Method for obtaining a high-strength metal material based on mim

Abstract

This invention relates to the field of metal powder processing technology and discloses a method for obtaining high-strength metal materials based on MIM (Metal Injection Molding). The method includes: preparing feedstock and injection molding to obtain a green body; degreasing the green body to retain residual carbon between 0.02% and 0.08% by mass; using capillary force generated at the particle contact area in the transition temperature zone of the sintering furnace to drive the residual carbon to migrate directionally to the sintering neck; introducing a reducing atmosphere and controlling the pressure fluctuations in the furnace to allow the reducing atmosphere to react with the residual carbon enriched at the sintering neck and precipitate metastable carbide pinning points; adjusting the atmosphere dew point to build a diffusion barrier and densify at the interface; and switching to a high-purity hydrogen atmosphere to drive the decomposition and solid solution of the pinning points. This invention utilizes capillary force to induce the directional precipitation of strengthening phases and eliminate them in the later stage, achieving a deep decoupling between strength improvement and ductility maintenance.

Description

Technical Field

[0001] This invention relates to a method for obtaining high-strength metal materials based on MIM (Metal Injection Molding), belonging to the field of metal powder processing technology. Background Technology

[0002] Currently, the capillary force field at the contact neck of powder particles is used to induce the directional migration of residual carbon on the surface, anchoring metastable carbides to the grain boundary migration path. The extremely low residual carbon content generates interfacial retardation pressure, avoiding the decrease in atomic cross-interface diffusion efficiency caused by conventional full-surface dispersion strengthening, thus enabling parts to achieve high density and maintain a fine-grained structure. The slope of the real-time linear shrinkage rate of the degreased blank during sintering is obtained and the dew point environment of the furnace atmosphere is adjusted to construct controlled chemical potential damping at the carbide-matrix interface, compensating for diffusion kinetic deviations caused by fluctuations in powder particle size distribution, and enabling the raw materials to complete densification and locking within a preset temperature range, thereby improving the consistency of the microstructure in the mass production of complex and precision parts.

[0003] The controlled atmosphere is forced to flow through the pores inside the degreased billet by a pulsed circulating pressure wave driven in the sintering furnace, breaking through the stagnant layer at the powder particle interface and ensuring that metastable carbide pinning points are uniformly precipitated throughout the radial range of the degreased billet, thus eliminating the difference in grain size gradient between the inside and outside of complex structural parts. Previous optimizations have mostly focused on the accuracy of the mold cavity or the later shaping process. Due to the limitations of equipment positioning and mold life, the physical reinforcement path is obviously limited. Existing solutions mostly rely on hard compaction to obtain high density. For example, Chinese invention patent with publication number CN113210606A discloses a method for re-pressing and re-firing of metal injection molding powder metallurgy. After pre-firing, the internal pores of the billet are compacted by secondary mechanical re-pressing. Although mechanical cold pressing increases the macro density of the material, it is easy to induce irreversible micro-damage or micro-cracks at the particle contact neck. Moreover, the uneven wall thickness of irregular parts makes the pressure transmission of re-pressing in one direction uneven, resulting in an anisotropic stress field inside the part.

[0004] Therefore, how to monitor the change rate of characteristic molecular signal concentration of degreasing by-products at the exhaust end of the sintering furnace to determine the pore connectivity state inside the powder pack, so that the timing of atmosphere switching is aligned with the real-time physical structure characteristics of the degreased billet, eliminate gas mass transfer lag caused by differences in furnace loading or fluctuations in part geometry, and enable the first controlled atmosphere to penetrate into the core of the part when the particle surface activity is strong, has become the technical problem to be solved by this invention. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A method for obtaining high-strength metallic materials based on MIM, comprising the following steps: Step 101: Prepare a feed containing metal powder and binder, and use the feed injection molding to obtain a green body; Step 102: Degreasing treatment is performed on the green blank. By adjusting the flow rate of the protective gas during the hot degreasing stage, the mass percentage of residual carbon on the surface of the metal particles in the obtained degreased blank is kept between 0.02% and 0.08%. Step 103: Place the degreased blank in the sintering furnace. In the transition temperature range before the temperature reaches the first temperature range, control the heating rate to be less than 3°C per minute. Use the capillary force formed by the geometric curvature of the particle contact area to drive the residual carbon to migrate to the sintering neck. Step 104: Heat to the first temperature range, introduce a reducing atmosphere containing alkane gas into the sintering furnace, and control the internal pressure of the sintering furnace to a first pressure value. With the second pressure value The pressure pulse drives the reducing atmosphere to flow in the pores inside the degreased blank, causing the reducing atmosphere to react with the residual carbon enriched at the sintering neck, resulting in the in-situ precipitation of metastable carbide pinning points with an average particle size of less than 100 nanometers at the sintering neck. Step 105: Heat to the second temperature range and hold. Collect the real-time sintering shrinkage rate of the degreased blank through the displacement detection device, calculate the slope of the real-time sintering shrinkage rate, and adjust the atmosphere dew point in the sintering furnace according to the deviation between the slope of the real-time sintering shrinkage rate and the shrinkage reference model characterizing the theoretical densification rate of the degreased blank. Form a diffusion barrier at the interface between the metastable carbide pinning point and the metal matrix, so that the metastable carbide pinning point maintains a non-coherent state before densification is completed to suppress grain boundary migration. Step 106: Heat to the third temperature range and switch to a high-purity hydrogen atmosphere. Use the reducing environment to drive the metastable carbide pinning points to decompose and solidify into the metal matrix.

