CN117758122A - Hard material resistant to corrosion of strong acid and strong alkali and preparation method thereof - Google Patents
Hard material resistant to corrosion of strong acid and strong alkali and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a hard material resistant to strong acid and alkali corrosion, which is Ti (C, N) -based cermet adopting an entropy alloy in CoCrNi as bonding metal, and belongs to the field of new powder metallurgy materials. The invention aims to solve the problems that the traditional hard material has poor corrosion resistance in corrosive media, especially strong acid media, and the adoption of the entropy alloy in the corrosion resistance CoCrNi as metal ceramic bonded metal easily causes poor decarburization and microstructure homogeneity, poor toughness and the like. The invention adopts Ti (C) with high C/N ratio 0.7, N 0.3 ) And a saturated carbon carbide additive raw material, which solves the problems that when the entropy alloy in CoCrNi is used as a metal ceramic bonding metal, brittle decarburized phases are easily formed, and the quality is unstable due to the addition of excessive carbon black; the wettability of an alloy system is improved by adopting micro-pressure instantaneous high-temperature liquid phase sintering, and the self-consistent regulation and control of the nitrogen content in the alloy are realized by argon nitrogen carrier gas supersolidus liquid phase sintering after full densification, so that the comprehensive performance of the alloy is comprehensively improved.
Description
Technical Field
The invention relates to a hard material resistant to corrosion of strong acid and strong alkali and a preparation method thereof, belonging to the field of new powder metallurgy materials.
Background
Hard materials include WC-based cemented carbides and Ti (C, N) -based cermets, which are classified into two major categories, bonded metals and unbonded metals. In corrosive media, the corrosion resistance of hard materials having a hard phase + metal bond phase structure is typically significantly reduced as the bond phase preferentially corrodes relative to non-bonded metal hard materials. The binder phase imparts strength and toughness to the hard material, also significantly reduces the sintering densification temperature of the alloy and promotes sintering densification. The practical application conditions generally have higher requirements on the strength, toughness, hardness, wear resistance and the like of the hard material, and obviously, the requirements limit the expansion of the application field of the non-bonded metal hard material.
Strong acid and strong alkali are common service conditions in the fields of petroleum, chemical industry, hydrometallurgy and the like, and are applied to the service conditions, so that higher requirements are put forward on the corrosion resistance of hard materials and the abrasion resistance related to the corrosion resistance. The prior literature report consistently shows that compared with WC-based hard alloy, ti (C, N) -based cermet has higher corrosion resistance and abrasion resistance; the acidic medium is extremely corrosive to hard materials relative to the alkaline medium. Therefore, development of hard materials which are resistant to strong acid and strong alkali, have good physical and mechanical properties and have strong applicability to extreme service conditions is needed. The previous research results show that moderately increasing the N content in Ti (C, N) -based cermet is beneficial to improving the corrosion resistance and high-temperature oxidation resistance of the cermet and improving the strength and toughness of the cermet, but improper control is easy to cause decarburization phase in the alloy and obviously reduced microstructure homogeneity caused by decarburization phase, obviously reduced wettability of a liquid phase sintered alloy system and inhibition of sintering densification of the alloy.
Disclosure of Invention
The first purpose of the invention is to improve the corrosion resistance and the comprehensive performance of the traditional hard material, and solve the problems that the traditional Ti (C, N) base metal ceramic taking Co-Ni as the bonding metal is poor in corrosion resistance in corrosive media, especially strong acid media, and the corrosion resistance of the Ti (C, N) base metal ceramic is easy to cause decarburization, and the microstructure homogeneity and the strength and toughness of the alloy related to the decarburization are poor by adopting the entropy alloy in the corrosion resistance CoCrNi as the bonding metal.
In order to achieve the above object, based on the Ti (C, N) -based cermet material design database established by the present inventors and the regulation limit principle of the alloy composition-microstructure-performance three-element matching design and preparation process on the microstructure, through material calculation and experimental verification, the Ti (C, N) -based cermet with hard material resistant to strong acid and alkali corrosion has a two-phase homogeneous structure of hard phase and binder phase, the entropy alloy binder phase in the CoCrNi matrix is uniformly distributed in the alloy, the Ti (C) 0.7 ,N 0.3 ) The average grain size of the base hard phase is smaller than 1.2 mu m, the porosity in the alloy is less than or equal to A02 and B00, and the base hard phase is in a full densification state; the composition characteristics are as follows: in the alloy component, the mass fraction of the entropy alloy in CoCrNi is less than 25 percent but more than 15 percent, WC occupies Ti (C 0.7 ,N 0.3 ) 20-30% of Mo 2 C is Ti (C) 0.7 ,N 0.3 ) 10 to 15 percent of the mass fraction, and the total mass fraction of (NbC+TaC) accounts for Ti (C) 0.7 ,N 0.3 ) 15-20% of NbC (NbC+TaC) by mass fraction, and 0-30% of the total mass fraction; said Ti (C) 0.7 ,N 0.3 ) The carbide alloy additive is a saturated carbon type compound with carbon content more than or equal to theoretical carbon content; the Ti (C, N) -based metal ceramic is prepared by adopting a three-stage target-oriented step-by-step pressure sintering process; the three-stage target is that micro-pressure instantaneous high-temperature liquid phase sintering improves wettability of an alloy system, cooling high-purity argon pressure liquid phase sintering promotes alloy full densification, and secondary cooling supersolidus argon-nitrogen mixed pressure liquid phase sintering realizes self-consistent regulation and control of nitrogen content in the alloy; the strong acid refers to acid with pH less than or equal to 1, and the strong base refers to alkali with pH more than or equal to 13; said Ti (C) 0.7 ,N 0.3 ) The base hard phase is Ti (C) 0.7 ,N 0.3 ) A hard phase in the cermet prepared as a raw material; the porosity is less than or equal toA02 Evaluation of B00, section 4 of metallographic determination according to national Standard GB/T3488.4-2022 "hard alloy microstructure: metallographic determination of porosity, non-carbon defects and decarburized phases.
