Defect Detection Method for Nickel-based Superalloy Components of Aeroengines

Abstract

The present invention provides a method for defect detection of nickel-based superalloy components of an aeroengine, comprising the following steps: performing numerical simulation of investment casting of nickel-based superalloy components; casting test pieces; sampling the parts of the test pieces with porosity defects; subjecting the samples to tensile testing at room temperature until fracture; performing morphology analysis on the fracture surfaces of the samples after tensile testing by means of a scanning electron microscope; using EDS and WDS to perform energy spectrum and spectrum analysis on at least 5 position points on the fracture surfaces of the samples after tensile testing; and determining whether there are defects of the double oxide film type in combination with the fracture surface morphology and the differences in the contents of O, Al, and Cr at the fracture surface and the non-fracture region. This method can effectively detect two-dimensional defects such as double oxide films that cannot be detected by conventional detection methods, and effectively avoid the fracture of aeroengine components and the structural failure of the entire engine caused by the existence of defects.

Description

Technical Field

[0001] The present invention relates to the technical field of aero-engine materials, and particularly to a method for detecting defects in nickel-based superalloy components of aero-engines. Background Art

[0002] The development of commercial aero-engines is a complex systems engineering integrating multiple disciplines and high-precision technologies, and has always been at the high point of high-tech. Only a few countries in the world can independently develop them. The realization of their performance indicators depends to a large extent on the improvement of material and manufacturing process technology levels. In addition, compared with military aero-engines, commercial aero-engines have the development requirements of long life, high reliability, low cost and airworthiness certification, which put higher requirements on the material technology and manufacturing process control of the engines.

[0003] Most reactive metals such as Al and Mg may cause microscopic defects such as double oxide films in the microstructure of castings due to surface fluctuations during alloy melting, pouring or flowing. Such defects are typical two-dimensional defects, with an area in the square millimeter range and a thickness in the micron range. They are not within the range of X-ray measurement nor within the range of ultrasonic detection, and it is difficult to detect such defects by conventional methods. Due to the lack of detection methods, such defects are usually difficult to capture. There is currently not enough experimental data and research showing the morphological characteristics of such defects in vacuum-cast superalloys, and little research has been carried out on their impact on performance. Casting fractures usually occur in weak areas with defects. When there are microscopic defects such as double oxide films in the casting test bars, the test bar fractures will tear along the double oxide film area. Therefore, the detection of such defects in superalloy castings for aero-engines is crucial, especially for nickel-based superalloy castings of aero-engines with high performance requirements. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: how to detect typical defects in nickel-based superalloy components of aero-engines.

[0005] To solve the above technical problem, the present invention adopts the following technical solution:

[0006] A method for detecting defects in nickel-based superalloy components of aero-engines, which comprises the following steps:

[0007] (1) Select the grade of nickel-based superalloy according to the nickel-based superalloy component to be cast;

[0008] (2) Conduct numerical simulation of investment casting of the nickel-based superalloy component to be cast, and this numerical simulation comprises the following steps:

[0009] (2-1) Use 3D design software to draw the 3D model of the nickel-based superalloy component to be cast and the gating and risering system, and import this 3D model into the casting CAE software;

[0010] (2-2) Perform mesh generation on this 3D model;

[0011] (2-3) Input the chemical composition, thermal physical properties parameters, and casting process parameters of the selected grade of nickel-based superalloy, as well as the boundary conditions including the mold shell material, mold shell temperature and thickness, and heat dissipation conditions into the casting CAE software for numerical simulation;

[0012] (2-4) Determine the positions where defects are likely to occur during the solidification process of the nickel-based superalloy into a component according to the simulation results;

[0013] (3) Test piece casting: Cast the test piece according to the casting process parameters, and connect a 3-mm diameter hose during the casting process. One end of this hose is connected to an inert gas tank, and the other end is equipped with a high-temperature resistant ceramic head. Pass inert gas into the casting mold through the high-temperature resistant ceramic head to generate bubbles, thereby introducing pore defects into the cast test piece. Control the size and position of the pore defects by controlling the gas flow rate, the position and direction of the ceramic head, and assist X-ray for on-line monitoring to ensure that pore defects are introduced at the positions where defects are likely to occur determined in step (2-4);

[0014] (4) Take samples from the parts of the test piece with pore defects, and the sampling positions should cover the positions where defects are likely to occur determined in step (2-4);

[0015] (5) Conduct a tensile test on the sample obtained in step (4) at room temperature until fracture;

[0016] (6) Prepare the fracture obtained in step (5) into an SEM sample, and perform morphology analysis on this SEM sample by scanning electron microscopy;

