Hard material resistant to strong acid and strong base corrosion and preparation method thereof

Abstract

The application relates to a kind of hard materials resistant to strong acid and strong base corrosion, which is a Ti (C, N) based cermet using CoCrNi medium entropy alloy as bonding metal, and belongs to the field of powder metallurgy new materials.The application aims to solve the problems of poor corrosion resistance of traditional hard materials in corrosive medium, especially in strong acid medium, and the problems of easy decarburization, poor microstructure homogeneity and poor strength and toughness caused by using corrosion-resistant CoCrNi medium entropy alloy as cermet bonding metal.The application uses high C / N ratio Ti (C 0.7, N 0.3 ) and saturated carbon carbide additive raw materials to solve the problems of easy brittle decarburization phase formation caused by using CoCrNi medium entropy alloy as cermet bonding metal and unstable quality caused by adding excessive carbon black;Micro-pressure instantaneous high-temperature liquid phase sintering is used to improve the wettability of alloy system, argon-nitrogen carrier gas super-solidus liquid phase sintering is used to realize self-consistent regulation and control of nitrogen content in the alloy after full densification, and the comprehensive performance is comprehensively improved.

Description

Technical Field

[0001] This invention relates to a hard material resistant to strong acid and alkali corrosion and its preparation method, belonging to the field of new powder metallurgy materials. Background Technology

[0002] Hard materials include WC-based cemented carbides and Ti(C,N)-based cermets, and are broadly classified into bonded metals and bondless metals. In corrosive media, the corrosion resistance of hard materials with a hard phase + metal bonded phase microstructure is typically significantly lower than that of bondless metal hard materials because the bonded phase corrodes preferentially. The bonded phase imparts strength and toughness to hard materials, and also significantly lowers the sintering densification temperature of the alloy and promotes sintering densification. Practical applications usually place high demands on the strength, toughness, hardness, and wear resistance of hard materials, which obviously limits the expansion of the application fields of bondless metal hard materials.

[0003] Strong acids and alkalis are common service conditions in petroleum, chemical, and hydrometallurgical industries. Applying these conditions places higher demands on the corrosion resistance and related wear resistance of hard materials. Existing literature consistently reports that Ti(C,N)-based cermets exhibit higher corrosion and wear resistance compared to WC-based cemented carbides; however, acidic media are extremely corrosive to hard materials compared to alkaline media. Therefore, there is an urgent need to develop hard materials that are resistant to both strong acids and alkalis, possess good physical and mechanical properties, and are highly suitable for extreme service conditions. Our previous research results indicate that moderately increasing the N content in Ti(C,N)-based cermets is beneficial for improving their corrosion resistance and high-temperature oxidation resistance, as well as their strength and toughness. However, improper control can easily lead to the formation of decarburized phases in the alloy, resulting in a significant reduction in the homogeneity of the microstructure. This, in turn, leads to a significant decrease in the wettability of the liquid-phase sintered alloy system, hindering the sintering and densification of the alloy. Summary of the Invention

[0004] The first objective of this invention is to improve the corrosion resistance and overall performance of traditional hard materials, and to address the problems of poor corrosion resistance of Ti(C,N)-based cermets with traditional Co-Ni as the binder metal in corrosive media, especially strong acid media, and the tendency of using corrosion-resistant CoCrNi medium-entropy alloys as binders to improve the corrosion resistance of Ti(C,N)-based cermets to lead to decarburization and related issues such as poor homogeneity of alloy microstructure and poor strength and toughness.

[0005] To achieve the above objectives, based on the Ti(C,N)-based cermet material design database established by the inventors, and the principle of the control limit of microstructure by the matching design of alloy composition, microstructure, and performance, a Ti(C,N)-based cermet resistant to strong acid and alkali corrosion was developed through material calculations and experimental verification. This cermet possesses a homogeneous two-phase structure of hard and binder phases, with the CoCrNi-based medium-entropy alloy binder phase uniformly distributed within the alloy. 0.7 N 0.3 The average grain size of the hard phase is less than 1.2 μm, and the porosity of the alloy is ≤A02, B00, indicating a fully densified state. It has the following compositional characteristics: in the alloy components, the mass fraction of the entropy alloy in CoCrNi is less than 25% but greater than 15%, and WC accounts for a significant portion of Ti(C). 0.7 N 0.3 The mass fraction of Mo2C is 20-30%, and the proportion of Mo2C in Ti(C) is 20-30%. 0.7 N 0.3 The mass fraction of (NbC+TaC) is 10-15%, and the total mass fraction of (NbC+TaC) accounts for 10-15% of the total mass fraction of Ti(C). 0.7 N 0.3 The Ti(C) content is 15-20% by mass, and NbC accounts for 0-30% of the total mass fraction of (NbC+TaC); 0.7 N 0.3 Both the Ti(C,N)-based cermet and the carbide alloy additives are saturated carbon compounds with a carbon content greater than or equal to the theoretical carbon content. The Ti(C,N)-based cermet is prepared using a three-stage target-oriented stepwise pressure sintering process. The three-stage targets are: micro-pressure instantaneous high-temperature liquid-phase sintering to improve the wettability of the alloy system; cooling high-purity argon pressure liquid-phase sintering to promote full densification of the alloy; and secondary cooling supersolid-phase argon-nitrogen mixed pressure liquid-phase sintering to achieve self-consistent control of the nitrogen content in the alloy. The strong acid refers to an acid with a pH ≤ 1, and the strong base refers to a base with a pH ≥ 13. 0.7 N 0.3 Ti(C)-based hard phase refers to the use of Ti(C)-based hard phase. 0.7 N 0.3 The hard phase in the metal ceramic prepared from raw material ); the evaluation of the porosity ≤A02, B00 is based on the national standard GB / T 3488.4—2022 "Metallographic determination of microstructure of cemented carbide - Part 4: Metallographic determination of porosity, non-combined carbon defects and decarburized phases".

