Electric pulse treatment method for eliminating pores and rapidly hardening additive manufacturing tool steel

Abstract

The invention provides an electric pulse treatment method for eliminating pores and rapidly hardening additive manufacturing tool steel, and belongs to the technical field of strengthening and toughening of additive manufacturing metal materials. The method comprises the following steps that an additive manufacturing tool steel sample is clamped on electric pulse treatment equipment; high-density direct-current pulse current is applied to the two ends of the additive manufacturing tool steel sample through copper electrodes till the material temperature rises to the aging temperature of 520 DEG C, and the additive manufacturing tool steel sample is strengthened; after the additive manufacturing tool steel sample is cooled to the room temperature, the direct-current pulse current the same as the direct-current pulse current in the step 2 is applied to the same position of the cooled additive manufacturing tool steel sample again; and the additive manufacturing tool steel sample is subjected to multiple times of electric pulse circulation treatment till the number of times reaches a target period, and then the sample is taken down. According to the method, the high-density direct-current pulse current is introduced into the additive manufacturing tool steel sample, the clamping positions of the positive electrode and the negative electrode are flexibly selected, the method is more flexible and efficient compared with traditional heat treatment, hot isostatic pressing and other post-treatment modes, and ultra-fast elimination and local strengthening of additive manufacturing sample pores are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of strengthening and toughening metal materials for additive manufacturing, and in particular to an electric pulse processing method for eliminating pores and rapidly hardening tool steel for additive manufacturing. Background Art

[0002] Metal additive manufacturing technology covers a series of high-precision processes such as powder bed fusion technology, direct metal laser sintering, selective laser melting and direct energy deposition. These technologies are known for their outstanding capabilities, can easily realize the production of complex structural parts, and show extremely high material utilization. In particular, martensitic steel created by additive manufacturing technology has shown extraordinary performance in strength, fracture toughness and energy absorption capacity after aging heat treatment, thus winning a wide range of industry applications. However, it is worth noting that in the precision process of metal additive manufacturing, if the energy input fails to meet the standard or the gas infiltrates accidentally, it may induce the formation of internal porosity defects. These pores are intertwined with factors such as the strong texture effect and a large number of residual dislocations generated during the manufacturing process, which together pose a severe challenge to the mechanical properties of the material, resulting in a significant decline in performance. In view of this, it is particularly critical and important to adopt an effective post-processing process to heal or significantly reduce these pores.

[0003] Currently, there are two main post-processing technologies used to strengthen additively manufactured metal materials and heal porosity defects generated during additive manufacturing technology. One is the muffle furnace heat treatment technology (Reference 1: J. Yan, X. Meng, B. Ou, Y. Xie, B. Cai, Y. Zhang, S. Fang. J. Mater. Res. Technol. 29 (2024) 969-981.), which is characterized by overall heat treatment causing deformation, long processing time, and low cost; the other is hot isostatic pressing technology (Reference 2: N. Mclean, MJ Bermingham, P. Colegrove, A. Sales, N. Soro, CH Ng, MS Dargusch. J. Mater. Process. Tech. 310 (2022) 117769.), which is characterized by overall treatment causing deformation, long processing time, and high cost. In addition to the above two main post-processing methods, there is an electric-assisted micro-forging technology (Document 3: LX Meng, HJ Yang, SGWang, HB Ji, XHShao, ZJ Zhang, DC Ren, X. Zhang, JB Yang, XHAn, YTPei, J. Th. M. De Hosson, R. Yang, ZF Zhang. Mater. Charact. 205 (2023) 113298.), which is characterized by deformation caused by applying pressure and a short action time. The above three post-processing methods all introduce deformation, which will lead to dimensional deviation. In addition, the electric-assisted forging technology continuously applies current for a long time during the forging process, resulting in large energy dissipation.

[0004] In summary, it is necessary to develop a post-processing technology that can perform local processing, does not cause deformation, and has high energy utilization to solve the above problems. Summary of the invention

[0005] In view of the above-mentioned technical problems that local processing is impossible and deformation is easy and utilization rate is low, an electric pulse processing method for eliminating pores and rapid hardening of additive manufacturing tool steel is provided.

[0006] The technical means adopted by the present invention are as follows:

[0007] An electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing comprises the following steps:

[0008] Step 1: Clamp the additively manufactured tool steel sample onto the electric pulse processing equipment;

[0009] Step 2: applying a direct current pulse current through copper electrodes at both ends of the additive manufacturing tool steel sample to strengthen the additive manufacturing tool steel sample;

[0010] Step 3: After the additive manufacturing tool steel sample is cooled to room temperature, the same DC pulse current as in step 2 is applied again to the cooled additive manufacturing tool steel sample at the same position; the additive manufacturing tool steel sample is cycled multiple times until the number of cycles reaches the target cycle, and then the sample is removed.

