Wear-resistant alloy coating drill bit and preparation method thereof

Abstract

The invention relates to the technical field of alloys, in particular to a wear-resistant alloy coating drill bit and a preparation method thereof. The drill bit is of a multi-layer composite coating structure, a bottom coating is formed by bottom alloy powder and modified powder through plasma spraying and laser remelting, and a top coating is formed by top alloy powder through spraying and remelting. According to the invention, the multi-layer coating structure and the modified powder are introduced, so that the compactness and the stress transfer path of the drill bit coating are optimized, the crack propagation risk is reduced, and the service life of the drill bit is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of alloys, and particularly to a wear-resistant alloy coating drill bit and a preparation method thereof. Background Art

[0002] With the rapid development of industrial manufacturing technology and the continuous improvement of process requirements for material processing, drill bits have become indispensable important tools in machining. In high-end manufacturing industries such as machinery manufacturing, aerospace, and automotive manufacturing, drill bits are widely used for drilling, cutting, and machining of metal materials. However, due to the challenging strength and hardness of the processed materials, drill bits are extremely vulnerable to wear and fatigue damage under high temperature, high pressure, and high-speed cutting conditions during actual use. Therefore, improving the wear resistance, cutting efficiency, and service life of drill bits has become a research hotspot in the industry.

[0003] Traditional drill bits are usually made of high-speed steel (HSS) or cemented carbide materials. Although high-speed steel is suitable for a wide range of processing environments due to its excellent toughness and machinability, its anti-wear performance is poor, and it is prone to softening or rapid wear due to the action of frictional heat. Cemented carbide drill bits, although having high hardness and wear resistance, are limited in their application environments and working conditions due to their brittleness. In addition, during the processing of these two types of drill bits, especially in the application on high-strength and high-hardness workpieces (such as hardened steel, stainless steel, heat-resistant alloys, etc.), they often fail due to rapid wear of the cutting part, peeling of the surface coating, or insufficient toughness. Therefore, in order to further improve the comprehensive performance of drill bits, more and more research has been carried out on applying surface engineering technology in the preparation process of high-performance drill bits.

[0004] In current surface engineering technologies, the coating method has gradually become an important process means to improve the performance of drill bits. By applying an anti-wear coating on the substrate surface, the wear resistance, impact resistance, and high-temperature stability of drill bits can be effectively enhanced. However, the currently commonly used coatings have relatively low bonding strength between the coating and the substrate, uneven interface stress distribution, and serious coating peeling phenomena during the processing, resulting in great limitations on the anti-peeling ability of the coating. In addition, the simple hard particle reinforcement technology in traditional coating processes, although it can endow the coating with high hardness, is prone to crack propagation in the coating under cutting load or thermal shock due to stress concentration inside the coating and mismatched physical properties with the substrate, thus shortening the service life of the drill bit. Therefore, how to achieve high-quality bonding between the coating and the substrate and optimize the internal stress distribution of the coating has become a key issue affecting the improvement of coating performance. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a wear-resistant alloy-coated drill bit and its preparation method, so as to solve the problems of insufficient wear resistance, low interfacial bonding strength and uneven stress distribution existing in the existing drill bit coatings, resulting in premature wear of the cutting edge and coating spalling, and seriously affecting the service life of the drill bit.

[0006] Based on the above purpose, the present invention provides a wear-resistant alloy-coated drill bit, including a drill bit and a surface coating; the surface coating is obtained by spraying a bottom-layer alloy powder and a modified powder on the cutting part of the drill bit in sequence, and after laser remelting treatment, a bottom-layer coating is obtained, and then a top-layer alloy powder is sprayed on the surface of the bottom-layer coating, and after light remelting treatment and vacuum heat treatment.

[0007] Further, the bottom-layer alloy powder is prepared from the following raw materials by weight: 50-60 parts of tungsten carbide, 30-40 parts of cobalt powder and 5-15 parts of chromium carbide.

[0008] Further, the top-layer alloy powder is prepared from the following raw materials by weight: 50-60 parts of tungsten carbide, 30-40 parts of molybdenum powder and 5-15 parts of chromium carbide.

