Functional gradient enhanced diamond thin-wall drill as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of superhard material tool manufacturing, and particularly relates to a functionally gradient enhanced diamond thin-wall drill and a preparation method and application thereof. The functionally gradient enhanced diamond thin-wall drill comprises a steel base body, the outer end of the steel base body is a drilling part of a cylindrical structure, and inclined grooves and drilling units are formed in the periphery of the drilling part at equal intervals; an anti-friction heat-conducting coating is cladded on the wall surface of the inclined groove; the drilling unit comprises a functional gradient nano-reinforced brazing filler metal layer and diamond abrasive particles brazed on the surface of the functional gradient nano-reinforced brazing filler metal layer through laser; the functional gradient nano-reinforced brazing filler metal layer comprises a transition layer, a reinforcing layer and a bonding layer which are sequentially arranged in the direction from the steel base body to the diamond abrasive particles. According to the diamond thin-wall drill, by designing the functional gradient nanometer enhanced brazing filler metal layer and the antifriction heat conduction coating and adopting the laser welding technology, multi-performance collaborative optimization of impact resistance, high abrasion resistance, strong heat dissipation and low friction of the diamond thin-wall drill can be achieved, and the service life of the diamond thin-wall drill is remarkably prolonged.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of superhard material tool manufacturing, and particularly relates to a functionally graded reinforced diamond thin-wall drill and a preparation method and application thereof. BACKGROUND

[0002] The diamond thin-wall drill has become a key tool in the precision machining of hard and brittle materials such as stone, ceramic and glass due to the high hardness and high wear resistance of diamond abrasive grains, and has been widely used in modern construction, aerospace, new energy, communication and electronics. At present, the diamond thin-wall drill is mainly prepared by hot-pressing sintering or electroplating, and there are common problems such as weak diamond holding force, mismatch between wear resistance and toughness of the matrix, low efficiency of chip removal and heat dissipation.

[0003] In recent years, laser brazing technology has attracted more and more attention because it can realize high-strength metallurgical bonding of diamond abrasive grains and filler alloy and efficient preparation of structured diamond tools. However, there are still the following problems in the use of existing laser brazed diamond tools: First, the composition and performance of the filler layer are single, which leads to the fact that the drilling unit cannot match the demand of multiple working conditions. The traditional laser brazed diamond thin-wall drill adopts a sandwich structure of "steel substrate-single component filler-diamond", without considering the difference in the coefficient of thermal expansion between the steel substrate and the filler and between the filler and the diamond, which leads to a large residual stress at the interface, directly weakens the interface bonding strength, and causes the abrasive grains to fall off. Moreover, the single composition of the filler makes the performance of the drilling unit single, which cannot meet the dual requirements of impact resistance near the steel substrate and high wear resistance on the outer surface, so that the traditional tool has a short service life and poor reliability in the machining of high-hardness stone or high-brittle ceramic, and it is difficult to meet the requirements of efficient and stable operation.

[0004] Second, the heat dissipation and friction reduction effect is poor, which aggravates the tool failure and machining precision. When the diamond tool drills hard and brittle materials, the instantaneous temperature in the cutting zone can reach 600-800℃, and if the heat cannot be dissipated in time, the diamond will be graphitized, its hardness will decrease from 10000HV to below 200HV, and it will lose the cutting ability. At the same time, the steel substrate of the traditional diamond thin-wall drill has a smooth cylindrical structure, and the friction coefficient between the steel substrate and the workpiece during drilling is as high as 0.5-0.8, which increases the drilling friction resistance, increases the energy consumption, and also aggravates the tool wear and affects the machining precision.

[0005] Third, the traditional laser brazed diamond is easy to float and move. The traditional laser brazing adopts "instantaneous high power" heating, the filler quickly melts and produces violent liquid flow, which easily wraps and moves the diamond abrasive grains; at the same time, the inert protective gas is locally blown to the molten pool during the traditional laser brazing, which blows the diamond abrasive grains to the edge of the molten pool, reducing the preparation precision of the diamond tool.

[0006] Fourth, the iron diffusion in the steel matrix affects the performance of the brazing material. The iron element in the steel matrix is easy to diffuse to the brazing material layer, and forms brittle intermetallic compounds with silicon, boron and other elements in the brazing material, which causes the brazing material layer to be brittle, reduces the overall mechanical properties of the thin-walled drill, causes the diamond abrasive particles to fall off prematurely, and significantly shortens the service life of the tool.

[0007] Therefore, how to comprehensively overcome the above-mentioned core technical bottlenecks in the application process of the diamond thin-walled drill has become a technical problem to be solved by the present application. SUMMARY

[0008] In order to solve the above-mentioned problems in the prior art, the present application aims to provide a functionally graded reinforced diamond thin-walled drill and its preparation method and application. The present application designs a functionally graded nano-reinforced brazing material layer and a friction-reducing and heat-conducting coating, and uses laser welding process, so as to realize the multi-performance synergistic optimization of the diamond thin-walled drill, such as "impact resistance, high wear resistance, strong heat dissipation and low friction", and significantly improve the service life of the diamond thin-walled drill.

[0009] In order to achieve the above-mentioned purposes, the first aspect of the present application adopts the following technical scheme: A functionally graded reinforced diamond thin-walled drill, comprising a steel matrix, the outer end of the steel matrix is a cylindrical structure drill cutting part, the outer periphery of the drill cutting part is provided with inclined grooves and drill cutting units at equal intervals; the wall surface of the inclined groove is coated with a friction-reducing and heat-conducting coating; the inclined grooves and the drill cutting units are alternately distributed; the drill cutting unit comprises a functionally graded nano-reinforced brazing material layer and diamond abrasive particles laser brazed on the surface of the functionally graded nano-reinforced brazing material layer; the functionally graded nano-reinforced brazing material layer comprises a transition layer, a strengthening layer and a bonding layer arranged in turn from the steel matrix to the diamond abrasive particles; The transition layer is composed of raw materials with the following weight percentages: Cr 10-18%, B 3-8%, Mo 5-8%, V 2-3%, toughening nano-phase 2.5-4.5%, Ce 0.1-1%, and the balance of Ni; the strengthening layer is composed of raw materials with the following weight percentages: Cr 6.5-9.5%, Si 4.5-6.5%, B 3.5-5.5%, Fe 2.5-4.5%, wear-resistant nano-phase 3.5-6.5%, Ce 0.1-1%, and the balance of Ni; the bonding layer is composed of raw materials with the following weight percentages: Cr 8-10%, Si 4.5-6.5%, B 3-5.5%, Fe 2.5-4.5%, Co 7.5-12.5%, W 2-5%, wear-resistant nano-phase 0.5-1.5%, Ce 0.1-1%, and the balance of Ni.

