A powder metallurgy method

Abstract

The application discloses a kind of high-efficiency environmental protection powder metallurgy method, by adding solidifying agent of specific formula to metal powder, significantly improve green strength and optimize sintering performance.The solidifying agent includes by mass percentage: polyethyleneimine 10-15%, isopropanol 15-25%, ethylene glycol monobutyl ether 25-35%, hydroxyethyl cellulose 0.3-2%, the rest is water, 0.1-1% metal nitrate can also be added to generate nano-enhanced phase in situ.Polyethyleneimine in solidifying agent and hydroxyethyl cellulose form three-dimensional network structure by hydrogen bond and coordination bond, so that green bending strength is 2-3 times higher than traditional process.Implementing high hard surface, high toughness core performance by using ultrasonic assisted mixing solvent during preparation, combined with gradient addition strategy.During sintering process, isopropanol and ethylene glycol monobutyl ether are volatilized in stages, PEI and HEC are completely decomposed into gas at 400-600 DEG C, and the residue is low and does not need to be degreased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of powder metallurgy, in particular to a powder metallurgy method for improving green strength and optimizing sintering performance by adding a curing agent. BACKGROUND

[0002] Powder metallurgy is a process of compacting metal powder and sintering into shape, widely used in mechanical, automotive and aerospace fields. In the traditional process, the green strength of the unsintered compact is low, and cracks or defects are easy to occur, resulting in a decrease in the yield of finished products. In the prior art, the green strength is often improved by adding a binder or a curing agent, but most binders leave impurities after sintering, or require a high-temperature degreasing process, increasing energy consumption and process complexity.

[0003] For example, the method for producing a powder metallurgy product provided in the patent for invention with publication number CN110856872A produces a powder mixture by agglomerating an organic binder and wax in a molten metallurgical manner, compacts the agglomerated powder mixture into a green body, and sintering after heat debinding the formed green body. However, the traditional curing agent has a high residual amount in the metal powder, and increasing the use amount of the curing agent will easily cause cracks in the product, thereby causing a low yield of finished products, and reducing the green body to be easily damaged and fragile during transfer. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a powder metallurgy method that significantly improves the green strength by adding a specific curing agent, while ensuring that the curing agent is largely decomposed and volatilized during the sintering process, with a small residual amount, to eliminate the need for separate handling of the curing agent in the prior art.

[0005] To achieve the above-mentioned purpose, the technical solutions provided by the present application are as follows:

[0006] A powder metallurgy method, comprising adding a curing agent consisting of the following mass percentage components to metal powder: polyethyleneimine, 10-15%, isopropyl alcohol, 15-25%, ethylene glycol monobutyl ether, 25-35%, hydroxyethyl cellulose, 0.3-2%, and the balance being water.

[0007] Further, the addition amount of the curing agent is 1-5% of the mass of the metal powder.

[0008] Further, the molecular weight of the polyethyleneimine ranges from 10,000 to 50,000 g / mol.

[0009] Further, the hydroxy substitution degree of the hydroxyethyl cellulose is 1.5-2.5.

[0010] Further, the curing agent also includes 0.1-1% of metal nitrate, which is decomposed into nano-oxide dispersed in the metal matrix during sintering.

[0011] Further, the preparation method of the curing agent includes:

[0012] S1, dissolve hydroxyethyl cellulose in water and stir until completely dispersed;

[0013] S2, add isopropyl alcohol and ethylene glycol monobutyl ether to the hydroxyethyl cellulose solution in sequence and mix uniformly to form an intermediate;

[0014] S3, stir the intermediate and simultaneously add polyethyleneimine dropwise to form a homogeneous solution.

[0015] Further,

[0016] In S1, the water temperature is controlled at 40-50℃, 800-1200 rpm mechanical stirring is used, and the stirring time is ≥30 min, so that the hydroxyethyl cellulose aqueous solution forms a transparent colloid;

[0017] In S2, ultrasonic assisted mixing is used to eliminate bubbles and improve the compatibility of isopropyl alcohol and ethylene glycol monobutyl ether in the hydroxyethyl cellulose aqueous solution;

[0018] In S3, 300-500 rpm mechanical stirring is used when adding polyethyleneimine to avoid local high concentration leading to flocculation;

[0019] It also includes S4: after the completion of polyethyleneimine dropwise, constant temperature curing.

