the solidification thermal state parameters of the supercooled impurity crystal risk zone, and obtain the maximum temperature difference between the main crystal and the main crystal; based on the ratio of the maximum temperature difference between the main crystal and the critical nucleation undercooling of the alloy, the module calculates the increase in the original shell thickness corresponding to the supercooled impurity crystal risk zone, and obtains the local increase in thickness. Output module 500: used to combine the local thinning thickness, the local thickening thickness and the original shell thickness to generate a shell local thickness distribution scheme.

[0090] The following describes, in conjunction with specific embodiments, a method and system for controlling the local thickness of a shell for directional solidification single-crystal blade defects, provided by the present invention.

[0091] This embodiment uses a nickel-based superalloy directionally solidified single-crystal blade with a crown as an example. The blade includes a tenon, rim plate, blade body, crown, and a blade body-crown transition region. The original ceramic shell uses a conventional silica sol ceramic shell material system with a thickness of 8.00 mm (0.00800 μm) and an equivalent thermal conductivity of 0.80 W / (m·K). This embodiment does not change the shell material system but only adjusts the local shell thermal resistance through local thinning and thickening.

[0092] This embodiment follows the aforementioned method flow for controlling the local thickness of the blade shell provided by the present invention. First, the three-dimensional model of the single-crystal blade, the original shell structure model, and historical defect detection results are obtained. Historical detection results show a recurring porosity risk zone at the blade crown edge and an undercooled impurity risk zone at the edge plate. The locations of historical defects are mapped onto the surface of the blade's three-dimensional model and further mapped onto the surface of the original shell structure model, identifying two regions to be controlled: the first region to be controlled is the porosity risk zone at the blade crown edge, and the second region to be controlled is the undercooled impurity risk zone at the outer edge of the edge plate.

[0093] A characteristic point P was selected within the loosening risk zone. The temperature-time curve of characteristic point P and the temperature field distribution along the main solidification direction in its neighborhood were obtained through directional solidification heat transfer simulation calibrated with measured temperatures. Under the original shell thickness conditions, thermocouple channel 1 was placed at the loosening characteristic point P, and thermocouple channel 10 was placed at a distance of 84.0 mm along the solidification direction of point P. The calculation window for local solidification characteristics was selected as 1525–1545 s, with 1535 s being the characteristic calculation time. After smoothing the temperature measurement curves, the temperature in channel 1 decreased from 1301.35 ℃ to 1298.45 ℃ within 1530-1540 s, thus the local cooling rate at point P was calculated to be 0.290 K / s. At 1535 s, the temperature in channel 1 was 1299.90 ℃, and the temperature in channel 10 was 1358.70 ℃, with a temperature difference of 58.80 K between the two measurement points. Combined with the distance between the two points of 0.0840 m, the local temperature gradient along the solidification direction at point P was calculated to be 700 K / m; the local cooling rate was: The original Niyama criterion value is: 1299.9 K1 / 2·s1 / 2 / m; converted to traditional units, it is 13.0 (℃·s)1 / 2 / cm.

[0094] like Figure 3 As shown, Figure 3The figure shows the temperature-time curves for the first characteristic point P in the loosening risk zone and the temperature measurement point 84 mm above it in the solidification direction. The horizontal axis represents the time during the directional solidification process, in seconds, ranging from 1525.0 s to 1545.0 s, corresponding to the local solidification characteristic calculation window at the location of the first characteristic point P. The vertical axis represents the temperature, in degrees Celsius (°C). The two curves in the figure correspond to the temperature-time data for channel 1 (at the loosening defect characteristic point P) and channel 10 (84 mm above P in the solidification direction), respectively. The channel 1 curve is located at the bottom of the figure, and the temperature continuously decreases from approximately 1301°C to approximately 1298°C in the interval from 1525.0 s to 1545.0 s, reflecting the cooling process of the first characteristic point P during the solidification stage. The channel 10 curve is located at the top of the figure, and the temperature remains around 1358°C to 1360°C in the same time interval, with a smaller decrease, reflecting that the temperature measurement position above P is still at a relatively high temperature level during this period. The temperature difference between the two curves at the characteristic time of 1535 s is 58.80 K. Combined with the distance between the two temperature measurement points of 84.0 mm, the local temperature gradient along the solidification direction at the first characteristic point P is calculated to be 700 K / m. The temperature drop of the channel 1 curve in the interval from 1530 s to 1540 s is calculated using differential methods to obtain a local cooling rate of 0.290 K / s. These two values ​​are used as solidification thermal state parameters input into the Niyama criterion calculation to obtain the original Niyama criterion values.

