A method for eliminating thermal cracks in nickel-based alloy additive repair

Abstract

The application discloses a method for eliminating thermal cracks in nickel-based alloy additive repair, which comprises the following steps: firstly, quantitatively analyzing elements contained in the nickel-based alloy, and simulating a solidification curve based on thermodynamics according to the elements; secondly, obtaining a CSI-fs curve based on the solidification curve; thirdly, designing a heat treatment system through thermodynamic simulation, and performing composition homogenization treatment on the nickel-based alloy; and finally, performing electron beam additive repair. Results show that the nickel-based alloy treated by the method does not produce cracks during the additive repair, i.e., the thermal cracks are eliminated, the connection is stable, and the crack-free additive repair is successfully realized.

Description

Technical Field

[0001] This invention belongs to the field of nickel-based alloy additive manufacturing and relates to a method for eliminating hot cracks in nickel-based alloy additive manufacturing. Background Technology

[0002] Nickel-based superalloys are metallic materials that can withstand large and complex stresses at temperatures above 600°C for extended periods and possess excellent high-temperature performance. Superalloys are commonly used to manufacture the most critical hot-end components in aero-engines: turbine blades. Nickel-based superalloy blades have complex compositions, demanding manufacturing processes, and low product yields; furthermore, under the combined effects of prolonged and complex alternating stresses and corrosive environments, superalloys are highly susceptible to damage. Therefore, compared to scrapping and replacing the entire workpiece, selecting appropriate methods to repair slightly damaged high-value blades to restore their microstructure and service performance as much as possible is of paramount importance.

[0003] The emergence of additive manufacturing technology has made it possible to successfully repair damaged high-temperature alloy blades. This technology mainly uses a high-density heat source to achieve selective melting and shaping, and then uses a layer-by-layer deposition method to manufacture three-dimensional complex shapes. Since the overall heat input is much smaller than that of fusion welding repair, the deformation introduced during repair manufacturing is smaller, the depth of the heat-affected zone is greatly reduced, and the elemental segregation behavior in the additive manufacturing area is controlled, resulting in a more uniform material microstructure.

[0004] However, in practice, the high-temperature alloy blades being repaired are typically fabricated using directional solidification technology, resulting in a cast substrate with significant internal elemental segregation. During additive repair, due to thermal cycling, the grain boundaries within the heat-affected zone (HAZ) of the substrate will liquefy due to elemental segregation and the accumulation of low-melting-point phases. The liquefied grain boundaries, under thermal stress, will then lead to crack formation. The presence of cracks in the HAZ directly indicates repair failure.

[0005] Therefore, there is an urgent need for a suitable method to solve the problem of hot cracking that occurs during the repair of nickel-based alloys. Summary of the Invention

[0006] To overcome the aforementioned problems, the inventors conducted intensive research and developed a method for eliminating hot cracks in the additive repair of nickel-based alloys. First, the elements contained in the nickel-based alloy were quantitatively analyzed, and the solidification curve was thermodynamically simulated accordingly. Then, the cracking tendency of the elements in the nickel-based alloy under segregated conditions was evaluated using the Sindo Kou solidification cracking model. Next, a heat treatment regime was designed through thermodynamic simulation to homogenize the composition of the nickel-based alloy. Finally, electron beam additive repair was performed. The results show that the nickel-based alloy treated using the method described in this invention did not develop cracks during additive repair, i.e., the heat-induced cracks disappeared, and the repair was stable, successfully achieving crack-free additive repair, thus completing this invention.

[0007] Specifically, the purpose of this invention is to provide a method for eliminating hot cracks in nickel-based alloy additive manufacturing, the method comprising:

[0008] Step 1: Quantitative analysis of the elements in the nickel-based alloy;

[0009] Step 2: Based on the element content in the nickel-based alloy, the solidification curve of the nickel-based alloy is obtained through thermodynamic simulation;

[0010] Step 3: Obtain the CSI-fs curve based on the solidification curve of the nickel-based alloy;

[0011] Step 4: Based on the CSI-fs curve, obtain the heat treatment scheme for nickel-based alloys through thermodynamic simulation;

[0012] Step 5: Heat-treat the nickel-based alloy, and use the heat-treated nickel-based alloy as a substrate for electron beam additive repair to eliminate hot cracks in the nickel-based alloy.