[0020] Further, the use method of the curing agent includes:

[0021] A1: the metal powder is pre-milled to a particle size D50=10-50 μm and dried to a water content ≤0.1%;

[0022] A2: mix the curing agent with the metal powder in a mixer to make the curing agent uniformly coat the surface of the particles, and the mixing humidity is ≤40% RH;

[0023] A3: the metal powder coated with the curing agent is pressed into a green body;

[0024] A4: the green body is placed in a 40-60℃ oven to dry and remove free curing agent;

[0025] A5: the dried green body is obtained by sintering process.

[0026] Further, in the A2, the metal powder comprises a surface layer powder and a core powder, the solidification agent addition amount of the surface layer powder > the solidification agent addition amount of the core powder, the content of hydroxyethyl cellulose in the mixed solidification agent of the surface layer powder is 1-2%, and the content of hydroxyethyl cellulose in the mixed solidification agent of the core powder is 0.3-0.8%.

[0027] Further, in the A5, the sintering process is carried out in stages according to temperature, including a first stage, a second stage and a third stage, the temperature end point of the first stage volatilizes isopropyl alcohol and ethylene glycol monobutyl ether, the temperature end point of the second stage pyrolyzes polyethyleneimine and hydroxyethyl cellulose, and the temperature end point of the third stage reaches the target temperature of the product.

[0028] The advantages and beneficial effects of the present application are that:

[0029] 1. The polyethyleneimine (PEI) and hydroxyethyl cellulose (HEC) in the solidification agent form a three-dimensional network structure through hydrogen bonds and coordination bonds, which makes the green body bending strength 2-3 times higher than that of the traditional solidification agent-free process, effectively avoiding cracks and powder loss problems during pressing and handling. Compared with paraffin binder, the present application uses water as the main solvent, isopropyl alcohol and ethylene glycol monobutyl ether as low-toxicity organic solvents, does not contain benzene or halogenated hydrocarbons, and significantly reduces VOCs emissions.

[0030] 2. The solidification agent can add 0.1-1% iron / aluminum nitrate precursor, and generate nano-Al2O3, Fe3O4 and other reinforcing phase particles during sintering to disperse strengthen the matrix.

[0031] 3. The surface layer uses high-HEC-content (1-2%) solidification agent, and the core uses low-HEC-content (0.3-0.8%) solidification agent, which realizes the synchronous optimization of high hardness of the surface layer and high toughness of the core, and is suitable for complex working condition parts. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is the infrared spectrum of the solidification agent of the present application;

[0033] Figure 2 is the gas phase spectrum of the solidification agent of the present application;

[0034] Figure 3 is the ion spectrum of the solidification agent of the present application;

[0035] Figure 4 is the nuclear magnetic resonance spectrum of the solidification agent of the present application;

[0036] Figure 5 is the preparation method flow chart of the solidification agent of the present application. DETAILED DESCRIPTION

[0037] The present application solves the core problems of low green strength, much residual after debinding and complex process in traditional powder metallurgy by the synergistic effect of curing agent formulation design and segmented temperature control sintering process, and the technical principle is as follows.

[0038] The curing agent component takes polyethyleneimine (PEI) as the main binder, and the primary / secondary amine groups (-NH2 / -NH-) in the molecular chain of the PEI form a large number of hydrogen bonds and coordination bonds with the defect sites on the surface oxides of the metal powder and / or other curing agent components, thereby constructing a three-dimensional network structure and significantly improving the green strength. The molecular weight of the PEI is controlled at 10,000-50,000 g / mol, and the chain length is moderate, which can not only penetrate the intergranular gap to enhance the binding force, but also avoid uneven dispersion caused by entanglement.

[0039] Hydroxyethyl cellulose (HEC) is used as a rheological modifier to form a gel network with water molecules through hydroxyl groups (-OH), thereby preventing the metal powder from settling when mixed with the curing agent and improving the stability of the slurry. As a preferred embodiment, the degree of substitution of the hydroxyl groups in the hydroxyethyl cellulose is 1.5-2.5, which balances the solubility and viscosity.

