Powder metallurgy method

Abstract

According to the efficient and environment-friendly powder metallurgy method, a curing agent of a specific formula is added into metal powder, so that the strength of a green body is remarkably improved, and the sintering performance is optimized. The curing agent comprises the following components in percentage by mass: 10-15% of polyethyleneimine, 15-25% of isopropanol, 25-35% of ethylene glycol monobutyl ether, 0.3-2% of hydroxyethyl cellulose and the balance of water, and 0.1-1% of metal nitrate can also be added to generate a nano reinforced phase in situ. In the curing agent, polyethyleneimine and hydroxyethyl cellulose form a three-dimensional network structure through hydrogen bonds and coordinate bonds, so that the bending strength of the green body is improved by 2-3 times compared with that of a traditional process. During preparation, an ultrasonic-assisted mixed solvent is adopted, and the high-hardness surface layer and the high-toughness core part of the part are realized in combination with a gradient adding strategy. In the sintering process, isopropanol and ethylene glycol monobutyl ether are volatilized in stages, PEI and HEC are completely decomposed into gas at the temperature of 400-600 DEG C, residues are low, and a degreasing procedure is not needed.

Description

Technical Field

[0001] The present invention relates to the technical field of powder metallurgy, and particularly to a powder metallurgy method for improving the green strength and optimizing the sintering performance by adding a curing agent. Background Art

[0002] Powder metallurgy is a process of pressing metal powders and sintering them into shape, which is widely used in fields such as machinery, automobiles, and aerospace. In traditional processes, the green strength of unsintered and compacted green compacts is low, and cracks or defects are likely to occur, resulting in a decrease in the finished product rate. In the prior art, the green strength is often improved by adding a binder or a curing agent. However, most binders leave residues after sintering or require a high-temperature degreasing process, increasing energy consumption and process complexity.

[0003] For example, a method for producing a powder metallurgy product provided by the invention patent with the publication number CN110856872A produces by a melting metallurgy method and forms a powder mixture by agglomerating with an organic binder and wax. The agglomerated powder mixture is pressed into a green compact and the formed green compact is heat-debounded and then sintered. However, the residual amount of traditional curing agents in metal powders is high. Increasing the amount of curing agent used easily leads to cracks in the product, thereby causing a low finished product rate. Decreasing it will cause the problem that the green compact is vulnerable to damage during transfer. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a powder metallurgy method. By adding a specific curing agent, the green strength is significantly improved, and at the same time, it is ensured that a large amount of the curing agent decomposes and volatilizes during the sintering process, with a small residual amount, so as to solve the problem that the prior art requires separate treatment of the curing agent.

[0005] To achieve the above purpose, the technical solution provided by the present invention is as follows: A powder metallurgy method, comprising adding a curing agent composed of the following mass percentage components to metal powders: polyethyleneimine, 10 - 15%, isopropanol, 15 - 25%, ethylene glycol monobutyl ether, 25 - 35%, hydroxyethyl cellulose, 0.3 - 2%, and the balance is water.

[0006] Further, the addition amount of the curing agent is 1 - 5% of the mass of the metal powders.

[0007] Further, the molecular weight range of the polyethyleneimine is 10000 - 50000 g / mol.

[0008] Further, the degree of hydroxyl substitution of the hydroxyethyl cellulose is 1.5 - 2.5.

[0009] Further, the curing agent further includes 0.1 - 1% of metal nitrate, and the metal nitrate decomposes into nano-oxides during the sintering process and is dispersed in the metal matrix.

[0010] Furthermore, the preparation method of the curing agent includes: S1. Dissolve hydroxyethyl cellulose in water and stir until completely dispersed; S2. Sequentially add isopropanol and ethylene glycol monobutyl ether to the aqueous solution of hydroxyethyl cellulose and mix evenly to form an intermediate; S3. Stir the intermediate and simultaneously dropwise add polyethyleneimine to form a homogeneous solution.

[0011] Furthermore, In S1, the water temperature is controlled at 40 - 50 °C, mechanical stirring is carried out at 800 - 1200 rpm, and the stirring time is ≥ 30 min to form a transparent colloid of the aqueous solution of hydroxyethyl cellulose; In S2, ultrasonic wave is used for auxiliary mixing to eliminate bubbles and improve the compatibility of isopropanol and ethylene glycol monobutyl ether in the aqueous solution of hydroxyethyl cellulose; In S3, when dropping polyethyleneimine, mechanical stirring is carried out at 300 - 500 rpm to avoid flocculation caused by too high local concentration; It also includes S4: After dropping polyethyleneimine, carry out constant-temperature aging.