[0017] (7) Use EDS and WDS to perform energy spectrum and spectral analysis on at least 5 position points of the fracture obtained in step (5);

[0018] (8) Judgment of defects of the duplex oxide film type:

[0019] A) If the fracture observed by the scanning electron microscope in step (6) is relatively smooth, and referring to the standard composition content of the selected grade of nickel-based superalloy, if the contents of O, Al, and Cr at the fracture are significantly higher than those in the non-fracture area, it is determined that there are defects of the duplex oxide film type;

[0020] B) If the fracture surface observed by SEM in step (6) includes a large number of cracks, and the contents of O, Al, and Cr at the fracture surface have no obvious difference from those in the non-fracture area, it is determined that there is no defect of the double oxide film type.

[0021] In one exemplary embodiment, the component is a turbine blade or a casing.

[0022] In one exemplary embodiment, in step (2-3), by optimizing the form, size, and opening position of the riser, the alloy casting temperature, the casting speed, and the mold shell temperature, and repeating the simulation until there are no obvious defects in the simulation results.

[0023] In one exemplary embodiment, in step (2-4), the Niyama criterion and the shrinkage cavity criterion are combined to analyze the defects of the casting.

[0024] In one exemplary embodiment, in step (3), the size of the porosity defect is controlled in the range of 5 μm - 1 mm.

[0025] In one exemplary embodiment, in step (4), the metal flow characteristics at the sampling location are consistent with the characteristic structure of the component body, and the sample can represent the microstructural characteristics of the component product.

[0026] Advantages of the present invention:

[0027] The defect detection method for nickel-based superalloy components of aeroengines described in this patent has invented for the first time a method for controllably manufacturing defects inside engine castings; combined with anatomical analysis for detection and verification; in aeroengines, a method for evaluating the fracture surface microstructure morphology of materials is proposed in combination with the requirements of first-piece inspection and periodic inspection, forming a core key technology and method criterion system such as a domestic engine material data evaluation method, laying a solid foundation for the airworthiness certification of domestic engine materials. At the same time, the test sampling methods and requirements for engine component parts such as blades and casings and the microscopic detection methods for defects such as double oxide films proposed in this patent can effectively detect two-dimensional defects such as double oxide films that cannot be detected by conventional detection methods, effectively avoiding the fracture of aeroengine component parts and the structural failure of the entire engine caused by the existence of defects. The idea shown by this method is also applicable to the microscopic detection and performance evaluation of raw materials and manufactured parts of engine composite material component parts. Description of the Drawings

[0028] Figure 1 is a flowchart of investment casting.

[0029] Figure 2 is a model diagram of a turbine blade.

[0030] Figure 3It is a simulation result diagram of the solidification process of casting a nickel-based superalloy into a turbine blade.

[0031] Figure 4 It is a simulation result diagram of shrinkage cavities in casting a nickel-based superalloy into a turbine blade.

[0032] Figure 5 It is a schematic diagram of the sampling positions for defect analysis of a turbine blade test piece.

[0033] Figure 6 It is a schematic diagram of introducing an inert gas into a casting mold during the casting process to generate bubbles. Specific embodiments

[0034] The present invention provides a method for detecting defects in nickel-based superalloy components of an aeroengine, which includes the following steps:

[0035] (1) According to the nickel-based superalloy component to be cast, select the grade of the nickel-based superalloy, where the component is a turbine blade or a casing;

[0036] (2) Conduct numerical simulation of investment casting of the nickel-based superalloy component to be cast, and this numerical simulation includes the following steps:

[0037] (2-1) Use 3D design software to draw the 3D models of the nickel-based superalloy component to be cast and the gating and risering system, and import this 3D model into casting CAE software;

[0038] (2-2) Conduct mesh generation of this 3D model;

[0039] (2-3) Input the chemical composition, thermal physical properties parameters, and casting process parameters of the selected grade of nickel-based superalloy, as well as boundary conditions including mold shell material, mold shell temperature and thickness, and heat dissipation conditions, into the casting CAE software, conduct numerical simulation, and repeat the simulation by optimizing the form, size, and opening position of the gating and risering, alloy casting temperature, casting speed, and mold shell temperature until there are no obvious defects in the simulation results;

[0040] (2-4) Determine the positions where defects are likely to occur during the solidification process of the nickel-based superalloy when casting into a component, where the Niyama criterion and the shrinkage cavity criterion are combined to analyze the defects of the casting;