[0040] The curing agent uses a composite solvent system (isopropyl alcohol + ethylene glycol monobutyl ether) to achieve pre-curing through rapid volatilization of isopropyl alcohol (boiling point 82.5℃), and slow volatilization of ethylene glycol monobutyl ether (boiling point 171℃) to maintain the plasticity of the metal powder green body and avoid cracks caused by drying stress concentration.

[0041] As a preferred embodiment, metal nitrate is selected and matched in the curing agent according to the composition of the metal raw material, and the metal nitrate can be decomposed into Al2O3, Fe3O4 and other nanoparticles (50-100 nm) in sintering, thereby pinning the grain boundaries and dispersively strengthening the matrix.

[0042] In view of the necessity to avoid premature curing to maintain the quality of the curing agent provided by the present application, which generally requires preparation on site, the present application further provides a preparation method for the curing agent, which solves the problems of easy stratification, residual bubbles and local flocculation of multi-component solutions by stepwise mixing, ultrasonic-assisted dispersion and sequential feeding control. First, the particles or powder of hydroxyethyl cellulose are dissolved in water and stirred until completely dispersed, the viscosity of the water is increased and the basic gel network is constructed, the solution viscosity is increased, and a stable matrix is provided for subsequent solvent mixing. Notably, 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 and shorten the dissolution time, while avoiding molecular chain breakage. Optionally, the shear force generated by high rotation speed can be used to destroy the hydrogen bonds between HEC particles during the above process, reducing or preventing the formation of unsolved micelles. After the dissolution of HEC, the solution viscosity increases significantly (e.g., the viscosity of a 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.

[0043] Isopropyl alcohol and ethylene glycol monobutyl ether are sequentially added to the aqueous solution of hydroxyethyl fiber and mixed uniformly to form an intermediate. Isopropyl alcohol (polar parameter P' = 3.9) has good miscibility with water (P' = 10.2), and preferential addition 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), avoiding drastic phase changes. Optionally, ultrasonic-assisted dispersion is applied during the mixing process. Ultrasonic waves generate micro-bubbles in the liquid and instantaneously collapse, releasing shock waves (local pressure > 100 MPa), forcing the breaking of intermolecular forces between solvents, promoting nanoscale mixing of isopropyl alcohol / ethylene glycol monobutyl ether and HEC solution. Ultrasonic energy destroys the gas-liquid interfacial tension, eliminating the bubbles generated during 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 (contact angle reduced by about 15°).

[0044] The intermediate is stirred and polyethyleneimine is added dropwise to form a homogeneous solution. PEI is a cationic polymer (pH = 8-10), which can directly and quickly cause electrostatic flocculation with negatively charged HEC (carboxyl ionization). Slow dropwise addition can maintain the local concentration below the critical flocculation concentration (CFC), avoiding agglomeration. Appropriate stirring during this process ensures that the PEI molecular chain gradually stretches and interweaves with the HEC network, forming a "PEI-HEC" interpenetrating network composite bonding phase. Optionally, the above curing agent is finally subjected to constant temperature curing to promote molecular chain relaxation and reconstruction, and hydrogen bonds and coordination bonds (PEI amino groups and metal oxides) are fully formed, with a solution Zeta potential absolute value > 30 mV and a stability extended to more than 72 hours.

[0045] The application further discloses a powder metallurgy method using the curing agent, and the method is specifically a pressing-sintering process using a mold. The mold can be provided with a gap for exhaust or exhaust holes. In the curing process of the green body, the green body can be divided into a surface layer and a core layer, and different curing agents are added to the surface layer and the core layer respectively to achieve better technical effects. Specifically, the surface layer is provided with high HEC content (1-2%) and high curing agent content (5%) to form a dense and high-hardness surface layer; and the core layer is provided with low HEC content (0.3-0.8%) and low curing agent content (1%) to achieve a high-toughness core layer.