[0013] The beneficial effects of this invention include:

[0014] (1) Traditional welding processes or high-density heat sources such as laser beams and electron beams are extremely prone to causing cracks in the heat-affected zone of the substrate. The method for eliminating hot cracks in nickel-based alloy additive manufacturing proposed in this invention is not only economical, but can also eliminate cracks in the heat-affected zone of nickel-based alloys and achieve successful repair.

[0015] (2) This invention obtains the solidification curve of nickel-based alloys through thermodynamic simulation and introduces the Sindo Kou solidification model to evaluate and predict the crack sensitivity of characteristic regions inside nickel-based alloys. For the first time, it establishes the intrinsic correlation between the distribution of high-temperature alloying elements and crack formation tendency. This method has universality and provides a new approach for electron beam additive repair of nickel-based alloys and even other metallic materials.

[0016] (3) This invention, by measuring the dendrite spacing of nickel-based alloys and selecting the heat treatment temperature according to the types of elements in the nickel-based alloy, simulates the distribution curve of elements in the nickel-based alloy over time, providing a scientific criterion for establishing a heat treatment system to achieve homogenization of the alloy composition. This method has universality and provides a reference for designing and optimizing heat treatment systems for nickel-based alloys and even other metallic materials.

[0017] (4) This invention combines homogenization heat treatment with control of electron beam additive repair process parameters to obtain a wider crack-free process window, providing theoretical support for the development and application of nickel-based alloy electron beam additive technology. Attached Figure Description

[0018] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0019] In the attached diagram:

[0020] Figure 1(a) shows the as-cast microstructure of the nickel-based alloy in Example 1;

[0021] Figure 1(b) shows the location of sampling points in the dendritic trunk region of the as-cast structure of the nickel-based alloy in Example 1;

[0022] Figure 1(c) shows the location of sampling points in the interdendritic region of the as-cast microstructure of the nickel-based alloy in Example 1;

[0023] Figure 1(d) shows the location of sampling points in the grain boundary region of the as-cast microstructure of the nickel-based alloy in Example 1;

[0024] Figure 2 The solidification curves, i.e., T-fs curves, show the solid volume fraction of the dendritic trunk region, interdendritic region, and grain boundary region in the nickel-based alloy at the end of solidification in Example 1 as a function of temperature.

[0025] Figure 3 The curve showing the change of CSI value as a function of solid volume fraction obtained by extracting the T-fs curve in Example 1 is shown, i.e., the CSI-fs curve;

[0026] Figure 4 The curves showing the changes in the content of different alloying elements over time at 1230℃ obtained from thermodynamic simulation in Example 1 are shown.

[0027] Figure 5 The microstructure of the repaired nickel-based alloy in Comparative Example 1 is shown.

[0028] Figure 6 The microstructure of the repaired nickel-based alloy in Comparative Example 2 is shown.

[0029] Figure 7 The microstructure of the repaired nickel-based alloy in Example 1 is shown. Detailed Implementation

[0030] The following will refer to the appendix. Figures 1(a) to 7Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0031] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0032] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this invention, and are only for the convenience of describing this 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 this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0034] According to the present invention, a method for eliminating hot cracks in nickel-based alloy additive manufacturing is provided, the method comprising:

[0035] Step 1: Quantitative analysis of the elements in the nickel-based alloy;

[0036] Step 2: Based on the element content in the nickel-based alloy, the solidification curve of the nickel-based alloy is obtained through thermodynamic simulation;

[0037] Step 3: Obtain the CSI-fs curve based on the solidification curve of the nickel-based alloy;

[0038] Step 4: Based on the CSI-fs curve, obtain the heat treatment scheme for nickel-based alloys through thermodynamic simulation;

[0039] Step 5: Heat-treat the nickel-based alloy, and use the heat-treated nickel-based alloy as a substrate for electron beam additive repair to eliminate hot cracks in the nickel-based alloy.

[0040] The above-mentioned methods for additive repair of nickel-based alloys are described in detail below.

[0041] Step 1: Quantitative analysis of the elements in the nickel-based alloy.

[0042] In step 1, it is preferable to use compositional analysis techniques such as electron probe microscopy to perform elemental analysis on the nickel-based alloy, that is, to obtain the types of elements contained in the nickel-based alloy; the method for determining the elemental content of the nickel-based alloy is not limited to any existing technical means that can obtain the elemental content of the nickel-based alloy.

