A gradient structure cubic boron nitride composite piece and a preparation method thereof

Abstract

The application discloses a gradient structure cubic boron nitride composite sheet and a preparation method thereof. The gradient structure cubic boron nitride composite sheet is composed of a hard alloy substrate, a gradient transition layer and a CBN layer from bottom to top. The gradient transition layer is composed of N layers of gradient layers. N is 4-18. From bottom to top, the layers are a first layer of gradient layer, a second layer of gradient layer, and a Nth layer of gradient layer in turn. Any one of the gradient layers is composed of CBN and hard alloy. The volume fraction of the hard alloy in the Nth layer is 5-30% less than that in the (N-1)th layer. The volume fraction of the CBN in the Nth layer is 5-30% more than that in the (N-1)th layer. The gradient transition layer with 4-18 layers of gradient layers is arranged, so that the thermal expansion coefficient of the transition layer is between the CBN and the hard alloy, the difference between the thermal expansion coefficients of the two materials is reduced, the residual stress in the composite sheet is reduced, and the use performance of the composite sheet is greatly improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of superhard material preparation, and particularly relates to a gradient structure cubic boron nitride composite sheet and a preparation method thereof. BACKGROUND

[0002] The cubic boron nitride composite sheet has high hardness, high wear resistance, low friction coefficient and good thermal stability, and shows high chemical inertness when processing iron-based materials, and is widely used in the processing of hard materials and black metal materials. The traditional manufacturing process of the cubic boron nitride composite sheet is to sinter the CBN powder and the hard alloy substrate at high temperature and high pressure at one time. Due to the difference in the thermal expansion coefficients of the two materials, the thermal residual stress at the material interface during the cooling and pressure releasing process is too large, which causes the CBN layer to easily produce cracks during use, resulting in CBN layer falling off, cracking and chipping, and gradually losing the cutting ability and failing, thereby reducing the service life of the cubic boron nitride composite sheet. SUMMARY

[0003] To overcome the shortcomings of the prior art, the first object of the application is to provide a gradient structure cubic boron nitride composite sheet. By setting the gradient transition layer, the thermal residual stress of the cubic boron nitride composite sheet can be effectively reduced, the problems of CBN layer falling off, cracking and chipping during the work of the cubic boron nitride composite sheet can be solved, and the service life of the cubic boron nitride composite sheet can be prolonged.

[0004] The second object of the application is to provide a preparation method of the gradient structure cubic boron nitride composite sheet. The 3D printing manufacturing process can optimize the product performance, improve the production efficiency and effectively control the production cost.

[0005] To achieve the above objects, the application adopts the following technical scheme:

[0006] The gradient structure cubic boron nitride composite sheet comprises, from bottom to top, a hard alloy substrate, a gradient transition layer and a CBN layer. The gradient transition layer comprises N gradient layers. N is 4-18. From bottom to top, the gradient layers are sequentially a first gradient layer, a second gradient layer, and sequentially to an Nth gradient layer. Any one of the gradient layers is composed of CBN and hard alloy. The volume fraction of the hard alloy in the Nth gradient layer is 5-30% less than the volume fraction of the hard alloy in the (N-1)th gradient layer, preferably 5-20%. The volume fraction of the CBN in the Nth gradient layer is 5-30% more than the volume fraction of the CBN in the (N-1)th gradient layer, preferably 5-20%.

[0007] The gradient structure cubic boron nitride composite sheet provided by the application can make the thermal expansion coefficient of the transition layer between CBN and hard alloy, reduce the difference between the thermal expansion coefficients of the two materials, reduce the residual stress in the composite sheet, and greatly improve the use performance.

[0008] Of course, the number of layers of the transition layer needs to be controlled within the scope of the application. If the number of layers of the transition layer is too small, the transition from hard alloy to diamond cannot be effectively realized, and the difference in physical and mechanical properties between the two materials cannot be reduced to achieve the purpose of relieving residual stress. The more the number of gradient layers is, the closer the composition distribution, microstructure and mechanical property distribution are to the ideal continuous gradient. However, too many layers will result in too large total layer thickness of the transition layer, and at the same time, due to the limited size of the composite sheet synthesized at present, the thickness of the hard alloy substrate and the diamond layer will be correspondingly reduced, which will reduce the wear resistance and cutting efficiency of the composite sheet.

[0009] In addition, the unreasonable change in the mass fraction of raw materials between any two layers in the gradient layer will affect the size of the residual stress at their interface, and further affect the use performance.