[0006] In this invention, the CoCrNi-based medium-entropy alloy includes an equiatomic CoCrNi-based medium-entropy alloy.

[0007] The Ti(C,N)-based cermet uses an alloyed CoCrNi medium-entropy alloy as the binder metal and employs a high C / N ratio Ti(C) alloy. 0.7 N0.3 The raw material is CoCrNi medium-entropy alloy powder, which is supplied in the form of alloy powder that has passed through a 400-mesh sieve and is flaked before use, with a one-dimensional size of less than 0.3 μm; Ti(C) 0.7 N 0.3 The raw material powder has a Fisher particle size of less than 2.0 μm, the TaC, NbC and Mo2C raw material powders all have a Fisher particle size of less than 1.5 μm, and the WC raw material powder has an average particle size of less than 0.4 μm in specific surface area, exhibiting high reactivity during sintering.

[0008] The Ti(C,N)-based cermet has a two-phase homogeneous structure with a fully densified state where porosity ≤ A02 and B00. The binder phase is uniformly distributed in the alloy. This is achieved by using Ti(C) with a high C / N ratio. 0.7 N 0.3 The process involves the flake formation of raw materials such as saturated carbon carbide additives and CoCrNi medium-entropy alloy powder, as well as wet grinding and sintering processes designed based on the intrinsic properties of the raw materials and alloy composition system.

[0009] The binder metal corresponds to the alloy component, and the binder phase corresponds to the phase in the alloy's microstructure. The alloy system design of this invention is based on the presence of highly corrosive media such as strong acids and alkalis, and the Ti(C) content in the alloy's microstructure. 0.7 N 0.3 The strong corrosion resistance matching between the hard phase and the medium-entropy alloy-based binder phase of CoCrNi, especially the medium-entropy alloy-based binder phase with equal atomic ratio, and the design principle of minimizing galvanic corrosion, combine fine grain strengthening, hardness and toughness matching. The self-consistent optimization of carbon and nitrogen control in the two-phase region realizes the extreme value regulation of strength. The high-temperature wettability of the alloy system is matched with the degree of suppression of grain growth. The volume expansion of oxidation products is complementary and stress is minimized. Therefore, the developed alloy has strong adaptability to various abrasive extreme service conditions and is also very economical.

[0010] The second objective of this invention is to develop a material that is resistant to both strong acids and strong alkalis, possesses excellent overall performance, and exhibits Ti(C) properties. 0.7 N 0.3 The two-phase homogeneous structure of the hard phase and the medium-entropy alloy-based binder phase of Ti(C)Ni, and the Ti(C)Ni hard phase. 0.7 N 0.3 This technology enables low-cost, industrial-scale preparation of Ti(C,N)-based cermets with an average grain size of less than 1.2 μm in the hard phase and a fully densified alloy state, promoting the quality upgrade and expansion of application fields of Ti(C,N)-based cermets.

[0011] To achieve the above objectives, the present invention provides a method for preparing a hard material resistant to strong acids and alkalis, comprising the following steps:

[0012] A. Preparation of wet-milled mixture: High-energy flake-treated CoCrNi medium-entropy alloy powder and Ti(C) powder are wet-milled with stirred ball mill. 0.7 N 0.3 The following ingredients are added: WC, Mo2C, TaC, and NbC. A forming agent comprising 2.3–2.5% of the total powder mass is then added, followed by wet milling. The resulting mixture should meet the following requirements: in the cermet alloy, the entropy alloy mass fraction of CoCrNi is less than 25% but greater than 15%, and WC accounts for a certain percentage of Ti(C). 0.7 N 0.3 The mass fraction of Mo2C is 20-30%, and the proportion of Mo2C in Ti(C) is 20-30%. 0.7 N 0.3 The mass fraction of (NbC+TaC) is 10-15%, and the total mass fraction of (NbC+TaC) accounts for 10-15% of the total mass fraction of Ti(C). 0.7 N 0.3 The Ti(C) content is 15-20% by mass, and NbC accounts for 0-30% of the total mass fraction of (NbC+TaC); 0.7 N 0.3 Both the CoCrNi and carbide alloying additives are saturated carbon compounds with a carbon content greater than or equal to the theoretical carbon content; the CoCrNi medium-entropy alloying raw material powder is supplied in the form of alloy powder that has passed through a 400-mesh sieve, and Ti(C) 0.7 N 0.3 The raw material powder has a Fisher particle size of less than 2.0 μm, the WC raw material powder has an average particle size of less than 0.4 μm, and the TaC, NbC, and Mo2C raw material powders all have a Fisher particle size of less than 1.5 μm.