[0006] Preferably, in step 104, the pore connectivity of the degreased blank is determined by monitoring the change rate of the formaldehyde characteristic molecule signal generated by the degreasing aid decomposition in the exhaust end of the sintering furnace; when the concentration change rate enters the preset stable range, a reducing atmosphere is triggered to be introduced, and the highly active surface effect after the pores are connected is used to allow the reducing atmosphere to penetrate to the sintering neck of the metal particle contact area.

[0007] Preferably, in step 101, by controlling the mixing temperature and shear rate, the binder forms a micron-scale coating layer on the surface of the metal powder particles, so as to provide a spatial distribution benchmark for the residual carbon mass percentage in step 102.

[0008] Preferably, in step 102, the degreasing process includes solvent degreasing and thermal degreasing, and the residual carbon mass percentage on the surface of the metal particles is locked by adjusting the protective gas flow rate during the thermal degreasing stage.

[0009] Preferably, in step 104, the reducing atmosphere is a hydrogen-based reducing atmosphere, and the reduction rate and carbonization rate on the surface of the metal particles are balanced by adjusting the partial pressure of the alkane gas.

[0010] Preferably, in step 105, a cyclic heating and cooling program is used within the second temperature range to make the sintering temperature fluctuate periodically with a preset range, and the residual stress at the sintering neck is dynamically relaxed by using transient thermal stress.

[0011] Preferably, before performing step 103, a surface activation step is further included: placing the degreased blank at an activation temperature and introducing a polar gas medium to construct highly chemically active defect sites on the oxide film on the surface of the metal particles, wherein the activation temperature is lower than a first temperature range.

[0012] Preferably, the defect sites are used to reduce the initial activation energy of the in-situ carbonization reaction in step 104, forming a uniformly distributed nucleation template on the surface of the metal particles, so as to guide the metastable carbide pinning points to precipitate uniformly in space.

[0013] Preferably, the interfacial resistance pressure generated by the metastable carbide pinning points on the surface of the metal particles The following quantitative relationship must be satisfied: ,in, For interfacial resistance pressure, For grain boundary energy, This represents the volume fraction of metastable carbide pinning points. The average particle size of the pinning points of the metastable carbide.

[0014] Preferably, the grain size of the metal matrix after step 106 is isotropic, and the yield strength of the obtained metal material is not lower than the yield strength of the material obtained by sintering the raw material metal powder under a single constant pressure reducing atmosphere.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In MIM high-strength metal materials, the capillary force field at the contact neck of powder particles is used to induce the directional migration of residual carbon on the surface, so that metastable carbides are anchored on the necessary migration path of grain boundaries. Under the set residual carbon retention amount, interfacial retardation pressure is generated, avoiding the decrease in atomic cross-interface diffusion efficiency caused by conventional full-surface dispersion strengthening, so that the parts achieve high density and maintain fine grain structure.

[0016] 2. Obtain the slope of the real-time linear shrinkage rate during the sintering process of the degreased billet and dynamically adjust the dew point environment of the furnace atmosphere. Construct controlled chemical potential damping at the interface between carbides and matrix to compensate for the diffusion kinetic deviation caused by the fluctuation of the original powder particle size distribution. This enables different batches of raw materials to complete densification and locking within the preset temperature range window, thereby improving the consistency of the mass production structure of complex and precision parts.