[0010] In a preferred embodiment, the hard alloy substrate and the hard alloy in the gradient layer are Co-WC, wherein the mass fraction of Co is 3-30%, and the mass fraction of WC is 70-97%.

[0011] In a preferred embodiment, the total thickness of the gradient transition layer is 0.04-5mm, the thickness of any one gradient layer is 0.01-0.5mm, and preferably 0.05-0.25mm.

[0012] The preparation method of the gradient structure cubic boron nitride composite sheet comprises the following steps: mixing CBN powder and a binder to obtain CBN mixture, respectively preparing CBN powder, Co powder, WC powder and a binder according to the design composition of each gradient layer to obtain N groups of gradient layer mixtures, mixing, granulating and drawing N+1 groups of filamentous materials by mixing the prepared CBN mixture and N groups of gradient layer mixtures, printing N+1 groups of green bodies by using a 3D printer, assembling the N+1 groups of green bodies and a hard alloy substrate to obtain a composite green body, and obtaining the gradient structure cubic boron nitride composite sheet by debinding and high temperature and high pressure synthesis of the composite green body.

[0013] In a preferred embodiment, the particle size of the CBN powder is 1-100μm, and the particle size of the Co powder and the WC powder is ≤100μm.

[0014] In a preferred embodiment, the mass ratio of CBN powder to binder in the CBN mixture is 2-20:1.

[0015] Preferably, the mass ratio of the total mass of CBN powder, Co powder and WC powder to the mass of the binder in any one of the N+1 groups of gradient layer mixtures is 2-20:1.

[0016] Preferably, the binder in the CBN mixture and the N groups of gradient layer mixtures each has the following composition by mass percentage: 20-70% of ethylene-vinyl acetate copolymer, 5-35% of polystyrene, 5-35% of polyurethane, 1-8% of hydrogenated styrene-butadiene block copolymer, 1-7% of dioctyl phthalate, 1-6% of vinyl bis-stearamide and 1-6% of stearic acid.

[0017] The binder in the present application uses ethylene-vinyl acetate copolymer, polystyrene and polyurethane as the three skeleton materials. The ethylene-vinyl acetate copolymer has good flexibility and filler compatibility due to the introduction of vinyl acetate monomer in the molecular chain, which is a key material for ensuring the flexibility of the wire material. The polystyrene has good flowability, which can promote the flow of the material during mixing to ensure its uniformity. The polyurethane has high elasticity like rubber and rigidity like plastic. Since the wire material not only needs to have good flexibility but also needs to have a certain rigidity, it can be stably clamped by the gear of the 3D printer and fed into the extrusion nozzle. The three skeleton materials complement each other. In addition, the use of the above three thermoplastic polymers as skeleton materials sets a gradient debinding temperature according to different binder components during the debinding process, so that a high debinding rate and a relatively complete green body are obtained, avoiding the decomposition of a single binder during debinding to generate pores, and the insufficient support of the green body causing cracks, collapse and other debinding defects.

[0018] The binder in the present application uses ethylene-vinyl acetate copolymer, polystyrene and polyurethane as the three skeleton materials. The ethylene-vinyl acetate copolymer has good flexibility and filler compatibility due to the introduction of vinyl acetate monomer in the molecular chain, which is a key material for ensuring the flexibility of the wire material. The polystyrene has good flowability, which can promote the flow of the material during mixing to ensure its uniformity. The polyurethane has high elasticity like rubber and rigidity like plastic. Since the wire material not only needs to have good flexibility but also needs to have a certain rigidity, it can be stably clamped by the gear of the 3D printer and fed into the extrusion nozzle. The three skeleton materials complement each other. In addition, the use of the above three thermoplastic polymers as skeleton materials sets a gradient debinding temperature according to different binder components during the debinding process, so that a high debinding rate and a relatively complete green body are obtained, avoiding the decomposition of a single binder during debinding to generate pores, and the insufficient support of the green body causing cracks, collapse and other debinding defects.

[0019] The inventors have found that it is crucial to control the composition of the binder within the scope of the present application. Only when the composition of the binder is within the above-mentioned range can the binder be adapted to the N+1 groups of different raw material powders, so as to ensure that the N+1 groups of printed wire materials prepared have good flexibility, flowability and uniformity, so as to obtain a green body with uniform performance.