[0043] The inventors discovered that the content of the same element is not the same in different regions of nickel-based alloys. In order to achieve a better repair effect, the element content of the dendritic trunk region, interdendritic region and grain boundary region of nickel-based alloys were measured respectively.

[0044] Furthermore, the elements include nickel and alloying elements contained in nickel-based alloys. The alloying elements include one or more of aluminum, titanium, tantalum, cobalt, chromium, molybdenum, tungsten, and hafnium. Typically, they mainly include aluminum, titanium, tantalum, cobalt, chromium, molybdenum, tungsten, and hafnium. Elements such as carbon and boron have large measurement errors during quantitative analysis and have little impact on the solidification curve, so they are not considered.

[0045] According to the preferred embodiment, before quantitative analysis, the nickel-based alloy is cut into regular shapes, and the surface of the nickel-based alloy is ground and polished to make the surface of the nickel-based alloy smooth, so that the irregular absorption of X-rays during quantitative analysis will not affect the measurement results due to unevenness; finally, it is ultrasonically cleaned and dried for later use.

[0046] Step 2: Based on the element content in the nickel-based alloy, the solidification curve of the nickel-based alloy is obtained through thermodynamic simulation.

[0047] In step 2, the solidification behavior of the dendritic trunk region, interdendritic region, and grain boundary region of the nickel-based alloy is simulated, and solidification curves of solid volume fraction as a function of temperature are obtained for the dendritic trunk region, interdendritic region, and grain boundary region of the nickel-based alloy, respectively.

[0048] In one embodiment, thermodynamic simulation software such as Jmatpro is used to simulate the solidification behavior of the dendritic trunk region, interdendritic region, and grain boundary region of the nickel-based alloy: the content of each element in the dendritic trunk region, interdendritic region, and grain boundary region of the nickel-based alloy is input into the thermodynamic simulation software such as Jmatpro, and solidification curves of the solid volume fraction at the end of solidification of the dendritic trunk region, interdendritic region, and grain boundary region of the nickel-based alloy as a function of temperature are simulated and generated.

[0049] Step 3: Obtain the CSI-fs curve based on the solidification curve of the nickel-based alloy.

[0050] In step 3, the CSI value (crack sensitivity index) is extracted based on the solidification curve of the nickel-based alloy. fs represents the solid volume fraction, and T represents the temperature. Based on the CSI value and the solid volume fraction, the CSI-fs curves of different regions (dendritic trunk region, interdendritic region, and grain boundary region) inside the nickel-based alloy can be obtained.

[0051] In step 3, based on the CSI-fs curves of different regions inside the nickel-based alloy, the inventors found that the CSI value of the grain boundary region is higher than that of the interdendritic region and the dendritic trunk region. Therefore, it was determined that the grain boundary region is most prone to cracking during the repair process.

[0052] In step 3, the Sindo Kou solidification cracking model is preferably introduced to further evaluate the cracking tendency of the heat-affected zone of nickel-based alloys. The Sindo Kou solidification cracking model is represented by the relationship between separation, growth, and supplementary terms. Specifically, the separation term is represented as follows: The growth term is represented as The supplementary item is represented as follows:

[0053] In the formula, T is the temperature, and ε local For local strain, This indicates the degree of plastic deformation that causes cracks to form between two adjacent grains; it is usually referred to as the separation term.

[0054] fs is the solid volume fraction, and β is the solidification shrinkage rate. This represents the force that causes two adjacent grains to grow towards each other in order to resist cracking; therefore, it is usually called the growth term.

[0055] z represents the dendrite growth direction, v z The rate at which the liquid replenishes the paste-like two-phase region during the liquid-solid transition along the z-axis, where t is time. As a supplementary term, it indicates the liquid phase replenishment in the grain boundary region to resist cracking;

[0056] In the later stage of solidification When the separation term is greater than the sum of the growth term and the supplement term, that is:

[0057]

[0058] At this point, it indicates that the nickel-based alloy has a high tendency to crack in the heat-affected zone during the repair process, and the repair is prone to failure; conversely, it indicates that the nickel-based alloy has a low tendency to crack in the heat-affected zone during the repair process.