In the invention, the CoCrNi-based medium entropy alloy comprises an equal atomic ratio CoCrNi-based medium entropy alloy.
The Ti (C, N) -based metal ceramic adopts an alloyed CoCrNi medium entropy alloy as a bonding metal, and adopts Ti (C) with high C/N ratio 0.7 ,N 0.3 ) Is the raw material; the supply state of the entropy alloy raw material powder in CoCrNi is that the alloy powder passes through a 400-mesh screen, and before use, the alloy powder is subjected to scalization treatment, and the one-dimensional size of the alloy powder is smaller than 0.3 mu m; ti (C) 0.7 ,N 0.3 ) The powder has a Fisher size of less than 2.0 μm and TaC, nbC, mo 2 The Fisher particle size of the raw material powder C is less than 1.5 mu m, the specific surface area average particle size of the raw material powder WC is less than 0.4 mu m, and the raw material powder C has high reactivity in the sintering process.
The Ti (C, N) -based metal ceramic has a two-phase homogeneous structure, the porosity is less than or equal to the full densification state of A02 and B00, the bonding phase is uniformly distributed in the alloy, and the Ti (C) with high C/N ratio is adopted 0.7 ,N 0.3 ) And the realization of the scalization treatment of the saturated carbon carbide additive raw material and the CoCrNi medium entropy alloy raw material powder, and the wet grinding and sintering process based on the intrinsic characteristic matching design of the raw material and alloy component system.
The bonding metal corresponds to the alloy component and the bonding corresponds to the phase in the microstructure of the alloy. The design of the alloy system is based on Ti (C) in the microstructure of the alloy under the existence of strong corrosive media such as strong acid, strong alkali and the like 0.7 ,N 0.3 ) The design principle that the strong corrosion resistance and galvanic corrosion between the base hard phase and the entropy alloy base bonding phase in CoCrNi, especially the entropy alloy base bonding phase in equal atomic ratio CoCrNi can be minimized is provided, the design principle that fine grain strengthening, hardness and toughness matching are achieved, the self-consistent optimization of two-phase region carbon and nitrogen control realizes the extreme strength regulation and control, the high-temperature wettability improvement of an alloy system is matched with the inhibition degree of grain growth, the volume expansion complementation and the stress minimization of oxidation generated products are achieved, and therefore, the developed alloy has strong adaptability to various abrasive extreme service conditionsThe method is strong in economy.
The second object of the present invention is to develop a composition which is resistant to both strong acid and strong alkali corrosion, excellent in combination properties, and has Ti (C) 0.7 ,N 0.3 ) Two-phase homogeneous structure of base hard phase and entropy alloy base binder phase in CoCrNi, ti (C) 0.7 ,N 0.3 ) The low-cost and industrialized preparation technology of the Ti (C, N) -based metal ceramic with the average grain size of the base hard phase smaller than 1.2 mu m and the alloy in a fully densified state promotes the quality upgrading and the expansion of the application field of the Ti (C, N) -based metal ceramic.
In order to achieve the above purpose, the preparation method of the hard material resistant to corrosion by strong acid and strong alkali of the invention comprises the following steps:
A. wet milling mixture preparation: coCrNi medium entropy alloy powder and Ti (C) subjected to wet stirring ball milling high-energy flaking treatment 0.7 ,N 0.3 )、WC、Mo 2 C. Compounding TaC and NbC, and adding a forming agent accounting for 2.3-2.5% of the total mass of the powder for wet grinding; the result of the batching is that the mass fraction of entropy alloy in CoCrNi in the metal ceramic alloy component is less than 25 percent but more than 15 percent, WC occupies Ti (C 0.7 ,N 0.3 ) 20-30% of Mo 2 C is Ti (C) 0.7 ,N 0.3 ) 10 to 15 percent of the mass fraction, and the total mass fraction of (NbC+TaC) accounts for Ti (C) 0.7 ,N 0.3 ) 15-20% of NbC (NbC+TaC) by mass fraction, and 0-30% of the total mass fraction; said Ti (C) 0.7 ,N 0.3 ) The carbide alloy additive is a saturated carbon type compound with carbon content more than or equal to theoretical carbon content; the supply state of the entropy alloy raw material powder in CoCrNi is alloy powder passing through a 400-mesh screen, ti (C) 0.7 ,N 0.3 ) The raw material powder has a Fisher particle size of less than 2.0 μm, and the WC raw material powder has a specific surface area average particle size of less than 0.4 μm and TaC, nbC, mo 2 The Fisher particle size of the raw material powder C is less than 1.5 mu m;
B. drying and granulating the wet-grinding mixture: preparing a spherical mixture with the average particle size smaller than 150 mu m by adopting a spray drying granulation or vacuum drying and mechanical granulation process;
C. powder forming: selecting a forming mode according to the shape and the size of the product and the production requirement of the traditional metal ceramic blank, wherein the forming mode comprises compression molding;
D. removing and sintering a forming agent: the forming agent is removed and sintered in a pressure sintering furnace; after the forming agent is removed, sintering is carried out by adopting a three-stage target-oriented step pressure sintering process; the three-stage target is that micro-pressure instantaneous high-temperature liquid phase sintering improves wettability of an alloy system, cooling high-purity argon pressure liquid phase sintering promotes alloy full densification, and secondary cooling supersolidus argon-nitrogen mixed pressure liquid phase sintering realizes self-consistent regulation and control of nitrogen content in the alloy; the sintering heat preservation temperature of the first stage is 1530-1550 ℃, the heat preservation time is 10-15 minutes, and then the sintering heat preservation temperature is cooled to 1480-1500 ℃ of the second stage at a cooling speed of 10-20 ℃/minute; after the second-stage heat preservation temperature is reached, high-purity argon is introduced to raise the pressure in the sintering furnace to 2.5-4.0 MPa, the total heat preservation time in the second stage is 60-100 minutes, and the temperature is cooled to 1380-1400 ℃ in the third-stage heat preservation temperature at a cooling speed of 10-20 ℃/min after heat preservation is finished; after the temperature of the third-stage heat preservation is reached, high-purity nitrogen is introduced to raise the pressure in the sintering furnace by 1-1.5 MPa based on the original pressure in the sintering furnace, and the total heat preservation time in the third stage is 30-50 minutes.
