Co-wc cemented carbide with multilayer gradient structure and preparation method and application thereof

Abstract

The application discloses a Co-WC hard alloy with a multilayer gradient structure and a preparation method and application thereof, the multilayer gradient structure is an N-layer gradient layer structure in which the content of Co increases layer by layer and the content of WC decreases layer by layer from a top layer to a bottom layer, wherein N is greater than 4; each layer in the gradient layer structure is composed of WC and Co; and the volume fraction of WC is greater than that of Co in the top layer. The hard alloy prepared by adopting the process combining 3D printing and powder metallurgy has high hardness, high wear resistance, high toughness and high impact resistance, the gradient structure layer designed can be accurately printed out through the 3D printing process, the thickness of each layer and the powder uniformity are ensured, the performance of the gradient structure hard alloy is optimized, and the production cost of the product is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a Co-WC cemented carbide with a multi-layer gradient structure and a preparation method and application thereof, in particular to a production process combining 3D printing technology and powder metallurgy method, and belongs to the field of cemented carbide manufacturing. BACKGROUND

[0002] Cemented carbide is a kind of cermet tool material prepared by powder metallurgy method, which takes refractory metal compounds (WC, TiC, TaC, NbC, etc.) as hard phase and transition metal (Fe, Co, Ni) as binder phase. It has the advantages of high strength, high hardness, good wear and corrosion resistance, and is widely used in drilling, mining, cutting tools, wear-resistant parts and other fields. With the development of modern science and technology, the market end users have higher and higher requirements on the use cost and efficiency of cemented carbide. Traditional cemented carbide cannot simultaneously have high hardness and high toughness, and cannot meet the development needs of future manufacturing industry. Therefore, it is necessary to develop a gradient structure cemented carbide that meets the requirements of high hardness on the surface and high toughness at the bottom.

[0003] The gradient structure cemented carbide presents a gradient distribution of cobalt in the organizational structure. Since the surface layer has a high WC content, it has high hardness and good wear resistance. The closer to the bottom of the alloy, the higher the cobalt content, and the better the toughness. In the rock drilling process, the cemented carbide can withstand higher loads before being destroyed, and better solves the contradiction between toughness and wear resistance, thereby attracting widespread attention. However, the current preparation of gradient structure cemented carbide is mainly through carburizing method. The popular processes include decarburized alloy carburizing and low-carbon alloy carburizing. However, the two methods have obvious shortcomings. The core technology of decarburization method is the distribution control of η phase, and the process stability and repeatability risk is large. The low-carbon method relies on the precise control of process equipment. Therefore, developing a new method for preparing gradient structure cemented carbide and reducing the cost of the alloy is of great significance for improving the application of gradient cemented carbide and is the development trend of future cemented carbide. SUMMARY

[0004] In view of the problem that the Co-WC cemented carbide in the prior art cannot simultaneously meet the requirements of high hardness and high toughness, the first object of the present application is to provide a Co-WC cemented carbide with a multi-layer gradient structure. The cemented carbide has a multi-layer gradient structure in which the cobalt content increases layer by layer and the WC content decreases layer by layer from the top layer to the bottom layer. Therefore, the alloy has the special properties of high hardness on the surface and high toughness at the bottom.

[0005] The second object of the present application is to provide a preparation method of Co-WC cemented carbide with a multi-layer gradient structure, which adopts the FDM manufacturing process in 3D printing, can optimize product performance, improve production efficiency, effectively control production cost, and accurately control the content of WC and Co in the gradient layer.

[0006] The third object of the present application is to provide an application of Co-WC cemented carbide with a multi-layer gradient structure, which is used as a raw material of a hard carbide ball tooth based on impact load, can fully utilize the special performance of high hardness of the surface layer and high toughness of the bottom layer, effectively break the rock and transmit energy, and prolong the service life of the material while increasing the breaking efficiency.

[0007] In order to achieve the above object, the present application provides a Co-WC cemented carbide with a multi-layer gradient structure, which is an N-layer gradient layer structure with the content of Co increasing layer by layer and the content of WC decreasing layer by layer from the top layer to the bottom layer, wherein N is greater than 4; each layer of the gradient layer structure is composed of WC and Co; the volume fraction of WC in the top layer is greater than the volume fraction of Co.

[0008] The Co-WC cemented carbide of the present application has a gradient layer structure with the content of Co increasing layer by layer and the content of WC decreasing layer by layer from the top layer to the bottom layer, and the volume fraction of WC in the top layer is greater than the volume fraction of Co, so that the YG3 hardness of the top layer of the alloy is very high, so that the rock can be fully broken, and the bottom layer has high toughness, so that it will not be easily broken. At the same time, the gradient layer gradually changes in a way that the number of layers is greater than 4, which can ensure that the load is evenly transmitted during application, improve the impact energy buffering effect, and not produce sudden changes.