[0020] Further preferably, the binder in the CBN mixture and the N groups of gradient layer mixture is composed of 40-55% ethylene-vinyl acetate copolymer, 20-25% polystyrene, 15-25% polyurethane, 4-5% hydrogenated styrene-butadiene block copolymer, 1-2% dioctyl phthalate, 2-3% vinyl bis stearamide and 1-2% stearic acid.

[0021] Preferably, the temperature of the mixing is 100-300℃ and the rotation speed of the drawing is 10-200rpm.

[0022] Preferably, the diameter of the N+1 groups of filamentous material is 1.65-1.85mm.

[0023] In the present application, the uniformity of the material extruded from the nozzle is ensured by first preparing N+1 groups of filamentous material and then melt extrusion molding.

[0024] Preferably, the printing speed in the 3D printing process is 10-300mm / s, the printing layer thickness is 0.01-0.5mm and the printing temperature is 100-350℃.

[0025] Further preferably, the 3D printing adopts a melt extrusion molding printer.

[0026] In actual operation, the printing parameters are first set, the model of each structure layer of the gradient structure cubic boron nitride composite sheet is drawn in the computer, the model is imported into the slicing software to set the printing parameters, then it is imported into the melt extrusion molding printer to implement printing, the filamentous material is put into the printer in batches, and the corresponding printing model is matched in sequence to print the green body of each structure layer of the gradient structure cubic boron nitride composite sheet.

[0027] Preferably, the composite green body is first placed in a cyclohexane solution for solvent debinding, and then is subjected to thermal debinding in a vacuum environment.

[0028] Further preferably, the temperature of the solvent debinding is 40-80℃ and the time of the solvent debinding is 2-6h.

[0029] Further preferably, the process of the thermal debinding is as follows: first, the temperature is raised from room temperature to 80-120℃ at a heating rate of 4-6℃ / min, and is kept for 0.5-1h; then the temperature is raised to 230-270℃ at a heating rate of 3-4℃ / min, and is kept for 2-2.5h; then the temperature is raised to 380-420℃ at a heating rate of 2.5-4℃ / min, and is kept for 1-1.5h; finally, the temperature is raised to 580-620℃ at a heating rate of 2-2.5℃ / min, and is kept for 1.5-2h.

[0030] In the heat debinding process of the application, the step-by-step debinding is carried out in the mode of gradient temperature rise based on the difference of the pyrolysis temperature range of different components of the binder, which can effectively ensure the integrity of the green body and the removal effect of the binder in the green body, and avoid the generation of debinding defects.

[0031] In the preferred scheme, the temperature for synthesizing the debinding composite green body is 1400-2200 DEG C, the pressure for synthesizing is 3-8 GPa, and the synthesizing time is 120-1000 s.

[0032] In the actual operation process, the debinding composite green body is put into a six / side / four / side / two side top press for synthesis, and after the synthesis is completed, the pressure is slowly released and the temperature is slowly lowered to obtain the gradient structure cubic boron nitride composite sheet.

[0033] Beneficial effects:

[0034] The application provides a gradient structure cubic boron nitride composite sheet, which sets 4-18 gradient transition layers composed of two materials in different proportions between the hard alloy and the CBN layer, and the thermal expansion coefficient of the transition layer is between the two materials, which can reduce the difference of the thermal expansion coefficient, reduce the residual stress in the composite sheet, and enhance the bonding strength of the material interface.

[0035] The application adopts the FDM 3D printing process to manufacture the gradient structure cubic boron nitride composite sheet green body, which can accurately print the designed gradient structure transition layer, ensure the thickness requirement of the transition layer and the uniformity of the powder, optimize the performance of the polycrystalline cubic boron nitride composite sheet, and also improve the production efficiency and reduce the production cost. DETAILED DESCRIPTION

[0036] Figure 1 The figure is a schematic diagram of the gradient structure cubic boron nitride composite sheet.

[0037] Figure 1 In the figure, 1 is a CBN layer, 2 is a gradient transition layer, and 3 is a hard alloy layer. DETAILED DESCRIPTION

[0038] In order to make the content of the application more easily understood, the application will be further described in detail according to the specific embodiments.

[0039] Example 1

[0040] The raw materials used are CBN powder and cemented carbide powder, wherein the cemented carbide powder contains 15% Co and 85% WC; the particle size of the CBN powder is 15 μm, and the particle size of the cemented carbide powder is 18 μm. The mass ratio of each powder in the CBN layer and the transition layer to the special binder is 8:1. The special binder comprises 55% ethylene-vinyl acetate copolymer, 20% polystyrene, 15% polyurethane, 5% hydrogenated styrene-butadiene block copolymer, 1% dioctyl phthalate, 2% vinyl bis-stearamide, and 2% stearic acid.