[0012] Furthermore, the usage method of the curing agent includes: A1. Pre-ball mill the metal powder to a particle size D50 = 10 - 50 μm and dry it to a water content of ≤ 0.1%; A2. Mix the curing agent and the metal powder in a mixer to make the curing agent uniformly coat the particle surface, and the mixing humidity is ≤ 40%RH; A3. Press the metal powder coated with the curing agent into a green body; A4. Place the green body in an oven at 40 - 60 °C to dry and remove the free curing agent; A5. Obtain the product by sintering the dried green body through a sintering process.

[0013] Furthermore, in A2, the metal powder includes surface layer powder and core powder. The addition amount of the curing agent in the surface layer powder is > the addition amount of the curing agent in the core powder. The content of hydroxyethyl cellulose in the mixed curing agent of the surface layer powder is 1 - 2%, and the content of hydroxyethyl cellulose in the mixed curing agent of the core powder is 0.3 - 0.8%.

[0014] Furthermore, in A5, the sintering process is carried out in temperature segments, including a first stage, a second stage, and a third stage. The temperature end point of the first stage causes isopropanol and ethylene glycol monobutyl ether to volatilize, the temperature end point of the second stage causes polyethyleneimine and hydroxyethyl cellulose to pyrolyze, and the temperature end point of the third stage reaches the product target temperature.

[0015] The advantages and beneficial effects of the present invention are as follows: 1. Polyethyleneimine (PEI) in the curing agent and hydroxyethyl cellulose (HEC) form a three-dimensional network structure through hydrogen bonds and coordination bonds, increasing the flexural strength of the green body by 2-3 times compared to the traditional process without a curing agent, effectively avoiding cracks and powder falling during pressing and handling. Compared with paraffin binders, the present invention uses water as the main solvent, and isopropanol and ethylene glycol monobutyl ether as low-toxic organic solvents, without benzene or halogenated hydrocarbons, and significantly reduces the VOCs emissions.

[0016] 2. Precursors such as 0.1-1% iron / aluminum nitrate can be added to the curing agent, and nano-Al2O3, Fe3O4 and other reinforcing phase particles are generated during sintering to disperse and strengthen the matrix.

[0017] 3. The curing agent with a high HEC content (1-2%) is used on the surface layer, and the curing agent with a low HEC content (0.3-0.8%) is used in the core, realizing the simultaneous optimization of high surface hardness and high core toughness, and is suitable for parts under complex working conditions. Description of the Drawings

[0018] Figure 1 is the infrared spectrum of the curing agent of the present invention; Figure 2 is the gas spectrum of the curing agent of the present invention; Figure 3 is the ion spectrum of the curing agent of the present invention; Figure 4 is the nuclear magnetic spectrum of the curing agent of the present invention; Figure 5 is the flow chart of the preparation method of the curing agent of the present invention. Detailed Embodiments

[0019] Through the synergistic effect of the curing agent formulation design and the segmented temperature-controlled sintering process, the present invention solves the core problems in traditional powder metallurgy such as low green body strength, excessive degreasing residue, and complex process. The technical principle is as follows.

[0020] The curing agent component uses polyethyleneimine (PEI) as the main binder. The primary amine / secondary amine groups (-NH2 / -NH-) in its molecular chain form a large number of hydrogen bonds and coordination bonds with the defect sites formed by the surface oxides of metal powders and / or other curing agent components, constructing a three-dimensional network structure and significantly improving the green body strength. The molecular weight of PEI is controlled at 10,000-50,000 g / mol, with a moderate chain length, which can not only penetrate the particle gaps to enhance the binding force, but also avoid uneven dispersion caused by entanglement.

[0021] Hydroxyethyl cellulose (HEC) is used as a rheology modifier. It forms a gel network with water molecules through hydroxyl groups (-OH), preventing sedimentation when metal powder is mixed with the curing agent and enhancing the stability of the slurry. As a preferred embodiment, the degree of substitution of hydroxyl groups in hydroxyethyl cellulose is 1.5 - 2.5, taking into account the balance between solubility and viscosity.

