CN106636834A - Method for inhibiting cemented carbide grain growth and ultra-fine grain cemented carbide preparation process - Google Patents

Abstract

A method for inhibiting the growth of ultrafine hard alloy grains and a preparation process for ultrafine hard alloys, wherein the method for inhibiting grain growth is to mix Co- VC micro-nano composite powder is added to WC powder, mixed evenly, compacted and sintered; Co-VC micro-nano composite powder is V ₂ O ₅ ‑Co ₃ O ₄ composite nano-powder prepared by liquid phase chemical precipitation method, after carbonization reduction The reaction is prepared. The preparation process of ultrafine-grained cemented carbide includes the steps of weighing Co-VC micro-nano composite powder, mixing with WC powder, molding a compact, and pressure sintering. The method of the invention is simple and convenient, can ensure that the VC in the binder phase is evenly distributed in the cemented carbide, and can effectively inhibit the abnormal growth of the WC crystal grains during sintering; The strength and other properties are superior to the existing cemented carbides that are added with inhibitors such as VC in a mixing method, and have the prospect of industrial scale production.

Description

Method for inhibiting grain growth of cemented carbide and preparation process of ultrafine-grained cemented carbide

technical field

The invention discloses a method for inhibiting the growth of hard alloy crystal grains and a preparation process of ultrafine-grained hard alloy, belonging to the technical field of hard alloy material preparation.

Background technique

Cemented carbide is an indispensable tool material in the modern machining industry. It is composed of one or more high-hardness refractory metal hard compounds (WC, VC, etc.) Metal (Co, Ni, Fe) or its alloys are used as the binder phase, and the cermet composite material is prepared by powder metallurgy. Its hard phase mainly plays the role of high hardness and high wear resistance, while the binder phase is to provide the necessary toughness and strength of the alloy material, making the cemented carbide a material with high hardness, high wear resistance, high toughness and high strength. characteristic. WC-Co cemented carbide is the largest and most widely used cemented carbide, which is composed of high hardness WC phase and Co binder phase, among which Co has particularly good wettability to WC. WC-Co cemented carbide materials have been widely used in the fields of cutting tool materials, wear-resistant materials, high-temperature and corrosion-resistant materials, and have replaced high-speed steel in many application fields. Especially widely used in cutting processing, it can cut ordinary metals, non-metallic materials, high-temperature alloys, titanium alloys and other difficult-to-machine materials, with high cutting efficiency and long service life.

Ultra-fine WC-Co cemented carbide has higher strength and hardness, which effectively solves the contradiction between the hardness and strength of traditional cemented carbide, and effectively expands the application field of cemented carbide. However, during the sintering process of ultrafine WC-Co cemented carbide, ultrafine WC powder is prone to the problem of uneven grain growth, which seriously limits the expansion of the use of cemented carbide materials. In the preparation process of ultra-fine cemented carbide, grain growth inhibitors VC, Cr ₃ C ₂ , etc. are usually added during ball milling to control the growth of WC grains. When the amount of grain growth inhibitors added is small, ball milling It is difficult to mix evenly during the process, and there will still be abnormal growth of WC grains during sintering; and when the addition amount is large, the grain growth inhibitor will hinder the densification process of the alloy sintering, resulting in poor mechanical properties of the alloy. Therefore, the uniform distribution of grain growth inhibitors such as VC in the WC-Co cemented carbide system is an important research direction for ultrafine-grained WC-Co cemented carbide.

Contents of the invention

The purpose of the present invention is to solve the problem of uneven distribution of grain growth inhibition in the existing conventional technology, and propose a method for inhibiting cemented carbide grain growth with simple process and convenient operation. The method can realize the uniform distribution of the grain growth inhibitor VC in the WC-Co cemented carbide system, and achieve the purpose of suppressing the abnormal growth of the WC grains and obtaining the WC-Co cemented carbide with uniform structure and excellent performance.

Another object of the present invention is to provide a method for preparing ultrafine-grained cemented carbide.

A method for inhibiting the growth of ultrafine cemented carbide grains in the present invention is to add Co-VC micro-nano composite powder to WC powder in the mixing process of the ultrafine cemented carbide preparation process, mix evenly, and press the blank ,sintering;

The Co-VC micro-nano composite powder is prepared from V ₂ O ₅ -Co ₃ O ₄ composite nano-powder prepared by a liquid phase chemical precipitation method through carbonization and reduction reaction.