[0017] 3. A three-stage controlled potential sintering logic is adopted to generate and eliminate strengthening phases. In the middle stage of sintering, in-situ precipitation of nano-scale carbides is used to pin grain boundaries. During the high-temperature stage of densification, a strong reducing atmosphere is switched to drive carbon atoms to dissolve into the matrix lattice, restoring the material's ductility and eliminating brittle phases in the matrix, thus solving the problem of balancing strength and toughness in high-strength powder metallurgy parts. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the process for preparing MIM high-strength metallic materials with graded control of key parameters in this invention. Figure 2 This is a graph showing the co-evolution of the furnace environment and pinning point growth kinetics under the pressure pulsation field of this invention. Figure 3 This is a diagram of the intelligent sintering hardware architecture and closed-loop control logic of the present invention, which features multi-source real-time feedback. Detailed Implementation

[0019] To make the technical problems to be solved, the technical solutions and the beneficial effects of the present invention clearer, the present invention will be further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the scope of protection of the present invention.

[0020] This invention provides a method for preparing high-strength metallic materials based on metal injection molding. By synergistically controlling the residual carbon content during the debinding stage and the non-equilibrium carbon potential during the sintering stage, uniformly distributed metastable carbide pinning points are generated in situ at the contact neck of powder particles. The interfacial diffusion barrier is adjusted using the real-time sintering shrinkage slope, achieving high densification while suppressing grain coarsening. Finally, high-temperature solution treatment drives carbon atoms into the metal matrix to restore the material's ductility. In the feed stage, which prepares the material containing metal powder and binder, the median particle size is selected... 10 m to 15 Metal powder of mass m was mixed with a composite polymer binder containing paraffin, polypropylene, and stearic acid in a twin-screw mixer. The mixing temperature was set to 160°C to 180°C, and the screw shear rate was controlled between 150 rpm and 200 rpm. This allowed the molten binder to form a uniform micron-sized coating layer on the surface of the metal powder particles. After mixing, the resulting feedstock was injected into a mold cavity under a pressure of 30 MPa to 50 MPa, and cooled to obtain a green compact. This provided a spatial distribution benchmark for determining the residual carbon percentage in subsequent processes. To lock in the residual carbon content in the degreased compact, a two-stage degreasing process was performed. Solvent degreasing was carried out in trichloroethylene solvent at 40°C, and the resulting degreased compact was placed in a hot degreasing furnace. Within the hot degreasing temperature range of 450°C to 600°C, the argon protective gas flow rate was dynamically adjusted by monitoring the rate of change of the total pressure inside the furnace in real time. When the pressure rise rate exceeds a preset threshold, The flow rate was increased to 5 L / min to accelerate the removal of volatile components, thereby ensuring that the residual carbon mass percentage on the surface of the metal particles in the resulting degreased preform is between 0.02% and 0.08%.

[0021] During the transition temperature range of the sintering heating process, the degreased blank is placed in the sintering furnace; when the temperature rises to the first temperature range... Within the previous temperature range of 400℃ to 700℃, the heating rate was controlled to be no higher than 3℃ / min; the capillary force field generated by the geometric curvature of the particle contact area was used to drive the amorphous carbon remaining on the particle surface to migrate directionally towards the particle contact neck, thereby achieving local enrichment of carbon components at the initiation site of grain boundary migration; the temperature was then increased to the first temperature range. Then, a hydrogen-based reducing atmosphere containing methane is introduced into the furnace, while a pressure pulsating permeation program is executed; the opening of the flow valve is alternately adjusted to maintain the furnace pressure at a first pressure value of 50 kPa. The second pressure value of 101 kPa The process involves cyclical fluctuations with a period of 300 seconds, using a pressure gradient to drive the reducing atmosphere to flow through the pores inside the degreased preform. During this process, the characteristic molecular signal of formaldehyde at the exhaust end of the furnace is monitored using gas chromatography, and its concentration change rate is calculated. ;when When the pressure drops to 0.0001% / min and enters a stable range, the internal pores of the degreased blank are determined to be interconnected. This triggers a reaction between the reducing atmosphere and the residual carbon enriched at the sintering neck, resulting in the in-situ precipitation of metastable carbide pinning points with an average particle size of less than 100 nanometers at the sintering neck. The central pressure response curve under a 5 kPa step pressure is captured by a pressure sensor, and the pressure relaxation time is extracted. A fluid permeation model was constructed based on Darcy's law, and the pulsation period was set. The driving reducing atmosphere completely penetrates the central pores of the degreased blank, combined with the formaldehyde characteristic signal concentration change rate. Once the signal enters the stable range of 0.0001% / min, it confirms that the internal closed pores have completed the material exchange to the carbide precipitation point and locks the pulse frequency. The reducing atmosphere is then driven by the pressure gradient to flow uniformly throughout the radial range of the degreased billet.