[0022] The curing agent uses a composite solvent system (isopropyl alcohol + ethylene glycol monobutyl ether). Through the rapid volatilization of isopropyl alcohol (boiling point 82.5 °C), pre-curing is achieved, and the slow volatilization of ethylene glycol monobutyl ether (boiling point 171 °C) maintains the plasticity of the green body of the metal powder, avoiding cracks caused by concentrated drying stress.

[0023] As a preferred embodiment, metal nitrates are selected and matched in the curing agent according to the composition of the metal raw material. Metal nitrates can be decomposed into nanoparticles (50 - 100 nm) such as Al2O3 and Fe3O4 during sintering, pinning grain boundaries and dispersion-strengthening the matrix.

[0024] Considering that it is necessary to avoid premature curing of the curing agent provided by the present invention to maintain its quality and usually it needs to be prepared and used immediately, the present invention further provides a method for preparing the curing agent. Through stepwise mixing, ultrasonic-assisted dispersion and sequential feeding control, problems such as easy stratification, bubble residue and local flocculation of multi-component solutions are solved. First, the particles or powder of hydroxyethyl cellulose are dissolved in water and stirred until completely dispersed, increasing the viscosity of water and constructing a basic gel network to enhance the solution viscosity and provide a stable matrix for subsequent solvent mixing. It should be noted that HEC is a cellulose derivative, and its solubility improves with increasing temperature, but it is prone to thermal degradation above 60 °C. 40 - 50 °C can accelerate the stretching of molecular chains, shorten the dissolution time, and at the same time avoid the breakage of molecular chains. Optionally, the shear force generated by high speed can be used to break the hydrogen bonds between HEC particles during the above process, reducing or preventing the formation of undissolved micelles. After the dissolution of HEC, the solution viscosity increases significantly (for example, the viscosity of 1% HEC aqueous solution can reach 1500 - 2500 mPa·s), providing a buffer for the subsequent addition of organic solvents and slowing down the phase separation trend.

[0025] Isopropanol and ethylene glycol monobutyl ether are successively added to an aqueous solution of hydroxyethyl cellulose and mixed evenly to form an intermediate. Isopropanol (polarity parameter P’ = 3.9) has good miscibility with water (P’ = 10.2). Adding it first can reduce the polarity of the system, creating a transitional environment for the subsequent introduction of highly hydrophobic ethylene glycol monobutyl ether (P’ = 4.1) and avoiding violent phase changes. Optionally, ultrasonic-assisted dispersion is applied during the mixing process. Ultrasonic waves generate microbubbles in the liquid and instantaneously collapse, releasing shock waves (local pressure > 100 MPa), which forcefully break the intermolecular forces between solvents and promote the nano-scale mixing of isopropanol / ethylene glycol monobutyl ether and the HEC solution. The ultrasonic energy destroys the gas-liquid interfacial tension and eliminates the bubbles generated by mixing. During this process, the ether bond (-O-) of ethylene glycol monobutyl ether forms weak hydrogen bonds with the hydroxyl groups of HEC, improving the interfacial compatibility (the contact angle is reduced by about 15°).

[0026] The intermediate is stirred while polyethyleneimine is added dropwise simultaneously to form a homogeneous solution. PEI is a cationic polymer (pH = 8 - 10). Adding it directly and rapidly is likely to cause electrostatic flocculation with negatively charged HEC (carboxyl ionization). Adding it dropwise slowly can maintain the local concentration below the critical flocculation concentration (CFC) and avoid agglomeration. During this process, the shear force brought about by appropriate stirring ensures that the PEI molecular chains are gradually stretched and intertwined with the HEC network, forming a composite bonding phase with an “PEI-HEC” interpenetrating network. Optionally, finally, the above curing agent is subjected to constant-temperature aging to promote the relaxation and reconstruction of molecular chains, fully form hydrogen bonds and coordination bonds (PEI amino groups and metal oxides), and the absolute value of the solution Zeta potential > 30 mV, extending the stability to more than 72 hours.