[0010] As a preferred embodiment, the outer diameter of the drill part is 6-120 mm, the wall thickness is 1.0-2.5 mm, and the length is 6-15 mm; the thickness of the functionally graded nano-reinforced brazing filler layer is 0.15-0.3 mm; and the thickness ratio of the transition layer, the strengthening layer and the bonding layer is (2-4):(4-7):(1-3).

[0011] As a preferred embodiment, the cross-sectional shape of the oblique groove is one of a rounded inverted trapezoid, a circular arc, and an elliptical arc; the oblique angle of the oblique groove is 30-60°, the depth is 0.3-0.5 mm, and the notch width is 0.5-5 mm; and the number of the oblique grooves is 6-30.

[0012] As a preferred embodiment, the friction-reducing and heat-conducting coating is a diamond-like carbon coating; and the thickness of the friction-reducing and heat-conducting coating is 0.3-0.5 mm.

[0013] As a preferred embodiment, the particle size of the diamond abrasive grains is 35-45 mesh; the surface of the diamond abrasive grains is plated with a plating layer having a thickness of 0.5-1 μm; the plating layer is one of a nickel plating layer, a chromium carbide plating layer, a tungsten carbide plating layer, and a titanium carbide plating layer; the toughening nano-phase is carboxyl-modified multi-walled carbon nanotubes and / or carboxyl-modified graphene nanosheets; and the wear-resistant nano-phase is one or more of cobalt-coated nano-tungsten carbide particles, cobalt-coated nano-yttrium oxide particles, and nano-cubic boron nitride particles.

[0014] In a second aspect, the present application provides a functional gradient reinforced diamond thin-wall drill, comprising: A method for preparing the functional gradient reinforced diamond thin-wall drill, comprising the following steps: S1, machining oblique grooves on the outer peripheral wall of the drill part on the steel base body, and then cleaning and drying to obtain a steel base body with oblique grooves; The transition layer, the strengthening layer and the bonding layer are prepared by weighing raw materials according to the chemical composition ratio, vacuum drying and ball milling to obtain transition layer brazing filler powder, strengthening layer brazing filler powder and bonding layer brazing filler powder; and then mixing the transition layer brazing filler powder, the strengthening layer brazing filler powder and the bonding layer brazing filler powder with solvents to obtain transition layer brazing filler paste, strengthening layer brazing filler paste and bonding layer brazing filler paste; S2, sequentially laying the transition layer brazing filler paste, the strengthening layer brazing filler paste and the bonding layer brazing filler paste on the wall surface between every two oblique grooves to form a blank state of the drill unit, and then fixing diamond abrasive grains on the laid bonding layer brazing filler paste; and prepositioning a friction-reducing and heat-conducting coating precursor on the wall surface of the oblique grooves of the steel base body; S3, the drilling unit treated in step S2 is subjected to laser brazing treatment, so that the functionally graded nano-enhanced brazing material layer is welded on the steel substrate, and the diamond abrasive particles are welded on the surface of the functionally graded nano-enhanced brazing material layer; subsequently, the laser cladding is performed on the inclined grooves of the pre-arranged friction-reducing and heat-conducting coating precursor, so as to form the friction-reducing and heat-conducting coating on the wall surface of the inclined grooves, thereby obtaining the functionally graded enhanced diamond thin-wall drill.

[0015] The preparation method of the present application adopts mechanical alloying powdering, gradient powder laying, laser brazing forming and in-situ coating synthesis as the core process, and can realize high-precision and low-damage laser brazing of the diamond thin-wall drill and comprehensively improve the performance of the diamond thin-wall drill.

[0016] As a preferred embodiment, in step S1, the temperature of the vacuum drying is 80-100 DEG C, and the time is 1-5 h; the ball-to-material ratio of the ball milling treatment is 6:1-8:1, the ball milling speed is 200-300 r / min, and the ball milling time is 8-15 h; the solvent is a mixed solution of acrylic acid and ethyl acetate; the addition amount of the solvent is 10%-20% of the mass of the brazing material powder. Further preferably, in the solvent, the mass concentration of the acrylic acid is 40-70%, and the mass concentration of the ethyl acetate is 30-60%.

[0017] As a preferred embodiment, in step S1, the viscosity of the transition layer brazing material paste, the strengthening layer brazing material paste and the bonding layer brazing material paste is 500-3000 mPa·s.

[0018] As a preferred embodiment, the laying adopts the hollow template method; the pre-arrangement adopts the micro-droplet jetting method; and the friction-reducing and heat-conducting coating precursor is a mixture of phenolic resin and anhydrous ethanol with a mass ratio of 1:(4-6).

[0019] The hollow template method is a gradient powder laying method known in the art, and the present application does not make a special limitation, which only needs to ensure the gradient powder laying effect. Meanwhile, the micro-droplet jetting method is also a conventional method for pre-arranging coating materials, and the present application does not make a special limitation, and the technical personnel can select the operation parameters conventionally.

[0020] As a preferred embodiment, in step S3, the process conditions of the laser brazing are as follows: the laser power is 150-600 W, the spot diameter is 0.2-0.8 mm, the scanning speed is 60-300 mm / min, the scanning overlap rate is 50%-70%, and the synchronous control speed of the workbench is 10-50 r / min; and the process conditions of the laser cladding are as follows: a nanosecond pulse laser is adopted, the laser power is 500-2000 W, the scanning speed is 120-1000 mm / min, the scanning overlap rate is 35%-45%, and the spot diameter is 1-3.5 mm.

[0021] The third aspect of the present application adopts the technical scheme as follows: An application of the functional gradient reinforced diamond thin-wall drill as described above is in the drilling of hard and brittle materials, wherein the hard and brittle materials are one or more of building stone, glass, ceramic, silicon crystal, and carbon fiber composite material.