The invention discloses a method for suppressing the growth of ultrafine cemented carbide crystal grains. The average particle size of the Co-VC micro-nano composite powder is 20-50nm.

The invention discloses a method for suppressing the growth of ultrafine cemented carbide grains. In the Co-VC micro-nano composite powder, the mass ratio of Co to VC is 15-40:1.

The present invention is a method for suppressing the growth of ultrafine cemented carbide grains. The Co-VC micro-nano composite powder is prepared by the following scheme:

The first step, preparation of V ₂ O ₅ -Co ₃ O ₄ composite nanopowder

Prepare a mixed solution with CoCl ₂ and NH ₄ VO ₃ , add oxalic acid to the mixed solution, stir to produce a precipitate, filter, filter the residue and dry it for 6-8 hours, then calcinate at 400-500°C for 2-4 hours to obtain Co ₃ O ₄ -V ₂ O ₅ composite nanopowder;

The second step, the preparation of Co-VC micro-nano composite powder

The Co ₃ O ₄ -V ₂ O ₅ composite nano-powder obtained in the first step is mixed evenly with carbon by ball milling. After molding the compact, the in-situ carbonization reaction is carried out in a vacuum atmosphere. The reaction temperature is 900-1100°C. Cool to obtain Co-VC micro-nano composite powder; Co ₃ O ₄ -V ₂ O ₅ composite nano-powder and carbon by mass ratio,

Co ₃ O ₄ -V ₂ O ₅ composite nanopowder: C=2.5～3:1 configuration;

The average particle size of carbon is 100-200nm, and the molding pressure is 50-100MPa;

In the first step, when taking CoCl ₂ and NH ₄ VO ₃ to configure the mixed solution, the dosage of CoCl ₂ and NH ₄ VO ₃ is as follows: in the prepared Co ₃ O ₄ -V ₂ O ₅ composite nanopowder, V ₂ O ₅ and Co ₃ O ₄ The mass ratio is determined;

In the Co ₃ O ₄ -V ₂ O ₅ composite nanopowder, the mass ratio of V ₂ O ₅ to Co ₃ O ₄ is:

V ₂ O ₅ : Co ₃ O ₄ = 1: 10-50;

The amount of oxalic acid added is 1.1 to 1.3 times of the theoretical amount of the total conversion of CoCl ₂ into Co ₃ O ₄ and the conversion of NH _{4 VO 3} into V ₂ O _{5 ; 3} The temperature of the mixed solution is the same;

The average particle size of the Co ₃ O ₄ -V ₂ O ₅ composite nano powder is 30-80 nm.

A kind of ultrafine-grain cemented carbide preparation process of the present invention, comprises the following steps:

The first step: according to the Co content in the designed cemented carbide material components, weigh the Co-VC micro-nano composite powder, mix it with WC powder and ball mill, and disperse evenly to obtain alloy powder; ball milling process parameters: in a planetary ball mill , the ball-to-material ratio is (6-12):1, the ball mill speed is 200-300 rpm, and the ball milling time is 30-50 hours; the average particle size of WC powder is 200-500nm; the average particle size of Co-VC micro-nano composite powder is 20 ~50nm;

Step 2: Add a molding agent to the alloy powder mixture obtained in the first step, stir evenly, pass through a 50-100 mesh sieve, and mold a blank with a molding pressure of 150-200 MPa; the molding agent is composed of paraffin wax and solvent gasoline in a mass ratio of 1 : (8 ~ 16) mixed;

Step 3: Place the green compact obtained in the second step in an argon atmosphere for pressure sintering. The furnace pressure is 3-10 MPa, the sintering temperature is 1380-1450°C, and the ultra-fine-grained WC-Co cemented carbide is obtained by cooling with the furnace. .

The invention discloses a process for preparing ultrafine-grained cemented carbide. The prepared ultrafine-grained cemented carbide consists of the following components by weight percentage:

Co: 8-12%; VC: 0.3-0.8%

The balance is WC; the weight percent sum of each component is 100%.

