A hot compression crack repair method that can replace hot isostatic pressing process

Abstract

The present invention relates to a hot compression crack repair method that can replace the hot isostatic pressing process, comprising the following steps: collecting melting point information of an alloy sample and determining a target temperature for hot compression; selecting multiple sets of different stress / strain parameters for hot compression experiments at the target temperature and comparing them with each other; metallographically preparing samples, observing and statistically analyzing the crack porosity, and determining whether the crack is clearly closed; if so, preliminarily determining the hot compression parameters; if not, adjusting the stress / strain parameters during the hot compression process until the crack is clearly closed; tilting the sample and performing hot compression again to determine whether the crack is closed; if so, finally determining the hot compression parameters; if not, continuing to adjust; and hot compressing the alloy part using the finalized hot compression parameters to achieve crack repair. Compared with the prior art, the present invention uses hot compression experiments to adjust and verify, ensuring that the obtained stress / strain parameters are accurate and effective, thereby achieving complete crack closure in two hot compression processes.

Description

Technical Field

[0001] The present invention belongs to the technical field of additive manufacturing, and in particular relates to a hot compression crack repair method that can replace a hot isostatic pressing process. Background Art

[0002] With the development of manufacturing technology, the demand for lightweight and integrated alloy parts in industrial applications is increasing day by day. Compared with traditional processes, laser additive manufacturing technology not only has the advantages of convenient design and integrated manufacturing, but also can reduce costs and shorten production cycles. Laser additive manufacturing is a process that uses laser as a high-energy beam heat source to melt powder or wire layer by layer, and then stacks the parts layer by layer to prepare them. Common laser additive manufacturing technologies mainly include selective laser melting (SLM) and laser solid forming (LSF).

[0003] However, in traditional processing technology, there are problems of cracks and pores caused by casting, welding, etc., which are more prominent in laser additive manufacturing. Porosity can be effectively controlled by optimizing additive manufacturing process parameters, controlling the quality of raw material powder, and reducing the oxygen content in the forming process. Cracks mainly include thermal cracks and loss of plasticity cracks, among which thermal cracks are always inevitable with the solidification process. The brittle temperature range (BTR) during the solidification process has an important influence on the generation and expansion of cracks. Generally, shortening the BTR period of liquid metal during the solidification process or reducing energy input and preheating the substrate can reduce the effect of thermal stress on solidification cracking. Despite this, the actual process still faces challenges such as poor process stability and high process cost.

[0004] Hot isostatic pressing (HIP) is currently a major post-processing method that can close cracks and pores without manipulating the alloy composition. By placing the product in a sealed container, applying equal pressure in all directions to the sample while simultaneously subjecting it to high temperature and pressure, the product is sintered and densified under the action of high temperature and pressure. HIP often requires large equipment and high energy consumption. Furthermore, in addition to the equipment being expensive and inconvenient to operate, the process design and optimization of HIP is complex, requiring continuous trial and adjustment of experimental plans. Long experimental cycles and high processing costs limit its application in actual production.

[0005] Therefore, the mainstream hot isostatic pressing process still faces challenges, and a new crack repair method is urgently needed to be developed. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the prior art such as long experimental cycle and high processing cost and to provide a hot compression crack repair method that can replace the hot isostatic pressing process.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A hot compression crack repair method that can replace the hot isostatic pressing process includes the following steps:

[0009] S1: Use differential scanning calorimetry to collect melting point information of the alloy sample and determine the target temperature of hot compression;

[0010] S2: Select multiple sets of different stress / strain parameters to conduct thermal compression experiments at the target temperature and compare them with each other;

[0011] S3: Metallographic sample preparation, followed by observation and statistics of crack pores;

[0012] S4: Compare the crack conditions of each group before and after hot compression to determine whether the cracks are obviously closed; if so, preliminarily determine the hot compression parameters and execute step S7; if not, execute step S5;

[0013] S5: Adjust the stress / strain parameters during hot compression based on crack closure;

[0014] S6: Determine whether the crack closure is obvious after the stress / strain parameters are adjusted in S5; if so, execute step S7; if not, return to step S5;

[0015] S7: Tilt the sample and perform hot compression again to determine whether the crack is closed; if so, finally determine the hot compression parameters; if not, return to step S5;

[0016] S8: Using the final determined hot compression parameters, hot compression is performed on the two axial directions of the alloy part in sequence to finally achieve crack repair.