[0009] Preferably, the average particle size of the tungsten carbide is 200-300 mesh; the average particle size of the cobalt powder is 250-350 mesh; the average particle size of the molybdenum powder is 250-350 mesh; the average particle size of the chromium carbide is 300-500 mesh.

[0010] Further, the preparation method of the modified powder is as follows: Add urea and cobalt nitrate hexahydrate to absolute ethanol, stir for 20-40 min, vacuum dry, then under a nitrogen atmosphere, heat up to 530-570 °C, calcine for 1.8-2.2 h, cool with the furnace, ball mill, the ball mill rotation speed is 250-350 rpm, and the ball mill time is 4-6 h to obtain the modified powder; the weight ratio of urea, cobalt nitrate hexahydrate and absolute ethanol is 50-70:3-7:80-120.

[0011] Further, the drill bit is pretreated by the following steps before spraying: Put the drill bit substrate into a 35-45 kHz ultrasonic cleaner, soak it with acetone for 10-20 min, then use 100-150 mesh brown fused alumina sand to perform sandblasting treatment on the cutting part of the drill bit at a pressure of 0.5-0.7 MPa for 25-35 s, and finally rinse with deionized water and dry with hot air to obtain a pretreated drill bit.

[0012] Further, the present invention also provides a preparation method of a wear-resistant alloy-coated drill bit, including the following steps: (1) Alloy powder preparation Tungsten carbide, cobalt powder, and chromium carbide are added to absolute ethanol, ball-milled and mixed, and then vacuum-dried to obtain the bottom-layer alloy powder; tungsten carbide, molybdenum powder, and chromium carbide are taken and added to absolute ethanol, ball-milled and mixed, and then vacuum-dried to obtain the top-layer alloy powder; (2) Plasma spraying and laser remelting treatment The bottom-layer alloy powder is sprayed on the cutting part of the drill bit, the coating thickness is controlled at 45 - 55 μm, then the modified powder coating is sprayed with a thickness controlled at 15 - 25 μm, and then scanning remelting is carried out. After remelting, it is air-cooled to room temperature to obtain the bottom-layer coating; the top-layer alloy powder is sprayed on the surface of the bottom-layer coating, the coating thickness is controlled at 90 - 110 μm, and then scanning remelting is carried out. After remelting, it is air-cooled to room temperature to obtain the top-layer coating; (3) Vacuum heat treatment The drill bit containing the bottom-layer coating and the top-layer coating is placed in a vacuum furnace, heated to 950 - 1000 °C at a rate of 10 - 20 °C / min, held for 25 - 35 min, cooled to 200 °C by introducing argon, and then taken out of the furnace to obtain the wear-resistant alloy coating drill bit.

[0013] Preferably, in step (1), the rotation speed of the ball milling is 180 - 220 rpm, and the time is 1.5 - 2.5 h.

[0014] Preferably, in step (2), the main gas flow rate during spraying is 40 - 50 L / min, the auxiliary gas flow rate is 10 - 15 L / min, the current is 500 - 700 A, the voltage is 65 - 75 V, and the spraying distance is 100 - 150 mm.

[0015] Preferably, the main gas is argon and the auxiliary gas is hydrogen.

[0016] Preferably, in step (2), the power of the scanning remelting of the bottom-layer coating is 650 - 750 W, the spot diameter is 0.6 - 1 mm, the scanning speed is 10 - 15 mm / s, and the overlap rate is 40 - 42%.

[0017] Preferably, in step (2), the power of the scanning remelting of the top-layer coating is 750 - 950 W, the spot diameter is 0.6 - 1 mm, the scanning speed is 10 - 15 mm / s, and the overlap rate is 40 - 42%.

[0018] Preferably, in step (3), the vacuum degree of the vacuum heat treatment is 4×10 -3 -6×10 -3 Pa.

[0019] The beneficial effects of the present invention: The present invention significantly improves the comprehensive performance of the drill bit by introducing a multi-layer coating structure and modified powder. The components in the modified powder can promote the directional growth of nanotubes and the formation of carbide networks, thereby significantly enhancing the mechanical anchoring effect and interfacial metallurgical bonding strength inside the drill bit coating. This high-strength bonding can not only effectively inhibit the propagation of cracks at the interface but also improve the stability of the drill bit coating, enabling it to exhibit excellent anti-spalling ability in high-pressure and high-speed cutting environments. The layered drill bit coating structure can optimize the stress transfer path, reduce the load in the stress concentration area, and effectively extend the service life of the coating.