[0027] The present invention further demonstrates a powder metallurgy method using the above curing agent, which is specifically realized by a pressing-sintering process using a mold. The mold can be selected with gap exhaust or exhaust holes opened. During the curing process of the green compact, optionally, the green compact is divided into a surface layer and a core part and different curing agents are added respectively to achieve better technical effects. Specifically, the surface layer uses a high HEC content (1 - 2%) + a high curing agent addition amount (5%) to form a dense and high-hard surface layer; the core part uses a low HEC content (0.3 - 0.8%) + a low curing agent addition amount (1%) to achieve a high-toughness core part.

[0028] During the process of powder metallurgy sintering, the curing agent can be removed by means of segmented temperature control. The method of segmented temperature control for removal includes: the first stage (25 - 300 °C): isopropanol and ethylene glycol monobutyl ether are completely volatilized; the second stage (300 - 600 °C): PEI and HEC are pyrolyzed into gases such as CO2, H2O, NH3, etc. (which can be verified by TGA-MS), and there is no carbon / nitrogen residue (EDS detection limit < 0.1 wt%); the third stage (600 - 1300 °C): the formation of metal particle diffusion necks is achieved, and near-full dense sintering (relative density ≥ 97%) is realized.

[0029] It is understandable that the temperature endpoints of the three stages are dynamically changing and are affected by the curing agent components and the green body. The present invention provides its calculation principle. Considering the dynamic change of the pressure in the mold during the mold pressing process, according to the ideal gas equation, pV = nRT.

[0030] In the formula: p is the air pressure in the mold, kPa; V is the gas volume, L; n is the total amount of gas, mol; R is the ideal gas constant, 8.314 J / (mol·K); T is the real-time temperature, K. Since p, n, and T in the mold are all dynamic values, and there is gas dissipation in V, it is relatively difficult to measure. Therefore, the present invention provides examples of the temperature endpoints of each stage.

[0031] The formula for the change of the liquid boiling point with pressure can be predicted by the Clausius-Clapeyron equation, but the problem is that it is applicable to pure substances. The Clausius-Clapeyron equation is: ( ) In the formula: P1, P2: two different pressures (e.g., P1 is the standard atmospheric pressure, P2 is the actual pressure, unit: Pa or atm); T1, T2: the boiling point temperatures corresponding to the pressures (unit: K); ΔHvap: the enthalpy of vaporization (unit: J / mol); R: the ideal gas constant (unit: 8.314 J / (mol·K)).

[0032] The temperature endpoint of the first stage is preferably selected from 170 - 300 °C; The temperature endpoint of the second stage is preferably selected from 300 - 600 °C; The temperature endpoint of the third stage is not lower than the sintering temperature of the raw material.

[0033] The following combines the drawings and examples to further describe the specific implementation manners of the present invention. The following examples are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention.

[0034] Example 1 A powder metallurgy method, the raw material uses Fe-2Ni-0.5Mo alloy powder (purchased from Osprey Metals), the initial particle size distribution D50 = 50 μm; it is ball-milled and refined using a planetary ball mill, zirconia grinding balls (diameter 5 mm), the ball-to-material ratio is 10:1, the rotation speed is 300 rpm, and the time is 4 hours. After ball-milling under argon protection, the powder D50 = 30 μm; then it is dried in a vacuum drying oven at 80 °C for 12 hours to make the moisture content ≤ 0.05%.

[0035] Preparation of the curing agent: Formulation: 12% PEI (purchased from Sigma-Aldrich, molecular weight 30,000 g / mol), 0.8% HEC (purchased from Ashland, degree of hydroxy substitution 2.0), 20% isopropyl alcohol (analytical grade), 30% ethylene glycol monobutyl ether (analytical grade), 37.2% deionized water; S1: Gradually add HEC to deionized water at 50 °C, and stir with a high-shear disperser (IKA T25, rotor diameter 18 mm) at 1000 rpm for 40 minutes to form a transparent colloid (viscosity 1200 mPa·s); S2: Add isopropyl alcohol and ethylene glycol monobutyl ether in sequence, transfer to an ultrasonic cleaning tank (40 kHz, power 200 W) and process for 10 minutes. The light transmittance of the solution is 95% (detected by a UV-Vis spectrophotometer, wavelength 600 nm); S3: Place the mixed solution in a constant-temperature magnetic stirrer, stir at 40 °C at 400 rpm, and dropwise add PEI at a rate of 0.8 mL / min through a peristaltic pump. After dropping, age at 40 °C for 2 hours to obtain a homogeneous solution.