The present invention adopts the above-mentioned process to prepare Co ₃ O ₄ -V ₂ O ₅ composite nano-powder through the method of chemical co-precipitation, and generates micro-nano powder with Co-VC composite structure through carbonization reduction reaction, which can make VC uniform distribution in the Co binder phase. During the sintering process, the grain growth inhibitor in the cemented carbide system can be uniformly dissolved in the liquid phase Co through the uniform addition of Co-VC composite structure powder, which reduces the solubility of WC in the binder phase and hinders the WC , The diffusion of C atoms, so it can effectively inhibit the dissolution and precipitation of W and C atoms, reduce the rate and probability of WC growing up through dissolution and precipitation in the binder phase, and refine the WC grains. Since VC and Co are uniformly mixed by chemical precipitation-carbonization reduction before sintering, the uniform distribution of VC prevents the abnormal growth of WC grains and improves the hardness and flexural strength of cemented carbide.

Compared with the preparation of WC-Co cemented carbide by common methods, the present invention has the following advantages:

1. The Co-VC composite structure powder prepared by the liquid phase method of the present invention realizes the uniform mixing of VC under the condition of high Co content. The cemented carbide is prepared after the powder is mixed with the WC powder. The cemented carbide composition according to the design The content of Co in the middle determines the amount of Co-VC composite structure powder added. After ball milling and mixing, VC is evenly distributed in WC powder along with Co, which realizes the uniform distribution of grain growth inhibitor VC in WC powder and achieves hardness. For the purpose of refining the microstructure and grains of the cemented carbide, its hardness and flexural strength are superior to those of the cemented carbide added with the grain growth inhibitor VC in the traditional ball milling mixing process.

2. It solves the problem of abnormal grain growth and grain refinement effect caused by the agglomeration of VC in the traditional mixing process, and improves the grain growth inhibitor's ability to inhibit grain growth. Effect.

In summary, the method adopted in the present invention is simple and convenient, and the grain growth inhibitor VC in the binder phase in the cemented carbide is evenly distributed, which can effectively inhibit the abnormal growth of WC crystal grains during sintering; The prepared ultra-fine cemented carbide has better properties such as hardness and flexural strength than the existing cemented carbide which is added with VC and other inhibitors by mixing materials, and has the prospect of industrial scale production.

Description of drawings

Accompanying drawing 1 is the transmission electron micrograph of the Co ₃ O ₄ -V ₂ O ₅ nanopowder prepared in Example 1 of the present invention.

Figure 2 is an energy spectrum diagram of Co ₃ O ₄ -V ₂ O ₅ nanopowder prepared in Example 1 of the present invention.

Accompanying drawing 3 is the metallographic photograph of 90%WC+9.6%Co+0.4%VC ultrafine-grain cemented carbide prepared in Example 1 of the present invention. (If any, please supplement the metallographic photos of Examples 2 and 3)

Accompanying drawing 4 is the metallographic photograph of 90%WC+9.6%Co+0.4%VC ultrafine grain cemented carbide prepared in the comparative example of the present invention.

It can be seen from the transmission electron microscope photo in Fig. 1 that the powder particle size of the Co ₃ O ₄ -V ₂ O ₅ composite structure prepared in Example 1 is 30-80 nm.

It can be seen from the energy spectrum in Fig. 2 that in the powder of Co ₃ O ₄ -V ₂ O ₅ composite structure, the weight percentages of each component are: V: 1.49%, Co: 21.91%, O: 76.6%.

It can be seen from the alloy metallographic photograph in Fig. 3 that the average grain size of the ultrafine-grained cemented carbide of 90% WC+9.6% Co+0.4% VC prepared in Example 1 of the present invention is 0.4 μm, and there is no abnormal growth of WC Grains appear.

As can be seen from the alloy metallographic photograph in Fig. 4: the average grain size of the ultrafine-grained cemented carbide of 90% WC+9.6% Co+0.4% VC prepared by the traditional ball milling method of adding VC in the comparative example of the present invention is 0.6 μm, And abnormally grown WC grains appeared.

detailed description

Comparative example:

The first step: weigh WC powder, Co powder and VC powder according to the cemented carbide material composition ratio designed by 90%WC+9.6%Co+0.4%VC, and the ball-to-material ratio in the planetary ball mill is 8:1, with Ball milling at a speed of 250 rpm for 48 hours to obtain an alloy powder mixture; the particle size of WC powder is 0.3 μm, the particle size of Co powder is 0.8 μm and the particle size of VC powder is 0.8 μm;

Step 2: Add a molding agent made of paraffin wax and solvent gasoline in a mass ratio of 1:8 to the alloy powder mixture obtained in the first step, stir evenly, pass through a 40-mesh sieve, and then mold it into a billet at 200MPa and place it in an argon atmosphere In the process, the sintering is carried out under the pressure of 7MPa, the sintering temperature is 1380°C, the sintering time is 2h, and the furnace is cooled to obtain 90% WC + 9.6% Co + 0.4% VC ultrafine grain cemented carbide.