[0020] The present invention realizes the densification and homogenization of the drill bit coating through laser remelting treatment, reduces the formation of potential defects, and enables the ideal connection of the gradient coating, further improving the anti-wear performance. With a reasonable heat treatment process, the toughness and hardness of the drill bit coating are balanced, meeting the high durability requirements under complex working conditions. In addition, the active components in the modified powder can be transformed into cobalt-based compounds and graphitized carbon networks during the remelting process, further enhancing the toughness and strength of the drill bit coating. This optimized process design significantly improves the cutting efficiency of the drill bit, making the drill bit have excellent stability and reliability. Detailed implementation manners

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0022] Example 1: Preparation of modified powder Add 50 g of urea and 3 g of cobalt nitrate hexahydrate to 80 g of absolute ethanol, stir for 20 min, dry under vacuum, then heat to 530 °C in a nitrogen atmosphere, calcine for 1.8 h, cool with the furnace, and ball mill at a ball mill speed of 250 rpm for 4 h to obtain the modified powder.

[0023] Example 2: Preparation of modified powder Add 60 g of urea and 5 g of cobalt nitrate hexahydrate to 100 g of absolute ethanol, stir for 30 min, dry under vacuum, then heat to 550 °C in a nitrogen atmosphere, calcine for 2 h, cool with the furnace, and ball mill at a ball mill speed of 300 rpm for 5 h to obtain the modified powder.

[0024] Example 3: Preparation of modified powder Add 70 g of urea and 7 g of cobalt nitrate hexahydrate to 120 g of absolute ethanol, stir for 40 min, dry under vacuum, then heat to 570 °C in a nitrogen atmosphere, calcine for 2.2 h, cool with the furnace, and ball mill at a ball mill speed of 350 rpm for 6 h to obtain the modified powder.

[0025] Example 4: Preparation of wear-resistant alloy coating drill bit Step 1: Pretreatment of the drill bit substrate Put the high-speed steel drill bit substrate into a 35 kHz ultrasonic cleaner, soak it in acetone for 10 min, then use 100-mesh brown fused alumina sand to perform sandblasting on the cutting part of the drill bit at a pressure of 0.5 MPa for 25 s, and finally rinse it with deionized water and dry it with hot air to obtain the pretreated drill bit; Step 2: Preparation of alloy powder Add 50 g of tungsten carbide (average particle size 250 mesh), 30 g of cobalt powder (average particle size 300 mesh), and 5 g of chromium carbide (average particle size 400 mesh) into 250 g of absolute ethanol, ball mill and mix them. The ball mill rotation speed is 180 rpm, the ball mill time is 1.5 h, and then vacuum dry to obtain the bottom-layer alloy powder; Take 50 g of tungsten carbide (average particle size 250 mesh), 30 g of molybdenum powder (average particle size 200 mesh), and 5 g of chromium carbide (average particle size 400 mesh) and add them into 250 g of absolute ethanol, ball mill and mix them. The ball mill rotation speed is 180 rpm, the ball mill time is 1.5 h, and then vacuum dry to obtain the top-layer alloy powder; Step 3: Plasma spraying and laser remelting treatment Load the bottom-layer alloy powder and the modified powder into the powder feeder, and set the spraying parameters: the main gas (Ar) flow rate is 40 L / min, the auxiliary gas (H 2 ) flow rate is 10 L / min, the current is 500 A, the voltage is 65 V, the spraying distance is 100 mm. First, spray the bottom-layer alloy powder on the cutting part of the pretreated drill bit, control the coating thickness at 45 μm, then spray the modified powder prepared in Example 1, control the coating thickness at 15 μm, and then use a fiber laser to scan and remelt the coating. The power is 650 W, the spot diameter is 0.6 mm, the scanning speed is 10 mm / s, the overlap rate is 40%, and after remelting, air-cool it to room temperature to obtain the bottom-layer coating; Load the top-layer alloy powder into the powder feeder, and set the spraying parameters: the main gas (Ar) flow rate is 40 L / min, the auxiliary gas (H 2 ) flow rate is 10 L / min, the current is 500 A, the voltage is 65 V, the spraying distance is 100 mm. Spray on the surface of the bottom-layer coating, control the coating thickness at 90 μm, use a fiber laser to scan and remelt the coating. The power is 750 W, the spot diameter is 0.6 mm, the scanning speed is 10 mm / s, the overlap rate is 40%, and after remelting, air-cool it to room temperature to obtain the top-layer coating; Step 4: Vacuum heat treatment Place the drill bit with the bottom-layer coating and the top-layer coating in a vacuum furnace (vacuum degree 4×10 -3 Pa), heat it to 950 °C at a rate of 10 °C / min, hold it for 25 min, introduce argon to cool it to 200 °C and then take it out of the furnace to obtain the wear-resistant alloy coating drill bit.