[0046] In the process of powder metallurgy sintering, the curing agent can be removed by using a segmented temperature control method. The segmented temperature control removal method comprises the following steps: in the first stage (25-300 DEG C), isopropyl alcohol and ethylene glycol monobutyl ether are completely volatilized; in the second stage (300-600 DEG C), PEI and HEC are pyrolyzed into CO2, H2O and NH3 (which can be verified by TGA-MS), and no carbon / nitrogen residue (the detection limit of EDS is less than 0.1 wt%) is left; and in the third stage (600-1300 DEG C), metal particle diffusion necks are formed to realize near-full density sintering (the relative density is greater than or equal to 97%).

[0047] It can be understood that the temperature end points of the three stages are dynamically changed, and are affected by the curing agent components and the green body. The application provides a calculation principle. In the process of mold pressing, the pressure in the mold dynamically changes. According to the ideal gas equation, pV = nRT.

[0048] In the formula, p is the gas pressure in the mold, kPa; V is the volume of the gas, L; n is the total amount of the gas, mol; R is the ideal gas constant, 8.314 J / (mol·K); and T is the real-time temperature, K. Since p, n and T in the mold are dynamic values, and the gas volume V is relatively difficult to measure due to gas dissipation, the application provides examples of the temperature end points of the stages.

[0049] The formula for the change of the boiling point of a liquid with pressure can be predicted by the Clausius-Clapeyron equation, which is applicable to pure substances.

[0050] ( )

[0051] In the formula, P1 and P2 are two different pressures (for example, P1 is the standard atmospheric pressure, and P2 is the actual pressure, in Pa or atm); T1 and T2 are the boiling point temperatures under the corresponding pressures (in K); ΔHvap is the vaporization enthalpy (in J / mol); and R is the ideal gas constant (in 8.314 J / (mol·K)).

[0052] The temperature end point of the first stage is preferably 170-300 DEG C;

[0053] The second stage temperature end point is preferably from 300 to 600°C.

[0054] The third stage temperature end point is not lower than the sintering temperature of the raw material.

[0055] The specific embodiments of the present application are further described below in conjunction with the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0056] Example 1

[0057] A powder metallurgy method, raw material Fe-2Ni-0.5Mo alloy powder (purchased from Osprey Metals), initial particle size distribution D50=50 μm; using a planetary ball mill for fine grinding, zirconia grinding balls (diameter 5 mm), ball-to-material ratio 10:1, rotation speed 300 rpm, time 4 hours, argon protection, after ball milling the powder D50=30 μm; then dried in a vacuum drying oven at 80°C for 12 hours to make the moisture content ≤0.05%.

[0058] Preparation of curing agent:

[0059] Formulation: PEI (purchased from Sigma-Aldrich, molecular weight 30,000 g / mol) 12%, HEC (purchased from Ashland, hydroxyl substitution degree 2.0) 0.8%, isopropanol (analytical pure) 20%, ethylene glycol monobutyl ether (analytical pure) 30%, deionized water 37.2%;

[0060] S1: HEC is gradually added to deionized water at 50°C, a high-shear disperser (IKA T25, rotor diameter 18 mm) is used to stir at 1000 rpm for 40 minutes to form a transparent colloid (viscosity 1200 mPa·s);

[0061] S2: Isopropanol and ethylene glycol monobutyl ether are added in turn, and transferred to an ultrasonic cleaning tank (40 kHz, power 200 W) for treatment for 10 minutes, the solution transmittance is 95% (UV-Vis spectrophotometer detection, wavelength 600 nm);

[0062] S3: The mixed solution is placed in a constant temperature magnetic stirrer, stirred at 400 rpm at 40°C, and PEI is added dropwise at a rate of 0.8 mL / min through a peristaltic pump, and after dropping, it is incubated at 40°C for 2 hours to obtain a homogeneous solution.