[0059] Based on the aforementioned model, focus on The reciprocal of this factor's influence on material cracking behavior This is commonly referred to as the Crack Sensitivity Index (CSI). A higher CSI value indicates smaller growth and replenishment terms in the criterion, and a greater likelihood that the separation term will exceed the sum of the growth and replenishment terms in the later stages of solidification. Therefore, the material is more susceptible to cracking, increasing the tendency to crack during repair. Furthermore, as the CSI value increases, the liquid replenishment channels along the grain boundaries lengthen, making liquid phase replenishment more difficult and creating conditions for further crack propagation during repair. Therefore, an increased CSI value signifies an increased tendency to crack during the repair of nickel-based alloys.

[0060] Step 4: Obtain the heat treatment scheme for nickel-based alloys based on the CSI-fs curve.

[0061] In this invention, based on the CSI-fs curve, it is determined that the grain boundary region is most prone to cracking during the repair process. Based on the Sindo Kou solidification cracking model, the separation term in the later stage of solidification is greater than the sum of the growth term and the replenishment term, which increases the cracking tendency of nickel-based alloys during the repair process. Therefore, the selection of heat treatment scheme is particularly important. A reasonable heat treatment scheme is beneficial to reduce the cracking tendency of nickel-based alloys during the repair process, thereby inhibiting the generation of cracks in the heat-affected zone after repair.

[0062] According to the present invention, based on CSI-fs curves, thermodynamic simulations are used to simulate the diffusion behavior of elements in nickel-based alloys, thereby obtaining a homogenization heat treatment scheme for the nickel-based alloys. Specific steps include: obtaining the distance between secondary dendrite arms based on the as-cast microstructure diagram of the nickel-based alloy; selecting a heat treatment temperature based on the characteristics of the nickel-based alloy; and, based on the secondary dendrite arm spacing and the heat treatment temperature, using thermodynamic simulation, for example, thermodynamic software, to obtain the distribution curves of elements within the nickel-based alloy over time, thereby obtaining the heat treatment scheme.

[0063] In one embodiment, a microscopic image of the as-cast microstructure was observed using an optical microscope, and the distance between secondary dendrite arms was measured. The longest secondary dendrite arm distance in the image, 60–80 μm, was selected as the distance for element diffusion during simulation. A heat treatment temperature of 1230–1250 °C was selected based on the characteristics of the nickel-based alloy. The inventors found that if the selected heat treatment temperature is too high, it will cause local melting of the low-melting-point phase, resulting in initial melting; if the selected heat treatment temperature is too low, the homogenization effect of the nickel-based alloy cannot be achieved. Based on the secondary dendrite arm spacing and heat treatment temperature, the distribution curves of alloying elements in the nickel-based alloy over time were simulated using thermodynamic software. The inventors found that when the heat treatment time exceeds 13 hours, all elements in the nickel-based alloy are completely homogenized. Finally, the optimal heat treatment scheme for achieving complete compositional homogenization in the nickel-based alloy was determined.

[0064] Typically, for nickel-based alloy materials, the heat treatment process includes the following steps: holding the nickel-based alloy at 1230–1250°C for 13–16 hours, and then naturally cooling it to room temperature.

[0065] According to the present invention, the room temperature is typically -10 to 40°C, for example 25°C.

[0066] Step 5: Heat-treat the nickel-based alloy, and use the heat-treated nickel-based alloy as a substrate for electron beam additive repair to eliminate hot cracks in the nickel-based alloy.

[0067] In step 5, the substrate is preferably cut into the shape to be processed, and nickel-based cast high-temperature alloy material is used as raw material for electron beam additive repair, which ultimately suppresses the generation of heat-affected zone cracks.

[0068] In step 5, the nickel-based casting high-temperature alloy material can be any one or more of DZ125, DZ404, DZ405, DZ406, DZ408, DZ411, DZ417G, DZ422, K213, K403, DD408, and DD426, and is preferably a nickel-based casting high-temperature alloy material with the same elements as the base material.

[0069] In step 5, the electron beam additive repair includes the following steps:

[0070] Step 5-1: Import the printed parts into the slicing software to generate the print file;

[0071] Step 5-2: Import the print file into the printing operation software and set the processing parameters for the printed parts;

[0072] Step 5-3: Perform electron beam additive repair based on the processing parameters.