The alloy material prepared in this example has a density of 14.53 g·cm ^-3 , a hardness of HRA93.4, a bending strength of 2800 MPa, an average grain size of 0.6 μm, and abnormally grown WC grains.

Example 1

Step 1: Preparation of Co ₃ O ₄ -V ₂ O ₅ Composite Nanopowder

Take 100g CoCl ₂ and 4.65g NH ₄ VO ₃ to prepare a mixed solution with a concentration of 0.4mol/L of CoCl ₂ and NH ₄ VO ₃ , add 0.44 mol/L, the same volume, and the same temperature of oxalic acid solution to the resulting mixed solution and mix evenly, Stirring produced precipitation; after 6 hours of aging, the precipitate was dried and calcined at 400°C for 4 hours to prepare Co ₃ O ₄ -V ₂ O ₅ composite nanopowder; V ₂ O ₅ : Co ₃ O ₄ =1:35.87.

The second step: preparation of Co-VC composite structure nanopowder

Weigh Co ₃ O ₄ -V ₂ O ₅ composite nano powder and C according to the designed cemented carbide material composition ratio, among which Co ₃ O ₄ -V ₂ O ₅ composite nano powder: C=2.7:1, mixed ball mill , to obtain a powder mixture; the alloy powder mixture is molded into a compact in a mold, and the molding pressure is 80 MPa; the compact is placed in a vacuum atmosphere for in-situ carbonization reaction, and the reaction temperature is 1000 ° C. The furnace was cooled to obtain a Co-VC composite structure micro-nano composite powder, and the mass ratio of Co to VC was 24:1.

Step 3: Weigh the Co-VC micro-nano composite powder and WC powder according to the cemented carbide material component distribution ratio designed by 90% WC+9.6% Co+0.4% VC, and the ball-to-material ratio in the planetary ball mill is 8:1 , and ball milled at a speed of 250 rpm for 48 hours to obtain an alloy powder mixture.

Step 4: Add a molding agent made of paraffin wax and solvent gasoline in a mass ratio of 1:8 to the alloy powder mixture obtained in the third step, stir evenly, pass through a 40-mesh sieve, and then mold it into a billet at 200MPa and place it in an argon atmosphere In the process, sintering is carried out under 7MPa pressure, the sintering temperature is 1380°C, the sintering time is 2h, and the furnace is cooled to obtain 90% WC + 9.6% Co + 0.4% VC ultrafine grain cemented carbide.

The alloy material prepared in this example has a density of 14.54 g·cm ^-3 , a hardness of HRA93.7, a bending strength of 3500 MPa, an average grain size of 0.4 μm, and no abnormally grown WC grains.

Example 2

Step 1: Preparation of Co ₃ O ₄ -V ₂ O ₅ Composite Nanopowder

Take 100g of CoCl ₂ and 2.99g of NH ₄ VO ₃ to prepare a mixed solution of CoCl ₂ and NH ₄ VO ₃ with a concentration of 0.6 mol/L, and add 0.72 mol/L, same volume, and same temperature oxalic acid solution to the resulting mixed solution And mix evenly, stir to produce precipitation; after 6 hours of aging, the precipitate is dried and calcined at 400°C for 2 hours to prepare Co ₃ O ₄ -V ₂ O ₅ composite nanopowder; V ₂ O ₅ : Co ₃ O ₄ = 1:50.