[0026] Example 5: Preparation of Wear-Resistant Alloy Coated Drill Bit Step 1: Pretreatment of Drill Bit Substrate Put the high-speed steel drill bit substrate into a 40 kHz ultrasonic cleaner, soak it with acetone for 15 min, then use 120-mesh brown fused alumina sand to perform sandblasting treatment on the cutting part of the drill bit for 30 s under a pressure of 0.6 MPa, and finally rinse it with deionized water and dry it with hot air to obtain the pretreated drill bit; Step 2: Preparation of Alloy Powder Add 55 g of tungsten carbide (average particle size 250 mesh), 35 g of cobalt powder (average particle size 300 mesh), and 10 g of chromium carbide (average particle size 400 mesh) into 300 g of absolute ethanol, ball mill and mix them, with a ball mill rotation speed of 200 rpm and a ball milling time of 2 h, and then perform vacuum drying to obtain the bottom layer alloy powder; Take 55 g of tungsten carbide (average particle size 250 mesh), 35 g of molybdenum powder (average particle size 200 mesh), and 10 g of chromium carbide (average particle size 400 mesh) and add them into 300 g of absolute ethanol, ball mill and mix them, with a ball mill rotation speed of 200 rpm and a ball milling time of 2 h, and then perform vacuum drying to obtain the top layer alloy powder; Step 3: Plasma Spraying and Laser Remelting Treatment Load the bottom layer alloy powder and the modified powder into the powder feeder, and set the spraying parameters: the main gas (Ar) flow rate is 45 L / min, the auxiliary gas (H 2 ) flow rate is 12 L / min, the current is 600 A, the voltage is 70 V, and the spraying distance is 120 mm. First, spray the bottom layer alloy powder on the cutting part of the pretreated drill bit, control the coating thickness to 50 μm, then spray the modified powder prepared in Example 2, control the coating thickness to 20 μm, and then use a fiber laser to scan and remelt the coating, with a power of 700 W, a spot diameter of 0.8 mm, a scanning speed of 12 mm / s, and a lap rate of 40%. After remelting, air-cool it to room temperature to obtain the bottom layer coating; Load the top layer alloy powder into the powder feeder, and set the spraying parameters: the main gas (Ar) flow rate is 45 L / min, the auxiliary gas (H 2 ) flow rate is 12 L / min, the current is 600 A, the voltage is 70 V, and the spraying distance is 120 mm. Spray on the surface of the bottom layer coating, control the coating thickness to 100 μm, use a fiber laser to scan and remelt the coating, with a power of 900 W, a spot diameter of 0.8 mm, a scanning speed of 12 mm / s, and a lap rate of 40%. After remelting, air-cool it to room temperature to obtain the top layer coating; Step 4: Vacuum Heat Treatment Place the drill bit containing the bottom layer coating and the top layer coating in a vacuum furnace (vacuum degree 5×10 -3 Pa), heat it to 980 °C at a rate of 15 °C / min, hold it for 30 minutes, introduce argon to cool it to 200 °C and then take it out of the furnace to obtain the wear-resistant alloy coated drill bit.