[0041] A 4-layer composition gradient layer of CBN powder and cemented carbide is designed, and the total layer thickness is 0.2 mm, and the thickness of each layer is 0.05 mm. The powder content gradually changes from the cemented carbide to the CBN layer as follows:

[0042] The cemented carbide powder content in the first layer is 80%, and the CBN powder content is 20%;

[0043] The cemented carbide powder content in the second layer is 60%, and the CBN powder content is 40%;

[0044] The cemented carbide powder content in the third layer is 40%, and the CBN powder content is 60%;

[0045] The cemented carbide powder content in the fourth layer is 20%, and the CBN powder content is 80%;

[0046] The present example provides a 3D printing manufacturing process of a gradient structure cubic boron nitride composite sheet, comprising the following steps:

[0047] 1) Mixing: mixing according to the gradient requirements, respectively preparing the mixed materials required for the corresponding CBN layer and transition layer.

[0048] 2) Wire drawing: sequentially placing various mixed materials into a mixing mill for mixing and granulation, and then placing the granular materials into a wire drawing machine to obtain a wire-shaped material with a diameter of 1.75 mm; wherein the mixing temperature is 185°C, and the wire drawing machine speed is 35 rpm.

[0049] 3) Model and parameter design: importing the model of each structural layer of the gradient structure cubic boron nitride composite sheet into a slicing software to set the printing parameters, and then importing it into a fused deposition modeling printer. The printing speed is 30 mm / s, the printing layer thickness is 0.05 mm, the remaining printing layer thickness is 0.4 mm, and the printing temperature is 230°C.

[0050] 4) Printing: placing the wire materials into the printer in batches, and sequentially matching the corresponding printing models to print the green bodies of each structural layer of the gradient structure cubic boron nitride composite sheet.

[0051] 5) Degreasing: the assembled green body was put into a cyclohexane solution and kept at 60°C for 4h, then it was put into a vacuum degreasing furnace, first from room temperature to 100°C at a rate of 5°C / min, kept at 100°C for 0.5h; then from 100°C to 250°C at a rate of 4°C / min, kept at 250°C for 2h; then from 250°C to 400°C at a rate of 4°C / min, kept at 400°C for 1.5h; finally from 400°C to 600°C at a rate of 2°C / min, kept at 600°C for 1.5h.

[0052] 6) High temperature and high pressure synthesis: the degreased part and the hard alloy substrate were put into a mold and sintered in a cubic press, the temperature was 1500°C, the pressure was 5GPa, and the sintering time was 240s, after sintering, the pressure was slowly released and the temperature was slowly lowered to obtain a gradient structure cubic boron nitride composite sheet.

[0053] The residual stress value of the cubic boron nitride composite sheet prepared by the above process was 489GPa, and the impact toughness was 5.32KJ.

[0054] Example 2

[0055] The raw materials used were CBN powder and hard alloy powder, wherein the Co content in the hard alloy powder was 10%, the WC content was 90%, the particle size of the CBN powder was 30μm, and the particle size of the hard alloy powder was 15μm. The mass ratio of each powder in the CBN layer and the transition layer to the special adhesive was 10:1. The special adhesive contained 50% ethylene-vinyl acetate copolymer, 25% polystyrene, 15% polyurethane, 5% hydrogenated styrene-butadiene block copolymer, 2% dioctyl phthalate, 2% vinyl bis-stearamide, and 1% stearic acid.

[0056] A gradient layer of 8 layers of CBN powder and hard alloy composition was designed, with a total layer thickness of 2mm and a thickness of 0.25mm per layer. The powder content gradually changed from hard alloy to CBN layer as follows:

[0057] The first layer of hard alloy powder content was 95%, and the CBN powder content was 5%;

[0058] The second layer of hard alloy powder content was 90%, and the CBN powder content was 10%;

[0059] The third layer of hard alloy powder content was 80%, and the CBN powder content was 20%;

[0060] The fourth layer of hard alloy powder content was 70%, and the CBN powder content was 30%;

[0061] The fifth layer of hard alloy powder content was 60%, and the CBN powder content was 40%;

[0062] The 6th layer has a cemented carbide powder content of 40% and a CBN powder content of 60%;

[0063] The 7th layer has a cemented carbide powder content of 30% and a CBN powder content of 70%;

[0064] The 8th layer has a cemented carbide powder content of 20% and a CBN powder content of 80%;

[0065] The present example provides a 3D printing manufacturing process of a gradient structure cubic boron nitride composite sheet, comprising the following steps:

[0066] 1) Mixing: mix according to the gradient requirements to obtain the mixed materials required for the corresponding CBN layer and transition layer, respectively.