[0017] Furthermore, in step S1, the specific steps of determining the target temperature of hot compression are: selecting a high-temperature alloy sample for differential scanning calorimetry (DSC) testing, heating the sample to a temperature near the melting point, processing the collected data, and taking the temperature corresponding to 10% of the integrated area of ​​the highest endothermic peak as the target temperature.

[0018] Furthermore, in step S2, in the thermal compression experiment, the insulation time of each control group is the same, which is 20-40 minutes, preferably 30 minutes.

[0019] Furthermore, in step S2, the cooling rate of each control group is the same, which is 8-12°C / min, preferably 10°C / min.

[0020] Furthermore, in step S2, in the hot compression experiment, the stress is kept constant during the compression process, the stress range is 5-15 MPa, and the strain does not exceed 1%.

[0021] Furthermore, in step S3, the specific steps of metallographic sampling and crack porosity statistics are: cutting the alloy sample perpendicular to the compression direction, observing the crack distribution and length using a metallographic microscope after metallographic sampling, and using Image J software to count the porosity of the cracks.

[0022] Furthermore, in step S4, whether the porosity decreases by 0.05% is used as a criterion for whether the closure is obvious.

[0023] Furthermore, in step S5, adjusting the stress / strain parameters includes adjusting the magnitude of the stress / strain and adjusting the compression time.

[0024] Furthermore, in step S7, the specific step of tilting the sample is: rotating the sample 90° to a plane perpendicular to the original compression direction and the material construction direction.

[0025] Furthermore, in step S8, the specific steps of the crack repair are: using the finally determined hot compression parameters to perform hot compression on the two axial directions of the alloy part in sequence, that is, applying external force to the stage where the grains have not yet begun to melt but the grain boundaries have remelted and resolidified, so that the sample can achieve a dense effect after solidification.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention processes the DSC test data of the alloy part sample to obtain the hot compression target temperature, adjusts and verifies it through hot compression experiments, ensures that the obtained stress / strain parameters are accurate and effective, and then achieves complete closure of the cracks under two hot compression processes.

[0028] (2) The present invention uses differential scanning calorimetry (DSC) to collect the melting point information of the target sample, processes the collected data using origin software, and takes the temperature corresponding to 10% of the integrated area of ​​the highest endothermic peak as the target temperature, which can accurately determine the target temperature of subsequent thermal compression.

[0029] (3) The present invention overcomes the problem of the influence of thermal crack defects generated in the laser additive manufacturing process on the organizational properties, and takes into account the possible anisotropy of the internal structure of the material and the orientation of the crack distribution. The two hot compression processes are carried out layer by layer, and the compression parameters are determined by common instruments and simple procedures.

[0030] (4) Compared with the traditional hot isostatic pressing method for repairing cracks, the present invention does not require large equipment and high-pressure energy consumption, and is adjusted and verified through hot compression experiments before formal hot compression to ensure that the obtained stress / strain parameters are accurate and effective, so that only two hot compressions are required in the final crack repair process to achieve crack closure and repair.

[0031] (5) Compared with the traditional hot isostatic pressing method for crack repair, the present invention can greatly shorten the early debugging process. Since the hot isostatic pressing process takes a long time each time, it often takes 7-8 hours for each experiment to find the appropriate parameters and verify the parameters. The repair method of the present invention only takes 30-60 minutes per experiment. Therefore, compared with the hot isostatic pressing process, it can avoid the long trial and error process and save a lot of time.

[0032] (6) Compared with the traditional hot isostatic pressing method for repairing cracks, the present invention can not only control costs, shorten process exploration and design time and processing cycle, and design reasonable compression parameters taking into account possible anisotropy, but also effectively save energy consumption and be easy to operate, which is conducive to its promotion and application in the field of additive manufacturing of alloy parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the process of the crack repairing method of the present invention.

[0034] Figure 2 This is a schematic structural diagram of the thermal compression device of Example 3 of the present invention.