[0022] The functional gradient reinforced diamond thin-wall drill of the present application has the following advantages and beneficial effects: (I) The present application precisely designs the components of each layer of the functional gradient nano-reinforced brazing material layer to realize the functional division of transition layer isolation and buffering, strengthening layer wear resistance, and adaptive bonding layer.

[0023] On the one hand, the Cr content in the transition layer is as high as 10-18%, which reacts with elements such as B, Mo, and V to form intermetallic compounds such as CrB, Cr3Mo2, and V2Cr. The structure of Cr-based intermetallic compounds is dense, and the crystal gap is small, which significantly increases the diffusion path length and diffusion resistance of Fe atoms, physically blocking the diffusion of Fe. Thermodynamically, the priority of Cr to combine with B and Mo is higher than that of Fe, further inhibiting the diffusion of Fe to the strengthening layer. Through physical blocking, thermodynamic competition, and diffusion path lengthening, the diffusion of Fe in the steel matrix to the strengthening layer, bonding layer, and diamond interface is blocked, preventing the brazing material layer from becoming brittle. At the same time, with Cr, Mo, W, V, toughening-type nano-phase, and wear-resistant-type nano-phase as the skeleton, Ni as the compatible matrix, and Si and B as auxiliary adjusting elements, the content gradient composition design of low thermal expansion coefficient elements / particles in the three layers of the transition layer, strengthening layer, and bonding layer (the highest Cr / Mo in the transition layer → the bonding layer containing W / Co → the strengthening layer with reduced Cr but containing Si) realizes the continuous thermal expansion coefficient transition from the steel matrix (high thermal expansion coefficient) → the transition layer → the bonding layer → the strengthening layer → the diamond (low thermal expansion coefficient), significantly reducing the interface residual stress, effectively improving the interfacial bonding strength of the diamond and the steel matrix, and thus preventing the diamond abrasive particles from falling off. On the other hand, the gradient distribution of W elements and nano-phase is reasonably controlled, the toughening-type nano-phase is used near the steel matrix end of the drilling unit, which has excellent impact resistance and can withstand dynamic impact loads during drilling; the wear-resistant-type nano-phase is used on the outer surface and metal W is introduced, which effectively enhances the hardness and wear resistance, achieves performance optimization of the drilling unit, realizes regional performance matching of "impact resistance - high wear resistance", and thus prolongs the tool life by more than 50%.

[0024] (II) The special inclined groove structure effectively expands the heat dissipation area, cooperates with the friction-reducing and heat-conducting coating, effectively improves the heat dissipation efficiency, avoids the graphitization of the diamond, and effectively reduces the friction coefficient of the coating, reduces friction loss, realizes the dual enhancement of heat dissipation and friction reduction performance, and thus is beneficial to improving the machining precision.

[0025] (Three) using the matching laser welding process, using a small diameter spot (0.2~0.8mm) instead of the traditional large spot (1~4mm), can realize local accurate heating, reduce the amount of brazing filler metal in the single heating area, reduce the overall flow intensity of the liquid brazing filler metal; At the same time, improve the scanning lap rate (50%~70%), make the brazing filler metal of adjacent scanning area gradually melt and connect with each other, avoid the local overheating caused by the intense flow of brazing filler metal.

[0026] Therefore, the functional gradient reinforced diamond thin-wall drill provided by the application has the comprehensive performance of impact resistance, high wear resistance, strong heat dissipation and low friction, greatly improves the service life of the diamond thin-wall drill, and is suitable for high-precision drilling of hard and brittle materials such as building stone, glass, ceramic, silicon crystal and carbon fiber composite material, and has a significant advantage in the scene with high requirements for tool wear resistance, heat dissipation and service life. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings involved in the application are briefly introduced as follows: Figure 1 It is a schematic diagram of the three-dimensional structure of the diamond thin-wall drill in the embodiment 1 of the application; Figure 2 It is a schematic diagram of the enlarged local structure of the diamond thin-wall drill in the embodiment 1 of the application; Figure 3 It is a schematic diagram of the three-dimensional structure of the steel matrix after laying the brazing filler metal layer in step S2 of the embodiment 1 of the application; Figure 4 It is a schematic diagram of the enlarged local structure of the steel matrix after laying the brazing filler metal layer in step S2 of the embodiment 1 of the application; Figure 5 It is a scanning electron microscope image of the drilling part of the diamond thin-wall drill prepared in the embodiment 1 of the application; Figure 6 It is a scanning electron microscope image of the drilling part of the diamond thin-wall drill prepared in the comparative example 4 of the application; Figure 7 It is a scanning electron microscope image of the drilling part of the diamond thin-wall drill prepared in the comparative example 5 of the application; Figure 8 It is a scanning electron microscope image of the drilling part of the diamond thin-wall drill prepared in the comparative example 6 of the application; Figure 9 It is a scanning electron microscope image of the drilling part of the diamond thin-wall drill prepared in the comparative example 7 of the application; Figure 10 It is a friction coefficient curve of the diamond thin-wall drill prepared in the embodiment 1 of the application and the comparative example 1, the comparative example 2, the comparative example 3 within 300s of drilling time; In the attached diagram, the components represented by each number are as follows: 1. Steel substrate; 2. Drilling section; 3. Angled groove; 31. Friction-reducing and thermally conductive coating; 4. Drilling unit; 41. Functionally graded nano-reinforced brazing filler metal layer; 411. Transition layer; 412. Reinforcing layer; 413. Bonding layer; 42. Diamond abrasive grains. Detailed Implementation

[0028] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments and test examples. However, those skilled in the art should understand that the embodiments are only used to illustrate the technical solution of the present invention and should not be regarded as limiting the scope of protection of the present invention. Based on the following embodiments, all other implementation schemes obtained by those skilled in the art without creative effort, such as implementation schemes obtained by modification, variation or simple substitution, should fall within the scope of protection of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the raw materials used are items commonly used in the art, publicly available, or commercially obtainable; and the terms used have their conventional meanings in the art. Specifically, the carboxylated modified multi-walled carbon nanotubes, cobalt-coated tungsten carbide nanoparticles, cobalt-coated yttrium oxide nanoparticles, and cubic boron nitride nanoparticles used in the following embodiments were purchased from Zhengzhou Yuzuan Precision Technology Co., Ltd. The diamond abrasives with coatings (nickel plating, tungsten carbide, or chromium carbide) used in the following embodiments were provided by Henan Yellow River Whirlwind Co., Ltd.; the thermoplastic linear phenolic resin, grade PF-8216, was purchased from Shandong Laiwu Runda New Material Co., Ltd.