[0067] 2) Wire drawing: put the mixed materials into the internal mixer for mixing and granulation, and then put the granular materials into the wire drawing machine to obtain a wire-shaped material with a diameter of 1.75 mm; wherein the mixing temperature is 190°C and the wire drawing machine speed is 50 rpm.

[0068] 3) Model and parameter design: import the model of each structural layer of the gradient structure cubic boron nitride composite sheet into the slicing software to set the printing parameters, and then import it into the fused deposition modeling printer. The printing speed is 25 mm / s, the transition layer printing layer thickness is 0.25 mm, the rest of the printing layer thickness is 0.4 mm, and the printing temperature is 220°C.

[0069] 4) Printing: put the wire material into the printer in batches, and print the green body of each structural layer of the gradient structure cubic boron nitride composite sheet by matching the corresponding printing model.

[0070] 5) Debinding: after the green body is assembled, it is placed in a cyclohexane solution at 70°C for 6 hours, and then it is placed in a vacuum debinding furnace for thermal debinding. First, increase from room temperature to 100°C at a rate of 6°C / min, and keep at 100°C for 0.5h; then increase from 100°C to 250°C at a rate of 4°C / min, and keep at 250°C for 2h; then increase from 250°C to 400°C at a rate of 4°C / min, and keep at 400°C for 1h; finally, increase from 400°C to 600°C at a rate of 2°C / min, and keep at 600°C for 2h.

[0071] 6) High temperature and high pressure synthesis: put the debound part into the mold and put it into the six-surface press for sintering. The temperature is 1800°C, the pressure is 7GPa, and the sintering time is 360s. After sintering, slowly release the pressure and cool down to obtain the gradient structure cubic boron nitride composite sheet.

[0072] The residual stress value of the cubic boron nitride composite sheet prepared by the above process is 312GPa, and the impact toughness is 7.45KJ.

[0073] Example 3

[0074] The raw materials used were CBN powder and cemented carbide powder, the cemented carbide powder having a Co content of 13% and a WC content of 87%. The CBN powder had a particle size of 50 μm and the cemented carbide powder had a particle size of 30 μm. The mass ratio of each powder to special binder in the CBN layer and the transition layer was 12:1. The special binder comprised 40% ethylene-vinyl acetate copolymer, 25% polystyrene, 25% polyurethane, 4% hydrogenated styrene-butadiene block copolymer, 1% dioctyl phthalate, 3% vinyl bis-stearamide and 2% stearic acid.

[0075] A 18-layer compositionally graded layer of CBN powder and cemented carbide was designed, the total layer thickness being 4.5 mm and the thickness of each layer being 0.25 mm. The powder content was gradually changed from cemented carbide to CBN layer as follows:

[0076] The first group had a cemented carbide powder content of 95% and a CBN powder content of 5%;

[0077] The second group had a cemented carbide powder content of 90% and a CBN powder content of 10%;

[0078] The third group had a cemented carbide powder content of 85% and a CBN powder content of 15%;

[0079] The fourth group had a cemented carbide powder content of 80% and a CBN powder content of 20%;

[0080] The fifth group had a cemented carbide powder content of 75% and a CBN powder content of 25%;

[0081] The sixth group had a cemented carbide powder content of 70% and a CBN powder content of 30%;

[0082] The seventh group had a cemented carbide powder content of 65% and a CBN powder content of 35%;

[0083] The eighth group had a cemented carbide powder content of 60% and a CBN powder content of 40%;

[0084] The ninth group had a cemented carbide powder content of 55% and a CBN powder content of 45%;

[0085] The tenth group had a cemented carbide powder content of 50% and a CBN powder content of 50%;

[0086] The eleventh group had a cemented carbide powder content of 45% and a CBN powder content of 55%;

[0087] The twelfth group had a cemented carbide powder content of 40% and a CBN powder content of 60%;

[0088] The thirteenth group had a cemented carbide powder content of 35% and a CBN powder content of 65%;