[0095] In this embodiment, based on the historical casting data and experimental calibration results of the alloy, the critical Niyama criterion value is taken as 15.0 (℃·s)1 / 2 / cm. Since 13.0 < 15.0, it is determined that there is a risk of porosity in this area, and the corresponding shell area needs to be locally thinned to reduce the local shell thermal resistance.

[0096] According to the formula for calculating the shell thickness after local thinning according to the present invention, the calculated value is 6.01 mm. Therefore, the target shell thickness after local thinning in the porosity risk area is 6.01 mm, and the local thinning amount is 1.99 mm. Meanwhile, this embodiment sets the minimum allowable thickness of the local thinning area to 60% of the original shell thickness, i.e., 4.80 mm. Since 6.01 mm > 4.80 mm, 6.01 mm is used as the actual design thickness of this porosity risk area.

[0097] Further calculations were performed on the local thermal resistance per unit area before and after the adjustment. The original shell thermal resistance per unit area was 0.0100 m²·K / W; after thinning, the local shell thermal resistance per unit area was 0.00751 m²·K / W. The adjusted local thermal resistance ratio was 0.751, meaning the local shell thermal resistance was reduced to approximately 75.1% of the original thermal resistance.

[0098] According to the equivalent control relationship established by the formula of this invention, the Niyama criterion value after thinning can be estimated by the following formula: 1499.5K1 / 2·s1 / 2 / m. This value is close to the critical Niyama criterion value of 1500 K1 / 2·s1 / 2 / m, indicating that the local thinning thickness calculated according to this invention can make the Niyama criterion value of the loosening risk zone reach the critical requirement.

[0099] In the actual shell-making process, the outer surface of the shell corresponding to the porous risk area is set as a local thinning window, with a window size of 18 mm × 14 mm and an area of ​​252 mm². 2 That is, 2.52 cm 2 Less than 4 cm 2 Therefore, it does not belong to a continuous large-area thinning zone. The thickness of the back layer in this area is reduced by local mechanical grinding after shell making, so that the local shell thickness reaches 6.01mm, and a thickness transition zone with a width of 6mm is set at the edge of the thinning zone.

[0100] Point A was selected at the outer edge of the undercooled impurity risk zone on the outer edge of the ferrule, and point B was selected inside the adjacent main crystal region. Temperature-time curves for points A and B were extracted using directional solidification heat transfer simulation calibrated with measured data. The results showed that, under the original shell thickness conditions, at a solidification time t=742 s, the temperature at point A was 1352 ℃, and the temperature at point B was 1386 ℃. Therefore, the maximum temperature difference between the impurity and the main crystal was 34 K. In this embodiment, based on the nucleation undercooling test and historical casting results of the alloy, the critical nucleation undercooling degree of the alloy was taken as 25 K. Since 34 K > 25 K, it was determined that the local shell thermal resistance of this undercooled impurity risk zone needs to be increased, and the corresponding shell region needs to be locally thickened.

[0101] Figure 4This graph compares the temperature-time curves and the maximum temperature difference during the directional solidification process for the second characteristic point (outer edge point A) and the third characteristic point (inner edge point B) in the supercooled impurity risk zone. The horizontal axis represents the time during the directional solidification process, in seconds, ranging from 0 to 3500 seconds, covering the entire process from casting to solidification completion; the vertical axis represents the temperature, in degrees Celsius, ranging from approximately 950°C to 1400°C. The blue curve corresponds to the temperature-time curve of the second characteristic point (channel 7, outer edge supercooled zone), and the orange curve corresponds to the temperature-time curve of the third characteristic point (channel 9, main crystal region). In the early stages of solidification, the temperatures of the two curves are similar. As the solidification process progresses, the temperature decrease rate of the blue curve (outer edge point A) is significantly faster than that of the orange curve (inner edge point B), reflecting the faster heat dissipation and stronger cooling characteristics of the outer edge region. At t = 742 s, the time is marked by a vertical dashed line in the figure. At this time, the temperature of the outer edge point A is 1352℃ and the temperature of the inner point B is 1386℃. The temperature difference between the two reaches the maximum value of 34 K during the solidification process, which exceeds the critical nucleation supercooling of the alloy by 25 K. It is determined that there is a risk of supercooled impurity crystal nucleation in this area, and the corresponding shell area needs to be locally thickened.