[0022] When the temperature rises to the second temperature range During the densification stage, the linear shrinkage of the defatted preform is collected in real time using a laser displacement detection device. And calculate the slope of real-time sintering shrinkage rate. The system compares the real-time slope with the pre-stored contraction baseline model. If it detects... If the deviation from the reference value exceeds 10%, the amount of water vapor introduced into the mixed atmosphere is adjusted; the atmosphere dew point is locked between -30℃ and -20℃, inducing chemical potential damping at the interface between the metastable carbide pinning points and the metal matrix; this damping effect slows down the solidification rate of residual carbon into the matrix, ensuring that the metastable carbide pinning points remain in a non-coherent state before densification is complete, generating interfacial resistance pressure. Satisfying quantitative relationships ,in, For interfacial resistance pressure, For grain boundary energy, This represents the volume fraction of metastable carbide pinning points. The average particle size of the metastable carbide pinning points; through the action of the aforementioned interfacial retardation pressure, grain boundary migration is suppressed and the densification of metal particles is completed; the displacement detection device reads the linear shrinkage amount every 50ms. The five-point cubic smoothing algorithm is applied to suppress sampling noise and calculate the real-time contraction slope. Compare with the pre-stored baseline slope function Obtain the deviation magnitude and trigger the dew point compensation logic. The proportional compensation coefficient β, ranging from 0.5 to 1.5 °C·s, is derived from atmospheric response hysteresis testing. Adjusting the amount of water vapor injected into the mixed atmosphere corrects the interfacial oxygen potential, inducing the formation of a solute-enriched layer with a thickness of 1–3 nm to generate interfacial hindrance pressure. To counteract the driving force of grain boundary migration, the deviation of yield strength of microstructure between different production batches is limited to within 5%.

[0023] To eliminate the microscopic residual stress accumulated in the sintering neck due to asymmetric diffusion, in the second temperature range The constant temperature section executes a periodic temperature control program; controlling the sintering temperature within a preset range of 20°C. Periodic temperature fluctuations are employed to drive dynamic relaxation of dislocations at the particle contact necks using transient thermal stress generated by temperature fluctuations, thereby suppressing the initiation of microcracks within the sintered body. After densification is completed, the temperature is raised to the third temperature range. The furnace atmosphere is switched to a high-purity hydrogen atmosphere with a purity of 99.999%. The strong reducing environment drives the decomposition of metastable carbide pinning points, allowing carbon elements to completely dissolve into the crystal lattice of the metal matrix. After performing this high-temperature solid solution step, the grain structure of the part exhibits uniform and refined characteristics. While eliminating brittle phases, the material's ductility is restored, ensuring that the yield strength of the final metal material is not lower than that of the material obtained by sintering the raw material metal powder under a single constant pressure reducing atmosphere.

[0024] Example 1: In specific industrial applications, when using metal injection molding to fabricate aviation fuel nozzle parts with large aspect ratios and uneven wall thickness, the main technical challenges are the uneven densification and localized grain coarsening caused by differences in diffusion kinetics in different parts of the part. To address these challenges, during the two-stage debinding process of the green blank, the argon flow rate in the hot debinding stage is adjusted. The percentage of residual carbon on the surface of the metal powder particles in the degreased blank is controlled between 0.02% and 0.08%, and the temperature is raised to the first temperature range. Previously, the heating rate was controlled to be no higher than 3℃ / min within the range of 400℃ to 700℃. The capillary force generated by the geometric curvature of the particle contact area was used to drive the residual carbon to migrate towards the sintering neck, causing local enrichment of the carbon component at the grain boundary migration initiation site. This provides the material basis for the subsequent precipitation of the strengthening phase. In the first temperature range... Inside, the pressure inside the sintering furnace is adjusted to a first pressure value of 50 kPa via a flow valve. The second pressure value of 101 kPa The process circulates in cycles of 300 seconds, driving a reducing atmosphere containing methane components into the pores inside the degreased blank and reacting with the residual carbon enriched at the sintering neck, resulting in the in-situ precipitation of metastable carbide pinning points with an average particle size of less than 100 nm at the sintering neck.