[0089] The 14th group of cemented carbide powder content is 30%, and the CBN powder content is 70%;

[0090] The 15th group of cemented carbide powder content is 25%, and the CBN powder content is 75%;

[0091] The 16th group of cemented carbide powder content is 20%, and the CBN powder content is 80%;

[0092] The 17th group of cemented carbide powder content is 15%, and the CBN powder content is 85%;

[0093] The 18th group of cemented carbide powder content is 10%, and the CBN powder content is 90%. The present example provides a 3D printing manufacturing process of a gradient structure cubic boron nitride composite sheet, comprising the following steps:

[0094] 1) Mixing: according to the gradient requirements, the mixed materials required for the corresponding CBN layer and transition layer are prepared respectively.

[0095] 2) Wire drawing: put the various mixed materials into the internal mixer in turn, mix and granulate, and then put the granular material into the drawing machine to obtain a wire-shaped material with a diameter of 1.75 mm; wherein the mixing temperature is 200°C, and the drawing machine speed is 45 rpm.

[0096] 3) Model and parameter design: import the model of each structure layer of the gradient structure cubic boron nitride composite sheet into the slicing software to set the printing parameters, and then import it into the fused deposition modeling printer. The printing speed is 45 mm / s, the transition layer printing layer thickness is 0.25 mm, the rest of the printing layer thickness is 0.4 mm, and the printing temperature is 220°C.

[0097] 4) Printing: put the wire material into the printer in batches, and print out the green body of each structure layer of the gradient structure cubic boron nitride composite sheet by matching the corresponding printing model in turn.

[0098] 5) Debinding: after the obtained green body is assembled, it is placed in a cyclohexane solution at 60°C for 5h, and then it is placed in a vacuum debinding furnace for thermal debinding. First, increase from room temperature to 90°C at a rate of 4°C / min, and keep at 90°C for 1h; then increase from 90°C to 200°C at a rate of 6°C / min, and keep at 200°C for 2.5h; then increase from 200°C to 450°C at a rate of 4°C / min, and keep at 450°C for 2h; finally, increase from 450°C to 600°C at a rate of 4°C / min, and keep at 600°C for 1.5h.

[0099] 6) High temperature and high pressure synthesis: put the debinding piece into the mold and put it into the six-surface press for sintering, the temperature is 1700°C, the pressure is 8GPa, and the sintering time is 400s. After sintering is completed, slowly release the pressure and cool down to obtain the gradient structure cubic boron nitride composite sheet.

[0100] The residual stress value of the cubic boron nitride composite piece prepared by the above process is 215 GPa, and the impact toughness is 8.85 KJ.

[0101] Comparative Example 1

[0102] The other conditions are the same as those in Example 1, and only one layer of gradient transition layer containing 50% diamond and 50% cemented carbide is designed. However, due to the small number of gradient layers, it is difficult to effectively transition from the cemented carbide layer to the diamond layer. The residual stress of the cubic boron nitride composite piece prepared in Example 1 and the composite piece in the present comparative example are tested under the same working conditions, and it is found that the residual stress value of the composite piece prepared in Comparative Example 1 is 659 GPa, which is much larger than that of the cubic boron nitride composite piece prepared in Example 1. Moreover, under the same drilling conditions, the cubic boron nitride layer of the composite piece in the present comparative example is more likely to fall off and be scrapped.

[0103] Comparative Example 2

[0104] The other conditions are the same as those in Example 2, but the binder formulation is: 10% ethylene-vinyl acetate copolymer, 15% polystyrene, 15% polyurethane, 30% hydrogenated styrene-butadiene block copolymer, 10% dioctyl phthalate, 10% vinyl bis stearamide and 10% stearic acid. Due to the low content of ethylene-vinyl acetate copolymer and the high content of other additives in the binder, the mixture is a sparse solid-liquid mixture during the mixing process, and it is impossible to obtain a usable printing filament by extruding through the drawing machine.

[0105] Comparative Example 3

[0106] The other conditions are the same as those in Example 3, but the heating rate during the debinding process is 10℃ / min. However, due to the too fast heating rate, the volatilization rate of the binder is too fast, which causes a large amount of gas to accumulate in the green body, and the increased gas pressure causes the green body to produce defects such as bubbling or cracking. The debinding green body with defects is used for synthesis, and the obtained cubic boron nitride composite piece has obvious cracks on the surface and uneven material distribution problems.