[0102] Substituting the numerical values ​​into the formula for calculating the target shell thickness after local thickening according to the present invention, the result is 10.88 mm. Therefore, the target shell thickness after local thickening in the supercooled impurity risk region is 10.88 mm, and the local thickening amount is 2.88 mm. Further calculation shows that the thermal resistance per unit area of ​​the shell after local thickening is 0.01360 m²·K / W, and the local thermal resistance ratio is 1.36, meaning that the local shell thermal resistance in this region is increased to 136% of the original thermal resistance.

[0103] Figure 5 This is a schematic diagram of the cross-sectional thickness distribution of a locally thickness-adjustable shell, divided into... Figure 5 (a) and Figure 5 (b) Both images are presented as an overlay of the blade cross-section outline (pink line) and the inner and outer outlines of the shell (black line). The green dots in the images are marked as the reference points for measuring the shell thickness, and the numbers next to them are the shell thickness measurements at the corresponding positions, in mm. Figure 5 (a) shows the cross-sectional thickness distribution under the original shell thickness condition. The shell thicknesses at the two measurement reference points Q2-1-1 and Q2-1-2 are marked as +6.22 mm and +7.88 mm, respectively, reflecting the actual thickness level of the original shell in the outer edge area of ​​the flange. Both are close to the original shell design thickness of 8.00 mm, and the deviation is within the normal fluctuation range of the process. Figure 5(b) To illustrate the cross-sectional thickness distribution of the locally thickened shell after fabrication according to the local thickness control scheme of the present invention, the shell thickness at Q2-1-1 is increased to +10.82 mm, while the shell thickness at Q2-1-2 remains at +7.88 mm. This deviates from the target thickness increase of 10.88 mm by -0.06 mm, which is within the preset allowable deviation range of ±0.30 mm. The comparison between the two figures clearly demonstrates the difference in shell cross-sectional thickness between the locally thickened area and the non-controlled area, as well as the spatial implementation of the local thickness control scheme in actual shell fabrication.

[0104] Based on the proportional thermal resistance compensation relationship, the maximum temperature difference between the impurity and the main crystal after local thickening is estimated to be 25.0 K. That is, after local thickening, the maximum temperature difference between the impurity and the main crystal is reduced to near the critical nucleation undercooling of the alloy, which meets the requirements for controlling undercooled impurities.

[0105] In the actual shell-making process, a backing slurry of the same material system is applied locally to the shell area corresponding to the outer edge of the flange, and a backing structure of the same material system is added to make the shell thickness in this area reach 10.88 mm. The thickened area is set along the outer edge of the flange, with a length of 26 mm and a width of 7 mm, and a thickness transition zone with a width of 6 mm is set at the edge of the thickened area.

[0106] Based on the above calculations, a local thickness distribution scheme for the shell was generated: the shell thickness in the porous risk area was 6.01 mm, the shell thickness in the supercooled impurity risk area was 10.88 mm, and the remaining non-controlled areas maintained the original shell thickness of 8.00 mm. After preparing the locally thickness-controlled shell, the shell thickness was measured using industrial CT. The measurement results are shown in Table 1.

[0107] Table 1. Shell thickness detection results after local thickness control shell preparation in this embodiment.

[0108] In Table 1, all the above deviations are within the preset allowable range of ±0.30 mm. Therefore, this locally thickness-controlled shell was used for directional solidification casting. After casting, the blades underwent industrial CT inspection, fluorescence detection, and metallographic examination. The results showed that the total loose volume at the blade crown edge decreased from 0.42 mm under the original shell conditions. 3 Reduced to 0.06 mm 3 The maximum single porosity equivalent diameter was reduced from 0.54 mm to 0.18 mm; no continuous supercooled impurity bands were observed at the outer edge of the rim plate. This demonstrates that this embodiment, through a combination of local thinning and local thickening, can simultaneously reduce the risk of porosity defects and supercooled impurity defects.