The second step: preparation of Co-VC composite structure nanopowder

Weigh Co ₃ O ₄ -V ₂ O ₅ composite nano powder and C according to the designed cemented carbide material composition ratio, among which Co ₃ O ₄ -V ₂ O ₅ composite nano powder: C=2.8:1, mixed ball mill , to obtain a powder mixture; the alloy powder mixture is molded into a compact in a mold, and the molding pressure is 100 MPa; the compact is placed in a vacuum atmosphere for in-situ carbonization reaction, and the reaction temperature is 1100 ° C. The furnace was cooled to obtain a Co-VC composite structure micro-nano composite powder, and the mass ratio of Co to VC was 39:1.

Step 3: Weigh the Co-VC micro-nano composite powder and WC powder according to the cemented carbide material composition ratio designed by 92%WC+7.8%Co+0.2%VC, and the ball-to-material ratio in the planetary ball mill is 8:1 , and ball milled at a speed of 200 rpm for 50 hours to obtain an alloy powder mixture.

Step 4: Add a molding agent mixed with paraffin wax and solvent gasoline in a mass ratio of 1:9 to the alloy powder mixture obtained in the third step, stir evenly, pass through a 40-mesh sieve, and mold it into a billet at 200MPa, then place it in an argon atmosphere In the process, the sintering is carried out under the pressure of 10MPa, the sintering temperature is 1400°C, the sintering time is 1h, and the furnace is cooled to obtain 92% WC + 7.8% Co + 0.2% VC ultrafine grain cemented carbide.

The alloy material prepared in this example has a density of 14.86 g·cm ^-3 , a hardness of HRA94.0, a flexural strength of 3000 MPa, an average grain size of 0.45 μm, and no abnormally grown WC grains.

Example 3

Step 1: Preparation of Co ₃ O ₄ -V ₂ O ₅ Composite Nanopowder

Take 100g of CoCl ₂ and 6.14g of NH ₄ VO ₃ to prepare a mixed solution of CoCl ₂ and NH ₄ VO ₃ with a concentration of 0.8 mol/L, and add 0.9 mol/L, same volume, and same temperature oxalic acid solution to the resulting mixed solution And mix evenly, stir to produce precipitation; after 4 hours of aging, the precipitate is dried and calcined at 450°C for 4 hours to prepare Co ₃ O ₄ -V ₂ O ₅ composite nanopowder; V ₂ O ₅ : Co ₃ O ₄ = 1:28.40.

The second step: preparation of Co-VC composite structure nanopowder

Weigh Co ₃ O ₄ -V ₂ O ₅ composite nano powder and C according to the designed cemented carbide material composition ratio, among which Co ₃ O ₄ -V ₂ O ₅ composite nano powder: C=2.9:1, mixed ball mill , to obtain a powder mixture; the alloy powder mixture is molded into a compact in a mold, and the molding pressure is 150 MPa; the compact is placed in a vacuum atmosphere for in-situ carbonization reaction, and the reaction temperature is 1050 ° C. The furnace is cooled to obtain a Co-VC composite structure micro-nano composite powder, and the mass ratio of Co to VC is 19:1.

Step 3: Weigh the Co-VC micro-nano composite powder and WC powder according to the cemented carbide material composition ratio designed by 88%WC+11.4%Co+0.6%VC, and the ball-to-material ratio in the planetary ball mill is 7:1 , and ball milled at a speed of 250 rpm for 40 hours to obtain an alloy powder mixture.

Step 4: Add a molding agent made of paraffin wax and solvent gasoline in a mass ratio of 1:8 to the alloy powder mixture obtained in the third step, stir evenly, pass through a 40-mesh sieve, and then mold it into a billet at 150MPa and place it in an argon atmosphere In the process, the sintering is carried out under the pressure of 10MPa, the sintering temperature is 1380°C, the sintering time is 1.5h, and the furnace is cooled to obtain 88% WC + 11.4% Co + 0.6% VC ultrafine grain cemented carbide.

The alloy material prepared in this example has a density of 14.55 g·cm ^-3 , a hardness of HRA93.3, a bending strength of 4000 MPa, an average grain size of 0.5 μm, and no abnormally grown WC grains.