[0011] Furthermore, the additively manufactured tool steel sample is prepared by laser powder bed fusion technology; the porosity range of the additively manufactured tool steel sample is 0.02 to 5.0‰.

[0012] Furthermore, the additive manufacturing tool steel sample is any one of the martensitic age-hardening steels 18Ni(200), 18Ni(250), 18Ni(300) and 18Ni(350) and the high alloy martensitic age-hardening steels 17-4PH and 15-5PH.

[0013] Furthermore, the area where strengthening is performed is a non-clamping area of ​​the additively manufactured tool steel sample, and local strengthening of the additively manufactured tool steel sample is achieved by adjusting the clamping position of the additively manufactured tool steel sample.

[0014] Furthermore, the application time of the single DC pulse current is: 0.2-1.0s; the density of the DC pulse current is: 60-150A / mm 2 ; The heating rate of the DC pulse current is 500 to 2000°C / s, and the temperature increase range caused by the DC pulse current is 480 to 540°C.

[0015] Furthermore, the peak temperature rise caused by a single DC pulse current is 520°C.

[0016] Furthermore, the current intensity of the DC pulse current is 800-1500A; and the total action time of the DC pulse current is 0.5-10s.

[0017] Furthermore, the target cycle is 1 to 10 times.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The present invention passes a direct current through the additive manufacturing tool steel sample, and the positive and negative electrode clamping positions are flexibly selected. Compared with traditional post-processing methods such as heat treatment and hot isostatic pressing, it is more flexible and efficient, and achieves local area strengthening.

[0020] 2. The present invention introduces a direct current pulse into the additive manufacturing tool steel sample. The current flows through the defect area to generate a vortex and concentrates in the pore tip area. Under the combined action of the thermal pressure stress generated by the Joule thermal effect and the pure electric non-thermal effect to promote atomic diffusion, the pore healing and shrinkage are effectively accelerated.

[0021] 3. The present invention passes a direct current through the clamping end of the additive manufacturing tool steel sample, and the current directly acts on the defect area. At the same time, the electrical energy is directly converted into thermal energy to increase the temperature of the sample, which greatly improves the energy utilization rate.

[0022] 4. The present invention does not apply any external force to the healing and strengthening area, and achieves efficient pore healing efficiency without generating plastic deformation, while quickly realizing dislocation strengthening and strengthening phase precipitation hardening, thereby greatly improving the material strength.

[0023] 5. The total current application time of the electric pulse of the present invention does not exceed 6s, and the total processing time does not exceed 10 minutes, which is much shorter than post-processing technologies such as hot isostatic pressing and electric-assisted micro-forging, greatly improving the production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 It is a schematic diagram of the device of the present invention.

[0026] Figure 2 Schematic diagram of pulse current parameters during the electric pulse treatment process of the present invention; wherein (a) represents the change of current intensity over time; and (b) represents the change of temperature over time.

[0027] Figure 3 The in-situ CT three-dimensional reconstruction model diagram of the pore defects in the electric pulse strengthening process of the present invention; among them, (a) the porosity diagram of the additively manufactured base material, (b) the pore distribution diagram of the same sample after 7 cycles of electric pulses, and (c) the pore distribution diagram of the same sample after 3 pulses again (total number of pulses 10 times).

[0028] Figure 4 The pore defect statistics during the electric pulse strengthening process of the present invention; wherein; (a) represents the volume fraction; (b) represents the healing rate.

[0029] Figure 5This is an analysis of the average orientation difference of the kernel during the electric pulse strengthening process of the present invention; wherein, (a) the average orientation difference of the base material; (b) the average orientation difference after one cycle of electric pulses; (c) the average orientation difference after 10 cycles of electric pulses.

[0030] Figure 6 The XRD diagrams of the samples after being treated with electric pulses for different cycles are shown in FIG.

[0031] Figure 7 The stress-strain curves of the samples after being treated with electric pulses for different times according to the present invention are shown in FIG.