[0109] Figure 6 The images show a comparison of industrial CT inspection results of crown porosity defects before and after applying the shell thinning method of this invention, divided into... Figure 6 (a) and Figure 6 (b) Two. Figure 6 (a) is an industrial CT three-dimensional reconstruction image of the blade crown area obtained by casting under the original shell thickness condition. The area marked with a bright color in the image is the distribution of detected porosity defects. It can be seen that there are multiple continuously distributed porosity defects at the edge of the blade crown. The defect volume is large, with the largest single porosity equivalent diameter reaching 0.54 mm. The defects are concentrated in strips along the edge of the blade crown, indicating that the feeding conditions in this area are insufficient under the original shell condition, and there are obvious shrinkage cavities during the solidification process. Figure 6 (b) is an industrial CT 3D reconstruction image of the blade crown region obtained after the shell region corresponding to the crown edge is thinned to 6.01 mm according to the local thinning method of the present invention. In the image, the highlighted areas are significantly reduced, the volume of porosity defects is greatly reduced, the maximum single porosity equivalent diameter is reduced to 0.18 mm, the previously continuously distributed porosity strips have disappeared, and only a few small and scattered residual porosity points remain. The comparison between the two images intuitively reflects the significant reduction in the risk of porosity defect formation after local thinning, which reduces the shell thermal resistance, increases the local temperature gradient, and makes the Niyama criterion value approach the critical value.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades, characterized in that, include: S1: Based on the three-dimensional model of the directional solidified single crystal blade and historical defect distribution data, defect risk mapping is performed on the original shell structure model to obtain the region to be controlled; The region to be regulated includes the loose risk region and the supercooled impurity crystal risk region; S2: Characterize the solidification thermal state of the region to be controlled under the original shell thickness conditions to obtain solidification thermal state parameters of multiple regions to be controlled. S3: Substitute the solidification thermal state parameters of the loosening risk zone into the Niyama criterion model to assess the loosening risk and obtain the original Niyama criterion value; calculate the reduction amount of the original shell thickness corresponding to the loosening risk zone based on the ratio of the original Niyama criterion value to the critical Niyama criterion value to obtain the local thinning thickness. S4: Extract the solidification thermal state parameters of the supercooled impurity risk zone by extracting the impurity main crystal temperature difference to obtain the maximum impurity main crystal temperature difference; calculate the increase in the original shell thickness corresponding to the supercooled impurity risk zone based on the ratio of the maximum impurity main crystal temperature difference to the critical nucleation undercooling of the alloy to obtain the local increase in thickness. S5: Combine the local thinning thickness, the local thickening thickness, and the original shell thickness to generate a shell local thickness distribution scheme.

2. The method for controlling the local thickness of the shell for defect control in directionally solidified single-crystal blades according to claim 1, characterized in that, Step S1 further includes: S11: Identify the location of defects in historical castings through defect detection methods to obtain data on the location of porosity defects and impurity defects; S12: Map the location data of the loose defects and the location data of the impurity crystals to the surface of the three-dimensional model of the directional solidified single crystal blade, and further map them to the surface of the original shell structure model to obtain the spatial distribution of the region to be controlled, characterized by spatial distribution.

3. The method for controlling the local thickness of the shell for defect control in directionally solidified single-crystal blades according to claim 1, characterized in that, Step S2 further includes: S21: For the loose risk zone, at least one first feature point is selected in the loose risk zone, and the temperature-time curve of the first feature point and the temperature field distribution of the corresponding neighborhood along the solidification direction are obtained through directional solidification heat transfer simulation. S22: Extract the cooling rate from the temperature-time curve of the first feature point at the solidification feature moment to obtain the local cooling rate; extract the temperature gradient from the temperature field distribution along the local heat flow direction to obtain the local temperature gradient. S23: For the supercooled impurity risk zone, a second feature point is selected at the outer edge of the impurity defect zone, and a third feature point is selected at the inner side of the adjacent main crystal zone. Through directional solidification heat transfer simulation, the temperature-time curves of the second feature point and the temperature-time curves of the third feature point are obtained respectively.

4. The method for controlling the local thickness of the shell for defect control in directionally solidified single-crystal blades according to claim 3, characterized in that, Step S3 further includes: S31: Using the local temperature gradient and the local cooling rate, calculate according to the Niyama criterion relationship to obtain the original Niyama criterion value; S32: Compare the original Niyama criterion value with the critical Niyama criterion value calibrated based on historical alloy casting data; when the original Niyama criterion value is less than the critical Niyama criterion value, use the square ratio of the original Niyama criterion value to the critical Niyama criterion value as the thermal resistance reduction coefficient to calculate the reduction of the original shell thickness and obtain the local thinning thickness; when the original Niyama criterion value is greater than or equal to the critical Niyama criterion value, it is determined that the porosity risk area does not need to be locally thinned.