[0009] As a preferred scheme, n is 4-18. Compared with the prior art, the Co-WC cemented carbide of the present application has a higher number of gradient layers, which is mainly because the thickness of each layer in the gradient layer of the Co-WC cemented carbide of the present application is relatively thin, so that multi-layer densification can be performed by combining debinding and sintering and hot isostatic pressing sintering, thereby maintaining the continuity and uniformity of impact load transmission and not producing sudden changes. The inventors found that if n is too small, the impact load cannot be effectively buffered, and the material is easily broken.

[0010] As a preferred scheme, the thickness of each layer in the gradient layer structure is greater than or equal to 0.05 mm, and the total thickness of the multi-layer gradient structure is 0.2-20 mm. The total thickness of the multi-layer gradient structure of the Co-WC cemented carbide prepared in the application is controlled between the thicknesses of traditional tools, but the Co-WC cemented carbide needs to maintain good wear resistance and impact resistance at the same time, so the thickness of each layer in the gradient layer structure needs to be controlled. If the thickness of the gradient layer structure is too small, in application, the YG3 hardness of the top layer of the alloy for crushing rocks is reduced and the cushioning ability of the bottom layer is also reduced, which can greatly reduce the effect. If the thickness of each layer in the gradient layer structure is too high, on the one hand, the number of gradient layers is limited, which leads to a decrease in the cushioning performance; on the other hand, it can cause difficulties in subsequent debinding, sintering and hot isostatic pressing processes, which leads to a decrease in the interfacial bonding force of the gradient layers.

[0011] The application also provides a preparation method of a Co-WC cemented carbide with a multi-layer gradient structure, which comprises the following steps: mixing and preparing N groups of mixtures with different WC and Co contents according to the designed proportions of WC powder, Co powder and binder; subjecting the N groups of mixtures to compounding, granulation and wire drawing to obtain N groups of wire-shaped materials; forming N groups of green bodies by 3D printing; and subjecting the green bodies to debinding and hot isostatic pressing and sintering treatment.

[0012] In the preparation method of the application, the wire-shaped material is first prepared, and then melt extrusion molding is performed, which can fully ensure the uniformity of the material extruded from the nozzle. By combining the 3D printing process and powder metallurgy, the designed gradient structure layer can be precisely printed, and the thickness of the gradient layer can be precisely controlled.

[0013] The inventors found that the gradient layer of Co-WC with extremely thin thickness and uniform composition can be printed by combining the 3D printing technology, and the thinnest thickness is only 0.05 mm. The uniformity of the material cannot be controlled at this thickness by the traditional powder laying process. Therefore, in the application, the number of gradient layers can be as large as possible under the condition of ensuring the total thickness of the cemented carbide, so as to realize the slow change of the Co powder content, reduce the bonding difficulty between the gradient layers, and further improve the performance of the Co-WC cemented carbide.

[0014] As a preferred scheme, the volume fraction ratio of the WC powder and the Co powder is (70-97%):(3-30%); further preferably, the volume fraction ratio of the WC powder and the Co powder is (80-97%):(3-20%). In the cemented carbide of the application, WC is the hard phase, and Co is the binder phase. Within the scope of the application, the higher the content of WC, the higher the hardness of the alloy, and the higher the content of Co, the higher the toughness of the alloy.

[0015] As a preferred solution, the total mass of the WC powder and the Co powder and the mass of the binder are in a ratio of (4-8):1.

[0016] As a preferred solution, the average particle size of the WC powder is 0.8-1.8 μm, and the average particle size of the Co powder is 0.5-1.0 μm. If the particle size of the WC and the Co is too large, the slurry cannot be printed due to serious agglomeration during the preparation of the slurry. Further preferably, the average particle size of the WC powder is 0.8-1.6 μm, and the average particle size of the Co powder is 0.8-1.0 μm.

[0017] As a preferred solution, the binder consists of the following components in terms of mass percentage: polyformaldehyde 25-75%, polyvinyl chloride 10-35%, polyurethane 5-35%, hydrogenated styrene-butadiene block copolymer 1-10%, dioctyl phthalate 1-10%, vinyl bis stearamide 1-5%, and paraffin 1-5%.

[0018] As a preferred solution, the mixing conditions are as follows: temperature 100-300 °C, and time 1-2 h.

[0019] As a preferred solution, the drawing process is as follows: the granular material is placed into an extrusion drawing machine, the drawing temperature is set to 100-300 °C, the rotation speed is set to 10-300 rpm, and the drawing is performed to obtain N groups of silk-like materials with different component proportions, the diameter of the silk-like material is 1-2 mm, and the drawing and winding are completed on a traction machine. Further preferably, the diameter of the silk-like material is 1.55-1.95 mm.

[0020] As a preferred solution, the parameters of the 3D printing are as follows: printing speed 10-300 mm / s, printing layer thickness 0.05-0.3 mm, printing temperature 100-350 °C, and nozzle temperature 100-240 °C.