[0025] Second temperature range During the densification stage, the laser displacement detection device monitors the linear shrinkage of the defatted preform in real time. To calculate the slope of real-time sintering shrinkage rate When the slope deviates from the reference value by more than 10%, the atmosphere dew point is locked between -30°C and -20°C, inducing chemical potential damping at the interface between the metastable carbide pinning point and the metal matrix, thereby generating interfacial blocking pressure. It satisfies the quantitative relationship ,in, For interfacial resistance pressure, For grain boundary energy, This represents the volume fraction of metastable carbide pinning points. The average grain size of the metastable carbide pinning points; utilizing this interfacial resistance pressure to suppress grain boundary migration before densification is complete, achieving simultaneous satisfaction of high densification requirements and grain size control requirements within a single heat treatment cycle; as the pores of the part close, in the third temperature range Switching to a high-purity hydrogen atmosphere with a purity of 99.999% drives the metastable carbide pinning points to decompose and completely dissolve into the metal matrix lattice, eliminating the brittle phase in the sintering neck and achieving uniform and refined microstructure. This ensures that the yield strength of the final aviation fuel nozzle part is not lower than that of the material obtained by sintering the raw material metal powder under a single constant pressure reducing atmosphere, and the elongation at break is not less than 15%. The degreasing residual components are transformed from impurities into a functional strengthening array.

[0026] Example 2: This experiment evaluates the effect of improving microstructure uniformity and toughness during the preparation of thick-walled 316L stainless steel structural parts. The experimental platform consists of a vacuum partial pressure sintering furnace equipped with an online gas chromatography monitoring unit and a laser displacement sensor. Data is obtained from real-time acquisition by this physical experimental platform, where the laser displacement sensor has a measurement resolution of 0.5. The sampling frequency was set to 20Hz, which is sufficient to support the accurate calculation of the sintering shrinkage slope. To verify the stability of the scheme in a real industrial environment, Gaussian white noise with a signal-to-noise ratio of 25dB was superimposed on the furnace pressure monitoring signal during the experiment, and a temperature control disturbance of 1.5℃ was preset. The key process parameter was the argon protective gas flow rate. The setting is controlled by the polymer thermal degradation rate. When an increase in the total pressure inside the furnace is detected, causing the carbon potential to deviate from the preset equilibrium state, the setting is adjusted by increasing the... To improve the efficiency of volatile component removal, the residual carbon mass percentage on the surface of metal particles in the degreased blank is kept between 0.02% and 0.08%. For a sample with a wall thickness of 20 mm, when the thermal degradation partial pressure rises to 500 Pa, Increase the speed from 2L / min to 5L / min.

[0027] During the verification process, the median particle size was selected. It is 12.4 Three groups of test samples with different wall thickness gradients were prepared using stainless steel powder of m, and a control group of samples was set up and sintered in a constant pressure reducing atmosphere. The temperature was raised to the first temperature range. In the previous temperature range of 400℃ to 700℃, the test samples were operated at a heating rate of 2.5℃ / min, utilizing the capillary force generated by the geometric curvature of the particle neck to drive the directional migration of residual carbon into the first temperature range. Then, the pressure pulsation permeation program was started, and the pressure was switched cyclically between 50 kPa and 101 kPa in 300s. Table 1 below records the microstructure and mechanical property test results of different groups after densification. The control group used the same powder and sintered at 1350℃ for 2h under constant pressure hydrogen environment.

[0028] Table 1: Comparison of Experimental Data

[0029] Observing the data in Table 1, the control group showed grain coarsening due to the lack of an interfacial hindrance mechanism, while samples 1 to 3 of this invention maintained a fine-grained structure under different wall thickness conditions, and the yield strength was no less than 1.4 times that of the control group. This is attributed to the pressure pulsating permeation process ensuring uniform diffusion of methane atmosphere inside the degreased blank, causing metastable carbide pinning points to precipitate in the entire radial range, thereby generating interfacial hindrance pressure. Satisfying quantitative relationships: ,in, This is the interfacial resistance pressure, expressed in Pa. This represents the grain boundary energy of 316L stainless steel at the sintering temperature, expressed in J / m. 2 ; The volume fraction of metastable carbide pinning points; The average particle size of the metastable carbide pinning points is expressed in meters (m). This value is calculated based on actual measurements. At 0.15% and When the size is less than 100 nm, the resulting resistance pressure is sufficient to counteract the grain boundary migration driving force.

[0030] To verify the rationality of the set range of residual carbon content, an out-of-range control group was designed. Table 2 below records the performance evolution when the residual carbon mass percentage deviates from the range of 0.02% to 0.08%. When the residual carbon percentage is below 0.015%, due to insufficient reactant concentration, the number of metastable carbide pinning points formed is sparse, which cannot generate sufficient interfacial retardation pressure, resulting in abnormal local grain growth. When the residual carbon percentage exceeds 0.12%, the excess carbon atoms cause the pinning points to coarsen and enter the coherent state prematurely. Moreover, after the final solid solution step, there are still undecomposed network carbides, which cause the elongation at break of the material to decrease from 18.5% to 6.2%, confirming that the residual carbon mass percentage range is a working window that takes into account both grain refinement and ductility recovery.