[0035] Figure 3 Schematic diagram of determining the target temperature of thermal compression in Example 3 of the present invention.

[0036] Figure 4 This is the strain-temperature curve measured in Example 3 of the present invention.

[0037] Figure 5 This is a metallographic microscopic observation image of the alloy sample selected in Example 3 of the present invention. DETAILED DESCRIPTION

[0038] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0039] Example 1:

[0040] A hot compression crack repair method that can replace the hot isostatic pressing process, such as Figure 1 As shown, it specifically includes the following steps:

[0041] S1: Use differential scanning calorimetry to collect melting point information of the alloy sample and determine the target temperature of hot compression;

[0042] S2: Select multiple sets of different stress / strain parameters to conduct thermal compression experiments at the target temperature and compare them with each other;

[0043] S3: Metallographic sample preparation, followed by observation and statistics of crack pores;

[0044] S4: Compare the crack conditions of each group before and after hot compression to determine whether the cracks are obviously closed; if so, preliminarily determine the hot compression parameters and execute step S7; if not, execute step S5;

[0045] S5: Adjust the stress / strain parameters during hot compression based on crack closure;

[0046] S6: Determine whether the crack closure is obvious after the stress / strain parameters are adjusted in S5; if so, execute step S7; if not, return to step S5;

[0047] S7: Tilt the sample and perform hot compression again to determine whether the crack is closed; if so, finally determine the hot compression parameters; if not, return to step S5;

[0048] S8: Using the final determined hot compression parameters, hot compression is performed on the two axial directions of the alloy part in sequence to finally achieve crack repair.

[0049] Example 2:

[0050] A hot compression crack repair method that can replace the hot isostatic pressing process includes the following steps:

[0051] S1: Use differential scanning calorimetry to collect melting point information of the alloy sample and determine the target temperature of hot compression;

[0052] The specific steps for determining the target temperature of the hot compression are: selecting a high-temperature alloy sample for differential scanning calorimetry testing, heating the sample to a temperature near the melting point, processing the collected data, and taking the temperature corresponding to 10% of the integrated area of ​​the highest endothermic peak as the target temperature.

[0053] S2: Select multiple sets of different stress / strain parameters to conduct thermal compression experiments at the target temperature and compare them with each other;

[0054] In the hot compression experiment, the holding time for each control group was the same, 30 minutes; the cooling rate for each control group was the same, 10°C / min. During the compression process, the stress was kept constant, ranging from 5 to 15 MPa, and the strain did not exceed 1%.

[0055] S3: Metallographic sample preparation, followed by observation and statistics of crack pores;

[0056] The specific steps are as follows: the alloy sample is cut perpendicular to the compression direction, the crack distribution and length are observed using a metallographic microscope after metallographic sample preparation, and the porosity of the crack is calculated using Image J software.

[0057] S4: Comparing the crack conditions of each group before and after hot compression, and determining whether the cracks are obviously closed, using whether the porosity decreases by 0.05% as the standard for whether the cracks are obviously closed; if so, preliminarily determining the hot compression parameters and executing step S7; if not, executing step S5;

[0058] S5: Adjusting stress / strain parameters during the hot compression process based on the crack closure situation, including adjusting the magnitude of stress / strain and adjusting the compression time.

[0059] S6: Determine whether the crack closure is obvious after the stress / strain parameters are adjusted in S5; if so, execute step S7; if not, return to step S5;

[0060] S7: Rotate the sample 90° to a plane perpendicular to the original compression direction and the material construction direction and perform hot compression again to determine whether the crack is closed; if so, finally determine the hot compression parameters; if not, return to step S5;

[0061] S8: Use the finalized hot compression parameters to sequentially perform hot compression on the two axial directions of the alloy part to ultimately achieve crack repair. The specific steps are: Use the finalized hot compression parameters to sequentially perform hot compression on the two axial directions of the alloy part, that is, apply external force to the stage where the grains have not yet begun to melt but the grain boundaries have remelted and resolidified, so that the sample achieves a dense effect after solidification.