[0063] The process route of the powder metallurgy process is as follows:

[0064] The 3% curing agent and metal powder were added to a V-type mixer (double motion mixing, rotation speed 25 rpm, mixing time 50 minutes), and the ambient humidity was 35% RH;

[0065] The metal powder was bidirectionally pressed using a hydraulic press with a pressure gradient loading (0→100 MPa for 30 seconds, 100→400 MPa for 10 seconds), and the pressure was maintained for 3 minutes. The green body size was Φ20 mm×10 mm;

[0066] The green body was dried in a hot air circulating oven at 50°C for 1 hour, and the residual amount of free solvent was <0.1%;

[0067] The dried green body was sintered in the following stages:

[0068] First stage: 25→300°C, heating rate 5°C / min, nitrogen flow rate 5 L / min (dew point -50°C);

[0069] Second stage: 300→600°C, heating rate 2°C / min;

[0070] Third stage: 600→1150°C, heating rate 8°C / min, holding time 2 hours, and the furnace was cooled to 200°C before removal.

[0071] Example 2

[0072] A powder metallurgy method, the raw material was Cu-10Sn-2 graphite (D50=20 μm) alloy powder, which was dried in a vacuum drying oven at 80°C for 12 hours to make the moisture content ≤0.1%.

[0073] Curing agent preparation:

[0074] Formulation: PEI (molecular weight 50,000 g / mol) 10%, HEC (hydroxyl substitution degree 2.5) 1.5%, isopropyl alcohol 18%, ethylene glycol monobutyl ether 28%, water 42.5%, and additionally 0.5% aluminum nitrate (Al(NO3)3·9H2O, National Pharmaceutical Group, analytical pure), and the amount of deionized water was 42.5%.

[0075] S1: HEC was gradually added to deionized water at 50°C, and a high-shear disperser was used to stir at 1000 rpm for 30 minutes to form a transparent colloid (viscosity 900 mPa·s);

[0076] S2: Isopropyl alcohol and ethylene glycol monobutyl ether were added in turn, and were transferred to an ultrasonic cleaning tank (40 kHz, power 200 W) for treatment for 20 minutes. The solution transmittance was 93% (UV-Vis spectrophotometer detection, wavelength 600 nm);

[0077] S3: The mixed solution was placed in a constant temperature magnetic stirrer, stirred at 500 rpm at 50°C, and PEI was added dropwise at a rate of 2 mL / min by peristaltic pump. After the dropwise addition was completed, the solution was incubated at 50°C for 2 hours to obtain a homogeneous solution.

[0078] The process route of the powder metallurgy process is as follows:

[0079] 5% of the curing agent and the metal powder were added to a V-type mixer (double motion mixing, rotation speed 30 rpm, mixing time 60 minutes), and the ambient humidity was 40% RH.

[0080] The metal powder was bidirectionally pressed using a hydraulic press with a pressure gradient loading (0→200 MPa for 40 seconds, 200→500 MPa for 20 seconds), and the pressure was maintained for 5 minutes. The green body size was Φ20 mm×10 mm.

[0081] The green body was dried in a hot air circulation oven at 60°C for 2 hours, and the residual amount of free solvent was <0.1%.

[0082] The dried green body was sintered in the following stages:

[0083] First stage: 25→300°C, heating rate 5°C / min, hydrogen (analytical pure) flow rate 2 L / min.

[0084] Second stage: 300→500°C, heating rate 5°C / min.

[0085] Third stage: 500→900°C, heating rate 10°C / min, holding time 1.5 hours, and the sample was removed after cooling to 300°C in the furnace.

[0086] During the sintering of the dried green body, in the second stage, the reaction 2Al(NO3)3→Al2O3+6NO2↑+3O2↑2Al(NO3)3 occurred in the 300-500°C interval. The decomposition end point was confirmed to be 480°C by TG-MS (Netzsch STA 449 F3), the particle size was 50-100 nm as shown by TEM, and the γ-Al2O3 phase was confirmed by SAED.

[0087] Example 3

[0088] A powder metallurgy method, which is different from Example 1, is as follows.

[0089] The curing agent was designed in layers: surface layer formula: PEI (molecular weight 10,000 g / mol) 15%, HEC (hydroxyl substitution degree 1.5) 2%, isopropyl alcohol 25%, ethylene glycol monobutyl ether 25%, and water 33%.