[0041] (3) Casting of test pieces: Pour the test pieces according to the casting process parameters, and connect a hose with a diameter of 3 mm during the casting process. One end of the hose is connected to an inert gas tank, and the other end is fitted with a high-temperature resistant ceramic head. Inert gas is introduced into the casting mold through the high-temperature resistant ceramic head to generate bubbles, thereby introducing pore defects into the cast test pieces. Control the size and position of the pore defects by controlling the gas flow rate, the position and direction of the ceramic head, and assisting with on-line monitoring using X-rays to ensure that pore defects are introduced at the positions where defects are likely to occur determined in step (2-4). The size of the pore defects is controlled within the range of 5 μm - 1 mm;

[0042] (4) Take samples from the parts of the test pieces with pore defects. The sampling positions should cover the positions where defects are likely to occur determined in step (2-4). The metal flow characteristics at the sampling locations are consistent with the characteristic structure of the component body, and the samples can represent the microstructural characteristics of the component product;

[0043] (5) Conduct a tensile test on the samples obtained in step (4) at room temperature until fracture;

[0044] (6) Prepare the fracture obtained in step (5) into an SEM sample, and conduct a morphological analysis of the SEM sample by scanning electron microscopy;

[0045] (7) Use EDS and WDS to perform energy spectrum and spectral analysis on at least 5 position points of the fracture obtained in step (5);

[0046] (8) Judgment of defects of the duplex oxide film type:

[0047] A) If the fracture observed by the scanning electron microscope in step (6) is relatively smooth, and referring to the standard component content of the selected grade of nickel-based superalloy, if the contents of O, Al, and Cr at the fracture are significantly higher than those in the non-fracture area, it is determined that there are defects of the duplex oxide film type;

[0048] B) If the fracture observed by the scanning electron microscope in step (6) includes a large number of cracks, and there is no significant difference in the contents of O, Al, and Cr at the fracture and in the non-fracture area, it is determined that there are no defects of the duplex oxide film type.

[0049] Examples

[0050] Taking the nickel-based superalloy casting of a turbine blade type aero-engine as an example, the specific method steps are described as follows:

[0051] (1) According to the nickel-based superalloy turbine blade to be cast, select the grade of nickel-based superalloy as K417G;

[0052] (2) Carry out numerical simulation of investment precision casting for nickel-based superalloy turbine blades to be cast, and this numerical simulation includes the following steps:

[0053] (2-1) Use 3D design software (such as CAD software like UG NX, Pro / E, CATIA, SolidWorks, Solidedge, CAXA, etc.) to draw the 3D model of the nickel-based superalloy turbine blade to be cast and the gating and risering system, and import this 3D model into the casting CAE software through interfaces such as stl;

[0054] (2-2) Conduct mesh generation for this 3D model, set the mold shell thickness to 6.0 mm, set the target number of meshes to 2,000,000, and the computer automatically generates meshes. The total number of meshes is 20,899,350, and the number of metal meshes is 1,731,169;

[0055] (2-3) Input the chemical composition, thermal physical properties parameters, and casting process parameters of the selected grade of nickel-based superalloy, as well as boundary conditions including mold shell material, mold shell temperature and thickness, and heat dissipation conditions into the casting CAE software for numerical simulation, where

[0056] Chemical composition (weight percentage): C 0.13 - 0.22, Al 4.8 - 5.7, Mo 2.5 - 3.5, V 0.6 - 0.9, Zr 0.05 - 0.09, Fe ≤ 1.0, S ≤ 0.010, P ≤ 0.015, Mn ≤ 0.2, Si ≤ 0.2, Cr 8.5 - 9.5, Ti 4.1 - 4.7, Co 9 - 11, B 0.012 - 0.024, and the balance is Ni.

[0057] Thermal physical properties parameter - liquidus temperature: 1335 °C;

[0058] Thermal physical properties parameter - solidus temperature: 1164 °C

[0059] Mold shell material: Mullite

[0060] Casting process: Under gravity conditions, the alloy pouring temperature is 1455 °C, the mold shell temperature is 950 °C, the pouring time is 2 s, and the heat transfer coefficient HTC between the alloy liquid and the mold shell is 1000 W / m 2 K, and by optimizing the form, size, and opening position of the gating and risering, the alloy pouring temperature, pouring speed, and mold shell temperature, repeat the simulation until there are no obvious defects in the simulation results;

[0061] (2-4) Determine the positions where defects are likely to occur during the solidification process of the nickel-based superalloy into components according to the simulation results, where