[0013] B. Drying and granulation of wet-milled mixture: Spray drying or vacuum drying and mechanical granulation processes are used to prepare spherical mixtures with an average particle size of less than 150 μm;

[0014] C. Powder forming: Based on the shape and size of the product, the forming method is selected according to the requirements of traditional metal-ceramic blank production, including compression molding;

[0015] D. Forming Agent Removal and Sintering: Forming agent removal and sintering are carried out in a pressure sintering furnace. After forming agent removal, a three-stage target-oriented stepwise pressure sintering process is adopted for sintering. The three-stage targets are: micro-pressure instantaneous high-temperature liquid phase sintering to improve the wettability of the alloy system; cooling high-purity argon pressure liquid phase sintering to promote the full densification of the alloy; and secondary cooling supersolid-phase argon-nitrogen mixed pressure liquid phase sintering to achieve self-consistent control of nitrogen content in the alloy. The first-stage sintering holding temperature is 1530-1550℃, and the holding time is 10-15 minutes, followed by a sintering rate of 10-20℃ / minute. The temperature is cooled to the second stage holding temperature of 1480–1500℃ at a cooling rate. After reaching the second stage holding temperature, high-purity argon gas is introduced to increase the pressure inside the sintering furnace to 2.5–4.0 MPa. The total holding time for the second stage is 60–100 minutes. After the holding time is completed, the temperature is cooled to the third stage holding temperature of 1380–1400℃ at a cooling rate of 10–20℃ / minute. After reaching the third stage holding temperature, high-purity nitrogen gas is introduced to increase the pressure inside the sintering furnace by 1–1.5 MPa based on the original furnace pressure. The total holding time for the third stage is 30–50 minutes.

[0016] In step A, the wet grinding medium for the high-energy flake treatment using wet stirred ball milling is alcohol, the stirring paddle speed of the stirred ball mill is 250-300 rpm, the mass ratio of cemented carbide grinding balls to CoCrNi medium-entropy alloy powder is (15-20):1, the wet grinding time is 15-20 hours, and the process is carried out under argon protection.

[0017] In step A, the forming agent added during the preparation of the wet-milled mixture can be a forming agent commonly used in the preparation of cemented carbide. Preferably, in step A, the forming agent added during the preparation of the wet-milled mixture is polyethylene glycol or paraffin wax, a drum ball milling process is used, alcohol is used as the wet milling medium, the mass ratio of cemented carbide grinding balls to the mixture is (4:1) to (5:1), and the wet milling time is 50 to 60 hours.

[0018] In step D, after the forming agent is removed, vacuum sintering is performed; when the temperature rises to 1430-1450℃, high-purity argon gas is introduced to make the pressure inside the sintering furnace reach 5-7 kPa, and this pressure is maintained until the temperature inside the sintering furnace reaches the temperature point of the second stage sintering, 1480-1500℃.

[0019] Ti(C,N)-based cermets can be prepared using Ti(C) 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 Different C / N ratio raw material powders, such as Ti(C), are used in the field of metal ceramics.0.5 N 0.5 Ti(C,N) is usually abbreviated as Ti(C,N) or TiCN. This invention utilizes Ti(C) with a high C / N ratio. 0.7 N 0.3 This invention addresses the problems of brittle decarburization easily forming when using CoCrNi medium-entropy alloys as the cermet binder metal due to the shift of the two-phase region of the alloy system towards the high-carbon side, and the instability in quality caused by adding excessive carbon black, by using raw material properties and saturated carbon carbide additives. The invention can solve the carbon control problem in the two-phase region of alloy systems with low binder metal content by adding trace amounts of carbon black, but prioritizes controlling the total carbon content of the alloy within the two-phase region by selecting raw materials with high carbon content. This invention uses Ti(C) with a high C / N ratio. 0.7 N 0.3 The raw materials also benefit the improvement of the wettability of the alloy system. Based on the excellent plastic deformation capacity and oxidation resistance of CoCrNi medium-entropy alloy, the wet stirring ball milling high-energy flake treatment technology developed in this invention can stably control the one-dimensional size of CoCrNi medium-entropy alloy powder to less than 0.3 μm, and achieve the one-dimensional particle size matching of CoCrNi medium-entropy alloy powder with other raw material powders. The micro-pressure instantaneous high-temperature liquid phase sintering under a 5-7 kPa argon atmosphere of this invention can significantly improve the wettability of the alloy system, accelerate the atomic diffusion between hard phase components and the formation of hard phase solid solution, and effectively inhibit the high-temperature evaporation of binder metal. The instantaneous high temperature can achieve control over grain growth kinetics and prevent abnormal growth of hard phase grains; cooling high-purity argon pressure liquid phase sintering can effectively promote the full densification of the alloy and effectively inhibit the abnormal grain growth of hard phase. Loading nitrogen before the alloy microstructure achieves full densification will hinder the densification of the alloy system. However, after the porosity in the alloy system is effectively eliminated, full densification is achieved, and the wettability of the alloy system is improved by microalloying of the hard phase alloy components in the binder phase, the alloy system is cooled to a low temperature above the solidus line of the alloy system. Then, argon-nitrogen mixed pressure liquid phase sintering with argon as the main component can achieve self-consistent control of carbon and nitrogen content in the alloy and inhibit the formation of harmful phases, thereby further improving the strength, toughness and corrosion resistance of the alloy. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of a -400 mesh CoCrNi medium-entropy alloy powder with equal atomic ratio prepared by gas atomization.