[0021] As a preferred solution, the 3D printing is performed using a fused deposition modeling printer.

[0022] As a preferred scheme, the defatting process adopts stepwise temperature rising and holding defatting in a defatting furnace with hydrogen, and the steps are as follows: rising from room temperature to 80-120 DEG C at a temperature rising rate of 4-6 DEG C / min, holding for 0.5-1 h; then rising to 230-270 DEG C at a temperature rising rate of 3-4 DEG C / min, holding for 2-2.5 h; then rising to 380-420 DEG C at a temperature rising rate of 2.5-4 DEG C / min, holding for 1-1.5 h; finally rising to 580-620 DEG C at a temperature rising rate of 2-2.5 DEG C / min, holding for 1.5-2 h. The stepwise temperature rising and holding defatting in the heat defatting process of the application is mainly based on the difference of pyrolysis temperature ranges of different components of the binder to carry out stepwise defatting, which can effectively ensure the integrity of the green body and the removal effect of the binder in the green body, and avoid producing defatting defects.

[0023] As a preferred scheme, the conditions of the hot isostatic pressing assembly sintering are as follows: the temperature is 1300-1500 DEG C, the sintering time is 30-90 min, argon is used as the pressure medium, the pressing pressure is 1-15 MPa, and the pressing time is 30-60 min. The hot isostatic pressing sintering process of the application can maximize the elimination of internal residual pores, improve the alloy performance, and can correct the carbon content of the alloy and eliminate the eta phase in the alloy organization by adjusting the atmosphere in the furnace.

[0024] The inventors find that the multi-layer Co-WC hard alloy with different contents designed in the application can be tightly combined and form a dense alloy through the defatting and hot isostatic pressing assembly sintering process.

[0025] The application provides a preparation method of a Co-WC hard alloy with a multi-layer gradient structure, and specifically comprises the following steps:

[0026] 1) batching: the multi-layer gradient structure hard alloy is composed of WC powder, Co powder and other raw materials, and special binders and the like, and the mass ratio of the total mass of the raw materials to the mass of the special binder is (4-8):1; wherein the volume fraction of the WC powder in the raw materials is 70-97%, the volume fraction of the Co powder is 3-30%, and the multi-component batching ratio of WC, Co and the binder and the like is designed;

[0027] 2) mixing: the WC powder and the Co powder are mixed, then placed in a mixer and the special binder is added for stirring, and after uniform stirring, a mixture is obtained, and N groups of mixtures with different component ratios are prepared by the same method;

[0028] 3) closed mixing: the N groups of mixtures are respectively placed in a closed mixer, and the speed, temperature, time and other parameters are set for closed mixing;

[0029] 4) Granulation: the prepared mixing material is placed into a granulator, and parameters such as granulation temperature and rotating speed are set to perform granulation, so that N groups of granules with different component proportions are obtained;

[0030] 5) Wire drawing: the prepared granules are placed into an extrusion wire drawing machine, and parameters such as temperature and rotating speed are set to perform wire drawing, so that N groups of wire-shaped materials with a diameter of 1-2 mm are obtained, and the materials are collected on a traction machine;

[0031] 6) Model establishment: a 3D model of the multi-layer gradient structure of the hard alloy is established in a computer, the model is imported into a slicing software to perform slicing setting, printing parameter setting and printing support setting, and the final slicing file is imported into an FDM molding 3D printer;

[0032] 7) Printing of green body: the printing material is connected with a feeding system of the FDM molding 3D printer, and printing is started according to the set printing parameters, i.e., a printing layer thickness of 0.05 mm or above and a nozzle temperature of 100-240 DEG C, so that N groups of green bodies with different component proportions are obtained;

[0033] 8) Degreasing: the obtained green body is placed in a degreasing furnace, and hydrogen reduction degreasing is performed by setting parameters such as heating speed, holding temperature and holding time;

[0034] 9) Assembly and sintering: according to the designed layer number and sequence, the degreased thin sheets are sequentially assembled in a sintering mold from the surface layer to the bottom layer, and then the mold is placed in a vacuum sintering hot isostatic pressing furnace to start heating to 1300-1500 DEG C and holding sintering for 30-90 min, and then hot isostatic pressing is performed in the same furnace, argon is used as a pressure medium, the pressing pressure is about 1-15 MPa, and the time is 30-60 min, so that the gradient structure hard alloy is prepared.

[0035] The application also provides an application of the Co-WC hard alloy with the multi-layer gradient structure, which is used as a raw material of a hard alloy ball tooth based on impact load, can fully utilize the special performance of high hardness of the surface layer and high toughness of the bottom layer, effectively crushes rocks and transmits energy, and prolongs the service life of the material while increasing the crushing efficiency.