[0032] In the figure: 1. Sample; 2. Copper electrode; 3. Thermal imaging camera; 4. DC power supply. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0034] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0035] like Figure 1-7 As shown, the present invention provides a method for eliminating pores and rapidly hardening tool steel in additive manufacturing by cyclic electric pulse treatment, the method using a high-energy direct current pulse device, such as Figure 1 The two ends of the "dog bone" tensile specimen 1 are clamped with copper electrode chucks 2, and a DC power supply 4 is used to pass a current through the two ends of the specimen. Figure 2 (a) shows a DC pulse current square wave. The current generates Joules inside the sample material to increase the temperature of the sample strengthening area. At the same time, the real-time temperature is measured using a thermal imaging camera 3. The applied current parameters make the sample reach the following Figure 2The peak temperature rise shown in (b) is about 520℃. After the sample cools down to room temperature, the same current is passed again. This process is repeated. When the target cycle is reached, the sample is removed and the experiment is stopped.

[0036] The method of the present invention comprises the following steps:

[0037] Step 1: Clamp the additively manufactured tool steel sample onto the electric pulse processing equipment;

[0038] Step 2: Strengthening the additively manufactured tool steel sample by applying a direct current pulse current through copper electrodes at both ends of the additively manufactured tool steel sample;

[0039] Step 3: After the additive manufacturing tool steel sample is cooled to room temperature, the same DC pulse current as in step 2 is applied again to the cooled additive manufacturing tool steel sample at the same position; the additive manufacturing tool steel sample is cycled multiple times until the number of cycles reaches the target cycle, and then the sample is removed.

[0040] In the present application, the additive manufacturing tool steel sample is prepared by laser powder bed fusion technology; the porosity range of the additive manufacturing tool steel sample is 0.02 to 5.0‰. Preferably, the additive manufacturing tool steel sample is any one of the martensitic type aging hardened steels 18Ni(200), 18Ni(250), 18Ni(300) and 18Ni(350) and the high alloy martensitic aging hardened steels 17-4PH and 15-5PH.

[0041] As a preferred embodiment of the present application, the area where strengthening is performed is the non-clamping area of ​​the additively manufactured tool steel sample, and local strengthening of the additively manufactured tool steel sample is achieved by adjusting the clamping position of the additively manufactured tool steel sample.

[0042] In this application, the application time of a single DC pulse current is: 0.2~1.0s; the density of the DC pulse current is: 60~150A / mm 2 The heating rate of the DC pulse current is 500-2000℃ / s, and the temperature rise range caused by the DC pulse current is 480-540℃. The peak temperature rise caused by a single DC pulse current is 520℃. The current intensity of the DC pulse current is 800-1500A; the total action time of the DC pulse current is 0.5-10s.

[0043] In this application, the target cycle is 1 to 10 times.

[0044] After cyclic electric pulse treatment by the method of the present application, the porosity of additively manufactured 18Ni300 tool steel is reduced from 0.07-0.09‰ to 0.01‰-0.03‰.

[0045] After cyclic electric pulse treatment, the average Kernel orientation difference of the additive manufacturing tool steel increased from 0.6~1 to 1.1~1.3. After 10 cycles of electric pulse, γ-Ni3(Ti,Al) precipitation phase appeared.

[0046] After cyclic electric pulse treatment, the tensile strength of additively manufactured tool steel increased from 1208MPa to 1338~1632MPa.

[0047] Example 1

[0048] In this embodiment, the steps of the new method for achieving pore elimination and rapid hardening of additive manufacturing tool steel by cyclic electric pulse treatment are as follows:

[0049] (1) The additively manufactured 18Ni(300) martensitic steel specimen was clamped on the electric pulse strengthening equipment;

[0050] (2) Apply a direct current of 1240A and a duration of 0.5s to both ends of the sample and heat it to the desired temperature of 520°C. The heating rate is 990°C / s. The current and temperature change with time are shown in Figure 2 shown.

[0051] (3) Wait for the sample to cool to room temperature, apply a DC current of 1240A / 0.5s to both ends of the sample again to raise the temperature to the expected temperature of 520°C, wait for the sample to cool to room temperature again, and repeat this process multiple times until the target cycle is reached.

[0052] Figure 3 This is the in-situ CT 3D reconstruction model of the pore defect during the electric pulse strengthening process. The observation window size is 2mm×6mm×8mm. After 7 cycles of electric pulse strengthening, the pore defect is Figure 3 (a) evolves into Figure 3 In (b), the number of pore defects is significantly reduced, and the defect volume is also significantly reduced. The electric pulse strengthening is applied for another 3 cycles, and the total number of cycles reaches 10. Compared with 7 cycles, the number of pore defects is reduced and the defect volume is also reduced.

[0053] Figure 4 The following is a statistical diagram of pore defects during the electric pulse strengthening process. After 7 cycles of electric pulse strengthening, the pore volume fraction decreased from the initial 0.087‰ to 0.036‰; after 10 cycles of electric pulse strengthening, the pore volume fraction decreased to 0.023‰. The healing rate of pore defects by electric pulse strengthening was 58.6% and 73.6% in 7 and 10 cycles, respectively.