[0090] Core formulation: PEI 10%, HEC 0.5%, isopropyl alcohol 20%, ethylene glycol monobutyl ether 30%, water 39.5%.

[0091] The 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 subject skin; the diameter of the cylinder = the wall thickness of the shell = 10 mm; the surface layer powder (with 5% solidifying agent added) and the core powder (with 1% solidifying agent added) are injected through a double-screw feeder, and the filling density deviation of the inner and outer layers is <1%.

[0092] Slowly heat up to 1300°C at 10°C / min, 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 part after sintering is ±0.05 mm.

[0093] Example 4

[0094] A powder metallurgy method, the raw material uses Ti-6Al-4V (D50=15 μm) alloy powder, dries in a vacuum drying box for 24 hours at 60°C, so that the moisture content is ≤0.1%.

[0095] Solidifying agent preparation:

[0096] Formulation: PEI (10,000 g / mol) 15%, HEC (hydroxyl substitution degree 1.5) 0.3%, isopropyl alcohol 25%, ethylene glycol monobutyl ether 35%, water 24.7%.

[0097] S1: gradually add HEC to 50°C deionized water, use a high-shear dispersing machine to stir at 1200 rpm for 20 minutes, form a transparent colloid (viscosity 1100 mPa·s);

[0098] S2: add isopropyl alcohol and ethylene glycol monobutyl ether in turn, transfer to an ultrasonic cleaning tank (40 kHz, power 200 W) for 60 minutes, the solution transmittance is 90% (UV-Vis spectrophotometer detection, wavelength 600 nm);

[0099] S3: place the mixed solution in a constant-temperature magnetic stirrer, stir at 300 rpm at 25°C, add PEI at a rate of 1 mL / min through a peristaltic pump, after dropping, 50°C constant-temperature curing for 3 hours, get a homogeneous solution.

[0100] The process route of the powder metallurgy process is as follows:

[0101] Add 2% solidifying agent and metal powder to a V-type mixer (double-motion mixing, rotation speed 10 rpm, mixing time 120 minutes), the environmental humidity is 38%RH;

[0102] The metal powder was pressed by hydraulic press in two directions, with pressure gradient loading (0→200 MPa for 20 seconds, 200→600 MPa for 60 seconds), and pressure maintaining for 20 minutes. The green compact had a size of Φ20 mm x 10 mm;

[0103] The green compact was dried in a hot air circulating oven at 70°C for 1 hour, and the residual amount of free solvent was less than 0.1%;

[0104] The dried green compact was sintered, and the sintering was divided into the following stages:

[0105] First stage: 25→300°C, heating rate 5°C / min, nitrogen flow rate 5 L / min (dew point -50°C);

[0106] Second stage: 300→600°C, heating rate 5°C / min;

[0107] Third stage: 600→1150°C, heating rate 10°C / min, holding for 2 hours, and then removed after cooling to 150°C in the furnace.

[0108] Example 5

[0109] A powder metallurgy method, which was different from Example 1 as follows. The raw material was 316L stainless steel powder (D50=40 μm), which was dried in a vacuum drying oven at 60°C for 24 hours, so that the water content was less than or equal to 0.1%.

[0110] Preparation of the curing agent:

[0111] Formulation: PEI (20,000 g / mol) 10%, HEC (hydroxyl substitution degree 2.5) 2%, isopropyl alcohol 15%, ethylene glycol monobutyl ether 25%, water 48%.

[0112] The sintering condition of powder metallurgy was under argon protection, and the sintering end point of the third stage was 1250°C, and the holding time was 2.5 hours at this temperature.

[0113] Comparative Example

[0114] The only difference from Example 1 was that paraffin wax adhesive was used, and the sintering cycle was 8 hours (including 4 hours of debinding).

[0115] The following methods were used to measure each of the above examples,

[0116] The green compact bending strength was measured by GB / T228.1, three-point bending method, span 15 mm, loading rate 0.5 mm / min;

[0117] The carbon residue of the curing agent was measured by EDS energy spectrum analysis, and the detection limit was 0.1 wt%;

[0118] The elongation was measured by GB / T 228.1, standard tensile specimen method, and the overall elongation of Example 3 was not measured due to the gradient structure.