[0036] Compared with the prior art, the application has the following beneficial effects:

[0037] 1) The Co-WC hard alloy with the gradient structure provided by the application has a multi-layer gradient structure in which the content of cobalt gradually increases from the top layer to the bottom layer, and the content of WC gradually decreases, the component gradient change is utilized to endow different parts of the hard alloy with different performances, the problem that the traditional hard alloy is difficult to simultaneously satisfy high hardness and high toughness is effectively solved, and a "double-high" alloy with high hardness of the surface layer and high toughness of the bottom layer is prepared.

[0038] 2) The present application adopts a fused deposition modeling (FDM) 3D printing process to manufacture a gradient structure cemented carbide green body, which can accurately print the designed gradient structure layer, and the printed filament material is uniform in composition, thereby ensuring that each gradient layer printed is uniform in composition, and the printing process can accurately control the layer thickness, ensure the uniformity of each layer thickness and powder, optimize the performance of the gradient structure cemented carbide, and at the same time, can improve the production efficiency and reduce the production cost.

[0039] 3) The Co-WC cemented carbide with a gradient structure has a high hardness of the surface layer and high toughness of the bottom, and is especially suitable for being used as a raw material for preparing drilling tools, which can significantly improve the drilling efficiency of the drilling tools and prolong the service life thereof. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A schematic diagram of the Co-WC cemented carbide with 8 gradient layers prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0041] In order to make the content of the present application more easily understood, the present application will be further described in detail according to the specific embodiments.

[0042] Example 1

[0043] The raw materials used are WC powder, Co powder and special binder, wherein the average particle size of the WC powder is 1.0 μm, the average particle size of the Co powder is 1.0 μm, and the special binder is composed of polyformaldehyde 60 wt%, polyvinyl chloride 15 wt%, polyurethane 10 wt%, hydrogenated styrene-butadiene block copolymer 5 wt%, dioctyl phthalate 5 wt%, vinyl bis-stearamide 3 wt%, and paraffin 2 wt%.

[0044] A 4-layer composition gradient layer composed of WC powder and Co powder is designed, the total layer thickness is 2.0 mm, and the thickness of each layer is 0.50 mm, and the powder content of the gradient layer is sequentially from the top layer to the bottom layer as follows:

[0045] The WC powder content of the first layer is 95 vol%, and the Co powder content is 5 vol%;

[0046] The WC powder content of the second layer is 90 vol%, and the Co powder content is 10 vol%;

[0047] The WC powder content of the third layer is 85 vol%, and the Co powder content is 15 vol%;

[0048] The WC powder content of the fourth layer is 80 vol%, and the Co powder content is 20 vol%;

[0049] The embodiment provides a 3D printing manufacturing process of the Co-WC hard alloy with a gradient structure, and steps are as follows:

[0050] 1) batching: the multi-layer gradient structure hard alloy is composed of WC powder, Co powder raw materials and special binders, and the mass ratio of the raw materials and the special binders is 8:1; the WC, Co and binder are proportioned according to the above-mentioned 4-layer proportioning design, and 4 groups of component batching ratios are obtained;

[0051] 2) mixing: the WC powder and the Co powder are mixed, then are placed in a mixer and the corresponding special binders are added for stirring, and after uniform stirring, a mixed material is obtained, and 4 groups of mixed materials with different component proportions are obtained by the same method;

[0052] 3) dense mixing: the 4 groups of mixed materials are respectively placed in a dense mixer, and parameters such as speed, temperature and time are set for dense mixing; wherein the dense mixing temperature is 195 DEG C, and the dense mixing time is 70 min;

[0053] 4) granulation: the prepared dense mixing material is placed in a granulator, and parameters such as granulation temperature and speed are set for granulation, and 4 groups of granular materials with different component proportions are obtained; wherein the granulation temperature is 150 DEG C, and the speed of the granulator is 55 rpm;

[0054] 5) wire drawing: the prepared granular material is placed in an extrusion wire drawing machine, and parameters such as temperature and speed are set for wire drawing, the wire drawing temperature is 225 DEG C, the speed of the wire drawing machine is 45 rpm, 4 groups of wire-shaped materials with different component proportions and a diameter of 1.80 mm are obtained, and traction and winding are completed on a traction machine;

[0055] 6) model establishment: a 3D model of the multi-layer gradient structure hard alloy is established in a computer, the model is imported into a slicing software for slicing setting, printing parameter setting and printing support setting, and the final slicing file is imported into an FDM molding 3D printer;

[0056] 7) printing of green body: the printing material is connected with a feeding system of the FDM molding 3D printer, and according to the set printing parameters, that is, the printing layer thickness is 0.3 mm, the nozzle temperature is 230 DEG C, the printing speed is 50 mm / s, and the printing temperature is 110 DEG C, the printing is started, and the printing is completed to obtain 4 groups of green bodies with different component proportions;

[0057] 8) debinding: the green body obtained by printing is placed in a debinding furnace, first heated from room temperature to 120 DEG C at a heating rate of 6 DEG C / min, kept for 0.5 h, then heated to 270 DEG C at a heating rate of 4 DEG C / min, kept for 2 h, then heated to 420 DEG C at a heating rate of 3 DEG C / min, kept for 1 h, and finally heated to 620 DEG C at a heating rate of 2 DEG C / min, kept for 2 h;

[0058] 9) Assembly sintering: according to the designed layer number and sequence, the defatted thin slices are assembled in the sintering mold from the top layer to the bottom layer, and then put into a vacuum sintering hot isostatic pressing furnace to start heating to 1370℃ and pressurizing for 1h, and then hot isostatic pressing is carried out in the same furnace, argon is used as the pressure medium, the pressing pressure is about 6MPa, and the time is 30min. After sintering, the furnace is cooled to prepare the gradient structure cemented carbide.