[0054] Figure 5This is the analysis of the geometric mean orientation difference of the Kernel after electric pulse treatment. After one cycle of electric pulse strengthening, the average difference increased from the initial 1.02 to 1.26; after 10 electric pulse strengthenings, the geometric mean difference decreased compared with 7 pulse treatments, but was still higher than the initial base material 1.02, reaching a final value of 1.13.

[0055] Figure 6 The XRD diagram after electric pulse treatment. After one cycle of electric pulse strengthening, the martensite α phase and γ phase did not change significantly; after 10 cycles of electric pulse strengthening, the proportion of martensite α phase decreased, and a new γ-Ni3(Ti,Al) precipitation strengthening phase appeared.

[0056] Figure 7 The stress-strain curve of the sample after electric pulse strengthening. The ultimate tensile strength of the initial base material sample is 1208MPa; after 1, 7, 10, and 14 cycles of electric pulse strengthening, the ultimate tensile strength increases to 1338MPa, 1405MPa, 1633MPa, and 1388MPa, respectively. In the 10th pulse, the total time of the electric pulse is 5s, and a 35% strength increase is achieved.

[0057] In summary, the new method proposed in the present invention for eliminating pores and rapidly hardening additively manufactured tool steel by cyclic electric pulse treatment can quickly and efficiently reduce the pore defects in additively manufactured tool steel without deformation, and greatly improve the tensile strength of additively manufactured tool steel materials or components through dislocation strengthening or precipitation strengthening. The key to the electric pulse strengthening method is to achieve rapid regulation of the additive manufacturing microstructure by changing current parameters such as the number of cycles of current intensity. The present invention does not apply any external force to the strengthening zone, and achieves efficient pore healing without plastic deformation. At the same time, the material strength is greatly improved by inducing microstructural transformation and strengthening phase precipitation. In addition, the total action time of the electric pulse of the present invention does not exceed 6s, and the total processing time does not exceed 10 minutes, which is much lower than post-processing technologies such as hot isostatic pressing and electrically assisted micro-forging, greatly improving the production efficiency and is expected to be widely used in practical engineering.

[0058] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0059] In the above embodiments of the present invention, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0060] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are only schematic. For example, the division of the units can be a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

[0061] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple units. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0062] In addition, each functional unit in each embodiment of the present invention may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0063] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk and other media that can store program codes.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing, characterized in that: The following steps are involved: Step 1: Clamp the additively manufactured tool steel sample onto the electric pulse processing equipment; Step 2: applying a direct current pulse current through copper electrodes at both ends of the additive manufacturing tool steel sample to strengthen the additive manufacturing tool steel sample; Step 3: After the additive manufacturing tool steel sample is cooled to room temperature, the same DC pulse current as in step 2 is applied again to the cooled additive manufacturing tool steel sample at the same position; the additive manufacturing tool steel sample is cycled multiple times until the number of cycles reaches the target cycle, and then the sample is removed.

2. The electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing according to claim 1, characterized in that: The additive manufacturing tool steel sample is prepared by laser powder bed fusion technology; the porosity range of the additive manufacturing tool steel sample is 0.02 to 5.0‰.

3. The electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing according to claim 1 or 2, characterized in that: The additive manufacturing tool steel sample is any one of the martensitic age-hardening steels 18Ni(200), 18Ni(250), 18Ni(300) and 18Ni(350) and the high alloy martensitic age-hardening steels 17-4PH and 15-5PH.

4. The electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing according to claim 1, characterized in that: The area where strengthening is performed is the non-clamping area of ​​the additively manufactured tool steel sample, and local strengthening of the additively manufactured tool steel sample is achieved by adjusting the clamping position of the additively manufactured tool steel sample.

5. The electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing according to claim 1, characterized in that: The application time of the single DC pulse current is: 0.2-1.0s; the density of the DC pulse current is: 60-150A / mm 2 ; The heating rate of the DC pulse current is 500 to 2000°C / s, and the temperature increase range caused by the DC pulse current is 480 to 540°C.

6. The electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing according to claim 5, characterized in that: The peak temperature rise caused by a single DC pulse current is 520°C.

7. The electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing according to claim 1, 5 or 6, characterized in that: The current intensity of the DC pulse current is 800-1500A; the total action time of the DC pulse current is 0.5-10s.

8. The electric pulse treatment method for eliminating pores and rapidly hardening tool steel for additive manufacturing according to claim 1, characterized in that: The target cycle is 1 to 10 times.

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