[0030] Example 1

[0031] This embodiment provides a functionally graded diamond thin-walled drill bit. (Refer to...) Figures 1-4 As shown, the system includes a steel substrate 1; the outer end of the steel substrate 1 is a cylindrical drilling section 2; the outer periphery of the drilling section 2 is provided with equally spaced oblique grooves 3 and drilling units 4. When the diamond thin-walled drill is in use, the steel substrate 1 drives the drilling section 2 to rotate at high speed. At the same time, the drilling units 4 rotate at high speed to achieve high-speed drilling of hard and brittle materials. Waste material scraped off during drilling is discharged through the oblique grooves 3. The walls of the oblique grooves 3 are coated with a friction-reducing and heat-conducting coating 31. When the diamond thin-walled drill is in use, the friction-reducing and heat-conducting coating 31 reduces wear, increases lubrication, and efficiently conducts heat during drilling, preventing the drill bit from overheating and affecting its drilling efficiency and service life. The oblique grooves 3 and drilling units 4 are alternately distributed, achieving higher drilling efficiency and chip removal efficiency, thus improving the smoothness of the drilling process.

[0032] Further, the drilling unit 4 comprises a functionally graded nano-reinforced filler layer 41 and diamond abrasive grains 42 laser brazed on the surface of the functionally graded nano-reinforced filler layer 41. When the diamond thin-wall drill is in use, the diamond abrasive grains 42 are arranged to first abrade and break the hard and brittle material to be drilled during the drilling process, and then the abraded and broken material is smoothly drilled and dropped through the gap between the friction-reducing and heat-conducting coating 31 and the diamond abrasive grains 42.

[0033] Further, the functionally graded nano-reinforced filler layer 41 comprises a transition layer 411, a strengthening layer 412 and a bonding layer 413 arranged in sequence from the steel base 1 to the diamond abrasive grains 42. When the diamond thin-wall drill is in use, the three-layer connected functionally graded nano-reinforced filler layer structure significantly reduces the residual stress of the brazed diamond interface and the filler layer, improves the wear resistance of the filler layer, thereby firmly welding the diamond abrasive grains 42 on the filler layer, making the drill bit more durable and less likely to be damaged.

[0034] More specifically, in this embodiment, the steel base 1 is made of 45 steel; the outer diameter of the drilling part 2 of the steel base 1 is 10 mm, the wall thickness is 1.5 mm, and the length is 8 mm. The cross section of the inclined groove 3 is circular arc shape, the inclination angle is 45°, the depth is 0.3 mm, and the slot width is 0.5 mm. The thickness of the functionally graded nano-reinforced filler layer 41 is 0.20 mm. The thickness of the transition layer 411 is 0.06 mm, the thickness of the strengthening layer 412 is 0.10 mm, and the thickness of the bonding layer 413 is 0.04 mm, and the thickness ratio of the three is 3:5:2. The friction-reducing and heat-conducting coating 31 is a diamond-like carbon coating with a thickness of 0.3 mm. The diamond abrasive grains 42 are 35 / 40 mesh diamond abrasive grains with a surface nickel plating layer of 0.15 μm thick.

[0035] Further, the transition layer 411 is composed of the following components by weight percentage: Cr 15%, B 5%, Mo 6%, V 2.5%, carboxyl-modified multi-walled carbon nanotubes 3.5%, Ce 0.5%, and Ni 67.5%. The strengthening layer 412 is composed of the following components by weight percentage: Cr 8%, Si 5.5%, B 4.5%, Fe 3.5%, cobalt-coated nano-tungsten carbide particles 4%, cobalt-coated nano-yttrium oxide particles 1.3%, Ce 0.5%, and Ni 72.7%. The bonding layer 413 is composed of the following components by weight percentage: Cr 9%, Si 5.5%, B 4.5%, Fe 3.5%, Co 10%, W 3.5%, nano-cubic boron nitride particles 1%, Ce 0.5%, and Ni 62.5%.

[0036] The above-mentioned method for preparing the functionally graded nano-reinforced diamond thin-wall drill comprises the following steps: Step S1, milling of the groove The 29 oblique grooves 3 with circular arc cross section and equal intervals are milled on the outer circumferential wall of the drilling part 2 of the steel base body 1 by using a numerical control machine tool, and then the milled workpiece is sequentially subjected to alkali washing, acid washing, distilled water washing, and room temperature air drying for standby. Specifically, the alkali washing is to immerse the milled drilling part 2 in a 10% NaOH solution at a temperature of 60℃ for 10 min; the acid washing is to immerse the alkali washed drilling part 2 in a 5% hydrochloric acid solution for 5 min; and the water washing is to clean to neutral with deionized water, so as to obtain the steel base body 1 with the oblique grooves 3.

[0037] Step S2, laying of the functionally graded nano-reinforced filler metal layer (1) The raw materials (Cr powder, Si powder, B powder, Fe powder, Co powder, W powder, Mo powder, V powder, Ce powder, Ni powder, carboxyl-modified multi-walled carbon nanotubes, cobalt-coated nano-tungsten carbide particles, cobalt-coated nano-yttrium oxide particles, and nano-cubic boron nitride particles) are weighed according to the chemical composition and proportioning of the transition layer, the strengthening layer, and the bonding layer, and then are placed in a vacuum drying oven for drying at 90℃ for 2h, and then are sieved through a 250-mesh sieve to remove agglomerated particles and ensure the dispersibility of the raw materials.

[0038] The dried raw materials are respectively loaded into stainless steel ball milling jars according to the chemical composition and proportioning of the transition layer, the strengthening layer, and the bonding layer, and are subjected to mechanical alloying ball milling according to the preset ball milling parameters to obtain transition layer filler metal powder, strengthening layer filler metal powder, and bonding layer filler metal powder. The parameters of the mechanical alloying ball milling are as follows: the ball-to-material ratio is 7:1, the ball milling speed is 250r / min, and the ball milling time is 10h. During the ball milling, 0.8% anhydrous ethanol based on the total mass fraction of the raw materials is added to the ball milling jar, high-purity argon is introduced, and staged ball milling is adopted, i.e., the ball milling is stopped for 1h for heat dissipation every 4h of ball milling, so as to avoid oxidation or performance change of the raw materials due to excessively high temperature during the ball milling. The particle sizes of the carboxyl-modified multi-walled carbon nanotubes, the cobalt-coated nano-tungsten carbide particles, the cobalt-coated nano-yttrium oxide particles, and the nano-cubic boron nitride particles are all 500nm, and the particle sizes of the other metal powder raw materials are 300 / 325 mesh.