[0059] After the gradient structure cemented carbide with multiple layers is prepared, its performance is tested. The impact resistance of the cemented carbide sample is measured by a pendulum impact tester, and the impact toughness is 10.1J / cm 2 , which is increased by 15% to 30% compared with the impact toughness of traditional cemented carbide; the bending strength is measured by a three-point bending method, and the bending strength is 4050MPa, which is significantly improved; the hardness of the cemented carbide is measured by a Vickers hardness tester, and the Vickers hardness is 1723HV, which is also increased compared with the traditional method. The above data shows that the gradient structure cemented carbide prepared by the present application has good high hardness and high toughness performance.

[0060] Example 2

[0061] The raw materials used are WC powder and Co powder and special binder, wherein the particle size of the WC powder is 1.0μm, the particle size of the Co powder is 1.0μm, and the special binder contains: polyformaldehyde 55wt%, polyvinyl chloride 20wt%, polyurethane 5wt%, hydrogenated styrene-butadiene block copolymer 10wt%, dioctyl phthalate 6wt%, vinyl bis stearamide 2wt%, and paraffin wax 2wt%.

[0062] A gradient layer composed of 8 layers of WC powder and Co powder is designed, and the total layer thickness is 2.40mm, and the thickness of each layer is 0.30mm, as shown in Figure 1 The powder content of the gradient layer from the top layer to the bottom layer is:

[0063] The first layer contains 97vol% of WC powder and 3vol% of Co powder;

[0064] The second layer contains 95vol% of WC powder and 5vol% of Co powder;

[0065] The third layer contains 93vol% of WC powder and 7vol% of Co powder;

[0066] The fourth layer contains 91vol% of WC powder and 9vol% of Co powder;

[0067] The fifth layer contains 89vol% of WC powder and 11vol% of Co powder;

[0068] The 6th layer WC powder content is 87 vol%, and the Co powder content is 13 vol%;

[0069] The 7th layer WC powder content is 85 vol%, and the Co powder content is 15 vol%;

[0070] The 8th layer WC powder content is 83 vol%, and the Co powder content is 17 vol%;

[0071] The 3D printing process of the Co-WC cemented carbide with gradient structure provided by the present example is as follows:

[0072] 1) batching: the multi-layer gradient structure cemented carbide is composed of WC powder, Co powder raw materials and special binder, and the mass ratio of the raw materials and the special binder is 4:1; 8 groups of ingredient batching ratios with different proportions of WC, Co and binder are designed according to the above 8-layer proportioning design;

[0073] 2) mixing: mix the WC powder and the Co powder, then place them in a mixer and add the corresponding special binder for stirring, and obtain a mixture after uniform stirring, and 8 groups of mixtures with different ingredient proportions are prepared by the same method;

[0074] 3) dense mixing: put the 8 groups of mixtures into a dense mixer, and set the rotation speed, temperature, time and other parameters for dense mixing; the dense mixing temperature is 200°C, and the dense mixing time is 80 min;

[0075] 4) granulation: place the prepared dense mixing material into a granulator, and set the granulation temperature, rotation speed and other parameters for granulation to obtain 8 groups of granular materials with different ingredient proportions; the granulation temperature is 135°C, and the rotation speed of the granulator is 30 rpm;

[0076] 5) wire drawing: place the prepared granular material into an extrusion wire drawing machine, and set the temperature, rotation speed and other parameters for wire drawing; the wire drawing temperature is 205°C, the rotation speed of the wire drawing machine is 40 rpm, 8 groups of wire-shaped materials with a diameter of 1.80 mm and different ingredient proportions are obtained, and the traction is completed on the traction machine;

[0077] 6) model establishment: establish a 3D model of the multi-layer gradient structure cemented carbide in a computer, import the model into a slicing software for slicing setting, printing parameter setting and printing support setting, and import the final slicing file into an FDM modeling 3D printer;

[0078] 7) printing green body: connect the printing material with the feeding system of the FDM modeling 3D printer, and start printing according to the set printing parameters, i.e. printing layer thickness 0.3 mm, nozzle temperature 220°C, printing speed 50 mm / s, and printing temperature 110°C, to obtain 8 groups of green bodies with different ingredient proportions;