[0021] Figure 2 These are scanning electron microscope (SEM) images of CoCrNi medium-entropy alloy powder with equal atomic ratio after wet-stirred ball milling and high-energy flake formation treatment.

[0022] Figure 3 It is Ti(C) in Example 1 0.7 N 0.3Scanning electron microscope image of the microstructure of a cermet containing 13.0WC-6.3TaC-2.7NbC-6.0Mo2C-22.0CoCrNi. Detailed Implementation

[0023] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0024] Example 1

[0025] The raw material was a CoCrNi medium-entropy alloy powder with an atomic ratio of -400 mesh, prepared by gas atomization. Its scanning electron microscope image is shown below. Figure 1 , Figure 1 The average particle size of the medium-entropy CoCrNi alloy powder is less than 13 μm. The wet-milling high-energy flake formation of the CoCrNi medium-entropy alloy powder was carried out under argon protection in an alcohol medium. The stirring speed was 280 rpm, the mass ratio of cemented carbide grinding balls to multi-principal element alloy gas-atomized powder was 18:1, and the wet milling time was 18 hours. Scanning electron microscope images of the equiatomic-scale CoCrNi medium-entropy alloy powder after high-energy flake formation are shown below. Figure 2 , Figure 2 The one-dimensional size of the medium-sized flake powder is less than 0.3 μm.

[0026] Using CoCrNi medium-entropy alloy flake powder with an atomic ratio after the above-mentioned high-energy flake treatment, and Ti(C) powder with Fisher particle sizes of 1.5, 1.2, 1.4, and 1.3 μm, respectively. 0.7 N 0.3 Ti(C) powder was prepared using TaC, NbC, Mo2C powders and WC powder with an average particle size of 0.30 μm as raw materials. 0.7 N 0.3 )-13.0WC-6.3TaC-2.7NbC-6.0Mo2C-22.0CoCrNi cermet (1 # Alloy), the values ​​listed in the alloy composition are the mass fractions of each powder component, %. Ti(C) 0.7 N 0.3 The total carbon content (mass fraction) in TaC, NbC, Mo2C and WC is 14.02%, 6.24%, 11.46%, 5.91% and 6.13%, respectively, all of which are saturated carbon-type compounds with carbon content greater than or equal to the theoretical carbon content.

[0027] A drum-type ball milling process was employed, using alcohol as the wet milling medium. The mass ratio of cemented carbide grinding balls to the mixture was 4:1, and the wet milling time was 60 hours. Polyvinyl alcohol forming agent, comprising 2.3% of the total powder mass, was added during wet milling. Spherical mixtures with an average particle size of less than 150 μm were prepared by spray drying granulation. Round rod samples were prepared using a dry-bag cold isostatic pressing process. Forming agent removal and sintering were carried out in a pressure sintering furnace. After removing the forming agent at 450℃, vacuum sintering was performed at a heating rate of 10℃ / min, holding at 800℃ and 1250℃ for 30 minutes each. When the temperature reached 1430℃, high-purity argon was introduced to increase the pressure inside the sintering furnace to 7 kPa, and the temperature was further increased to 1530℃ and held for 15 minutes. Subsequently, the temperature was lowered to 1480℃ at a cooling rate of 10℃ / min, and high-purity argon was introduced to increase the pressure inside the sintering furnace to 2.5 MPa. The total holding time at 1480℃ was 90 minutes. Then, the temperature was lowered to 1380℃ at a cooling rate of 20℃ / min, and high-purity nitrogen was introduced to increase the pressure inside the sintering furnace by 1 MPa, reaching 3.5 MPa. The total holding time at 1380℃ was 50 minutes, followed by furnace cooling. The sintered round bar product was then cut into Type B specimens for bending strength testing using diamond cutting tools. The scanning electron microscope image of the microstructure of the metal-ceramic in this embodiment is shown below. Figure 3 Test results show that the alloy is Ti(C) 0.7 N 0.3 The alloy has a homogeneous two-phase structure consisting of a hard phase and an equiatomic CoCrNi medium-entropy alloy-based binder phase. The binder phase is uniformly distributed in the alloy, and the average grain size of the hard phase is 0.9 μm.