[0039] (2) The transition layer filler metal powder, the strengthening layer filler metal powder, and the bonding layer filler metal powder prepared above are respectively weighed, and solvents are respectively added to the three kinds of filler metal powders. The solvent is a mixture of 55% acrylic acid and 45% ethyl acetate in mass concentration. The solvent addition amount is 15% of the mass percentage of the filler metal powder. After sufficient stirring and mixing, the transition layer filler metal paste, the strengthening layer filler metal paste, and the bonding layer filler metal paste with a viscosity of 2000-2500mPa•s are respectively prepared, so as to ensure that the filler metal paste has good printability and formability.

[0040] (3) The transition layer brazing paste, the strengthening layer brazing paste and the bonding layer brazing paste are sequentially laid on the wall surface between every two inclined grooves 3 to form the blank state of the drilling unit 4. Specifically, the laying adopts a hollow template method, and the specific process is as follows: The transition layer hollow template, the strengthening layer hollow template and the bonding layer hollow template of the light-cured resin material are printed by using the SLA technology, and the process parameters are as follows: laser wavelength 355 nm, laser power 3000 mw, spot diameter 0.1 mm, layer thickness 50 μm, exposure time 8 s and scanning speed 8000 mm / s. The inner diameter size of the transition layer hollow template is 0.01 mm larger than the outer diameter size of the drilling part 2 of the steel base body 1, and the thickness is the same as that of the transition layer 411; the inner diameter size of the strengthening layer hollow template is 0.01 mm larger than the outer diameter size of the transition layer hollow template, and the thickness is the same as that of the strengthening layer 412; the inner diameter size of the bonding layer hollow template is 0.01 mm larger than the outer diameter size of the strengthening layer hollow template, and the thickness is the same as that of the bonding layer 413; the axial lengths of the three kinds of hollow templates are the same, and are 1.2 times of the axial length of the drilling part 2, and the hollow patterns of the hollow templates are the same as the shape of the drilling unit 4. Specifically, the thickness of the transition layer hollow template obtained by the SLA printing is 0.06 mm, and the inner diameter is 10.01 mm; the thickness of the strengthening layer hollow template is 0.1 mm, and the inner diameter is 10.08 mm; and the thickness of the bonding layer hollow template is 0.04 mm, and the inner diameter is 10.19 mm.

[0041] The transition layer hollow template prepared above is accurately positioned by the positioning pin and closely adheres to the wall surface between every two inclined grooves 3 obtained in step S1, the transition layer brazing paste prepared in the above step (2) is placed on the transition layer hollow template, the transition layer brazing paste is filled into the template hollow area by using a scraper, and it is ensured that the brazing paste fills the hollow area of the template. Then the steel base body with the laid transition layer brazing paste is placed into a low-temperature oven, and is cured at 90℃ for 12 min, after being taken out, the transition layer hollow template is removed, and the laying of the transition layer brazing paste is completed.

[0042] Next, the strengthening layer hollow template is closely adhered to the wall surface between the transition layer laid inclined grooves 3, the strengthening layer template is adjusted so that the hollow area thereof is aligned with the area where the transition layer brazing paste is laid, then the transition layer laying operation method is used to lay the strengthening layer brazing paste and to cure it, after the curing is completed, the strengthening layer hollow template is removed.

[0043] The laying of the bonding layer brazing paste is completed by referring to the operation mode of the transition layer and the strengthening layer, and the difference from the previous two layers is that the bonding layer brazing paste directly removes the bonding layer hollow template after filling the hollow area of the template, and does not perform curing treatment, so as to reserve the tackiness and facilitate the fixation of the subsequent diamond abrasive grains 42.

[0044] Step S3, fixation of diamond abrasive grains The step S2 is performed immediately after the brazing filler paste is laid on the bonding layer, and before the brazing filler paste is solidified. The drilling part 2 of the thin-walled drill is fixed on the rotary workbench, and the diamond abrasive grains 42 are uniformly scattered on the brazing filler paste as the thin-walled drill slowly rotates (at a speed of 10 r / min). After the diamond abrasive grains 42 are completely covered on the gradient filler layer, the assembly of the thin-walled drill drilling unit 4 is completed. Then, the thin-walled drill is placed in a 120℃ oven for 45 min to solidify the brazing filler paste and ensure that the diamond abrasive grains 42 are firmly fixed.

[0045] Step S4, prepositioning of the friction-reducing and heat-conducting coating The friction-reducing coating precursor (with a viscosity of 300 mPa·s) is sprayed on the inner wall of the inclined groove 3 by using the droplet spraying technology (droplet diameter of 200 μm, spraying frequency of 2.5 kHz, and distance between the nozzle and the inner wall of the groove 3 of 5 mm) to ensure that the precursor uniformly covers the inner wall of the inclined groove 3, thereby laying a foundation for the formation of the friction-reducing and heat-conducting coating 31 (specifically, a diamond-like carbon coating).

[0046] Step S5, laser brazing The workpiece after the prepositioning of the friction-reducing and heat-conducting coating in step S4 is fixed on the synchronous control rotary workbench of the laser additive equipment, and the rotary workbench is enclosed in a quartz glass cover that can be protected by argon. The three-dimensional model of the drilling unit 4 is imported into the control system of the laser additive equipment, the laser scanning brazing path is planned, the laser brazing process parameters are set, and laser brazing is performed. The laser power is 300 W, the spot diameter is 0.2 mm, the scanning speed is 100 mm / min, the scanning overlap rate is 65%, the synchronous control rotary workbench rotates at a speed of 40 r / min, and the argon flow in the quartz glass cover is 15 L / min. The laser is started, and the laser beam is used to scan and braze the diamond abrasive grains 42 through the quartz glass, so that the functionally gradient nano-enhanced filler layer 41 is welded on the steel substrate 1, and the diamond abrasive grains 42 are welded on the surface of the functionally gradient nano-enhanced filler layer 41. After brazing, the argon atmosphere is maintained for 8 s, and the gas source is turned off after the brazing area temperature drops below 500℃ to avoid oxidation of the brazing area.