[0031] Table 2: Boundary Verification Table for Key Parameters

[0032] Experimental results confirm that by synergistically regulating the migration of degreasing residual carbon and the pressure pulsation carbonization reaction, the present invention can construct a thermally stable damping structure by utilizing the in-situ chemical response within the material without changing the material composition, thus solving the deviation in grain coarsening patterns during the densification process of metal injection molded parts.

[0033] Example 3: This example combines Figures 1 to 3 This describes a method for obtaining high-strength metallic materials based on MIM, such as... Figure 1As shown, in step 101, a green body is obtained by preparing a feedstock containing metal powder and binder and injection molding. In step 102, the green body undergoes degreasing and residual carbon control. The residual carbon is kept within a certain range by adjusting the protective gas flow rate. to In the intermediate temperature range, step 103 is executed, in which capillary force is used to drive the residual carbon to migrate directionally to the sintering neck during the heating process. Then, step 104 is executed, in which pressure pulsation is used to drive the reducing atmosphere during the reaction stage in the first temperature range, and metastable carbide pinning points are precipitated in situ at the sintering neck. During the densification process in the second temperature range in step 105, the atmosphere dew point is adjusted to build a diffusion barrier and maintain the incoherent state to suppress grain boundary migration. At the same time, the real-time sintering shrinkage rate slope calculated from the displacement detection device is received as data feedback to close the loop and adjust the atmosphere. Finally, step 106 is executed, in which a high-purity hydrogen atmosphere is switched during the solid solution stage in the third temperature range to drive the pinning points to decompose and solidify, and finally a high-strength metal material is obtained.

[0034] like Figure 2 As shown in the figure, the graph uses time (s) as the horizontal axis to display the variation curves of three physical quantities: the number of pinning points, the average particle size of the pinning points, and the furnace pressure. The furnace pressure is shown in the figure. Presented as in to A sawtooth waveform that fluctuates periodically; the number of pinning points increases over time ( The pressure showed a rapid increase followed by a stabilization, while the average particle size of the pinning points (nm) showed a continuous increasing trend, indicating that as the pressure pulsation proceeded, the number of pinning points increased along with the evolution of particle size; for example... Figure 3 As shown, this architecture uses a vacuum partial pressure sintering furnace and its internal degreased blanks as the core of the physical reaction. Externally, it is coordinated with a pressure pulsation control unit, an atmosphere dew point adjustment unit, a laser displacement detection device, and an online gas chromatograph. The intelligent feedback control center at the top level of the system is responsible for slope calculation and logical judgment. It interacts with each execution unit through the data link shown by the dotted line: the intelligent feedback control center sends a pulsation command to the pressure pulsation control unit, driving it to output a circulating pressure wave to the sintering furnace. At the same time, it sends a dew point correction command to the atmosphere dew point adjustment unit to adjust the controlled atmosphere input to the sintering furnace. The laser displacement detection device emits a laser beam to the sintering furnace and receives the reflected signal, transmitting the collected shrinkage data back to the control center. The online gas chromatograph samples and analyzes the exhaust gas from the sintering furnace and feeds back the concentration signal to the intelligent feedback control center, thus constructing a complete closed-loop control circuit.

[0035] Example 4: In the production of precision parts facing uncertainties in microstructure evolution due to batch-to-batch fluctuations in powder properties, in order to determine the fluctuation period in the pressure pulsation permeation process, in-situ measurement of the permeability of the degreased preform was performed based on Darcy's law. Specifically, a 5 kPa instantaneous pressure step was applied to the sintering furnace before the start of step 104, and the relaxation time of the pressure at the center of the degreased preform was recorded using a differential pressure sensor with a resolution better than 10 Pa. According to the relaxation time Establish pressure fluctuation cycle The selection logic is based on the pressure fluctuation cycle. Meets a relaxation time of at least 10 times. The constraints, if the measured relaxation time If it is 25 seconds, then the pressure fluctuation period will be... The time was set to 300 seconds to ensure that the reducing atmosphere completely penetrated into the center of the degreased blank within each pressure pulse cycle. To adjust the atmosphere dew point environment, linear shrinkage curves of standard samples from the same batch were recorded under a constant hydrogen atmosphere of 101 kPa before sintering to obtain the baseline shrinkage rate slope function. In step 105, the controller reads the linear contraction amount collected by the laser displacement detection device every 50ms. The slope of the real-time sintering shrinkage rate was calculated using a five-point cubic smoothing algorithm. When the slope of real-time sintering shrinkage rate is monitored Deviation from baseline shrinkage slope function When the amplitude exceeds 10%, the atmosphere dew point is corrected by adjusting the water vapor injection rate. The adjustment amount of the atmosphere dew point satisfies the following linear mapping relationship: ,in, This is the dew point adjustment increment, in °C; This is the proportional compensation coefficient, and its value ranges from 0.5℃. s to 1.5℃ Between s; The slope of the real-time sintering shrinkage rate is expressed in units of 1 / s; The slope value represents the baseline shrinkage rate at the corresponding temperature, in units of 1 / s. By locking the dew point within the range of -30℃ to -20℃, the oxygen potential at the interface between the metastable carbide pinning point and the metal matrix is ​​altered, forming a solute-rich layer with a thickness between 1nm and 3nm at the interface, thereby regulating the interfacial resistance pressure. .