[0028] Example 2

[0029] -400 mesh CoCrNi medium-entropy alloy powder with equiatomic ratio, prepared by gas atomization, was used as raw material. The wet-milling high-energy flake formation of the CoCrNi medium-entropy alloy powder was carried out under argon protection in an alcohol medium. The stirring speed was 250 rpm, the mass ratio of cemented carbide grinding balls to multi-principal element alloy gas-atomized powder was 20:1, and the wet milling time was 15 hours.

[0030] Using CoCrNi medium-entropy alloy flake powder with an atomic ratio after the above-mentioned high-energy flake treatment, and Ti(C) powder with Fisher particle sizes of 1.6, 1.2, and 1.3 μm, respectively. 0.7 N 0.3 Ti(C) powder was prepared using TaC and Mo2C powders, and WC powder with an average particle size of 0.25 μm as raw materials. 0.7 N 0.3 )-15.4WC-10.0TaC-5.0Mo2C-18.0CoCrNi cermet (2 #Alloy), the values ​​listed in the alloy composition are the mass fractions of each powder component, %. Ti(C) 0.7 N 0.3 The total carbon content (mass fraction) in TaC, Mo2C, and WC were 14.40%, 6.24%, 5.91%, and 6.16%, respectively.

[0031] A drum-type ball milling process was employed, using alcohol as the wet milling medium. The mass ratio of cemented carbide grinding balls to the mixture was 5:1, and the wet milling time was 50 hours. Paraffin wax forming agent, comprising 2.5% of the total powder mass, was added during wet milling. Spherical mixtures with an average particle size of less than 150 μm were prepared by spray drying granulation. Type B specimens for flexural strength testing were prepared using a compression molding process. Forming agent removal and sintering were carried out in a pressure sintering furnace. After removing the forming agent at 480℃, vacuum sintering was performed at a heating rate of 10℃ / min, holding at 800℃ and 1250℃ for 30 minutes each. When the temperature reached 1450℃, high-purity argon gas was introduced to increase the pressure inside the sintering furnace to 5 kPa, and the temperature was further increased to 1550℃ and held for 10 minutes. Subsequently, the temperature was lowered to 1500℃ at a cooling rate of 10℃ / min, and high-purity argon gas was introduced to increase the pressure inside the sintering furnace to 4.0 MPa. The total holding time at 1500℃ was 60 minutes. Then, the temperature was lowered to 1400℃ at a cooling rate of 10℃ / min, and high-purity nitrogen gas was introduced to increase the pressure inside the sintering furnace by 1.5 MPa from the original furnace pressure, reaching 5.5 MPa. The total holding time at 1400℃ was 30 minutes, followed by furnace cooling. Test results showed that the average grain size of the hard phase in the alloy was 1.0 μm.

[0032] Example 3

[0033] -400 mesh CoCrNi medium-entropy alloy powder with equiatomic ratio, prepared by gas atomization, was used as raw material. The wet-milling high-energy flake treatment of the CoCrNi medium-entropy alloy powder was carried out under argon protection in an alcohol medium. The stirring speed was 300 rpm, the mass ratio of cemented carbide grinding balls to multi-principal element alloy gas-atomized powder was 15:1, and the wet milling time was 20 hours.

[0034] Using CoCrNi medium-entropy alloy flake powder with an atomic ratio after the above-mentioned high-energy flake treatment, and Ti(C) powder with Fisher particle sizes of 1.6, 1.2, 1.4, and 1.3 μm, respectively. 0.7 N 0.3 Ti(C) powder was prepared using TaC, NbC, Mo2C powders and WC powder with an average particle size of 0.25 μm as raw materials. 0.7 N 0.3 )-11.0WC-6.4TaC-1.6NbC-8.0Mo2C-20.0CoCrNi cermet (3 #Alloy), the values ​​listed in the alloy composition are the mass fractions of each powder component, %. Ti(C) 0.7 N 0.3 The total carbon content (mass fraction) in TaC, NbC, Mo2C and WC is 14.40%, 6.24%, 11.46%, 5.91% and 6.16%, respectively.

[0035] A drum-type ball milling process was employed, using alcohol as the wet milling medium. The mass ratio of cemented carbide grinding balls to the mixture was 5:1, and the wet milling time was 55 hours. Paraffin wax forming agent, comprising 2.5% of the total powder mass, was added during wet milling. Spherical mixtures with an average particle size of less than 150 μm were prepared by spray drying granulation. Type B specimens for flexural strength testing were prepared using a compression molding process. Forming agent removal and sintering were carried out in a pressure sintering furnace. After removing the forming agent at 480℃, vacuum sintering was performed at a heating rate of 10℃ / min, holding at 800℃ and 1250℃ for 30 minutes each. When the temperature reached 1440℃, high-purity argon gas was introduced to increase the pressure inside the sintering furnace to 6 kPa, and the temperature was further increased to 1540℃ and held for 12 minutes. Subsequently, the temperature was lowered to 1490℃ at a cooling rate of 20℃ / min, and high-purity argon gas was introduced to increase the pressure inside the sintering furnace to 3.0 MPa. The total holding time at 1490℃ was 100 minutes. Then, the temperature was lowered to 1390℃ at a cooling rate of 10℃ / min, and high-purity nitrogen gas was introduced to increase the pressure inside the sintering furnace by 1.0 MPa to 4.0 MPa. The total holding time at 1390℃ was 40 minutes, followed by furnace cooling. Test results showed that the average grain size of the hard phase in the alloy was 0.8 μm.