[0062] First, analyze the filling process and results of the casting: Observe the flow patterns, temperatures, velocities, etc. at different moments during the filling process. Pay attention to whether there are situations where the temperature of the molten metal is lower than the liquidus during the filling process. If the temperature is lower than the liquidus, there may be potential risks such as cold shuts and misruns. If there are vortices in the flow of the molten metal, there may be slag inclusions and other impurities that cannot float to the surface. When two streams of molten metal collide in the mold cavity, there may be welding lines and possibly cold shuts. Check the temperature distribution of the molten metal after pouring. Whether the temperature distribution of the molten metal in the mold cavity is higher at the top and lower at the bottom, which is beneficial for feeding. According to the simulation results, it can be known that during the pouring process and at the end of pouring, the temperature exceeds the liquidus. Only during the filling process, there is turbulence. Although pouring is carried out under high vacuum conditions, it is still prone to micro-defects such as inclusions and oxide skins. Analyze the solidification process and results, observe the solidification progress sequence diagram of each part of the casting. During the solidification process of the casting, whether the riser remains liquid and solidifies last, and whether the feeding channels are connected, as Figure 3 。Carry out the pore criterion to judge the shrinkage cavity of the casting. The set value of the shrinkage cavity criterion is 0.0001 - 10, and on the color scale, it corresponds to a shrinkage cavity rate of 0.001% - 10%. The darker the color, the less the pore content. The area with the darkest color indicates that the shrinkage cavity rate is zero, that is, there is no shrinkage cavity, while the white area indicates that the shrinkage cavity rate is very high, and its value is close to 10%. The corresponding shrinkage cavity rates can all find corresponding values on the color scale, as Figure 4 shown. Use the Niyama criterion and the shrinkage cavity criterion together to analyze the defect problems of the casting;

[0063] (3) Cast test pieces: Cast test pieces according to the casting process parameters, and connect a 3 - mm - diameter hose during the casting process. One end of the hose is connected to an inert gas tank, and the other end is fitted with a high - temperature - resistant ceramic head. Pass inert gas into the casting mold through the high - temperature - resistant ceramic head to generate bubbles, thereby generating pore defects in the cast test pieces. Control the size and position of the pore defects by controlling the gas flow rate, the position and direction of the ceramic head, and assisting with on - line monitoring by X - ray to ensure that pore defects are introduced at the positions where defects are likely to appear determined in steps (2 - 4). The size of the pore defects is controlled within the range of 5μm - 1mm;

[0064] Engine nickel - based superalloy blades are usually manufactured by investment casting. Investment casting is to make an investment pattern (abbreviated as wax pattern) with investment casting materials and form a mold assembly. Then, apply multiple layers of refractory materials on the surface of the mold assembly. After drying and solidifying, heat the mold assembly to melt out the mold material, and pour molten metal after high - temperature roasting to obtain an investment casting. Its specific process flow is as Figure 1 shown.

[0065] (4) Take samples from the parts of the test piece with porosity defects. The sampling positions shall cover the positions where defects are likely to occur determined in steps (2-4). The metal flow characteristics at the sampling locations shall be consistent with the characteristic structure of the component body, and the samples shall be able to represent the microstructural characteristics of the component product. For turbine blades, the sampling design is carried out in accordance with Figure 5 Make the sampling design.

[0066] (5) Conduct a tensile test on the samples obtained in step (4) at room temperature until fracture;

[0067] (6) Prepare the fracture surfaces obtained in step (5) into SEM samples, and conduct morphology analysis on these SEM samples through a scanning electron microscope;

[0068] (7) Use EDS and WDS to conduct energy spectrum and spectrum analysis on at least 5 position points of the fracture surfaces obtained in step (5);

[0069] (8) Judgment of defects of the duplex oxide film type:

[0070] A) If the fracture surfaces observed by the scanning electron microscope in step (6) are relatively smooth, and referring to the standard component content of the selected nickel-based superalloy grade, if the O, Al, and Cr contents at the fracture surfaces are significantly higher than those in the non-fracture regions, it is determined that there are defects of the duplex oxide film type. For the K417G nickel-based alloy used in this embodiment, according to the standard component percentage content, the Al content is 4.8-5.7, and the Cr content is 8.5-9.5. If the energy spectrum and spectrum show that the O content > 3, the Al content > 6, and at the same time the Cr content > 9.5, it is determined that there are defects of the duplex oxide film type;

[0071] B) If the fracture surfaces observed by the scanning electron microscope in step (6) include a large number of cracks, and there is no obvious difference in the O, Al, and Cr contents at the fracture surfaces and those in the non-fracture regions, it is determined that there are no defects of the duplex oxide film type.