[0073] In step 5-1, the printing model is imported into the slicing software, and the slice thickness, melting gap, and rotation angle between slices are set.

[0074] In step 5-1, the thickness of the slice is 0.06 to 0.1 mm, for example 0.07 mm; the melting gap is usually 0.09 to 0.12 mm, for example 0.10 mm; and the rotation angle between the slices is generally 90°.

[0075] In step 5-2, the processing parameters include an electron beam power and scanning speed ratio between 0.3 and 0.5; preferably, the electron beam power ranges from 200 to 900 W, and the scanning speed ranges from 500 to 4000 mm / s. It should be noted that during electron beam repair, the ratio of electron beam power to scanning speed should be moderate. When the electron beam power is too high and the scanning speed is too low, the heat input is large, resulting in severe overheating and burning, poor formability of the repaired parts, and easy generation of internal defects. When the electron beam power is too low and the scanning speed is too high, the heat input is small, and the powder cannot be melted, making it impossible to process and form. Generally, an electron beam power and scanning speed ratio of 0.3 to 0.5 is more suitable.

[0076] In step 5, before electron beam additive repair, the substrate is preheated to 1000–1100°C, for example, 1050°C. Preheating the substrate improves the conductivity of the nickel-based cast high-temperature alloy powder deposited on the substrate, thereby preventing powder bursting or blowing; at the same time, the high-temperature preheating effect reduces residual stress during the additive repair process, further suppressing cracking.

[0077] Example

[0078] The present invention is further described below through specific examples; however, these examples are merely exemplary and do not constitute any limitation on the scope of protection of the present invention.

[0079] Example 1

[0080] The nickel-based alloy made from DZ125 was cut into 5mm×5mm×1.5mm blocks using a wire cutting machine, ground on gauze paper, polished with silk polishing cloth, then ultrasonically cleaned and dried for later use.

[0081] (1) Elemental analysis of the nickel-based alloy was performed using electron probe microscopy (EPMA). The contents of nickel, aluminum, titanium, tantalum, cobalt, chromium, molybdenum, tungsten, and hafnium in the dendritic trunk region, interdendritic region, and grain boundary region of the nickel-based alloy were determined respectively. The electron probe was fixed at the test point on the surface of the nickel-based alloy, and the sampling point was located as follows: Figures 1(a) to 1(d) As shown, the characteristic X-rays emitted by the nickel-based alloy were analyzed using a spectrometer to obtain the energy dispersive spectrum of that point. Based on the peak positions on the spectrum, the wavelength and energy of each characteristic X-ray can be determined, thus identifying the types of elements contained therein. By measuring the intensity values ​​of the main characteristic X-rays of each element and comparing them with the corresponding spectral intensity values ​​of a standard sample with known composition, the content of nickel, aluminum, titanium, tantalum, cobalt, chromium, molybdenum, tungsten, and hafnium was finally obtained.

[0082] Figure 1(a) shows a schematic diagram of the dendritic trunk region, interdendritic region, and grain boundary region of the as-cast microstructure of a nickel-based alloy (represented as the original as-cast microstructure in the figure). Figure 1(b) shows a diagram of the location of sampling points in the dendritic trunk region of the as-cast microstructure. Figure 1(c) shows a diagram of the location of sampling points in the interdendritic region of the as-cast microstructure. Figure 1(d) shows a diagram of the location of sampling points in the grain boundary region of the as-cast microstructure.

[0083] (2) Next, Jmatpro software was used to simulate the solidification behavior of the dendritic trunk region, interdendritic region, and grain boundary region: the measured contents of nickel, aluminum, titanium, tantalum, cobalt, chromium, molybdenum, tungsten, and hafnium were input, and then the "Phase and Properties" function under the Solidification module was selected. The simulation process was started, and after the simulation was completed, the solidification curve of solid volume fraction as a function of temperature was output. This curve is shown in the figure. Figure 2 As shown;

[0084] Table 1 shows the elemental contents of nickel, aluminum, titanium, tantalum, cobalt, chromium, molybdenum, tungsten, and hafnium measured at different sampling points in the as-cast microstructure of nickel-based alloys:

[0085] Table 1. Elemental content of different characteristic regions inside nickel-based alloys as determined by EPMA