[0079] 8) Degreasing: the green body obtained by printing is placed in a degreasing furnace, first heated from room temperature to 120℃ at a heating rate of 6℃ / min, kept for 0.5h; then heated to 270℃ at a heating rate of 4℃ / min, kept for 2h; then heated to 420℃ at a heating rate of 3℃ / min, kept for 1h; finally heated to 620℃ at a heating rate of 2℃ / min, kept for 2h;

[0080] 9) Assembly and sintering: according to the designed number of layers and sequence, the thin slices after degreasing are assembled in the sintering mold from the top layer to the bottom layer, and then put into a vacuum sintering hot isostatic pressing furnace to start heating to 1370℃ and pressurize and keep for 30min, and then hot isostatic pressing is carried out in the same furnace, using argon as the pressure medium, the pressing pressure is about 6MPa, and the time is 30min. After sintering, the gradient structure cemented carbide is prepared by cooling in the furnace.

[0081] After the gradient structure cemented carbide with multiple layers is prepared, its performance is tested. The impact resistance of the cemented carbide sample is measured by a pendulum impact tester, and the impact toughness is 10.5J / cm 2 , which is 15%-30% higher than that of traditional cemented carbide; the bending strength is measured by a three-point bending method, and the bending strength is 4202MPa, which is significantly improved; the hardness of the cemented carbide is measured by a Vickers hardness tester, and the Vickers hardness is 1843HV, which is also improved compared with the traditional method. The above data shows that the gradient structure cemented carbide prepared by the present application has good high hardness and high toughness performance. Compared with the 4-layer structure in Example 1, the bending strength and Vickers hardness can be further enhanced with the increase of the number of layers in the gradient structure.

[0082] Example 3

[0083] The raw materials used are WC powder and Co powder and special binder, wherein the particle size of the WC powder is 1.0μm, the particle size of the Co powder is 1.0μm, and the special binder comprises: polyformaldehyde 50wt%, polyvinyl chloride 15wt%, polyurethane 15wt%, hydrogenated styrene-butadiene block copolymer 5wt%, dioctyl phthalate 10wt%, vinyl bis stearamide 2wt%, and paraffin wax 3wt%.

[0084] A gradient layer composed of 18 layers of WC powder and Co powder is designed, with a total layer thickness of 1.8mm and a thickness of each layer of 0.10mm, and the powder content of the gradient layer is sequentially from the top layer to the bottom layer:

[0085] The first group of WC powder content is 97vol%, and the Co powder content is 3vol%;

[0086] The second group of WC powder content is 96vol%, and the Co powder content is 4vol%;

[0087] The WC powder content of the 3rd group is 95 vol%, and the Co powder content is 5 vol%;

[0088] The WC powder content of the 4th group is 94 vol%, and the Co powder content is 6 vol%;

[0089] The WC powder content of the 5th group is 93 vol%, and the Co powder content is 7 vol%;

[0090] The WC powder content of the 6th group is 92 vol%, and the Co powder content is 8 vol%;

[0091] The WC powder content of the 7th group is 91 vol%, and the Co powder content is 9 vol%;

[0092] The WC powder content of the 8th group is 90 vol%, and the Co powder content is 10 vol%;

[0093] The WC powder content of the 9th group is 89 vol%, and the Co powder content is 11 vol%;

[0094] The WC powder content of the 10th group is 88 vol%, and the Co powder content is 12 vol%;

[0095] The WC powder content of the 11th group is 87 vol%, and the Co powder content is 13 vol%;

[0096] The WC powder content of the 12th group is 86 vol%, and the Co powder content is 14 vol%;

[0097] The WC powder content of the 13th group is 85 vol%, and the Co powder content is 15 vol%;

[0098] The WC powder content of the 14th group is 84 vol%, and the Co powder content is 16 vol%;

[0099] The WC powder content of the 15th group is 83 vol%, and the Co powder content is 17 vol%;

[0100] The WC powder content of the 16th group is 82 vol%, and the Co powder content is 18 vol%;

[0101] The WC powder content of the 17th group is 81 vol%, and the Co powder content is 19 vol%;

[0102] The WC powder content of the 18th group is 80 vol%, and the Co powder content is 20 vol%.

[0103] The 3D printing manufacturing process of the Co-WC hard alloy with gradient structure provided in the embodiment is as follows:

[0104] 1) batching: the multi-layer gradient structure cemented carbide is composed of WC powder, Co powder raw material and special binder, and the mass ratio of the raw material and the special binder is 6:1; 18 groups of component batching ratios of WC, Co and binder with different proportions are designed according to the above-mentioned 18 layers;

[0105] 2) mixing: the WC powder and the Co powder are mixed, then placed in a mixer and added with the special binder for stirring, and after uniform stirring, a mixed material is obtained, and 18 groups of mixed materials with different component proportions are prepared by the same method;

[0106] 3) density mixing: the 18 groups of mixed materials are respectively placed in a density mixer, and the parameters such as speed, temperature and time are set for density mixing; the density mixing temperature is 190℃, and the density mixing time is 65min;