In the step A, the wet grinding medium for the wet stirring ball milling high-energy flaking treatment is alcohol, the rotation speed of a stirring paddle for stirring ball milling is 250-300 revolutions per minute, the mass ratio of the hard alloy grinding ball to the entropy alloy powder in CoCrNi is (15-20): 1, the wet grinding time is 15-20 hours, and the process is carried out under the protection of argon.
In the step A, the forming agent added in the preparation of the wet grinding mixture can be a forming agent commonly used in the preparation process of hard alloy. Preferably, in the step A, the forming agent added in the preparation of the wet-milling mixture is polyethylene glycol or paraffin, a roller ball milling process is adopted, a wet-milling medium is alcohol, the mass ratio of the hard alloy grinding balls to the mixture is (4:1) - (5:1), and the wet-milling time is 50-60 hours.
In the step D, after the forming agent is removed, vacuum sintering is carried out; when the temperature is raised to 1430-1450 ℃, high-purity argon is introduced to enable the pressure in the sintering furnace to reach 5-7 kPa, and the pressure is maintained until the temperature in the sintering furnace reaches 1480-1500 ℃ of the temperature point of the second-stage sintering.
Ti (C, N) -based cermets may be used for the preparation of Ti (C, N) -based cermets 0.3 ,N 0.7 )、Ti(C 0.4 ,N 0.6 )、Ti(C 0.5 ,N 0.5 ) And Ti (C) 0.7 ,N 0.3 ) The raw material powders with different C/N ratios are equal. In the field of cermets, ti (C 0.5 ,N 0.5 ) Typically abbreviated as Ti (C, N) or TiCN. The invention adopts Ti (C) with high C/N ratio 0.7 ,N 0.3 ) And a saturated carbon carbide additive raw material, which solves the problems that a brittle decarburized phase is easily formed by adopting a CoCrNi entropy alloy as a metal ceramic bonding metal due to the fact that a two-phase region of an alloy system is deviated to a high carbon side, and the quality is unstable due to the addition of excessive carbon black; the invention can solve the problem of controlling carbon in the two-phase region of the alloy system with low bonding metal content by adding trace carbon black, but preferably realizes the control of the total carbon content of the alloy in the two-phase region by selecting raw materials with high carbon content. The invention adopts Ti (C) with high C/N ratio 0.7 ,N 0.3 ) The raw materials are also beneficial to improving the wettability of the alloy system. Based on the excellent plastic deformation capability and oxidation resistance intrinsic characteristics of the entropy alloy in CoCrNi, the wet stirring ball milling high-energy flaking treatment technology developed by the invention can stably control the one-dimensional size of the entropy alloy powder in CoCrNi to be smaller than 0.3 mu m, and can realize the matching of the one-dimensional size of the entropy alloy powder in CoCrNi with the particle sizes of other raw material powders. The micro-pressure instantaneous high-temperature liquid phase sintering under the argon atmosphere of 5-7 kPa can obviously improve the wettability of an alloy system, accelerate the atomic diffusion among hard phase components and the formation of a hard phase solid solution, effectively inhibit the high-temperature evaporation of bonded metal, realize the control of the growth dynamics of crystal grains at the instantaneous high temperature and prevent the abnormal growth of the crystal grains of the hard phase; the cooling high-purity argon pressure liquid phase sintering can effectively promote the full densification of the alloy and effectively inhibit the growth of the abnormal grains of the hard phase. The nitrogen loading prior to full densification of the alloy structure can hinder densification of the alloy system. But after the pores in the alloy system are effectively eliminated, the full densification is realized, the microalloy of the hard phase and Jin Zuyuan in the bonding phase improves the wettability of the alloy system for the second time, the temperature is reduced for the second time to exceed that of the alloy systemUnder the low temperature condition of the solidus of the alloy system, argon-nitrogen mixed pressure liquid phase sintering with argon as a main component can realize self-consistent regulation and control of carbon and nitrogen content in the alloy and inhibit formation of harmful phases, thereby further improving the toughness and corrosion resistance of the alloy.