[0036] The process route of the powder metallurgy process is as follows: Add 3% curing agent and metal powder to a V-type mixer (double motion mixing, rotation speed 25 rpm, mixing time 50 minutes), and the ambient humidity is 35%RH; Bidirectionally press the metal powder with a hydraulic press, load the pressure gradient (0→100 MPa takes 30 seconds, 100→400 MPa takes 10 seconds), hold the pressure for 3 minutes, and the green compact size is Φ20 mm×10 mm; Place the green compact in a hot air circulation oven and dry at 50 °C for 1 hour, and the residual amount of free solvent <0.1%; Sinter the dried green compact, and the sintering is carried out in the following stages: The first stage: 25→300 °C, heating rate 5 °C / min, nitrogen flow rate 5 L / min (dew point -50 °C); The second stage: 300→600 °C, heating rate 2 °C / min; The third stage: 600→1150 °C, heating rate 8 °C / min, hold for 2 hours, and take out after cooling to 200 °C with the furnace.

[0037] Example 2 A powder metallurgy method uses Cu-10Sn-2 graphite (D50 = 20 μm) alloy powder as raw material, dries it in a vacuum drying oven at 80 °C for 12 hours to make its moisture content ≤0.1%.

[0038] Preparation of curing agent: Formula: 10% PEI (molecular weight 50,000 g / mol), 1.5% HEC (hydroxyl substitution degree 2.5), 18% isopropanol, 28% ethylene glycol monobutyl ether, 42.5% water. Additionally, 0.5% aluminum nitrate (Al(NO3)3·9H2O, from Sinopharm Chemical Reagent Co., Ltd., analytical grade) is added, and the amount of deionized water is 42.5%.

[0039] S1: Gradually add HEC into deionized water at 50°C, and stir with a high-shear disperser at 1000 rpm for 30 minutes to form a transparent colloid (viscosity 900 mPa·s). S2: Add isopropanol and ethylene glycol monobutyl ether in sequence, transfer to an ultrasonic cleaning tank (40 kHz, power 200 W) and process for 20 minutes. The light transmittance of the solution is 93% (detected by a UV-Vis spectrophotometer at a wavelength of 600 nm). S3: Place the mixture in a constant-temperature magnetic stirrer, stir at 50°C at 500 rpm, and drip PEI at a rate of 2 mL / min through a peristaltic pump. After dripping, keep it at a constant temperature of 50°C for 2 hours to obtain a homogeneous solution.

[0040] The process route of powder metallurgy is as follows: Add 5% curing agent and metal powder into a V-type mixer (dual motion mixing, rotation speed 30 rpm, mixing time 60 minutes), and the environmental humidity is 40%RH. Bidirectionally press the metal powder with a hydraulic press, load the pressure gradient (0→200 MPa takes 40 seconds, 200→500 MPa takes 20 seconds), keep the pressure for 5 minutes, and the green compact size is Φ20 mm×10 mm. Place the green compact in a hot air circulation oven and dry at 60°C for 2 hours, and the residual amount of free solvent is <0.1%. Sinter the dried green compact, and the sintering is carried out in the following stages: The first stage: 25→300°C, heating rate 5°C / min, hydrogen (analytical grade) flow rate 2 L / min. The second stage: 300→500°C, heating rate 5°C / min. The third stage: 500→900°C, heating rate 10°C / min, keep the temperature for 1.5 hours, and take it out after cooling to 300°C with the furnace.

[0041] When sintering the dry green body, in the second stage, the reaction 2Al(NO3)3→Al2O3+6NO2↑+3O2↑ occurs in the temperature range of 300 - 500 °C. The decomposition end point is confirmed to be 480 °C by thermogravimetric analysis coupled with mass spectrometry (TG-MS, Netzsch STA 449 F3). Transmission electron microscopy (TEM) shows that its particle size is 50 - 100 nm, and selected area electron diffraction (SAED) confirms the formation of the γ-Al2O3 phase.

[0042] Example 3 A powder metallurgy method, which is different from Example 1 as follows.

[0043] The curing agent adopts a layered design: surface layer formula: PEI (molecular weight 10,000 g / mol) 15%, HEC (hydroxyl substitution degree 1.5) 2%, isopropanol 25%, ethylene glycol monobutyl ether 25%, water 33%; Core formula: PEI 10%, HEC 0.5%, isopropanol 20%, ethylene glycol monobutyl ether 30%, water 39.5%.