Claims (10)

1. A method for suppressing the growth of ultrafine cemented carbide grains is to add Co-VC micro-nano composite powder to WC powder in the mixing process of ultrafine cemented carbide preparation process, after mixing evenly, pressure billet, sintering; The Co-VC micro-nano composite powder is prepared from V ₂ O ₅ -Co ₃ O ₄ composite nano-powder prepared by a liquid phase chemical precipitation method through carbonization and reduction reaction. 2. A method for suppressing the growth of ultrafine cemented carbide grains according to claim 1, characterized in that: the average particle size of the Co-VC micro-nano composite powder is 20-50 nm. 3. A method for suppressing the growth of ultrafine cemented carbide grains according to claim 1, characterized in that: in the Co-VC micro-nano composite powder, the mass ratio of Co to VC is 25-40: 1. 4. according to a kind of method described in any one of claim 1-3 suppressing superfine cemented carbide grain growing up, it is characterized in that: described Co-VC micro-nano composite powder is prepared by adopting the following scheme: The first step, preparation of V ₂ O ₅ -Co ₃ O ₄ composite nanopowder Prepare a mixed solution with CoCl ₂ and NH ₄ VO ₃ , add oxalic acid to the mixed solution, stir to produce a precipitate, filter, and calcinate the filter residue at 400-500°C to obtain Co ₃ O ₄ -V ₂ O ₅ composite nanopowder; The second step, the preparation of Co-VC micro-nano composite powder Mix the Co ₃ O ₄ -V ₂ O ₅ composite nanopowder obtained in the first step with carbon evenly, and then carry out in-situ carbonization reaction in a vacuum atmosphere. Micro-nano composite powder; Co ₃ O ₄ -V ₂ O ₅ composite nano-powder and carbon by mass ratio, Co ₃ O ₄ -V ₂ O ₅ composite nanopowder: C=2.5～3:1 configuration. 5. A method for suppressing the growth of ultrafine cemented carbide grains according to claim 4, characterized in that: in the first step, when CoCl ₂ , NH ₄ VO ₃ are configured to mix the solution, CoCl ₂ , NH ₄ The amount of VO ₃ is determined according to the mass ratio of V ₂ O ₅ to Co ₃ O ₄ in the prepared Co ₃ O ₄ -V ₂ O ₅ composite nanopowder. 6. A method for suppressing the growth of ultrafine cemented carbide grains according to claim 5, characterized in that: in the Co ₃ O ₄ -V ₂ O ₅ composite nanopowder, V ₂ O ₅ and Co ₃ O The mass proportioning of ₄ is: V ₂ O ₅ :Co ₃ O ₄ =1:30-50. 7. A kind of method for suppressing the growth of ultrafine cemented carbide grains according to claim 6 is characterized in that: the add-on of oxalic acid is converted into CoCl by CoCl ₂ all ₃ O ₄ , NH ₄ VO ₃ all change into 1.1-1.3 times of the sum of the theoretical amount of V ₂ O ₅ is added; the temperature of the added oxalic acid is the same as that of the mixed solution of CoCl ₂ and NH ₄ VO ₃ . 8. A method for suppressing the growth of ultrafine cemented carbide grains according to claim 7, characterized in that: in the first step, the filter residue is formed for 6-8 hours, then dried, and then calcined for 2-4 hours. 9. A method for suppressing the growth of ultrafine cemented carbide grains according to claim 8, characterized in that: in the second step, Co ₃ O ₄ -V ₂ O ₅ composite nanopowder and carbon ball milling are mixed evenly , in-situ carbonization reaction is carried out after compacting, the average particle size of Co ₃ O ₄ -V ₂ O ₅ composite nano powder is 30-80nm, the average particle size of carbon is 100-200nm, and the molding pressure is 50-100MPa. 10. A preparation process for ultrafine-grained cemented carbide, comprising the steps of: The first step: according to the Co content in the designed cemented carbide material components, weigh the Co-VC micro-nano composite powder, mix it with WC powder and ball mill, and disperse evenly to obtain alloy powder; ball milling process parameters: in a planetary ball mill , the ball-to-material ratio is (6-12):1, the ball mill speed is 200-300 rpm, and the ball milling time is 30-50 hours; the average particle size of WC powder is 200-500nm; the average particle size of Co-VC micro-nano composite powder is 20 ~50nm; The second step: molding the alloy powder mixture obtained in the first step into a compact, and the molding pressure is 150-200 MPa; Step 3: Place the green compact obtained in the second step in an argon atmosphere for pressure sintering. The furnace pressure is 3-10 MPa, the sintering temperature is 1380-1450°C, and the ultra-fine-grained WC-Co cemented carbide is obtained by cooling with the furnace. .