[0119] Technical effects are as follows:

[0120]

[0121] As shown in the above table, the green body bending strength of all examples is significantly higher than that of the traditional process by 2-4 times. The solidifying agent used in the present application is completely decomposed, and the residual carbon content is less than 0.1%, which can effectively avoid the pores and performance decline caused by the residual paraffin in the traditional process. The elongation of the sintered body is increased by 20-140% compared with the traditional process (5-7%), and the elongation of Example 4 (titanium-based) reaches 12%, which meets the high toughness requirement.

[0122] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A powder metallurgical method, characterized in that, The solidifying agent is added to the metal powder, which is composed of the following mass percentage components: polyethyleneimine, 10-15%, isopropyl alcohol, 15-25%, ethylene glycol monobutyl ether, 25-35%, hydroxyethyl cellulose, 0.3-2%, and the balance is water; The addition amount of the solidifying agent is 1-5% of the mass of the metal powder; The molecular weight of the polyethyleneimine ranges from 10,000 to 50,000 g / mol; The hydroxyl substitution degree of the hydroxyethyl cellulose is 1.5-2.5; The powder metallurgy method is implemented with a hot air circulating oven, and the residual carbon content of the solidifying agent in the powder metallurgy part is <0.1wt%, and the green body bending strength of the powder metallurgy part is ≥10.2MPa; The method for using the solidifying agent comprises the following steps: A1: The metal powder is pre-milled to a particle size D50=10-50μm and dried to a water content ≤0.1%; A2: The solidifying agent is mixed with the metal powder in a mixer to evenly coat the surface of the particles, and the mixing humidity is ≤40%RH; A3: The metal powder coated with the solidifying agent is pressed into a green body in a mold; A4: The green body is dried in an oven at 40-60℃ to remove free solidifying agent; A5: The dried green body is obtained by a sintering process; In the A2, the metal powder includes a surface layer powder and a core powder, and 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 solidifying agent of the surface layer powder is greater than that of the core powder, the content of hydroxyethyl cellulose in the mixed solidifying agent of the surface layer powder is 1-2%, and the content of hydroxyethyl cellulose in the mixed solidifying agent of the core powder is 0.3-0.8%; In the A5, the sintering process is carried out in stages according to temperature, including a first stage, a second stage and a third stage; The temperature end point of the first stage is ≥ the boiling point of isopropyl alcohol and ethylene glycol monobutyl ether; The temperature end point of the second stage is ≥ the pyrolysis temperature of polyethyleneimine and hydroxyethyl cellulose; The temperature end point of the third stage is ≥ the target temperature of the product.

2. The powder metallurgy method according to claim 1, characterized in that The solidifying agent also includes 0.1-1% of a metal nitrate, which decomposes into nano-oxide dispersed in the metal matrix during the sintering process.

3. The method for preparing the curing agent as described in claim 1, characterized in that, The method comprises the following steps: S1: Dissolve the hydroxyethyl cellulose in water and stir until completely dispersed; S2: Add isopropyl alcohol and ethylene glycol monobutyl ether to the aqueous solution of hydroxyethyl cellulose in sequence and mix uniformly to form an intermediate; S3: Stir the intermediate and simultaneously add polyethyleneimine dropwise to form a homogeneous solution.

4. The preparation method according to claim 3, characterized in that, In the S1, the water temperature is controlled at 40-50℃, mechanical stirring is used at 800-1200 rpm, and the stirring time is ≥30 min, so that the aqueous solution of hydroxyethyl cellulose forms a transparent colloid; In the S2, ultrasonic assisted mixing is used to eliminate bubbles and improve the compatibility of isopropyl alcohol and ethylene glycol monobutyl ether in the aqueous solution of hydroxyethyl cellulose; In the S3, mechanical stirring is used at 300-500 rpm when adding polyethyleneimine to avoid local high concentration leading to flocculation. Also included is S4: constant temperature ripening after the polyethyleneimine dropwise addition is complete. Also included is S4: constant temperature ripening after the polyethyleneimine dropwise addition is complete.

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