[0027] Example 6: Preparation of Wear-Resistant Alloy Coated Drill Bit Step 1: Pretreatment of Drill Bit Substrate Put the high-speed steel drill bit substrate into a 45 kHz ultrasonic cleaner, soak it with acetone for 20 min, then use 150-mesh brown fused alumina sand to perform sandblasting treatment on the cutting part of the drill bit under a pressure of 0.7 MPa for 35 s, and finally rinse it with deionized water and dry it with hot air to obtain a pretreated drill bit; Step 2: Preparation of Alloy Powder Add 60 g of tungsten carbide (average particle size 250 mesh), 40 g of cobalt powder (average particle size 300 mesh), and 15 g of chromium carbide (average particle size 400 mesh) into 350 g of absolute ethanol, ball mill and mix them. The ball mill rotation speed is 220 rpm, the ball mill time is 2.5 h, and vacuum drying is carried out to obtain the bottom layer alloy powder; Take 60 g of tungsten carbide (average particle size 250 mesh), 40 g of molybdenum powder (average particle size 200 mesh), and 15 g of chromium carbide (average particle size 400 mesh) and add them into 350 g of absolute ethanol, ball mill and mix them. The ball mill rotation speed is 220 rpm, the ball mill time is 2.5 h, and vacuum drying is carried out to obtain the top layer alloy powder; Step 3: Plasma Spraying and Laser Remelting Treatment Load the bottom layer alloy powder and the modified powder into the powder feeder, and set the spraying parameters: the main gas (Ar) flow rate is 50 L / min, the auxiliary gas (H 2 ) flow rate is 15 L / min, the current is 700 A, the voltage is 75 V, the spraying distance is 150 mm. First, spray the bottom layer alloy powder on the cutting part of the pretreated drill bit, control the coating thickness at 55 μm, then spray the modified powder prepared in Example 3, control the coating thickness at 25 μm, and then use a fiber laser to scan and remelt the coating. The power is 750 W, the spot diameter is 1 mm, the scanning speed is 15 mm / s, the overlap rate is 42%, and after remelting, air-cool it to room temperature to obtain the bottom layer coating; Load the top layer alloy powder into the powder feeder, and set the spraying parameters: the main gas (Ar) flow rate is 50 L / min, the auxiliary gas (H 2 ) flow rate is 15 L / min, the current is 700 A, the voltage is 75 V, the spraying distance is 150 mm. Spray on the surface of the bottom layer coating, control the coating thickness at 110 μm, use a fiber laser to scan and remelt the coating. The power is 950 W, the spot diameter is 1 mm, the scanning speed is 15 mm / s, the overlap rate is 42%, and after remelting, air-cool it to room temperature to obtain the top layer coating; Step 4: Vacuum Heat Treatment Place the drill bit containing the bottom layer coating and the top layer coating in a vacuum furnace (vacuum degree 6×10 -3 Pa), heat it to 1000 °C at a rate of 20 °C / min, hold it for 35 min, introduce argon gas to cool it to 200 °C and then take it out of the furnace to obtain the wear-resistant alloy coated drill bit.

[0028] Comparative Example 1: The difference between Comparative Example 1 and Example 5 is that in Step 3, the modified powder was not sprayed; Comparative Example 2: The difference between Comparative Example 2 and Example 5 is that in Step 3, the modified powder was not sprayed, and the modified powder was added to the bottom alloy powder, with an addition amount of 40 g; Comparative Example 3: The difference between Comparative Example 2 and Example 5 is that in Step 3, the modified powder was not sprayed, and the modified powder was added to the top alloy powder, with an addition amount of 20 g; Comparative Example 4: The difference between Comparative Example 4 and Example 5 is that cobalt hexahydrate nitrate was not added to the modified powder; Comparative Example 5: The difference between Comparative Example 5 and Example 5 is that the power of the bottom layer coating scanning and remelting is 900 W; Performance test: Wear resistance test: According to GB / T 12444-2006, a ring-block wear test was carried out. It was paired with a GCr15 steel counter-ring (HRC62-64) on an MM-200 type friction and wear testing machine. The test load was set to 200 N, the rotation speed was 400 rpm, and the duration was 30 min. An electronic balance was used to measure the wear amount, and the results are shown in Table 1.