[0072] All the features disclosed in this specification, or all the steps in the disclosed methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

[0073] Any feature disclosed in this specification, unless specifically stated, can be replaced by other equivalent or similar-purpose alternative features. Unless specifically stated, each feature is only an example in a series of equivalent or similar features.

[0074] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which these exemplary embodiments belong. The terminology used in the description herein is for the purpose of describing exemplary embodiments only and is not intended to be limiting of the exemplary embodiments. Thus, the overall inventive concept is not intended to be limited to the specific embodiments illustrated herein. Although preferred methods and materials are described herein, other methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention.

[0075] Unless otherwise indicated, all numbers expressing quantities of ingredients, chemical and molecular properties, reaction conditions, etc. used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and the appended claims are approximations that may vary depending upon the desired properties sought to be obtained by the exemplary embodiments herein. At the very least, each numerical parameter should be construed in light of the number of significant digits and the ordinary rounding method.

[0076] While the numerical ranges and parameters setting forth the broad scope of the exemplary embodiments are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Each numerical range given throughout the specification and claims will include every narrower numerical range that falls within such broader numerical range as if such narrower numerical ranges were also expressly written herein. In addition, any numerical value reported in the examples can be used to define the upper or lower endpoint of a broader compositional range disclosed herein.

Claims

1. A method for defect detection of a nickel-based superalloy component of an aeroengine, comprising the following steps: (1) Select the grade of nickel-based superalloy according to the nickel-based superalloy component to be cast; (2) Conduct numerical simulation of investment casting of the nickel-based superalloy component to be cast, and this numerical simulation includes the following steps: (2-1) Use 3D design software to draw the 3D models of the nickel-based superalloy component to be cast and the gating and risering system, and import this 3D model into casting CAE software; (2-2) Conduct mesh generation for this 3D model; (2-3) Input the chemical composition, thermal physical properties parameters and casting process parameters of the selected grade of nickel-based superalloy, as well as boundary conditions including mold shell material, mold shell temperature and thickness and heat dissipation conditions into the casting CAE software for numerical simulation; (2-4) Determine the positions where defects are likely to occur during the solidification process of the nickel-based superalloy into a component according to the simulation results; (3) Test piece casting: Cast the test piece according to the casting process parameters, and connect a hose with a diameter of 3 mm during the casting process. One end of this hose is connected to an inert gas tank, and the other end is equipped with a high-temperature resistant ceramic head. Pass inert gas into the casting mold through the high-temperature resistant ceramic head to generate bubbles, thereby introducing pore defects in the cast test piece. Control the size and position of the pore defects by controlling the gas flow rate, the position and direction of the ceramic head and assisting with X-ray for on-line monitoring, ensuring that pore defects are introduced at the positions where defects are likely to occur determined in step (2-4), and the size of the pore defects is controlled within the range of 5 μm - 1 mm; (4) Take samples from the parts of the test piece with pore defects, and the sampling positions need to cover the positions where defects are likely to occur determined in step (2-4); (5) Conduct a tensile test on the sample obtained in step (4) at room temperature until fracture; (6) Prepare the fracture obtained in step (5) into an SEM sample, and conduct morphology analysis on this SEM sample through a scanning electron microscope; (7) Use EDS and WDS to conduct energy spectrum and spectrum analysis on at least 5 position points of the fracture obtained in step (5); (8) Judgment of defects of the double oxide film type: A) If the fracture observed by the scanning electron microscope in step (6) is relatively smooth, and referring to the standard component content of the selected grade of nickel-based superalloy, if the contents of O, Al and Cr at the fracture are significantly higher than the contents of O, Al and Cr in the non-fracture area, it is determined that there are defects of the double oxide film type; B) If the fracture observed by the scanning electron microscope in step (6) includes a large number of cracks, and there is no obvious difference in the contents of O, Al and Cr at the fracture and in the non-fracture area, it is determined that there are no defects of the double oxide film type.

2. The method according to claim 1, wherein the component is a turbine blade or a casing.

3. The method according to claim 1 or 2, wherein in step (2-3), by optimizing the form, size and opening position of the gating and risering, the alloy casting temperature, the casting speed and the mold shell temperature, repeat the simulation until there are no obvious defects in the simulation results.

4. The method according to claim 1 or 2, wherein in step (2-4), the Niyama criterion and the shrinkage cavity criterion are used in combination to analyze the defects of the casting.

5. The method according to claim 1 or 2, wherein in step (3), the size of the porosity defect is controlled within the range of 5 μm - 1 mm.

6. The method according to claim 1 or 2, wherein in step (4), the metal flow characteristics at the sampling location are consistent with the characteristic structure of the component body, and the sample can represent the microstructure characteristics of the component product.

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