[0044] Powder metallurgy pressing adopts double-layer step-by-step pressing; the inner layer is pressed into a cylindrical blank, and the outer layer powder is pressed into a shell blank outside the main leather material. The diameter of the cylinder = the wall thickness of the shell = 10 mm. The surface layer powder (added with 5% curing agent) and the core powder (added with 1% curing agent) are injected through a twin-screw feeder, and the filling density deviation between the inner and outer layers is < 1%.

[0045] Slowly heat up to 1300 °C at a rate of 10 °C / min and sinter for 5 hours. The core shrinkage rate is 1.2%; the surface layer shrinkage rate: 0.8% (high HEC content inhibits shrinkage); the total height tolerance of the sintered part is ±0.05 mm.

[0046] Example 4 A powder metallurgy method uses Ti-6Al-4V (D50 = 15 μm) alloy powder as raw material, dries it in a vacuum drying oven at 60 °C for 24 hours to make its moisture content ≤ 0.1%.

[0047] Preparation of the curing agent: Formula: PEI (10,000 g / mol) 15%, HEC (hydroxyl substitution degree 1.5) 0.3%, isopropanol 25%, ethylene glycol monobutyl ether 35%, water 24.7%.

[0048] S1: Gradually add HEC to deionized water at 50 °C, stir with a high-shear disperser at 1200 rpm for 20 minutes to form a transparent colloid (viscosity 1100 mPa·s); S2: Add isopropanol and ethylene glycol monobutyl ether in sequence, transfer to an ultrasonic cleaning tank (40 kHz, power 200 W) for treatment for 60 minutes, and the light transmittance of the solution is 90% (detected by a UV-Vis spectrophotometer, wavelength 600 nm); S3: Place the mixture in a constant-temperature magnetic stirrer, stir at 300 rpm at 25 °C, and dropwise add PEI at a rate of 1 mL / min through a peristaltic pump. After dropping, age at a constant temperature of 50 °C for 3 hours to obtain a homogeneous solution.

[0049] The process route of the powder metallurgy process is as follows: Add 2% curing agent and metal powder to a V-type mixer (dual motion mixing, rotation speed 10 rpm, mixing time 120 minutes), and the ambient humidity is 38%RH; Bidirectionally press the metal powder with a hydraulic press, load the pressure gradient (0 → 200 MPa takes 20 seconds, 200 → 600 MPa takes 60 seconds), hold the pressure for 20 minutes, and the green compact size is Φ20 mm × 10 mm; Place the green compact in a hot air circulation oven and dry at 70 °C for 1 hour, and the residual amount of free solvent < 0.1%; Sinter the dried green compact, and the sintering is carried out in the following stages: The first stage: 25 → 300 °C, heating rate 5 °C / min, nitrogen flow rate 5 L / min (dew point -50 °C); The second stage: 300 → 600 °C, heating rate 5 °C / min; The third stage: 600 → 1150 °C, heating rate 10 °C / min, hold for 2 hours, and take out after furnace cooling to 150 °C.

[0050] Example 5 A powder metallurgy method, the differences from Example 1 are as follows. The raw material uses 316L stainless steel powder (D50 = 40 μm), and is dried in a vacuum drying oven at 60 °C for 24 hours to make its moisture content ≤ 0.1%.

[0051] Curing agent preparation: Formulation: PEI (20,000 g / mol) 10%, HEC (hydroxyl substitution degree 2.5) 2%, isopropanol 15%, ethylene glycol monobutyl ether 25%, water 48%.

[0052] The sintering condition of the powder metallurgy is argon protection, and the sintering end point of the third stage is 1250 °C, and hold for 2.5 hours at this temperature.

[0053] Comparative example The difference from Example 1 is only that a paraffin binder is used, and the sintering cycle is 8 hours (including 4 hours of debinding).

[0054] The above embodiments were measured separately using the following methods: The green body flexural strength was measured using GB / T228.1, three-point bending method, span 15 mm, loading rate 0.5 mm / min; The residual carbon content of the curing agent was analyzed by EDS energy spectrum analysis, detection limit (0.1 wt%); The elongation was measured using GB / T 228.1, standard tensile specimen method. In Example 3, the overall elongation was not measured due to the gradient structure.