[0086] Percentage content / % Al Ti Cr Co Ni Mo Hf Ta W As-cast dendritic trunk 4.761 1.084 8.884 10.915 61.324 1.54 0.771 2.606 7.083 As-cast state - grain boundary 6.854 1.539 5.129 7.7 65.603 1.025 1.483 4.79 4.893 As-cast - interdendritic 5.28 1.124 8.427 10.159 61.944 1.374 0.863 3.515 6.143

[0087] (3) Based on the solidification curve, the crack sensitivity index under different solid volume fractions was obtained. Plot the CSI-fs curves at the end of solidification corresponding to the dendritic trunk / interdendritic region of the substrate to assess the cracking tendency, such as... Figure 3 As shown, the CSI value at the grain boundary is higher than that in the interdendritic region and the dendritic trunk region. Therefore, the grain boundary is the most prone to cracking during the additive repair process.

[0088] (4) Based on the CSI-fs curve, it was found that composition homogenization is needed to reduce the cracking tendency at the grain boundaries of nickel-based alloys. Therefore, a heat treatment regime or scheme needs to be designed. Jmatpro software was used to simulate the element diffusion behavior under different heat treatment regimes: the measured contents of Al, C, Ti, Cr, Co, Ni, Mo, Hf, Ta, and W were input, then the "Homogenisation" function under the Solidification module was selected, and the Homogenization temperature and Secondary dendrite arm spacing were input. The simulation process was then started. After the simulation, the distribution of different alloying elements (Al, Ti, Ta, Cr, Co, and W) in the nickel-based alloy as a function of homogenization time (i.e., holding time) was output. The results are as follows: Figure 4 As shown;

[0089] The simulation results determined the heat treatment method for the nickel-based alloy: the nickel-based alloy was cut into cylinders with a radius of 40 mm and a height of 15 mm using a wire EDM machine, and the temperature of the muffle furnace was increased from room temperature to 1230℃ at a heating rate of 0.66 mm / s. The cut cylindrical samples were placed in the muffle furnace and held for 16 hours, and then naturally cooled to room temperature.

[0090] (5) After heat treatment, electron beam additive repair experiments were conducted using this substrate. First, the substrate surface was polished using a surface grinder, and then ultrasonically cleaned and dried. DZ125 powder was filled into the forming chamber of the printing equipment, and then the substrate was placed in. The equipment door and vent valve were closed, and vacuuming was started, followed by filling with high-purity argon. Then, the high-voltage power supply was turned on, and the substrate was preheated to 1050°C using electron beam defocusing. The created printed parts were imported into the slicing software to generate printing files. The length and width of the printed parts were both 10mm, and the height was 10mm. The slicing thickness was set to 0.07mm. The network frame and the printed parts were sliced, the melting gap was 0.1mm, and the printing layer rotation angle was 90°.

[0091] The generated print file was imported into the printing software. The electron beam power was set to 240W, and the scanning speed to 600mm / s. Processing then began. After the additive manufacturing repair was completed, the equipment automatically shut down for cooling, the high-voltage power supply was turned off, the inert gas was shut off, and the vacuum was shut off. The microstructure of the repaired sample was observed, and the effect is shown below. Figure 7 As shown.

[0092] Figure 2 The solidification curves of the dendritic trunk region, interdendritic region, and grain boundary region of the nickel-based alloy are shown. It can be seen that the grain boundary region is more prone to liquefaction in the later stage of solidification compared to the intragranular regions (dendritic trunk and interdendritic regions). For the same solidification interval (e.g., solid volume fraction Fs changes from 0.95 to 1.00), the temperature change range of the grain boundary region is much larger than that of the interdendritic and dendritic trunk regions. When the interdendritic and dendritic trunk regions complete the liquid-solid transition, the grain boundary region is still in a liquefied state (containing a liquid phase). Therefore, this region is extremely prone to cracking during additive repair.

[0093] Figure 3 The CSI-fs curves of the dendritic trunk region, interdendritic region, and grain boundary region of the nickel-based alloy are shown. It can be seen that the CSI value at the grain boundary in the as-cast alloy (corresponding to Fs tending to 1 at the end of solidification) is higher than that in the interdendritic trunk region and the dendritic trunk region. Therefore, the grain boundary is the most likely place to generate cracks during the additive repair process.