[0047] Step S6, preparation of the friction-reducing and heat-conducting coating According to the shape of the oblique groove 3, the laser scanning path is planned, and the preset friction-reducing coating precursor is scanned and processed by adjusting the laser parameters to perform in-situ synthesis of the friction-reducing and heat-conducting coating 31. Among them, the laser used is a pulsed laser with a pulse width of nanoseconds, a laser power of 1200W, a scanning speed of 600mm / min, a scanning overlap rate of 40%, and a spot diameter of 2mm. The light-thermal effect of the laser makes the friction-reducing coating precursor react in-situ to generate the friction-reducing and heat-conducting coating 31. Based on this, the functional gradient enhanced diamond thin-wall drill of this embodiment is prepared.

[0048] Embodiment 2

[0049] This embodiment provides a functional gradient enhanced diamond thin-wall drill, which has the same structure and composition as embodiment 1. The difference from embodiment 1 is that the outer diameter of the drilling part 2 of the steel base body 1 is 20mm, the wall thickness is 2.0mm, and the length is 12mm. The cross section of the oblique groove 3 is an elliptical arc shape, the inclination angle is 50°, the depth is 0.4mm, and the slot width is 1mm. The thickness of the functional gradient nano-enhanced solder layer 41 is 0.24mm. The thickness of the transition layer 411 is 0.072mm, the thickness of the strengthening layer 412 is 0.144mm, the thickness of the bonding layer 413 is 0.024mm, and the thickness ratio of the three is 3:6:1. The friction-reducing and heat-conducting coating 31 is a diamond-like carbon coating with a thickness of 0.4mm. The diamond abrasive grains 42 are 35 / 40 mesh diamond abrasive grains with a surface coated with a 0.12μm thick tungsten carbide plating layer.

[0050] This embodiment provides a preparation method of the above-mentioned functional gradient enhanced diamond thin-wall drill. The preparation process is changed accordingly in terms of composition and structure, and the difference from embodiment 1 is that in step S5, the laser power is 450W, the spot diameter is 0.5mm, the scanning speed is 200mm / min, and the scanning overlap rate is 60%; in step S6, the laser power is 1500W, and the rest of the process and parameters are the same as embodiment 1.

[0051] Embodiment 3

[0052] The embodiment provides a functionally gradient reinforced diamond thin-wall drill, which is basically same in structure and composition with the embodiment 1. The difference from the embodiment 1 is that the outer diameter of the drilling part 2 of the steel base 1 is 50 mm, the wall thickness is 2.5 mm, and the length is 15 mm. The cross section of the oblique groove 3 is a rounded inverted trapezoid, the inclination angle is 60°, the depth is 0.5 mm, and the notch width is 2.5 mm. The thickness of the functionally gradient nano-reinforced solder layer 41 is 0.26 mm. The thickness of the transition layer 411 is 0.052 mm, the thickness of the strengthening layer 412 is 0.13 mm, and the thickness of the bonding layer 413 is 0.078 mm, and the thickness ratio of the three is 2:5:3. The thickness of the friction-reducing and heat-conducting coating 31 is 0.5 mm. The diamond abrasive grains 42 are 40 / 45 mesh diamond abrasive grains with a 0.1 μm thick chromium carbide plating layer on the surface.

[0053] The embodiment provides a preparation method of the functionally gradient reinforced diamond thin-wall drill, and the difference from the embodiment 1 is that, in the step S5, the laser power is 550 W, the spot diameter is 0.8 mm, the scanning speed is 240 mm / min, and the scanning overlap rate is 50%; in the step S6, the laser power is 2000 W, and the scanning speed is 850 mm / min, and the rest of the process and parameters are the same as those in the embodiment 1.

[0054] Comparative Example 1 The comparative example provides a diamond thin-wall drill, and the difference from the embodiment 1 is that the oblique groove 3 and the friction-reducing and heat-conducting coating 31 are not arranged, and the rest of the process and parameters are the same as those in the embodiment 1.

[0055] Comparative Example 2 The comparative example provides a diamond thin-wall drill, and the difference from the embodiment 1 is that the friction-reducing and heat-conducting coating 31 is not arranged, and the rest of the process and parameters are the same as those in the embodiment 1.

[0056] Comparative Example 3 The comparative example provides a diamond thin-wall drill, and the difference from the embodiment 1 is that the friction-reducing and heat-conducting coating 31 is replaced by a molybdenum disulfide-based composite coating, and the rest of the process and parameters are the same as those in the embodiment 1. When the molybdenum disulfide-based composite coating is prepared, the mass percentage composition of the friction-reducing coating precursor used is: 80% tungsten cobalt carbide, 12% copper, and the rest is MoS2.

[0057] Comparative Example 4 The comparative example 1 provides a diamond thin-wall drill, the structure and the preparation method of which are different from those of the example 1 in that the functional gradient nano-reinforced filler layer 41 is replaced by a single-layer non-gradient nano-reinforced filler layer. The single-layer non-gradient nano-reinforced filler layer is composed of the same components as the bonding layer of the example 1, specifically, Cr 9%, Si 5.5%, B 4.5%, Fe 3.5%, Co 10%, W 3.5%, nano-cubic boron nitride particles 1%, Ce 0.5%, and Ni 62.5% by weight.

[0058] Comparative Example 5 The comparative example 1 provides a diamond thin-wall drill, the structure and the preparation method of which are different from those of the example 1 in that the functional gradient nano-reinforced filler layer 41 is replaced by a single-layer non-gradient nano-reinforced filler layer. The single-layer non-gradient nano-reinforced filler layer is composed of the same components as the bonding layer of the example 1, specifically, Cr 9%, Si 5.5%, B 4.5%, Fe 3.5%, Co 10%, W 3.5%, nano-cubic boron nitride particles 1%, Ce 0.5%, and Ni 62.5% by weight.

[0059] Comparative Example 6 The comparative example 1 provides a diamond thin-wall drill, the structure and the preparation method of which are different from those of the example 1 in that the functional gradient nano-reinforced filler layer 41 is replaced by a single-layer non-gradient nano-reinforced filler layer. The single-layer non-gradient nano-reinforced filler layer is composed of the same components as the bonding layer of the example 1, specifically, Cr 9%, Si 5.5%, B 4.5%, Fe 3.5%, Co 10%, W 3.5%, nano-cubic boron nitride particles 1%, Ce 0.5%, and Ni 62.5% by weight.