[0062] Example 3:

[0063] This embodiment provides a method for repairing cracks by hot compression that can replace the hot isostatic pressing process. The method includes the following steps:

[0064] Step 1: Select the target material. Take CM247 alloy as an example. Process the sample into a DSC specimen and polish the sample surface. DSC can be used to determine the temperature at which a grain does not melt but the grain boundary melts. The thermogravimetric curve of the sample heated to about 1400°C is obtained. The collected data is processed using Origin software. The horizontal axis where the integrated area of ​​10% of the highest peak is located is taken as the target temperature. Figure 3 As shown, the target temperature at this time is determined to be around 1375°C (however, during the experiment, due to instrument reasons, the temperature can be appropriately lowered to around 1200°C while increasing the stress in order to achieve the expected experimental effect).

[0065] Step 2: Set several different sets of stress / strain parameters and perform hot compression at a constant stress at the temperature determined in the previous step. Each set of heat treatments uses the same 30-minute hold time. After the hold time is complete, set the cooling rate to 10°C / min. This experiment uses a constant stress, with parameters ranging from 5 MPa to 15 MPa. (If the target temperature is too high and the experimental instrument does not function properly, the target temperature can be lowered while increasing the stress / strain parameters.)

[0066] To eliminate other factors that may interfere with the experiment, a control group without pressure should be set up. The shape of the compressed sample should be a regular rectangular parallelepiped that meets the requirements of the instrument. The stress should be kept constant during the compression process, and the strain should not exceed 1%. The compression direction should be perpendicular to the material construction direction. Figure 4 As shown in the figure, the strain-temperature curves of different parameters at the target temperature are tested to determine whether the experimental conditions such as temperature change, sample deformation, and stress during the experiment are appropriate.

[0067] The thermal compression device used in this embodiment is a DIL805 quenching dilatometer. Figure 2 As shown, the alloy sample is clamped by two indenters, which can provide a stable pressure of less than 20kN at high temperatures. Surrounding the alloy sample is an inductor coil, which utilizes a composite design of gas and water channels to achieve rapid and stable heating and cooling. The two wires attached to the sample are used to connect to temperature sensors. A ceramic rod connected to a displacement sensor is located on the side of the indenter. When the sample is strained, the ceramic rod moves, causing the displacement sensor reading to change.

[0068] Step 3: Metallographic sample preparation, observation of crack length and distribution, and calculation of porosity. The specific steps are as follows: cut the sample perpendicular to the compression direction, observe the crack distribution and length using a metallographic microscope after metallographic sample preparation, use Image J software to calculate the porosity of the crack, and compare it with the porosity obtained before the experiment to obtain the changes in the crack before and after the hot compression process.

[0069] Step 4: Compare the crack conditions before and after the experiment and between the control groups. Use whether the porosity decreases by 0.05% as the standard for whether the crack is obviously closed to determine whether it is obviously closed. If so, proceed to step 7; otherwise, proceed to step 5. Figure 5 a is the metallographic photograph of the original alloy sample. Figure 5 b is a metallographic photograph at 1200℃ for 30min and 15Mpa, showing that the number of cracks is significantly reduced.

[0070] Step 5: Adjust the stress / strain parameters during the hot compression process based on the crack closure. Adjusting the stress / strain parameters includes adjusting the magnitude of the stress / strain and the compression time. The initial compression time is set to 10 minutes.

[0071] Step 6: Determine whether the crack closure is obvious after adjusting the parameters. If so, proceed to step 7; if not, return to step 5.

[0072] Step 7: Observe and count the crack pores of the tilted sample after hot compression to determine whether the crack is closed. If so, complete the determination of the experimental parameters after rotating the sample. If not, expand the selection range of stress / strain parameters and return to step 5.

[0073] In step 7, the sample is rotated 90° to a plane perpendicular to the original compression direction and the material construction direction, and a hot compression experiment is performed using the hot compression parameters determined in step 4 or step 6. The parameters of the hot compression control group at this time are also the same as those of the previous control group. A process similar to step 5 is performed, that is, metallographic sample preparation and crack observation and porosity statistics.