[0094] Figure 4The curves showing the changes in the content of different alloying elements in a nickel-based alloy at 1230℃ with holding time are presented. It can be seen that at the homogenization temperature of 1230℃, the refractory element Ta is completely homogenized after 3 hours, and the refractory element W is basically homogenized after 13 hours. Therefore, at the homogenization temperature of 1230℃, all elements are homogenized after 13 hours.

[0095] Comparative Example

[0096] Comparative Example 1

[0097] Electron beam additive repair of nickel-based alloys was performed in a manner similar to that in Example 1, except that the nickel-based alloys were not heat-treated; instead, electron beam additive repair was performed directly. The final repaired sample is shown below. Figure 5 As shown, the repaired sample exhibits numerous cracks in both the heat-affected zone and the repaired zone, with severe tearing.

[0098] Comparative Example 2

[0099] Electron beam additive repair of nickel-based alloys was performed in a manner similar to that in Example 1, the difference being that the heat treatment was carried out at 1230°C for 3 hours. The final repaired sample is shown below. Figure 6 As shown, it can be seen that the repaired sample still has a large number of cracks in both the heat-affected zone and the repair zone.

[0100] The present invention has been described in detail above with reference to preferred embodiments and exemplary examples. However, it should be noted that these specific embodiments are merely illustrative explanations of the invention and do not constitute any limitation on the scope of protection of the invention. Various improvements, equivalent substitutions, or modifications can be made to the technical content and embodiments of the present invention without departing from the spirit and scope of protection of the invention, and all such modifications fall within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method of eliminating hot cracking in nickel-based alloy additive repair, characterized by, The method comprises: Step 1, respectively, the elements of the nickel-based alloy dendrite stem region, interdendritic region and grain boundary region are quantitatively analyzed, and the elements for quantitative analysis include nickel element and alloying element; Step 2, input the element content of nickel-based alloy dendrite stem region, interdendritic region and grain boundary region in thermodynamic simulation software, simulate and generate the solidification curve of solid phase volume fraction of nickel-based alloy dendrite stem region, interdendritic region and grain boundary region at the end of solidification with temperature change; Step 3, according to the solidification curve of nickel-based alloy, the CSI-fs curve is obtained; Step 4, based on the CSI-fs curve, it is judged that the grain boundary region is most likely to produce cracks during the repair process, in order to eliminate the risk, the nickel-based alloy needs to be homogenized heat treated, including: obtaining the distance between secondary dendrite arms according to the as-cast microstructure of nickel-based alloy, selecting the heat treatment temperature according to the characteristics of nickel-based alloy, obtaining the distribution curve of elements in nickel-based alloy with time change based on the secondary dendrite arm spacing and heat treatment temperature, and then obtaining the heat treatment scheme; Step 5, heat treatment is carried out on the nickel-based alloy, and the nickel-based alloy after heat treatment is used as the base material for electron beam additive repair to eliminate the thermal cracks of the nickel-based alloy, and the electron beam additive repair comprises the following steps: Step 5-1, the printing part is imported into the slicing software to generate a printing file; Step 5-2, the printing file is imported into the printing operation software, and the processing parameters of the printing part are set; Step 5-3, based on the processing parameters, electron beam additive repair is carried out.

2. The method of claim 1, wherein, The alloying elements include one or more of aluminum, titanium, tantalum, cobalt, chromium, molybdenum, tungsten and hafnium.

3. The method of claim 1, wherein, In step 3, according to the solidification curve of nickel-based alloy, the CSI value is extracted, and according to the CSI value and the solid phase volume fraction, the CSI-fs curve of the nickel-based alloy dendrite stem region, interdendritic region and grain boundary region is obtained.

4. The method of claim 1, wherein, In step 4, based on the CSI-fs curve, the diffusion behavior of elements in nickel-based alloy is simulated to obtain the homogenization heat treatment scheme of nickel-based alloy.

5. The method of claim 1, wherein, In step 4, the heat treatment scheme comprises the following steps: the nickel-based alloy is kept at 1230-1250 DEG C for 13-16 h, and then naturally cooled to room temperature.

6. The method of claim 1, wherein, In step 5-2, the processing parameters include: the ratio of electron beam power and scanning speed is between 0.3-0.5, the electron beam power range is 200-900 W, and the scanning speed range is 500-4000 mm / s.

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