[0055] The technical effects are as follows: As can be seen from the above table, the green body flexural strength of all embodiments is significantly 2-4 times higher than that of the traditional process. The curing agent used in the present invention decomposes completely, and the residual carbon content is <0.1%, which can effectively avoid the pores and performance degradation caused by paraffin residue in the traditional process. The elongation of the sintered body is increased by 20-140% compared with the traditional process (5-7%). In Example 4 (titanium-based), it reaches 12%, meeting the high toughness requirements.

[0056] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A powder metallurgy method, characterized in that, It includes adding a curing agent composed of the following mass percentage components to metal powder: polyethyleneimine, 10 - 15%, isopropanol, 15 - 25%, ethylene glycol monobutyl ether, 25 - 35%, hydroxyethyl cellulose, 0.3 - 2%, and the balance is water.

2. The powder metallurgy method according to claim 1, characterized in that, The addition amount of the curing agent is 1 - 5% of the mass of the metal powder.

3. The powder metallurgy method according to claim 1, wherein The molecular weight range of the polyethyleneimine is 10000 - 50000 g / mol.

4. The powder metallurgy method according to claim 1, characterized in that The degree of hydroxy substitution of the hydroxyethyl cellulose is 1.5 - 2.

5.

5. The powder metallurgy method according to any one of claims 1-4, characterized in that, The curing agent further includes 0.1 - 1% of metal nitrate, and the metal nitrate decomposes into nano-oxides during sintering and disperses in the metal matrix.

6. The preparation method of the curing agent according to any one of claims 1-4, characterized in that, It includes the following steps: S1. Dissolve hydroxyethyl cellulose in water and stir until completely dispersed; S2. Sequentially add isopropanol and ethylene glycol monobutyl ether to the aqueous solution of hydroxyethyl cellulose and mix evenly to form an intermediate; S3. Stir the intermediate and simultaneously dropwise add polyethyleneimine to form a homogeneous solution.

7. According to the method for preparing the curing agent according to claim 6, characterized in that, In S1, the water temperature is controlled at 40 - 50°C, mechanical stirring is carried out at 800 - 1200 rpm, and the stirring time is ≥30 min to form a transparent colloid of the aqueous solution of hydroxyethyl cellulose; In S2, ultrasonic assistance is used for mixing to eliminate bubbles and improve the compatibility of isopropanol and ethylene glycol monobutyl ether in the aqueous solution of hydroxyethyl cellulose; In S3, mechanical stirring is carried out at 300 - 500 rpm when dropwise adding polyethyleneimine to avoid local high concentration leading to flocculation; It further includes S4: Carry out constant-temperature aging after the dropwise addition of polyethyleneimine is completed.

8. The method for using the curing agent according to any one of claims 1 to 4, characterized in that, It includes the following steps: A1: Pre-ball mill the metal powder to a particle size D50 = 10 - 50μm and dry it to a water content of ≤0.1%; A2: Mix the curing agent and the metal powder in a mixer to uniformly coat the surface of the particles, and the mixing humidity is ≤40%RH; A3: Press the metal powder coated with the curing agent in a mold to form a green body; A4: Place the green body in an oven at 40 - 60°C to dry and remove the free curing agent; A5: Obtain the product through a sintering process for the dried green body.

9. The method for using the curing agent according to claim 8, wherein In A2, the metal powder includes surface layer powder and core powder. After the core powder is pressed into a green body, the surface layer powder is rolled into a green body outside the core green body through a mold. The addition amount of the curing agent in the surface layer powder > the addition amount of the curing agent in the core powder. The content of hydroxyethyl cellulose in the mixed curing agent of the surface layer powder is 1 - 2%, and the content of hydroxyethyl cellulose in the mixed curing agent of the core powder is 0.3 - 0.8%.

10. The method for using the curing agent according to claim 8, wherein, In A5, the sintering process is carried out in temperature segments, including the first stage, the second stage, and the third stage; The temperature end point of the first stage ≥ the boiling points of isopropanol and ethylene glycol monobutyl ether; The temperature end point of the second stage ≥ the pyrolysis temperatures of polyethyleneimine and hydroxyethyl cellulose; The temperature end point of the third stage ≥ the product target temperature.

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