[0074] Step 8: Based on the experimental parameters determined in steps 5 and 7, the experimental parameters for closing the cracks before and after rotating the sample are used to implement a hot compression crack repair method that can replace the hot isostatic pressing process. The specific steps are: using a hot compression device to perform hot compression in two axial directions in sequence, that is, applying external force to the stage where the grain boundaries have not yet begun to melt and remelt and resolidify, so that the sample can achieve a dense effect after solidification. The pressure required for the experiment is very small to avoid severe compression deformation of the material. At the same time, the equipment required for the experiment is not demanding, and it can provide stable unidirectional pressure in an environment where the grain boundary remelting temperature of the material is used as the target temperature.

[0075] Compared with the traditional hot isostatic pressing method for repairing cracks, the present invention can not only control costs, shorten process exploration and design time and processing cycle, take into account possible anisotropy to design reasonable compression parameters, but also effectively save energy consumption, is easy to operate, and is conducive to promotion and application.

[0076] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A hot compression crack repair method that can replace the hot isostatic pressing process, characterized in that: The following steps are involved: S1: Use differential scanning calorimetry to collect melting point information of the alloy sample and determine the target temperature of hot compression; S2: Select multiple sets of different stress / strain parameters to conduct thermal compression experiments at the target temperature and compare them with each other; S3: Metallographic sample preparation, followed by observation and statistics of crack pores; S4: Compare the crack conditions of each group before and after hot compression to determine whether the cracks are obviously closed; if so, preliminarily determine the hot compression parameters and execute step S7; if not, execute step S5; S5: Adjust the stress / strain parameters during hot compression based on crack closure; S6: Determine whether the crack closure is obvious after adjusting the stress / strain parameters in S5; If yes, go to step S7, if no, go back to step S5; S7: Tilt the sample and perform hot compression again to determine whether the crack is closed; if so, finally determine the hot compression parameters; if not, return to step S5; S8: Using the final determined hot compression parameters, hot compression is performed on the two axial directions of the alloy part in sequence to finally achieve crack repair; In step S1, the specific steps of determining the target temperature of the hot compression are: selecting a high-temperature alloy sample for differential scanning calorimetry testing, heating the sample to a temperature near the melting point, processing the collected data, and taking the temperature corresponding to 10% of the integrated area of ​​the highest endothermic peak as the target temperature; In step S4, whether the porosity decreases by 0.05% is used as the criterion for whether the closure is obvious; In step S7, the specific step of tilting the sample is: rotating the sample 90° to a plane perpendicular to the original compression direction and the material construction direction.

2. The method for repairing cracks by hot compression that can replace the hot isostatic pressing process according to claim 1, characterized in that: In step S2, in the thermal compression experiment, the holding time of each control group is the same, which is 20-40 minutes.

3. The method for repairing cracks by hot compression that can replace the hot isostatic pressing process according to claim 1, characterized in that: In step S2, in the thermal compression experiment, the cooling rate of each control group is the same, which is 8-12°C / min.

4. The method for repairing cracks by hot compression that can replace the hot isostatic pressing process according to claim 1, characterized in that: In step S2, in the hot compression experiment, the stress is kept constant during the compression process, the stress range is 5-15 MPa, and the strain does not exceed 1%.

5. The method for repairing cracks by hot compression that can replace the hot isostatic pressing process according to claim 1, characterized in that: In step S3, the specific steps of metallographic sample preparation and crack porosity statistics are as follows: The alloy samples were cut perpendicular to the compression direction. After metallographic sample preparation, the crack distribution and length were observed using a metallographic microscope, and the porosity of the cracks was calculated using Image J software.

6. The method for repairing cracks by hot compression that can replace the hot isostatic pressing process according to claim 1, characterized in that: In step S5, adjusting the stress / strain parameters includes adjusting the magnitude of the stress / strain and adjusting the compression time.

7. The method for repairing cracks by hot compression that can replace the hot isostatic pressing process according to claim 1, characterized in that: In step S8, the specific steps of the crack repair are: The final determined hot compression parameters are used to perform hot compression on the two axial directions of the alloy parts in turn, that is, external force is applied at the stage when the grains have not yet started to melt but the grain boundaries are remelted and re-solidified, so that the sample can achieve a dense effect after solidification.

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