[0036] Comparative Example 1

[0037] Cobalt powder with Fisher particle sizes of 1.2 and 2.5 μm and nickel carbonyl were used as binder metals. All other raw materials and process parameters were the same as in Example 1. The composition of Comparative Example 1 was Ti(C) 0.7 N 0.3 )-13.0WC-6.3TaC-2.7NbC-6.0Mo2C-11.0Co-11.0Ni(4 # alloy).

[0038] Scanning electron microscopy observations showed that the alloys of the three examples (1) # Up to 3 # All alloys possess Ti(C) 0.7 N 0.3 The two-phase homogeneous structure consists of a hard base phase and a CoCrNi medium-entropy alloy-based binder phase, as shown in Comparative Example 1 (4). # Alloy) has Ti(C) 0.7 N 0.3 A homogeneous two-phase structure consisting of a hard base phase and a Co-Ni-based binder phase; 1# Up to 4 # The binder phase is uniformly distributed in the alloy, and there is no micro-aggregation of the binder phase. The porosity of the alloy is ≤A02 and B00, and it is in a fully densified state.

[0039] The physical and mechanical properties of the alloy were tested according to the relevant national standards. # Up to 4 # The physical and mechanical properties of the alloys are shown in Table 1. The dimensions of the type B specimen used for the bending strength test were (20±1) mm × (6.5±0.25) mm × (5.25±0.25) mm. As shown in Table 1, all four alloys exhibit excellent physical and mechanical properties, but compared to traditional Co-Ni alloys using Ni as the binder metal... # Alloy, the present invention uses an equiatomic CoCrNi medium-entropy alloy as a binder metal. # Up to 3 # The hardness and toughness of the alloy were improved simultaneously.

[0040] Solutions of H₂SO₄, HCl, and HNO₃ with pH = 1, and a NaOH solution with pH = 13 were prepared respectively. Electrochemical corrosion experiments were conducted on an electrochemical workstation under constant temperature conditions of 25 ± 1℃. A saturated calomel electrode was used as the reference electrode, a platinum sheet electrode as the auxiliary electrode, and the sample to be tested as the working electrode. The test sample was a polished disc, and during testing, the sample was placed in a working area of ​​1 cm². 2 The sample was placed in a polytetrafluoroethylene (PTFE) fixture. Before the electrochemical corrosion experiment, the sample was immersed in the test medium for 60 minutes, and the open-circuit potential curve was measured to obtain a stable open-circuit potential. Subsequently, electrochemical impedance spectroscopy (EIS) was performed at the open-circuit potential, with a frequency range of 10 Hz. -2 ~10 5 The voltage amplitude was 5mV and the Hz was constant. After EIS measurement, potentiodynamic polarization curves were tested, with a scan range from -0.8 to 2V and a potential scan rate of 0.5mV / s. The electrochemical corrosion kinetic parameters obtained from the test, namely the self-corrosion current density (J / s), were determined. corr ), and charge transfer resistance (R ct See Table 2. The corrosion rate is negatively correlated with the self-corrosion current density and positively correlated with the charge transfer resistance. Taking Comparative Example 1, 4... # Using the alloy as a reference, in three strong acids, the corresponding alloys in Examples 1 to 3 are 1 # Up to 3 # The average self-corrosion current density of the alloy decreased by ~89%, and the average charge transfer resistance increased by ~780%; in NaOH solution, 1 # Up to 3 #The alloy exhibits a ~70% reduction in average self-corrosion current density and a ~210% increase in average charge transfer resistance. This is in contrast to traditional Co-Ni alloys used as binder metals. # Alloy, the present invention uses an equiatomic CoCrNi medium-entropy alloy as a binder metal. # Up to 3 # The corrosion resistance of the alloy was significantly improved in both strong acids and strong alkalis, with the improvement in corrosion resistance in strong acids being more significant.

[0041] Table 1 shows the physical and mechanical properties of the alloys in the three examples and Comparative Example 1.

[0042]

[0043] Table 2 shows the electrochemical corrosion kinetic parameters of the alloys in the three examples and Comparative Example 1.

[0044]

[0045] Comparative Example 2

[0046] The CoCrNi medium-entropy alloy was not subjected to flake treatment; other experimental raw materials, alloy composition, and preparation process were the same as in Example 2. Bending strength test results showed that the bending strength of the alloy was between 700 and 1300 MPa, significantly lower than that of the alloy in Example 1.