[0036] Interface resistance pressure The physical mechanism that produces this phenomenon satisfies the following equation: ,in, This is the interfacial resistance pressure, expressed in Pa. This is the grain boundary energy after dew point adjustment, expressed in J / m.2 ; The volume fraction of metastable carbide pinning points; The average particle size of the metastable carbide pinning points, in meters; when the real-time sintering shrinkage slope is monitored... When the temperature is higher than the reference value, the grain boundary energy is reduced by raising the dew point to -22°C. This allows for in-situ adjustment of the interface resistance pressure without altering the physical dimensions of the pinning points. To inhibit grain growth, in the process of verifying the uniformity of the microstructure after densification, the compositional data of the exhaust end of the sintering furnace was collected using an online gas chromatograph, and the concentration change rate of formaldehyde characteristic molecules was calculated. When the rate of change of concentration When the pressure pulsation rate stabilizes below 0.0001% / min for more than 10 minutes, it is determined that the internal pores of the part have completed the material exchange to the carbide precipitation points. The pressure pulsation is then automatically terminated and the temperature is raised to the third temperature range. Perform solution treatment.

[0037] Example 5: In the mass production preparation scenario for precision parts, to eliminate the interference of furnace loading density on the determination of sintering kinetics, a sintering shrinkage reference data calibration procedure is implemented. Before the first batch of processing, a standard sample with the same material as the part to be produced is placed at the center of the effective heating zone of the sintering furnace. The temperature is programmed to rise under a constant hydrogen atmosphere of 101 kPa, and the linear shrinkage of the standard sample is recorded in real time using a laser displacement detection device. The controller performs filtering operations on the displacement signal and calculates the shrinkage slope as a function of temperature. It then performs a weighted average operation on the collected slope data to obtain the baseline shrinkage slope function. and the baseline shrinkage rate slope function It is stored inside the controller as an input reference for subsequent process adjustments.

[0038] To determine the proportional compensation coefficient in the control logic In the first temperature range Before the end of the test, an atmosphere response hysteresis test was performed at a constant temperature. This involved adjusting the steam flow rate to trigger a 5°C dew point step signal within the furnace, and simultaneously recording the time required for the ambient dew point value to rise to 90% of its amplitude using a dew point sensor. A proportional compensation coefficient was then determined based on this time period. The quantified value is such that it is at 0.5℃ s to 1.5℃ Within the range of s, thereby driving the atmosphere dew point adjustment increment in subsequent densification steps. Corrected real-time sintering shrinkage slope The procedure corrects for fluctuations in gas source path within the furnace body, thus mitigating the time lag caused by different gas source paths and reducing interfacial pressure resistance. Maintaining atomic diffusion balance at the interface during the densification stage limits the deviation in microstructure yield strength between different production batches to within 5%.