[0060] Comparative Example 7 The comparative example 1 provides a diamond thin-wall drill, the structure and the preparation method of which are different from those of the example 1 in that the functional gradient nano-reinforced filler layer 41 is replaced by a single-layer non-gradient nano-reinforced filler layer. The single-layer non-gradient nano-reinforced filler layer is composed of the same components as the bonding layer of the example 1, specifically, Cr 9%, Si 5.5%, B 4.5%, Fe 3.5%, Co 10%, W 3.5%, nano-cubic boron nitride particles 1%, Ce 0.5%, and Ni 62.5% by weight.

[0061] Comparative Example 8 The comparative example 1 provides a diamond thin-wall drill, the structure and the preparation method of which are different from those of the example 1 in that the functional gradient nano-reinforced filler layer 41 is replaced by a single-layer non-gradient nano-reinforced filler layer. The single-layer non-gradient nano-reinforced filler layer is composed of the same components as the bonding layer of the example 1, specifically, Cr 9%, Si 5.5%, B 4.5%, Fe 3.5%, Co 10%, W 3.5%, nano-cubic boron nitride particles 1%, Ce 0.5%, and Ni 62.5% by weight.

[0062] Test Example 1, Analysis of Appearance and Morphology The appearance and morphology of the drilling part of the diamond thin-wall drill prepared in the example 1 and the comparative examples 4, 5, 6, 7 were analyzed by using a scanning electron microscope, and the obtained scanning electron microscope images are shown in FIGS. 1-4, respectively. Figures 5-9

[0063] As shown in FIGS. 1-4, the diamond thin-wall drill prepared in the example 1 has a better appearance and morphology than the diamond thin-wall drills prepared in the comparative examples 4, 5, 6, and 7. Figures 5-9 ​It can be seen that the thin-walled diamond drill prepared by the method of the present invention in Example 1 exhibits excellent laser brazing morphology, good wettability of the brazing filler metal on the diamond, no cracks in the joint, and no formation of Fe-based intermetallic compounds. In Comparative Example 4, only the bonding layer was used as the brazing filler metal, resulting in the formation of a large amount of iron-carbon compounds at the diamond interface and the appearance of cracks. Comparative Example 5, without a reinforcing layer, although there were no iron-carbon compounds at the interface, resulted in numerous cracks in the joint. The transition layer of Comparative Example 6 lacked Mo, V, and carboxyl-modified multi-walled carbon nanotubes, leading to the formation of iron-carbon compounds and cracks in the joint. The reinforcing layer of Comparative Example 7, without the addition of low-expansion-coefficient reinforcing phases such as cobalt-coated nano-tungsten carbide and cobalt-coated nano-yttrium oxide, also resulted in numerous cracks in the joint. This demonstrates that the complete brazing filler metal layer structure and the addition of specific components in the present invention are crucial for ensuring brazing quality and preventing the formation of iron-carbon compounds and cracks.

[0064] Experimental Example 2: Friction Performance Analysis The friction coefficients of the diamond thin-walled drills prepared in Example 1, Comparative Examples 1, 2, and 3 were measured using a friction and wear testing machine after drilling for 300 seconds. The resulting friction coefficient curves are shown below. Figure 10 As shown.

[0065] Depend on Figure 10 It can be seen that the diamond thin-walled drill of Example 1 has the lowest average friction coefficient and good long-term stability. Comparative Example 1 has the highest average friction coefficient; after grooves were opened in the drilling part of the steel substrate in Comparative Example 2, the average friction coefficient was lower than that of Comparative Example 1, but the friction coefficient stability was poor in the first 80 seconds; Comparative Example 3 used a molybdenum disulfide-based composite coating as a friction-reducing and heat-conducting coating, which reduced the friction coefficient to a certain extent, but its average friction coefficient was still higher than that of Example 1. Overall, Example 1 has the best friction performance.

[0066] Experiment Example 3: Application Performance Test Drilling tests were conducted on the diamond thin-walled drills prepared in Examples 1-3 and Comparative Examples 1-8 (10 parallel samples were tested for each type of diamond thin-walled drill). The drilling equipment was a Dongcheng angle grinder, the drilling speed was 11800 r / min, the feed rate was 0.5 mm / s, and the drilling material was Marco Polo ceramic tile with a Mohs hardness of 6 and a thickness of 10 mm. The number of drilled holes, the diamond loss, whether there were cracks or chips on the upper and lower surfaces of the ceramic tile after drilling, the surface roughness of the inner wall of the drilled hole, and the crack condition of the drilling unit were statistically analyzed. The test results are shown in Table 1.

[0067] Table 1. Drilling performance test results of diamond thin-walled drills

[0068] As can be seen from the data in Table 1, the diamond thin-wall drills prepared in Examples 1-3 of the present application are obviously superior to the conventional drill bits in the comparative examples in drilling accuracy, surface quality and service life, and fully embody the superiority of the present application.

[0069] According to the above test results, the functional gradient reinforced diamond thin-wall drill provided by the present application has the comprehensive performance of impact resistance, high wear resistance, strong heat dissipation and low friction, can significantly improve the service life of the diamond thin-wall drill, and is suitable for high-precision drilling of hard and brittle materials such as building stone, glass, ceramic, silicon crystal and carbon fiber composite material, and has a significant advantage in the scene with high requirements for tool wear resistance, heat dissipation and service life.

[0070] The above embodiments fully prove the feasibility and excellent effect of the technical scheme of the present application. The person skilled in the art can make conventional adjustment of parameters according to actual production conditions and requirements on the basis of the above examples, and such adjustment all falls within the protection scope of the present application.