[0047] Comparative Example 3

[0048] Except for the sintering process, the alloy composition and preparation process were the same as in Example 2. After the forming agent was removed at 480°C, vacuum sintering was performed at a heating rate of 10°C / min, holding at 800°C and 1250°C for 30 minutes each. When the temperature reached 1450°C, high-purity argon gas was introduced to increase the pressure inside the sintering furnace to 5 kPa. The temperature was then further increased to 1500°C, and high-purity argon gas was introduced to raise the pressure inside the sintering furnace to 4.0 MPa. The total holding time at 1500°C was 60 minutes, followed by furnace cooling. The bending strength test results showed that the bending strength of the alloy was between 1500 and 2010 MPa, significantly lower than that of the alloy in Example 2.

[0049] Comparative Example 4

[0050] Except for the sintering process, the alloy composition and preparation process were the same as in Example 2. Forming agent removal and sintering were carried out in a pressure sintering furnace. After the forming agent was removed at 480°C, vacuum sintering was performed at a heating rate of 10°C / min, holding at 800°C and 1250°C for 30 minutes each. When the temperature reached 1450°C, high-purity argon gas was introduced to increase the pressure inside the sintering furnace to 5 kPa, and the temperature was further increased to 1550°C, holding for 10 minutes. Subsequently, the temperature was reduced to 1500°C at a cooling rate of 10°C / min, and high-purity argon gas was introduced to increase the pressure inside the sintering furnace to 4.0 MPa. The total holding time at 1500°C was 60 minutes, followed by furnace cooling. Test results showed that the alloy's hardness and Palmqvist fracture toughness were 1880 HV30 and 11.68 MPa·m, respectively. 1 / 2 , relative to 2 # The alloy exhibits hardness differences close to the measurement error, but its toughness is significantly reduced. In H2SO4 at pH=1, the self-corrosion current density increases by approximately 29%, the charge transfer resistance decreases by approximately 110%, and the corrosion resistance is significantly reduced.

[0051] Comparative Example 5

[0052] Except for the Ti(C,N) raw material, the other raw materials, alloy composition, and preparation process are the same as in Example 2. The Ti(C,N) raw material used is Ti(C) 0.5 N 0.5 The alloy has a Fisher particle size of 1.2 μm and a total carbon content (mass fraction) of 9.80%. Microstructural observation results show that there are obvious decarburized phases of varying sizes and uneven distribution in the alloy. Bending strength test results show that the bending strength of the alloy is between 520 and 720 MPa, which is significantly lower than the bending strength of the alloy in Example 2.

[0053] Comparative Example 6

[0054] Except for the differences in TaC, Mo2C, and WC raw material powders, the other raw materials, alloy composition, and preparation process were the same as in Example 2. The Fisher particle sizes of the TaC and Mo2C raw material powders were 1.3 and 1.2 μm, respectively, with total carbon contents (mass fraction) of 6.19% and 5.80%, respectively. The WC raw material powder had an average particle size of 0.20 μm and a total carbon content (mass fraction) of 6.09%. Microstructural observations revealed the presence of distinctly sized and unevenly distributed decarburized phases in the alloy. Bending strength tests showed that the bending strength of the alloy ranged from 490 to 750 MPa, significantly lower than that of the alloy in Example 2.

[0055] Comparative Example 7

[0056] The raw materials TaC, Mo2C, and WC were the same as in Comparative Example 6. The remaining raw materials, alloy composition, and preparation process were the same as in Example 2. Nano-carbon black was added to maintain the same total carbon content in the alloy as in Example 2. Microstructural observation showed that the alloy had a two-phase structure with no decarburized phase, but the microstructure uniformity was poor. Bending strength tests showed that the alloy's bending strength ranged from 1850 to 2450 MPa, with an average of 2105 MPa, significantly lower than the bending strength of the alloy in Example 2.