[0039] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for obtaining a high-strength metal material based on MIM, characterized in that, Includes the following steps: Step 101: Prepare a feed containing metal powder and binder, and use the feed injection molding to obtain a green body; Step 102: Degreasing treatment is performed on the green blank. By adjusting the flow rate of the protective gas during the hot degreasing stage, the mass percentage of residual carbon on the surface of the metal particles in the obtained degreased blank is kept between 0.02% and 0.08%. Step 103: Place the degreased blank in the sintering furnace. In the transition temperature range before the temperature reaches the first temperature range, control the heating rate to be less than 3°C per minute. Use the capillary force formed by the geometric curvature of the particle contact area to drive the residual carbon to migrate to the sintering neck. Step 104, heating to a first temperature range, introducing a reducing atmosphere containing alkane gas into the sintering furnace, controlling the internal pressure of the sintering furnace to cycle between a first pressure value and a second pressure value The pressure fluctuation drives the reducing atmosphere to flow in the internal pores of the debinding blank, and makes the reducing atmosphere react with the residual carbon enriched at the sintering neck, so as to precipitate metastable carbide pinning points with an average particle size of less than 100 nanometers in situ at the sintering neck.​ Step 105: Heat to the second temperature range and hold. Collect the real-time sintering shrinkage rate of the degreased blank using a displacement detection device, calculate the slope of the real-time sintering shrinkage rate, and adjust the atmosphere dew point in the sintering furnace based on the deviation between the real-time sintering shrinkage rate slope and the shrinkage benchmark model characterizing the theoretical densification rate of the degreased blank. This creates a diffusion barrier at the interface between the metastable carbide pinning points and the metal matrix, maintaining the metastable carbide pinning points in a non-coherent state before densification is complete to suppress grain boundary migration. The linear shrinkage amount collected by the laser displacement detection device is read every 50ms using a controller. The slope of the real-time sintering shrinkage rate was calculated using a five-point cubic smoothing algorithm. When the slope of real-time sintering shrinkage rate is monitored Deviation from baseline shrinkage slope function When the amplitude exceeds 10%, the atmosphere dew point is corrected by adjusting the water vapor injection rate. The adjustment amount of the atmosphere dew point satisfies the following linear mapping relationship: ,in, This is the dew point adjustment increment, in °C; This is the proportional compensation coefficient, and its value ranges from 0.5℃. s to 1.5℃ Between s; The slope of the real-time sintering shrinkage rate is expressed in units of 1 / s; This represents the baseline shrinkage slope value at the corresponding temperature, in units of 1 / s; Step 106: Heat to the third temperature range and switch to a high-purity hydrogen atmosphere. Use the reducing environment to drive the metastable carbide pinning points to decompose and solidify into the metal matrix.

2. The method for obtaining a high-strength metal material based on MIM according to claim 1, characterized in that, In step 104, the pore connectivity of the degreased blank is determined by monitoring the change rate of the formaldehyde characteristic molecule signal generated by the degreasing aid decomposition in the exhaust end of the sintering furnace; when the concentration change rate enters the preset stable range, a reducing atmosphere is triggered to be introduced, and the highly active surface effect after the pores are connected is used to allow the reducing atmosphere to penetrate to the sintering neck of the metal particle contact area.

3. The method for obtaining high-strength metallic materials based on MIM according to claim 1, characterized in that, In step 101, by controlling the mixing temperature and shear rate, the binder forms a micron-scale coating layer on the surface of the metal powder particles, so as to provide a spatial distribution benchmark for the residual carbon mass percentage in step 102.

4. The method for obtaining high-strength metallic materials based on MIM according to claim 1, characterized in that, In step 102, the degreasing process includes solvent degreasing and thermal degreasing, and the residual carbon mass percentage on the surface of the metal particles is locked by adjusting the protective gas flow rate during the thermal degreasing stage.

5. The method for obtaining high-strength metallic materials based on MIM according to claim 1, characterized in that, In step 104, the reducing atmosphere is a hydrogen-based reducing atmosphere, and the reduction rate and carbonization rate on the surface of the metal particles are balanced by adjusting the partial pressure of the alkane gas.

6. The method for obtaining high-strength metallic materials based on MIM according to claim 1, characterized in that, In step 105, a cyclic heating and cooling program is used within the second temperature range to make the sintering temperature fluctuate periodically with a preset range, and the residual stress at the sintering neck is dynamically relaxed by using transient thermal stress.

7. The method for obtaining high-strength metallic materials based on MIM according to claim 1, characterized in that, Before performing step 103, a surface activation step is also included: placing the degreased blank at an activation temperature and introducing a polar gas medium to construct highly chemically active defect sites on the oxide film on the surface of the metal particles, wherein the activation temperature is lower than a first temperature range.

8. The method of claim 7, wherein the MIM high-strength metal material is obtained by the steps of: By utilizing defect sites to lower the initial activation energy of the in-situ carbonization reaction in step 104, a uniformly distributed nucleation template is formed on the surface of the metal particles to guide the uniform spatial precipitation of metastable carbide pinning points. ​ 9. The method for obtaining high-strength metallic materials based on MIM according to claim 1, characterized in that, The interfacial resistance pressure generated by metastable carbide pinning points on the surface of metal particles The following quantitative relationship must be satisfied: ,in, For interfacial resistance pressure, For grain boundary energy, This represents the volume fraction of metastable carbide pinning points. The average particle size of the pinning points of the metastable carbide.

10. The method of claim 1, wherein the MIM high strength metal material is obtained by the steps of: The grain size of the metal matrix after step 106 is isotropic, and the yield strength of the obtained metal material is not lower than the yield strength of the material obtained by sintering the raw material metal powder under a single constant pressure reducing atmosphere. ​

Images