Claims

1. A functionally graded diamond thin-walled drill bit, comprising a steel matrix (1), wherein the outer end of the steel matrix (1) is a cylindrical drilling section (2), characterized in that, The outer periphery of the drilling section (2) is provided with slanted grooves (3) and drilling units (4) at equal intervals; the walls of the slanted grooves (3) are coated with a friction-reducing and heat-conducting coating (31); the slanted grooves (3) and the drilling units (4) are alternately distributed; the drilling unit (4) includes a functionally graded nano-reinforced brazing filler layer (41) and diamond abrasive grains (42) laser-brazed to the surface of the functionally graded nano-reinforced brazing filler layer (41); the functionally graded nano-reinforced brazing filler layer (41) includes a transition layer (411), a reinforcing layer (412), and a bonding layer (413) arranged sequentially from the steel substrate (1) to the diamond abrasive grains (42). The transition layer (411) is composed of the following raw materials by weight percentage Composition: Cr 10-18%, B 3-8%, Mo 5-8%, V 2-3%, toughening nanophase 2.5-4.5%, Ce 0.1-1%, Ni balance; the reinforcing layer (412) is composed of the following raw materials in weight percentages. Composition: Cr 6.5-9.5%, Si 4.5-6.5%, B 3.5-5.5%, Fe 2.5-4.5%, wear-resistant nanophase 3.5-6.5%, Ce 0.1-1%, Ni balance; the bonding layer (413) is composed of the following raw materials in weight percentages. Composition: Cr 8-10%, Si 4.5-6.5%, B 3-5.5%, Fe 2.5-4.5%, Co 7.5-12.5%, W 2-5%, wear-resistant nanophase 0.5-1.5%, Ce 0.1-1%, Ni balance.

2. The functionally graded diamond thin-walled drill bit according to claim 1, characterized in that, The outer diameter of the drilled part (2) is 6-120 mm, the wall thickness is 1.0-2.5 mm, and the length is 6-15 mm; the thickness of the functionally graded nano-reinforced brazing filler layer (41) is 0.15-0.3 mm; the thickness ratio of the transition layer (411), the reinforcing layer (412), and the bonding layer (413) is (2-4):(4-7):(1-3).

3. The functionally graded diamond thin-walled drill bit according to claim 1, characterized in that, The cross-sectional shape of the inclined groove (3) is one of the following: rounded inverted trapezoid, arc, or elliptical arc; the inclination angle of the inclined groove (3) is 30° to 60°, the depth is 0.3 to 0.5 mm, and the groove width is 0.5 to 5 mm; the number of inclined grooves (3) is 6 to 30.

4. The functionally graded diamond thin-walled drill bit according to claim 1, characterized in that, The friction-reducing and thermally conductive coating (31) is a diamond-like carbon coating; The thickness of the friction-reducing and thermally conductive coating (31) is 0.3~0.5mm.

5. The functionally graded diamond thin-walled drill bit according to claim 1, characterized in that, The diamond abrasive grains (42) have a particle size of 35-45 mesh; the surface of the diamond abrasive grains (42) is coated with a coating with a thickness of 0.5-1 μm; the coating is one of nickel coating, chromium carbide coating, tungsten carbide coating, and titanium carbide coating; the toughening nanophase is carboxylated modified multi-walled carbon nanotubes and / or carboxylated modified graphene nanosheets; the wear-resistant nanophase is one or more of cobalt-coated tungsten carbide nanoparticles, cobalt-coated yttrium oxide nanoparticles, and cubic boron nitride nanoparticles.

6. A method for preparing functionally graded diamond thin-walled diamond as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. A slanted groove (3) is machined on the outer peripheral wall of the drilled part (2) on the steel substrate (1), and then cleaned and dried to obtain a steel substrate (1) with a slanted groove (3). In addition, according to the chemical composition ratio of the transition layer (411), the reinforcing layer (412), and the bonding layer (413), the raw materials are weighed and subjected to vacuum drying and ball milling to obtain transition layer brazing powder, reinforcing layer brazing powder, and bonding layer brazing powder; the transition layer brazing powder, reinforcing layer brazing powder, and bonding layer brazing powder are respectively mixed with solvent to obtain transition layer brazing paste, reinforcing layer brazing paste, and bonding layer brazing paste; S2. The transition layer brazing paste, the reinforcing layer brazing paste and the bonding layer brazing paste are sequentially laid on the wall surface between each two inclined grooves (3) to form the blank state of the drilling unit (4). Then, diamond abrasive grains (42) are fixed on the laid bonding layer brazing paste. In addition, a friction-reducing and heat-conducting coating precursor is pre-placed on the wall surface of the inclined groove (3) of the steel substrate (1). S3. The drilling unit (4) after step S2 is laser brazed so that the functionally graded nano-reinforced brazing layer (41) is welded onto the steel substrate (1) and the diamond abrasive grains (42) are welded onto the surface of the functionally graded nano-reinforced brazing layer (41). Then, the inclined groove (3) of the pre-placed friction-reducing and thermally conductive coating precursor is laser clad to form a friction-reducing and thermally conductive coating (31) on the wall surface of the inclined groove (3), thereby preparing the functionally graded reinforced diamond thin-walled drill.

7. The method for preparing functionally graded diamond thin-walled drill bit according to claim 6, characterized in that, In step S1, the vacuum drying temperature is 80-100℃ and the time is 1-5h; the ball-to-material ratio of the ball milling process is 6:1-8:1, the ball milling speed is 200-300r / min, and the ball milling time is 8-15h; the solvent is a mixture of acrylic acid and ethyl acetate; the amount of solvent added is 10%-20% of the mass of the solder powder.

8. The method for preparing functionally graded diamond thin-walled drill bit according to claim 6, characterized in that, In step S2, the laying is carried out using a perforated template method; the pre-setting is carried out using a micro-droplet spraying method; and the friction-reducing and thermally conductive coating precursor is a mixture of phenolic resin and anhydrous ethanol in a mass ratio of 1:(4~6).

9. The method for preparing functionally graded diamond thin-walled diamond according to claim 6, characterized in that, In step S3, the laser brazing process conditions are as follows: laser power of 150-600W, spot diameter of 0.2-0.8mm, scanning speed of 60-300mm / min, scanning overlap rate of 50%-70%, and synchronous control of the stage rotation speed of 10-50r / min; the laser cladding process conditions are as follows: using a nanosecond pulsed laser, laser power of 500-2000W, scanning speed of 120-1000mm / min, scanning overlap rate of 35%-45%, and spot diameter of 1-3.5mm.

10. An application of functionally graded diamond thin-walled drill as described in any one of claims 1 to 5, characterized in that, Application in drilling and machining of hard and brittle materials; the hard and brittle materials are one or more of building stone, glass, ceramics, silicon crystal, and carbon fiber composite materials.

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