Drawings
FIG. 1 is a scanning electron micrograph of an entropy alloy powder in a-400 mesh equiatomic ratio CoCrNi prepared by aerosolization.
FIG. 2 is a scanning electron microscope photograph of an entropy alloy powder in an equal atomic ratio CoCrNi after being subjected to wet stirring ball milling high-energy flaking treatment.
FIG. 3 is a diagram of Ti (C) in example 1 0.7 ,N 0.3 )-13.0WC-6.3TaC-2.7NbC-6.0Mo 2 Scanning electron microscope photograph of C-22.0CoCrNi metal ceramic microstructure.
Detailed Description
The invention is further described below with reference to examples and figures.
Example 1
The powder of the entropy alloy in the CoCrNi with the equal atomic ratio of-400 meshes prepared by gas atomization is used as a raw material, a scanning electron microscope picture is shown in a figure 1, and the average particle size of the powder in the figure 1 is smaller than 13 mu m. The high-energy flaking treatment of the entropy alloy powder in CoCrNi by wet stirring and ball milling is carried out in an alcohol medium under the protection of argon, the rotating speed of a stirring paddle is 280 revolutions per minute, the mass ratio of a hard alloy grinding ball to multi-principal element alloy gas atomization powder is 18:1, and the wet grinding time is 18 hours. The scanning electron microscope photograph of the entropy alloy powder in the equal atomic ratio CoCrNi after the high-energy flaking treatment is shown in figure 2, and the one-dimensional size of the flaking powder in figure 2 is smaller than 0.3 mu m.
Adopting the powder of the entropy alloy flake in the CoCrNi with equal atomic ratio after the high-energy flaking treatment, and Ti (C) with the Fisher particle sizes of 1.5, 1.2, 1.4 and 1.3 mu m respectively 0.7 ,N 0.3 )、TaC、NbC、Mo 2 Preparation of powder C of WC powder having a specific surface area average particle diameter of 0.30 μm as a raw material Ti (C) 0.7 ,N 0.3 )-13.0WC-6.3TaC-2.7NbC-6.0Mo 2 C-22.0CoCrNi cermet (1 # Alloy) and the values listed in the alloy components are the mass fraction of each powder component. Ti (C) 0.7 ,N 0.3 )、TaC、NbC、Mo 2 The total carbon content (mass fraction) in C and WC is 14.02%, 6.24%, 11.46%, 5.91% and 6.13%, respectively, and the C and WC are saturated carbon compounds with carbon content not less than theoretical carbon content.
Adopting a roller ball milling process, wherein a wet milling medium is alcohol, the mass ratio of the hard alloy grinding balls to the mixture is 4:1, the wet milling time is 60 hours, and a polyvinyl alcohol forming agent accounting for 2.3 percent of the total mass fraction of the powder is added during wet milling. And preparing a spherical mixture with the average particle size smaller than 150 mu m by adopting spray drying granulation. The round bar sample was prepared by a dry bag cold isostatic pressing forming process. The removal of the forming agent and sintering are carried out in a pressure sintering furnace. After the forming agent is removed at 450 ℃, vacuum sintering is carried out, the heating rate is 10 ℃/min, and the temperature is respectively kept at 800 ℃ and 1250 ℃ for 30 minutes; when the temperature is raised to 1430 ℃, high-purity argon is introduced to enable the pressure in the sintering furnace to reach 7kPa, the temperature is continuously raised to 1530 ℃, and the temperature is kept for 15 minutes; then the temperature is reduced to 1480 ℃ at the speed of 10 ℃/min, high-purity argon is introduced, the pressure in the sintering furnace is increased to 2.5MPa, and the total heat preservation time at 1480 ℃ is 90 min; then the temperature is reduced to 1380 ℃ at the cooling rate of 20 ℃/min, high-purity nitrogen is introduced to enable the pressure in the sintering furnace to be increased by 1MPa on the basis of the original pressure in the furnace, the total heat preservation time is 50 min at 1380 ℃, and then the sintering furnace is cooled along with the furnace. Cutting the sintered round bar product into a B-type sample for bending strength test by adopting a diamond cutting tool. The scanning electron microscope photograph of the microstructure of the metal ceramic in the embodiment is shown in fig. 3. The test results show that the alloy is Ti (C 0.7 ,N 0.3 ) The base hard phase and the entropy alloy base binding phase in the CoCrNi with equal atomic ratio have two-phase homogeneous structures, the binding phase is uniformly distributed in the alloy, and the average grain size of the hard phase is 0.9 mu m.
Example 2
Adopts-400 mesh equal atomic ratio CoCrNi intermediate entropy alloy powder prepared by gas atomization as a raw material. The high-energy flaking treatment of the entropy alloy powder in CoCrNi by wet stirring and ball milling is carried out in an alcohol medium under the protection of argon, the rotating speed of a stirring paddle is 250 revolutions per minute, the mass ratio of a hard alloy grinding ball to multi-principal element alloy gas atomization powder is 20:1, and the wet grinding time is 15 hours.