[0107] 4) granulation: the prepared density mixed material is placed in a granulator, and the parameters such as granulation temperature and speed are set for granulation to obtain 18 groups of granular materials with different component batching ratios; the granulation temperature is 120℃, and the speed of the granulator is 50rpm;

[0108] 5) wire drawing: the prepared granular material is placed in an extrusion wire drawing machine, and the parameters such as temperature and speed are set for wire drawing, the wire drawing temperature is 200℃, the speed of the wire drawing machine is 35rpm, 18 groups of wire-shaped materials with a diameter of 1.75mm and different component batching ratios are obtained, and traction and winding are completed on a traction machine;

[0109] 6) model establishment: a 3D model of the multi-layer gradient structure cemented carbide is established in a computer, the model is imported into a slicing software for slicing setting, printing parameter setting and printing support setting, and the final slicing file is imported into an FDM modeling 3D printer;

[0110] 7) printing of green body: the printing material is connected with the feeding system of the FDM modeling 3D printer, and according to the set printing parameters, i.e. printing layer thickness 0.1mm, nozzle temperature 225℃, printing speed 50mm / s and printing temperature 110℃, printing is started, and 18 groups of green bodies with different component batching ratios are obtained after printing and forming;

[0111] 8) debinding: the printed green body is placed in a debinding furnace, first heated from room temperature to 120℃ at a heating rate of 6℃ / min, kept for 0.5h; then heated to 270℃ at a heating rate of 4℃ / min, kept for 2h; then heated to 420℃ at a heating rate of 3℃ / min, kept for 1h; finally heated to 620℃ at a heating rate of 2℃ / min, kept for 2h;

[0112] 9) Assembly sintering: according to the designed layer number and sequence, the defatted thin slices are assembled in the sintering mold from the top layer to the bottom layer, and then put into a vacuum sintering hot isostatic pressing furnace to start heating to 1370℃ and pressurizing for 30min, and then hot isostatic pressing is carried out in the same furnace, argon is used as the pressure medium, the pressing pressure is about 6MPa, and the time is 60min. After sintering, the gradient structure cemented carbide is prepared by furnace cooling.

[0113] After the gradient structure cemented carbide with multiple layers is prepared, its performance is tested. The impact resistance of the cemented carbide sample is measured by a pendulum impact tester, and the impact toughness is 10.9J / cm 2 , which is 15%-30% higher than that of the traditional cemented carbide; the bending strength is measured by a three-point bending method, and the bending strength is 4317MPa, which is significantly improved; the hardness of the cemented carbide is measured by a Vickers hardness tester, and the Vickers hardness is 1888HV, which is also improved compared with the traditional method. The above data shows that the gradient structure cemented carbide prepared by the present application has good performance, and the more the number of gradient layers, the higher the performance.

[0114] Comparative Example 1

[0115] The other conditions are the same as those in Example 1, and only three layers of gradient cemented carbide are designed. The top layer is WC powder with a content of 97vol%, Co powder with a content of 3vol%, the middle layer is WC powder with a content of 90vol%, Co powder with a content of 10vol%, and the bottom layer is WC powder with a content of 80vol%, Co powder with a content of 20vol%. Due to the small number of gradient layers, the impact load cannot be effectively buffered and transmitted. The impact toughness of the gradient cemented carbide prepared in Example 1 and the gradient cemented carbide in this comparative example is tested under the same working conditions, and the result shows that the impact toughness of the gradient cemented carbide prepared in Comparative Example 1 is 8.0J / cm 2 , which is much smaller than that of the gradient cemented carbide prepared in Example 1.

[0116] Comparative Example 2

[0117] The impact resistance of the YG3 cemented carbide (i.e. without gradient layer structure) drill bit is measured by a pendulum impact tester, and the impact toughness is 8.2J / cm 2 ; the bending strength is measured by a three-point bending method, and the bending strength is 1200MPa; the hardness is measured to be 91.0HRA (equivalent to Vickers hardness of 1300HV); and compared with the traditional YG3 cemented carbide drill bit, the performance indicators of the gradient cemented carbide drill bit are improved.

[0118] Comparative Example 3

[0119] Other conditions are same with example 3, but design a gradient cemented carbide with total layer thickness of 27mm and each gradient layer thickness of 1.5mm. Because the gradient layer is thicker, the effect of impact load transmission is not good, and the force mutation is produced. The impact toughness of the gradient cemented carbide prepared in example 3 and the gradient cemented carbide in the comparative example 3 is tested under the same working condition, and the result shows that the impact toughness of the gradient cemented carbide prepared in comparative example 3 is 6.8J / cm 2 , which is far less than that of the gradient cemented carbide prepared in example 3. The too thick gradient layer is easy to cause the loss of the advantage of the gradient gradual transmission of impact load, and it is difficult to well ensure the density of the too thick gradient layer in the sintering process, and the strength loss problem may occur in the combined part.