Claims

1. A hard material resistant to strong acids and alkalis, characterized in that: The strong acid refers to an acid with a pH ≤ 1, the strong base refers to a base with a pH ≥ 13, and the hard material refers to a Ti(C, N)-based cermet; the Ti(C, N)-based cermet has a homogeneous two-phase structure of hard phase and binder phase, with the CoCrNi-based medium-entropy alloy binder phase uniformly distributed in the alloy, and Ti(C 0.7 , N 0.3 The average grain size of the hard phase in the Ti(C,N)-based alloy is less than 1.2 μm, and the porosity of the alloy is ≤A02, B00, indicating a fully densified state. In the Ti(C,N)-based cermet alloy, the mass fraction of the entropy alloy in CoCrNi is less than 25% but greater than 15%, and WC accounts for a significant portion of the Ti(C,N) content. 0.7 , N 0.3 The mass fraction of Mo2C is 20-30%, and Mo2C accounts for 20-30% of Ti(C). 0.7 , N 0.3 The mass fraction of (NbC+TaC) is 10-15%, and the total mass fraction of (NbC+TaC) accounts for 10-15% of the total mass fraction of Ti(C). 0.7 , N 0.3 The Ti(C) content is 15-20% of the total mass fraction, and NbC accounts for 0-30% of the total mass fraction of (NbC+TaC); 0.7 , N 0.3 Both the carbide alloy additives and the carbide alloy additives are saturated carbon-type compounds with a carbon content greater than or equal to the theoretical carbon content. The hard material resistant to strong acids and alkalis is prepared by the following steps: A. Preparation of wet-milled mixture: High-energy flake-treated CoCrNi medium-entropy alloy powder and Ti(C) powder were wet-milled using a stirring ball mill. 0.7 , N 0.3 The following ingredients are added: WC, Mo2C, TaC, and NbC. A forming agent accounting for 2.3-2.5% of the total powder mass fraction is added, followed by wet milling. The resulting mixture should meet the following requirements: in the cermet alloy components, the entropy alloy mass fraction of CoCrNi is less than 25% but greater than 15%, and WC accounts for a certain percentage of Ti(C). 0.7 , N 0.3 The mass fraction of Mo2C is 20-30%, and Mo2C accounts for 20-30% of Ti(C). 0.7 , N 0.3 The mass fraction of (NbC+TaC) is 10-15%, and the total mass fraction of (NbC+TaC) accounts for 10-15% of the total mass fraction of Ti(C). 0.7 , N 0.3 The Ti(C) content is 15-20% of the total mass fraction, and NbC accounts for 0-30% of the total mass fraction of (NbC+TaC); 0.7 , N 0.3 Both the CoCrNi medium-entropy alloying raw material powder and the carbide alloying additives are saturated carbon-type compounds with a carbon content greater than or equal to the theoretical carbon content; the CoCrNi medium-entropy alloying raw material powder is supplied in the form of alloy powder that has passed through a 400-mesh sieve and is subjected to flake treatment before use, with a one-dimensional size of less than 0.3 μm; Ti(C 0.7 , N 0.3 The raw material powder has a Fisher particle size of less than 2.0 μm, the WC raw material powder has an average particle size of less than 0.4 μm with a specific surface area, and the TaC, NbC, and Mo2C raw material powders all have a Fisher particle size of less than 1.5 μm. B. Drying and granulation of wet-milled mixture: Spray drying or vacuum drying and mechanical granulation processes are used to prepare spherical mixtures with an average particle size of less than 150 μm; C. Powder forming: Based on the shape and size of the product, the forming method is selected according to the requirements of traditional metal-ceramic blank production, including compression molding; D. Forming Agent Removal and Sintering: Forming agent removal and sintering are carried out in a pressure sintering furnace. After forming agent removal, a three-stage target-oriented stepwise pressure sintering process is adopted for sintering. The three-stage targets are: micro-pressure instantaneous high-temperature liquid phase sintering to improve the wettability of the alloy system; cooling high-purity argon pressure liquid phase sintering to promote the full densification of the alloy; and secondary cooling supersolid-phase argon-nitrogen mixed pressure liquid phase sintering to achieve self-consistent control of nitrogen content in the alloy. The first-stage sintering holding temperature is 1530~1550℃, and the holding time is 10~15 minutes, followed by cooling at 10~20℃ / minute. The furnace is rapidly cooled to the second-stage holding temperature of 1480~1500℃. After reaching the second-stage holding temperature, high-purity argon gas is introduced to increase the pressure inside the sintering furnace to 2.5~4.0MPa. The total holding time for the second stage is 60~100 minutes. After the holding time is completed, the furnace is cooled at a rate of 10~20℃ / minute to the third-stage holding temperature of 1380~1400℃. After reaching the third-stage holding temperature, high-purity nitrogen gas is introduced to increase the pressure inside the sintering furnace by 1~1.5MPa based on the original furnace pressure. The total holding time for the third stage is 30~50 minutes.

2. The hard material resistant to strong acid and alkali corrosion according to claim 1, characterized in that: The CoCrNi-based medium-entropy alloys include CoCrNi-based medium-entropy alloys with equal atomic ratios.

3. The hard material resistant to strong acid and alkali corrosion according to claim 1, characterized in that: In step A, the wet grinding medium for the high-energy flake treatment using wet stirred ball milling is alcohol, the stirring paddle speed of the stirred ball mill is 250~300 rpm, the mass ratio of cemented carbide grinding balls to CoCrNi medium-entropy alloy powder is (15~20):1, the wet grinding time is 15~20 hours, and it is carried out under argon protection.

4. The hard material resistant to strong acid and alkali corrosion according to claim 1, characterized in that: In step A, the forming agent added in the preparation of the wet-milled mixture is polyethylene glycol or paraffin wax. The process is a drum ball mill, the wet milling medium is alcohol, the mass ratio of cemented carbide grinding balls to the mixture is (4:1) to (5:1), and the wet milling time is 50 to 60 hours.

5. The hard material resistant to strong acid and alkali corrosion according to claim 1, characterized in that: In step D, after the forming agent is removed, vacuum sintering is performed; when the temperature rises to 1430~1450℃, high-purity argon gas is introduced to make the pressure inside the sintering furnace reach 5~7kPa, and this pressure is maintained until the temperature inside the sintering furnace reaches the temperature point of the second stage sintering, 1480~1500℃.

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