[0029] Coating bonding strength test: According to the standard of GB / T 8642-2002, the bonding strength was measured by the scratch method. A WS-2005 type scratch testing machine was used, with a diamond indenter cone angle of 120° and a radius of 0.2 mm. The scratch length was 5 mm, the loading rate was 100 N / min, and the critical load was taken as the minimum load value when the acoustic emission signal mutated. Before the test, the surface of the specimen was cleaned with acetone. The test environment temperature was (25±2)°C, and the relative humidity was ≤60%. The results are shown in Table 1.

[0030] Cutting performance test: An end face drilling test was carried out on a CA6140 type lathe. A 45 steel specimen (HB190-210) was used, and the cutting parameters were set as: rotation speed 800 r / min, feed rate 0.2 mm / r, and hole depth 30 mm. After every 5 consecutive holes were machined, a tool microscope (magnification 50×) was used to measure the flank wear amount (VB value). When VBmax≥0.3 mm, it was judged as failure.

[0031] Table 1 Performance test results Wear amount (mg) Minimum load value (N) Cutting performance (number of failed holes) Example 4 13.5 62.9 55 Example 5 12.3 65.2 55 Example 6 11.1 64.1 60 Comparative Example 1 25.6 48.7 30 Comparative Example 2 16.7 58.1 40 Comparative Example 3 18.9 54.3 35 Comparative Example 4 14.5 60.2 45 Comparative Example 5 12.5 62.4 35 Data analysis: From the data of Examples 4-6 in Table 1, it can be seen that the modified powder and multi-layer coating process of the present invention significantly improve the wear resistance, bonding strength and cutting performance of the coating. The generation of this technical effect may be related to the interface strengthening effect of cobalt-catalyzed carbon nanotubes and the synergistic characteristics of the molybdenum-based top coating.

[0032] From the data of Example 5 and Comparative Example 1 in Table 1, it can be seen that the addition of the modified powder significantly improves the wear resistance, bonding strength and cutting performance of the coating. This may be due to the mechanical anchoring effect formed by cobalt-catalyzed carbon nanotubes. The stepped modulus distribution generated by the layered spraying process may optimize the stress transfer path, reducing the peak value of the interfacial shear stress. During the laser remelting process, the active nitrogen atoms in the modified layer may participate in the formation of a cobalt nitride transition phase. This interfacial compound layer can effectively inhibit crack propagation.

[0033] From the data of Example 5 and Comparative Examples 2-3 in Table 1, it can be seen that the strengthening effect of directly adding the modified powder to the bottom or top powder is lower than that when it is located alone in the intermediate layer. This may be because when located in the intermediate layer, the modified powder can be orderly transformed into a graphitized carbon structure under the catalysis of the bottom cobalt and its own cobalt. This directionally growing carbon nanotube network may enhance the toughness of the coating. More energy is required to consume for the carbon tube pulling-out force during its fracture process. And when located in the intermediate layer, it helps to avoid the formation of brittle intermetallic compounds.

[0034] From the data of Example 5 and Comparative Example 4 in Table 1, it can be seen that the cobalt in the modified powder can further promote the strengthening effect of the modified powder. This is mainly because the cobalt in the modified powder further promotes the directional growth of the carbon nanotube network, enhancing the mechanical anchoring effect.

[0035] From the data of Example 5 and Comparative Example 5 in Table 1, it can be seen that too high bottom laser power may lead to abnormal growth of carbon nanotubes and may also cause matrix softening, thereby affecting the wear resistance, bonding strength and cutting performance.