Adopting the powder of the entropy alloy flake in the CoCrNi with equal atomic ratio after the high-energy flaking treatment, and respectively obtaining Ti (C) with the Fisher particle size of 1.6, 1.2 and 1.3 mu m 0.7 ,N 0.3 )、TaC、Mo 2 Preparation of powder C of WC powder having a specific surface area average particle diameter of 0.25 μm as a raw material Ti (C) 0.7 ,N 0.3 )-15.4WC-10.0TaC-5.0Mo 2 C-18.0CoCrNi cermet (2 # Alloy) and the values listed in the alloy components are the mass fraction of each powder component. Ti (C) 0.7 ,N 0.3 )、TaC、Mo 2 The total carbon content (mass fraction) in C and WC was 14.40%, 6.24%, 5.91% and 6.16%, respectively.
Adopting a roller ball milling process, wherein a wet milling medium is alcohol, the mass ratio of the hard alloy grinding balls to the mixture is 5:1, the wet milling time is 50 hours, and a paraffin wax forming agent accounting for 2.5 percent of the total mass of the powder is added during wet milling. And preparing a spherical mixture with the average particle size smaller than 150 mu m by adopting spray drying granulation. And preparing a B-type sample for bending strength test by adopting a compression molding process. The removal of the forming agent and sintering are carried out in a pressure sintering furnace. After the forming agent is removed at 480 ℃, vacuum sintering is carried out, the heating rate is 10 ℃/min, and the temperature is respectively kept at 800 ℃ and 1250 ℃ for 30 minutes; when the temperature is raised to 1450 ℃, high-purity argon is introduced to enable the pressure in the sintering furnace to reach 5kPa, the temperature is continuously raised to 1550 ℃, and the temperature is kept for 10 minutes; then the temperature is reduced to 1500 ℃ at the cooling rate of 10 ℃/min, high-purity argon is introduced, the pressure in the sintering furnace is increased to 4.0MPa, and the total heat preservation time at 1500 ℃ is 60 minutes; then the temperature is reduced to 1400 ℃ at the cooling rate of 10 ℃/min, high-purity nitrogen is introduced to ensure that the pressure in the sintering furnace is increased by 1.5MPa on the basis of the original pressure in the furnace, the total heat preservation time of 5.5MPa and 1400 ℃ is 30 minutes, and then the sintering furnace is cooled along with the furnace. The test results showed that the average grain size of the hard phase in the alloy was 1.0 μm.
Example 3
Adopts-400 mesh equal atomic ratio CoCrNi intermediate entropy alloy powder prepared by gas atomization as a raw material. The high-energy flaking treatment of the entropy alloy powder in CoCrNi by wet stirring and ball milling is carried out in an alcohol medium under the protection of argon, the rotating speed of a stirring paddle is 300 revolutions per minute, the mass ratio of a hard alloy grinding ball to multi-principal element alloy gas atomization powder is 15:1, and the wet grinding time is 20 hours.
Adopting the powder of the entropy alloy flake in the CoCrNi with equal atomic ratio after the high-energy flaking treatment, and Ti (C) with the Fisher particle sizes of 1.6, 1.2, 1.4 and 1.3 mu m respectively 0.7 ,N 0.3 )、TaC、NbC、Mo 2 Preparation of powder C of WC powder having a specific surface area average particle diameter of 0.25 μm as a raw material Ti (C) 0.7 ,N 0.3 )-11.0WC-6.4TaC-1.6NbC-8.0Mo 2 C-20.0CoCrNi cermet (3 # Alloy) and the values listed in the alloy components are the mass fraction of each powder component. Ti (C) 0.7 ,N 0.3 )、TaC、NbC、Mo 2 The total carbon content (mass fraction) in C and WC was 14.40%, 6.24%, 11.46%, 5.91% and 6.16%, respectively.
Adopting a roller ball milling process, wherein a wet milling medium is alcohol, the mass ratio of the hard alloy grinding balls to the mixture is 5:1, the wet milling time is 55 hours, and a paraffin wax forming agent accounting for 2.5 percent of the total mass of the powder is added during wet milling. And preparing a spherical mixture with the average particle size smaller than 150 mu m by adopting spray drying granulation. And preparing a B-type sample for bending strength test by adopting a compression molding process. The removal of the forming agent and sintering are carried out in a pressure sintering furnace. After the forming agent is removed at 480 ℃, vacuum sintering is carried out, the heating rate is 10 ℃/min, and the temperature is respectively kept at 800 ℃ and 1250 ℃ for 30 minutes; when the temperature is raised to 1440 ℃, high-purity argon is introduced to enable the pressure in the sintering furnace to reach 6kPa, the temperature is continuously raised to 1540 ℃, and the temperature is kept for 12 minutes; then the temperature is reduced to 1490 ℃ at the cooling rate of 20 ℃/min, high-purity argon is introduced, the pressure in the sintering furnace is increased to 3.0MPa, and the total heat preservation time at 1490 ℃ is 100 min; then the temperature is reduced to 1390 ℃ at a temperature reduction rate of 10 ℃ per minute, high-purity nitrogen is introduced to enable the pressure in the sintering furnace to be increased by 1.0MPa on the basis of the original pressure in the furnace, the total heat preservation time of the sintering furnace reaches 4.0MPa, the total heat preservation time of the sintering furnace at 1390 ℃ is 40 minutes, and then the sintering furnace is cooled along with the furnace. The test results showed that the average grain size of the hard phase in the alloy was 0.8 μm.