Claims

1. A Co-WC cemented carbide with a multilayer gradient structure, characterized in that: The multilayer gradient structure is an N-layer gradient layer structure in which the Co content increases layer by layer and the WC content decreases layer by layer from the top layer to the bottom layer, wherein N is 4-18; each layer of the gradient layer structure is composed of WC and Co; The volume fraction of WC in the top layer is greater than the volume fraction of Co; the thickness of each layer of the gradient layer structure is greater than or equal to 0.05 mm, and the total thickness of the multilayer gradient structure is 0.2-20 mm; The preparation process of the Co-WC cemented carbide is as follows: WC powder, Co powder and a binder are mixed and prepared into N groups of mixed materials with different WC and Co contents according to the designed proportions; the N groups of mixed materials are subjected to compounding, granulation and wire drawing respectively to obtain N groups of wire-shaped materials; The N groups of wire-shaped materials are subjected to 3D printing to form N groups of green bodies; The green bodies are subjected to debinding and hot isostatic pressing assembly sintering treatment to obtain the Co-WC cemented carbide; The binder is composed of the following components in terms of mass percentage: polyformaldehyde 25-75%, polyvinyl chloride 10-35%, polyurethane 5-35%, hydrogenated styrene-butadiene block copolymer 1-10%, dioctyl phthalate 1-10%, vinyl bis stearamide 1-5% and paraffin 1-5%; The Co-WC cemented carbide is used as a raw material for hard alloy ball teeth based on impact load; The volume fraction ratio of the WC powder to the Co powder is (70-97%):(3-30%).

2. A method of producing a Co-WC cemented carbide with a multilayer gradient structure according to claim 1, characterized in that: The WC powder, Co powder and a binder are mixed and prepared into N groups of mixed materials with different WC and Co contents according to the designed proportions; the N groups of mixed materials are subjected to compounding, granulation and wire drawing respectively to obtain N groups of wire-shaped materials; the N groups of wire-shaped materials are subjected to 3D printing to form N groups of green bodies; The green bodies are subjected to debinding and hot isostatic pressing assembly sintering treatment to obtain the Co-WC cemented carbide; The binder is composed of the following components in terms of mass percentage: polyformaldehyde 25-75%, polyvinyl chloride 10-35%, polyurethane 5-35%, hydrogenated styrene-butadiene block copolymer 1-10%, dioctyl phthalate 1-10%, vinyl bis stearamide 1-5% and paraffin 1-5%.

3. The preparation method of the Co-WC cemented carbide with a multilayer gradient structure according to claim 2, characterized in that: The mass ratio of the total mass of the WC powder and the Co powder to the mass of the binder is (4-8):1; The average particle size of the WC powder is 0.8-1.8 μm, and the average particle size of the Co powder is 0.5-1.0 μm.

4. The preparation method of the Co-WC cemented carbide with a multilayer gradient structure according to claim 2, characterized in that: The compounding conditions are as follows: the temperature is 100-300 ℃, and the time is 1-2 h.

5. The method of claim 2, wherein the Co-WC cemented carbide with a multi-layer gradient structure is prepared by the steps of: The specific process of the wire drawing is as follows: the granular material is placed into an extrusion wire drawing machine, the temperature of the wire drawing is set to 100-300 ℃, the rotating speed is set to 10-300 rpm, the wire-shaped material with a diameter of 1-2 mm and different component proportions is obtained by wire drawing, and the traction is completed on a traction machine. ​ 6. A method of producing a Co-WC cemented carbide with a multilayer gradient structure according to any one of claims 2-5, c h a ra cte ri zed i n that: The parameters of the 3D printing are as follows: printing speed is 10-300 mm / s, printing layer thickness is 0.05-0.3 mm, printing temperature is 100-350 DEG C, and nozzle temperature is 100-240 DEG C.

7. A method of producing a Co-WC cemented carbide with a multilayer gradient structure according to claim 6, characterized in that: The debinding process is carried out in a debinding furnace with hydrogen, and the process is as follows: heating from room temperature to 80-120 DEG C at a heating rate of 4-6 DEG C / min, and keeping the temperature for 0.5-1 h; then heating to 230-270 DEG C at a heating rate of 3-4 DEG C / min, and keeping the temperature for 2-2.5 h; then heating to 380-420 DEG C at a heating rate of 2.5-4 DEG C / min, and keeping the temperature for 1-1.5 h; finally heating to 580-620 DEG C at a heating rate of 2-2.5 DEG C / min, and keeping the temperature for 1.5-2 h.

8. A method of producing a Co-WC cemented carbide with a multilayer gradient structure according to claim 7, characterized in that: The conditions of the hot isostatic pressing assembly sintering are as follows: temperature is 1300-1500 DEG C, sintering time is 30-90 min, argon is used as pressure medium, pressing pressure is 1-15 MPa, and pressing time is 30-60 min.

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