[0036] Those of ordinary skill in the art should understand that: the discussion of any above embodiment is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the idea of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A wear-resistant alloy coated drill bit, characterized in that: It includes a drill bit and a surface coating; the surface coating is obtained by spraying a bottom alloy powder and a modified powder on the cutting part of the drill bit in sequence, and then undergoing laser remelting treatment to obtain a bottom coating, and then spraying a top alloy powder on the surface of the bottom coating, and then undergoing optical remelting treatment and vacuum heat treatment to obtain the bottom coating; The bottom alloy powder is prepared from the following raw materials by weight: 50-60 parts of tungsten carbide, 30-40 parts of cobalt powder and 5-15 parts of chromium carbide; The top alloy powder is prepared from the following raw materials by weight: 50-60 parts of tungsten carbide, 30-40 parts of molybdenum powder and 5-15 parts of chromium carbide; The preparation method of the modified powder is as follows: urea and cobalt nitrate hexahydrate are added to anhydrous ethanol, stirred for 20-40 minutes, vacuum dried, and then heated to 530-570° C. in a nitrogen atmosphere, calcined for 1.8-2.2 hours, cooled with the furnace, and ball milled at a ball milling speed of 250-350 rpm for a ball milling time of 4-6 hours to obtain a modified powder; The weight ratio of the urea, cobalt nitrate hexahydrate and anhydrous ethanol is 50-70:3-7:80-120.

2. The wear-resistant alloy coated drill bit according to claim 1, characterized in that: The average particle size of the tungsten carbide is 200-300 meshes; the average particle size of the cobalt powder is 250-350 meshes; the average particle size of the molybdenum powder is 250-350 meshes; and the average particle size of the chromium carbide is 300-500 meshes.

3. The wear-resistant alloy coated drill bit according to claim 1, characterized in that: The drill bit is pretreated by the following steps before spraying: the drill bit base is placed in a 35-45kHz ultrasonic cleaning machine, soaked in acetone for 10-20 minutes, and then 100-150 mesh brown corundum sand is used to perform sandblasting on the cutting part of the drill bit for 25-35 seconds at an air pressure of 0.5-0.7MPa, and finally rinsed with deionized water and dried with hot air to obtain a pretreated drill bit.

4. A method for preparing a wear-resistant alloy coated drill according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Alloy powder preparation Tungsten carbide, cobalt powder and chromium carbide are added to anhydrous ethanol, ball milled and mixed, and vacuum dried to obtain a bottom alloy powder; tungsten carbide, molybdenum powder and chromium carbide are added to anhydrous ethanol, ball milled and mixed, and vacuum dried to obtain a top alloy powder; (2) Plasma spraying and laser remelting The bottom alloy powder is sprayed on the cutting part of the drill bit, and the coating thickness is controlled to be 45-55μm, and then the modified powder coating is sprayed to control the thickness of 15-25μm, and then scanning remelting is performed, and air cooling is performed to room temperature after remelting to obtain the bottom coating; the top alloy powder is sprayed on the surface of the bottom coating, and the coating thickness is controlled to be 90-110μm, and then scanning remelting is performed, and air cooling is performed to room temperature after remelting to obtain the top coating; (3) Vacuum heat treatment The drill bit including the bottom coating and the top coating is placed in a vacuum furnace, heated to 950-1000°C at 10-20°C / min, kept warm for 25-35min, cooled to 200°C after passing argon gas, and then taken out of the furnace to obtain a wear-resistant alloy coated drill bit.

5. The method for preparing a wear-resistant alloy coated drill bit according to claim 4, characterized in that: The ball milling speed in step (1) is 180-220 rpm and the time is 1.5-2.5 h.

6. The method for preparing a wear-resistant alloy coated drill bit according to claim 4, characterized in that: In the step (2), the main gas flow rate of the spraying is 40-50 L / min, the auxiliary gas flow rate is 10-15 L / min, the current is 500-700 A, the voltage is 65-75 V, and the spraying distance is 100-150 m; the main gas is argon and the auxiliary gas is hydrogen.

7. The method for preparing a wear-resistant alloy coated drill bit according to claim 4, characterized in that: In the step (2), the scanning remelting power of the bottom coating is 650-750 W, the spot diameter is 0.6-1 mm, the scanning speed is 10-15 mm / s, and the overlap rate is 40-42%.

8. The method for preparing a wear-resistant alloy coated drill bit according to claim 4, characterized in that: In the step (2), the scanning remelting power of the top coating is 750-950 W, the spot diameter is 0.6-1 mm, the scanning speed is 10-15 mm / s, and the overlap rate is 40-42%.

9. The method for preparing a wear-resistant alloy coated drill bit according to claim 4, characterized in that: The vacuum degree of the vacuum heat treatment in step (3) is 4×10 -3 -6×10 -3 Pa.