Comparative example 1
Cobalt powder and nickel carbonyl with the Fisher particle sizes of 1.2 and 2.5 mu m are adopted as bonding metals, the rest raw materials and the process parameters are the same as those of the example 1,the composition of comparative example 1 is Ti (C 0.7 ,N 0.3 )-13.0WC-6.3TaC-2.7NbC-6.0Mo 2 C-11.0Co-11.0Ni(4 # Alloy).
Scanning electron microscope observation results showed that the alloy of three examples (1 # To 3 # Alloy) all having Ti (C) 0.7 ,N 0.3 ) Two-phase homogeneous structure of base hard phase and entropy alloy base binder phase in CoCrNi, comparative example 1 (4 # Alloy) of Ti (C) 0.7 ,N 0.3 ) A two-phase homogeneous structure of a base hard phase and a Co-Ni-based binder phase; 1 # To 4 # The bonding phases in the alloy are uniformly distributed in the alloy, the microscopic aggregation phenomenon of the bonding phases does not exist, the porosities in the alloy are not more than A02 and not more than B00, and the porosity in the alloy is in a full densification state.
Detecting physical and mechanical properties of the alloy according to corresponding national standards, 1 # To 4 # The physical and mechanical properties of the alloy are shown in Table 1. The dimensions of the type B specimen for flexural strength test were (20.+ -. 1) mm (6.5.+ -. 0.25) mm (5.25.+ -. 0.25) mm. As can be seen from Table 1, the 4-group alloys have excellent physical and mechanical properties, but are 4 as binder metal compared with the conventional Co-Ni # Alloy, equal atomic ratio CoCrNi entropy alloy of the invention is used as 1 of bonding metal # To 3 # The hardness and toughness of the alloy are synchronously improved.
H with pH=1 2 SO 4 、HCl、HNO 3 Solution and NaOH solution at ph=13. The electrochemical corrosion test is carried out at an electrochemical workstation under the constant temperature condition of 25+/-1 ℃. The saturated calomel electrode is used as a reference electrode, the platinum sheet electrode is used as an auxiliary electrode, and the sample to be measured is used as a working electrode. The test sample is a grinding and polishing wafer, and the sample is placed in a working area of 1cm during test 2 Is a polytetrafluoroethylene clamp. Before electrochemical corrosion test, the sample is soaked in the test medium for 60min, and then the open circuit potential curve measurement is carried out to obtain stable open circuit potential, and then Electrochemical Impedance Spectroscopy (EIS) test under the open circuit potential is carried out, wherein the frequency range is 10 -2 ～10 5 Hz, voltage amplitude was 5mV. After EIS measurement, an electrokinetic potential polarization curve test is carried out, the scanning range of the test is from-0.8V to 2V, and the potential scanning speed is 0.5mV/s. Test resultsThe electrochemical corrosion kinetic parameters obtained, i.e. the self-corrosion current density (J corr ) And a charge transfer resistor (R ct ) See table 2. The corrosion rate has a negative correlation with the self-corrosion current density and a positive correlation with the charge transfer resistance. At 4 in comparative example 1 # The alloys were used as reference, corresponding to 1 in examples 1 to 3 among three strong acids # To 3 # The average self-corrosion current density of the alloy is reduced by 89 percent, and the average charge transfer resistance is improved by 780 percent; in NaOH solution, 1 # To 3 # The average self-corrosion current density of the alloy is reduced by 70 percent, and the average charge transfer resistance is improved by 210 percent. 4 as a bond metal relative to conventional Co-Ni # Alloy, equal atomic ratio CoCrNi entropy alloy of the invention is used as 1 of bonding metal # To 3 # The corrosion resistance of the alloy in strong acid and strong alkali is obviously improved, wherein the corrosion resistance in strong acid is obviously improved.
Table 1 physical and mechanical properties of the alloys of three examples and comparative example 1
TABLE 2 electrochemical corrosion kinetic parameters for the alloys of three examples and comparative example 1
Comparative example 2
The entropy alloy in CoCrNi is not subjected to flaking treatment, and other experimental raw materials, alloy components and preparation processes are the same as those in example 2. The bending strength test result shows that the bending strength of the alloy is between 700 and 1300MPa, which is obviously lower than that of the alloy in the embodiment 1.
Comparative example 3
The alloy composition and preparation process were the same as in example 2, except that the sintering process was different. After the forming agent is removed at 480 ℃, vacuum sintering is carried out, the heating rate is 10 ℃/min, and the temperature is respectively kept at 800 ℃ and 1250 ℃ for 30 minutes; when the temperature is raised to 1450 ℃, high-purity argon is introduced to enable the pressure in the sintering furnace to reach 5kPa, the temperature is continuously raised to 1500 ℃, high-purity argon is introduced to enable the pressure in the sintering furnace to be raised to 4.0MPa, the total heat preservation time at 1500 ℃ is 60 minutes, and then the sintering furnace is cooled. The bending strength test result shows that the bending strength of the alloy is between 1500 and 2010MPa, which is obviously lower than that of the alloy in the embodiment 2.