[0107] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a gradient structure cubic boron nitride composite sheet, characterized by: CBN powder is mixed with a binder to obtain a CBN mixture; CBN powder, Co powder, and WC powder are respectively mixed with a binder according to the designed components of each gradient layer to obtain N groups of gradient layer mixtures; the prepared CBN mixture and the N groups of gradient layer mixtures are respectively mixed, granulated, and drawn to obtain N+1 groups of filaments; the N+1 groups of filaments are printed using a 3D printer to obtain N+1 groups of green compacts; the N+1 groups of green compacts are assembled with a cemented carbide substrate to obtain a composite green compact; the composite green compacts are degreased and subjected to high temperature and high pressure synthesis to obtain gradient structure cubic boron nitride composite sheets; The binder in the CBN mixture and the N-group gradient layer mixture is composed of the following by mass percentage: 20-70% ethylene-vinyl acetate copolymer, 5-35% polystyrene, 5-35% polyurethane, 1-8% hydrogenated styrene-butadiene block copolymer, 1-7% dioctyl phthalate, 1-6% vinyl bisstearamide, and 1-6% stearic acid; The gradient structured cubic boron nitride composite sheet consists, from bottom to top, of a cemented carbide substrate, a gradient transition layer, and a CBN layer. The gradient transition layer consists of N gradient layers, where N is 4 to 18, and from bottom to top, they are the first gradient layer, the second gradient layer, and so on to the Nth gradient layer. Any layer in the gradient layer is composed of CBN and cemented carbide, wherein the volume fraction of the cemented carbide in the Nth layer is 5 to 30% less than the volume fraction of the cemented carbide in the N-1th layer, and the volume fraction of the CBN in the Nth layer is 5 to 30% more than the volume fraction of the CBN in the N-1th layer.

2. The method for preparing a gradient structure cubic boron nitride composite sheet according to claim 1, wherein: The particle size of the CBN powder is 1 to 100 μm, and the particle size of the Co powder and the WC powder is ≤ 100 μm; In the CBN mixture, the mass ratio of CBN powder to binder is 2-20:1; In any set of gradient layer mixtures, the mass ratio of the total mass of CBN powder, Co powder, and WC powder to the binder is 2~20:

1.

3. The method for preparing a gradient structure cubic boron nitride composite sheet according to claim 1, wherein: The mixing temperature is 100-300°C, and the wire drawing speed is 10 rpm-200 rpm; The diameters of the N+1 groups of filamentous materials are all between 1.65 mm and 1.85 mm.

4. The method for preparing a gradient structure cubic boron nitride composite sheet according to claim 1, wherein: During the 3D printing process, the printing speed is 10-300 mm / s, the printing layer thickness is 0.01 mm-0.5 mm, and the printing temperature is 100-350°C.

5. The method for preparing a gradient structure cubic boron nitride composite sheet according to claim 1, wherein: The composite green body is first placed in a cyclohexane solution for solvent degreasing, and then subjected to thermal degreasing in a vacuum environment; The solvent degreasing temperature is 40°C to 80°C, and the solvent degreasing time is 2 to 6 hours; The thermal degreasing process is as follows: first, heating from room temperature to 80°C to 120°C at a heating rate of 4°C / min, and keeping warm for 0.5 to 1 hour; then heating to 230°C to 270°C at a heating rate of 3°C / min, and keeping warm for 2 to 2.5 hours; then heating to 380°C to 420°C at a heating rate of 2.5°C / min, and keeping warm for 1 to 1.5 hours; finally, heating to 580°C to 620°C at a heating rate of 2°C / min, and keeping warm for 1.5 to 2 hours.

6. The method for preparing a gradient structure cubic boron nitride composite sheet according to claim 1, wherein: The temperature of the high-temperature and high-pressure synthesis is 1400° C. to 2200° C., the synthesis pressure is 3 to 8 GPa, and the synthesis time is 120s to 1000s.

7. The method for preparing a gradient structure cubic boron nitride composite sheet according to claim 1, characterized in that: The cemented carbide in the cemented carbide substrate and the gradient layer is Co-WC, wherein the mass fraction of Co is 3-30%, and the mass fraction of WC is 70-97%.

8. The method for preparing a gradient structure cubic boron nitride composite sheet according to claim 1, characterized in that: The total thickness of the gradient transition layer is 0.04-5 mm, and the thickness of any gradient layer is 0.01-0.5 mm.

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