5. A method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades according to claim 4, characterized in that, Step S32 also includes: The local thinning thickness is compared with the preset minimum allowable thickness; when the local thinning thickness is less than the minimum allowable thickness, the minimum allowable thickness is used as the actual design thickness of the loosening risk zone; when the local thinning thickness is greater than or equal to the minimum allowable thickness, the local thinning thickness is used as the actual design thickness of the loosening risk zone.

6. The method for controlling the local thickness of the shell for defect control in directionally solidified single-crystal blades according to claim 3, characterized in that, Step S4 further includes: S41: Perform time-by-time difference calculation on the temperature-time curve of the second feature point and the temperature-time curve of the third feature point, and take the maximum difference during the solidification process to obtain the maximum temperature difference of the impurity main crystal. S42: Compare the maximum temperature difference of the main impurity crystal with the critical nucleation undercooling of the alloy; when the maximum temperature difference of the main impurity crystal is greater than the critical nucleation undercooling of the alloy, use the ratio of the maximum temperature difference of the main impurity crystal to the critical nucleation undercooling of the alloy as the thermal resistance amplification factor to amplify the original shell thickness and obtain the local thickening thickness; when the maximum temperature difference of the main impurity crystal is less than or equal to the critical nucleation undercooling of the alloy, it is determined that the undercooled impurity risk area does not need to be locally thickened.

7. The method for controlling the local thickness of the shell for defect control in directionally solidified single-crystal blades according to claim 1, characterized in that, Step S5 further includes: S51: Integrate and arrange the actual design thickness of the loose risk area, the local thickening thickness, and the original shell thickness of the non-controlled area, and set a thickness transition area between each thickness difference area to generate a shell local thickness distribution scheme. S52: When the local thinning area corresponding to the loose risk area is a continuous large-area thinning area, the continuous large-area thinning area is divided into multiple discrete thinning windows, and the original shell thickness area or thickness transition area is retained between two adjacent discrete thinning windows; the multiple discrete thinning windows are arranged in an array, strip, grid or along the extension direction of the loose risk area.

8. The method for controlling the local thickness of the shell for defect control in directionally solidified single-crystal blades according to claim 7, characterized in that, Step S52 is followed by: S53: After preparing a locally thickness-adjustable shell according to the local thickness distribution scheme, the shell thickness of the local thinning area, the local thickening area and the thickness transition area is measured to obtain the measured thickness of each area. S54: Compare the measured thickness with the design thickness corresponding to the local thickness distribution scheme of the shell. When the deviation exceeds the preset allowable range, perform local repair or local recoating on the local thickness control shell.

9. A method for controlling the local thickness of a shell for defect control in directionally solidified single-crystal blades according to claim 8, characterized in that, The preparation methods for the local thinning area include: local placement of wax sheet for masking, local mechanical polishing after shell making, and local sandblasting for thinning after shell making; the preparation methods for the local thickening area include: local application of backing slurry, local application of shell layer of the same material system, and local addition of backing layer structure of the same material system; the preparation of the local thinning area and the local thickening area are carried out without changing the original shell material system.

10. A shell local thickness control system for defect control in directionally solidified single-crystal blades, used to execute the shell local thickness control method for defect control in directionally solidified single-crystal blades as described in any one of claims 1 to 9, characterized in that, include: Mapping module: Used to perform defect risk mapping on the original shell structure model based on the 3D model of the directionally solidified single crystal blade and historical defect distribution data, to obtain the region to be controlled; The region to be regulated includes the loose risk region and the supercooled impurity crystal risk region; Characterization module: used to characterize the solidification thermal state of the region to be controlled under the original shell thickness conditions, and obtain solidification thermal state parameters of multiple regions to be controlled; The first assessment module is used to substitute the solidification thermal state parameters of the loosening risk zone into the Niyama criterion model to assess the loosening risk and obtain the original Niyama criterion value; based on the ratio of the original Niyama criterion value to the critical Niyama criterion value, the original shell thickness corresponding to the loosening risk zone is calculated to obtain the local thinning thickness. The second evaluation module is used to extract the temperature difference between the main crystal and the main crystal of the supercooled impurity crystal from the solidification thermal state parameters of the supercooled impurity crystal risk zone, and obtain the maximum temperature difference between the main crystal and the main crystal. Based on the ratio between the maximum temperature difference between the main crystal and the critical nucleation undercooling of the alloy, the module calculates the increase in the original shell thickness corresponding to the supercooled impurity crystal risk zone, and obtains the local increase in thickness. Output module: used to combine the local thinning thickness, the local thickening thickness and the original shell thickness to generate a local thickness distribution scheme for the shell.

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