Comparative example 4
The alloy composition and preparation process were the same as in example 2, except that the sintering process was different. The removal of the forming agent and sintering are carried out in a pressure sintering furnace. After the forming agent is removed at 480 ℃, vacuum sintering is carried out, the heating rate is 10 ℃/min, and the temperature is respectively kept at 800 ℃ and 1250 ℃ for 30 minutes; when the temperature is raised to 1450 ℃, high-purity argon is introduced to enable the pressure in the sintering furnace to reach 5kPa, the temperature is continuously raised to 1550 ℃, and the temperature is kept for 10 minutes; then the temperature is reduced to 1500 ℃ at the cooling rate of 10 ℃/min, high-purity argon is introduced, the pressure in the sintering furnace is increased to 4.0MPa, the total heat preservation time of 1500 ℃ is 60 minutes, and then the furnace is cooled. The test results show that the hardness and Palmqvist fracture toughness of the alloy are 1880HV30 and 11.68 MPa.m respectively 1/2 Relative to 2 # The hardness difference of the alloy is close to the measurement error, but the toughness is obviously reduced; h at ph=1 2 SO 4 The self-corrosion current density is improved by 29 percent, the charge transfer resistance is reduced by 110 percent, and the corrosion resistance is obviously reduced.
Comparative example 5
The raw materials, alloy compositions and preparation processes were the same as in example 2 except that the Ti (C, N) raw materials were different. The Ti (C, N) raw material is Ti (C) 0.5 ,N 0.5 ) The Fisher size was 1.2 μm and the total carbon content (mass fraction) was 9.80%. Microstructure observations indicate that significant non-uniform size and non-uniformly distributed decarburized phases appear in the alloy. The bending strength test result shows that the bending strength of the alloy is between 520 and 720MPa, which is obviously lower than that of the alloy in the embodiment 2.
Comparative example 6
Removing TaC and Mo 2 C and WC raw material powders are different from each otherThe remainder of the raw materials, alloy components and preparation process were the same as in example 2.TaC and Mo 2 The Fisher particle size of the raw material powder C is 1.3 and 1.2 μm respectively, and the total carbon content (mass fraction) is 6.19% and 5.80% respectively; the WC raw material powder had a specific surface area average particle diameter of 0.20 μm and a total carbon content (mass fraction) of 6.09%. Microstructure observations indicate that significant non-uniform size and non-uniformly distributed decarburized phases appear in the alloy. The bending strength test result shows that the bending strength of the alloy is between 490 and 750MPa, which is obviously lower than that of the alloy in the embodiment 2.
Comparative example 7
TaC、Mo 2 C and WC raw materials are the same as in comparative example 6, and the rest raw materials, alloy components and preparation process are the same as in example 2, and the total carbon content in the alloy is the same as in example 2 by adding nano carbon black. Microstructure observation results show that the alloy has a two-phase structure, a decarburized phase does not appear, but microstructure uniformity is poor. The bending strength test result shows that the bending strength of the alloy is 1850-2450 MPa, the average value of the bending strength is 2105MPa, and the bending strength is obviously lower than that of the alloy in the example 2.
Claims (8)
1. A hard material resistant to corrosion by strong acids and strong bases, characterized by: the strong acid is acid with the pH value less than or equal to 1, the strong base is alkali with the pH value more than or equal to 13, and the hard material is Ti (C, N) -based cermet; the Ti (C, N) -based metal ceramic has a two-phase homogeneous structure of a hard phase and a bonding phase, the bonding phase of the entropy alloy in the CoCrNi matrix is uniformly distributed in the alloy, and the Ti (C) 0.7 ,N 0.3 ) The average grain size of the base hard phase is smaller than 1.2 mu m, the porosity in the alloy is less than or equal to A02 and B00, and the base hard phase is in a full densification state; in the Ti (C, N) -based cermet alloy component, the mass fraction of the entropy alloy in CoCrNi is less than 25 percent but more than 15 percent, and WC accounts for Ti (C 0.7 ,N 0.3 ) 20-30% of Mo 2 C is Ti (C) 0.7 ,N 0.3 ) 10 to 15 percent of the mass fraction, and the total mass fraction of (NbC+TaC) accounts for Ti (C) 0.7 ,N 0.3 ) 15-20% of NbC (NbC+TaC) by mass fraction, and 0-30% of the total mass fraction; said Ti (C) 0.7 ,N 0.3 ) And carbide alloy additive areSaturated carbon type compound with carbon content more than or equal to theoretical carbon content; the Ti (C, N) -based metal ceramic is prepared by adopting a three-stage target-oriented step-by-step pressure sintering process; the three-stage target is that micro-pressure instantaneous high-temperature liquid phase sintering improves wettability of an alloy system, cooling high-purity argon pressure liquid phase sintering promotes alloy full densification, and secondary cooling supersolidus argon-nitrogen mixed pressure liquid phase sintering realizes self-consistent regulation and control of nitrogen content in the alloy.
2. A hard material resistant to corrosion by strong acids and strong bases according to claim 1, characterized in that: the CoCrNi-based medium entropy alloy comprises an equal atomic ratio CoCrNi-based medium entropy alloy.
3. A hard material resistant to corrosion by strong acids and strong bases according to claim 1, characterized in that: the Ti (C, N) -based metal ceramic adopts an alloyed CoCrNi medium entropy alloy as a bonding metal, and adopts Ti (C) with high C/N ratio 0.7 ,N 0.3 ) Is the raw material; the supply state of the entropy alloy raw material powder in CoCrNi is that the alloy powder passes through a 400-mesh screen, and before use, the alloy powder is subjected to scalization treatment, and the one-dimensional size of the alloy powder is smaller than 0.3 mu m; ti (C) 0.7 ,N 0.3 ) The powder has a Fisher size of less than 2.0 μm and TaC, nbC, mo 2 The Fisher particle size of the raw material powder C is less than 1.5 μm, and the specific surface area average particle size of the raw material powder WC is less than 0.4 μm.
4. A hard material resistant to corrosion by strong acids and strong bases according to claim 1, characterized in that: the Ti (C, N) -based metal ceramic has a two-phase homogeneous structure, the porosity is less than or equal to the full densification state of A02 and B00, the bonding phase is uniformly distributed in the alloy, and the Ti (C) with high C/N ratio is adopted 0.7 ,N 0.3 ) And the realization of the scalization treatment of the saturated carbon carbide additive raw material and the CoCrNi medium entropy alloy raw material powder, and the wet grinding and sintering process based on the intrinsic characteristic matching design of the raw material and alloy component system.
5. A preparation method of a hard material resistant to corrosion of strong acid and strong alkali is characterized by comprising the following steps: the method comprises the following steps:
A. wet milling mixture preparation: coCrNi medium entropy alloy powder and Ti (C) subjected to wet stirring ball milling high-energy flaking treatment 0.7 ,N 0.3 )、WC、Mo 2 C. Compounding TaC and NbC, and adding a forming agent accounting for 2.3-2.5% of the total mass of the powder for wet grinding; the result of the batching is that the mass fraction of entropy alloy in CoCrNi in the metal ceramic alloy component is less than 25 percent but more than 15 percent, WC occupies Ti (C 0.7 ,N 0.3 ) 20-30% of Mo 2 C is Ti (C) 0.7 ,N 0.3 ) 10 to 15 percent of the mass fraction, and the total mass fraction of (NbC+TaC) accounts for Ti (C) 0.7 ,N 0.3 ) 15-20% of NbC (NbC+TaC) by mass fraction, and 0-30% of the total mass fraction; said Ti (C) 0.7 ,N 0.3 ) The carbide alloy additive is a saturated carbon type compound with carbon content more than or equal to theoretical carbon content; the supply state of the entropy alloy raw material powder in CoCrNi is alloy powder passing through a 400-mesh screen, ti (C) 0.7 ,N 0.3 ) The raw material powder has a Fisher particle size of less than 2.0 μm, and the WC raw material powder has a specific surface area average particle size of less than 0.4 μm and TaC, nbC, mo 2 The Fisher particle size of the raw material powder C is less than 1.5 mu m;
B. drying and granulating the wet-grinding mixture: preparing a spherical mixture with the average particle size smaller than 150 mu m by adopting a spray drying granulation or vacuum drying and mechanical granulation process;
C. powder forming: selecting a forming mode according to the shape and the size of the product and the production requirement of the traditional metal ceramic blank, wherein the forming mode comprises compression molding;
D. removing and sintering a forming agent: the forming agent is removed and sintered in a pressure sintering furnace; after the forming agent is removed, sintering is carried out by adopting a three-stage target-oriented step pressure sintering process; the three-stage target is that micro-pressure instantaneous high-temperature liquid phase sintering improves wettability of an alloy system, cooling high-purity argon pressure liquid phase sintering promotes full densification of the alloy, and secondary cooling super-solidus argon-nitrogen mixed pressure liquid phase sintering realizes self-consistent regulation and control of nitrogen content in the alloy; the sintering heat preservation temperature of the first stage is 1530-1550 ℃, the heat preservation time is 10-15 minutes, and then the sintering heat preservation temperature is cooled to 1480-1500 ℃ of the second stage at a cooling speed of 10-20 ℃/minute; after the second-stage heat preservation temperature is reached, high-purity argon is introduced to raise the pressure in the sintering furnace to 2.5-4.0 MPa, the total heat preservation time in the second stage is 60-100 minutes, and the temperature is cooled to 1380-1400 ℃ in the third-stage heat preservation temperature at a cooling speed of 10-20 ℃/min after heat preservation is finished; after the temperature of the third-stage heat preservation is reached, high-purity nitrogen is introduced to raise the pressure in the sintering furnace by 1-1.5 MPa based on the original pressure in the sintering furnace, and the total heat preservation time in the third stage is 30-50 minutes.
6. The method for preparing the hard material resistant to corrosion by strong acid and strong alkali according to claim 5, wherein the method comprises the following steps: in the step A, the wet grinding medium for the wet stirring ball milling high-energy flaking treatment is alcohol, the rotation speed of a stirring paddle for stirring ball milling is 250-300 revolutions per minute, the mass ratio of the hard alloy grinding ball to the entropy alloy powder in CoCrNi is (15-20): 1, the wet grinding time is 15-20 hours, and the process is carried out under the protection of argon.
7. The method for preparing the hard material resistant to corrosion by strong acid and strong alkali according to claim 5, wherein the method comprises the following steps: in the step A, the forming agent added in the preparation of the wet-milling mixture is polyethylene glycol or paraffin, a roller ball milling process is adopted, a wet-milling medium is alcohol, the mass ratio of the hard alloy grinding balls to the mixture is (4:1) - (5:1), and the wet-milling time is 50-60 hours.
8. The method for preparing the hard material resistant to corrosion by strong acid and strong alkali according to claim 5, wherein the method comprises the following steps: in the step D, after the forming agent is removed, vacuum sintering is carried out; when the temperature is raised to 1430-1450 ℃, high-purity argon is introduced to enable the pressure in the sintering furnace to reach 5-7 kPa, and the pressure is maintained until the temperature in the sintering furnace reaches 1480-1500 ℃ of the temperature point of the second-stage sintering.
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