A nickel-copper-based diamond composite material, its electron beam additive manufacturing process and applications

Abstract

The present invention discloses a nickel-copper-based diamond composite material, an electron beam additive manufacturing process thereof, and an application thereof. The method is to mix nickel-copper-based binder phase powder and diamond powder and then form them by a powder bed powder spreading type electron beam additive manufacturing process, thus obtaining the product. The present invention expands the preparation method of diamond composite materials, realizes the near-net shaping of diamond composite materials, reduces the subsequent processing cost of diamond composite materials, and shortens the production cycle. At the same time, this method has high process stability and is suitable for the rapid and stable preparation of diamond tools such as drilling tools, grinding tools, and work molds with specific complex configurations.

Description

Technical Field

[0001] The present invention relates to a diamond composite material, a preparation method and an application thereof, and particularly relates to a nickel-copper-based diamond composite material, an electron beam additive manufacturing process and an application thereof, belonging to the field of composite material preparation. Background Art

[0002] Metal-based diamond composite materials have been widely used in the fields of drilling tools, grinding tools, industrial dies, etc. The literature "Matrix material for a new 3D-printed diamond-impregnated bit with grid-shaped matrix" (International Journal of Refractory Metals & Hard Materials, 2019, 82: 199-207) and the literature "Perspectives of metal-diamond composites additive manufacturing using SLM-SPS and other techniques for increased wear-impact resistance" (International Journal of Refractory Metals & Hard Materials, 2020, 88: 105192) both put forward different complex structure design ideas for metal-based diamond composite materials. These diamond composite materials with complex configurations are difficult to be machined into the required specific shapes by subtractive manufacturing such as cutting or grinding, while additive manufacturing for preparing metal-based diamond composite materials has the advantage of near-net shaping, and can realize the integrated structure-function preparation of diamond tools with complex configurations.

[0003] Currently, the additive manufacturing processes used to prepare diamond composites mainly employ lasers as the energy source. However, due to the high reflectivity of copper-based diamond composites to lasers, and the fact that the laser additive manufacturing process cannot achieve the steps of substrate preheating and powder bed pre-sintering, serious cracking phenomena are prone to occur in a series of brittle materials such as metal-based diamond composites prepared, which restricts the industrial feasibility of using the laser additive manufacturing process for the preparation of metal-based diamond composites. The review "Research Progress on the Anti-Cracking Behavior of Laser Additive Manufacturing of Superalloys" (2022, 33: 26-42) summarized the causes and characteristics of three typical cracks, namely liquefaction cracks, solidification cracks, and solid-state cracks, that occur in laser additive manufacturing, and proposed corresponding anti-cracking ideas and strategies. However, there are still great challenges in truly achieving stable anti-cracking forming in industrial production by adopting these strategies. The literature "Quantitative investigation of thermal evolution and graphitisation of diamond abrasives in powder bed fusion-laser beam of metal-matrix diamond composites" (Virtual and Physical Prototyping, 18: 1, e2121224) prepared metal-based diamond composites using the laser additive manufacturing process. However, the reported density of the composites was extremely low (below 90%), and there were still cracks and spalling phenomena in the microstructural images of the samples with better formability selected and presented by the authors, which indicates that the laser additive manufacturing process is not applicable to the forming of metal-based diamond composites to a certain extent. Moreover, the energy of the laser beam is low, and it can only melt fine powders of 15-53 μm, which may cause dangers such as combustion and explosion in industrial production, and may also be inhaled into the human body causing health damage, presenting many potential safety hazards.

[0004] Therefore, it is urgent to find a new process that can not only effectively inhibit diamond graphitization and cracking but also realize the near-net shaping of brittle diamond materials with complex structures in order to meet the application of nickel-copper-based diamond composites in complex configuration molds. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, the first object of the present invention is to provide a preparation method for nickel-copper-based diamond composites. By utilizing the high-vacuum environment and rapid printing characteristics of the electron beam additive manufacturing process, diamond graphitization can be avoided to a certain extent, thereby obtaining dense nickel-copper-based diamond composites. At the same time, the stable forming of nickel-copper-based diamond composites with complex configurations can be realized through the electron beam additive manufacturing process.

[0006] The second object of the present invention is to provide a nickel - copper - based diamond composite material, which has the advantages of high density, high wear resistance and high toughness.

[0007] The third object of the present invention is to provide an application of a nickel - copper - based diamond composite material prepared by an electron beam additive manufacturing process. The method of the present invention is carried out under normal pressure throughout the process, does not involve dangerous operations such as mechanical ball milling and fine powder transfer, and is suitable for industrial production. After the process optimization of the prepared nickel - copper - based diamond, the simultaneous improvement of toughness and wear resistance is achieved, and it can be used for near - net - shape forming of diamond tools with complex configurations such as drill bits, grinding tools, and industrial molds.

[0008] To achieve the above - mentioned technical objects, the present invention provides a preparation method of a nickel - copper - based diamond composite material, which is obtained by mixing nickel - copper - based binder phase powder and diamond powder and then forming them by a powder bed electron beam additive manufacturing process.

[0009] As a preferred embodiment, the electron beam additive manufacturing process includes: preheating, powder spreading, pre - sintering and forming treatment.

[0010] In the technical solution of the present invention, since the nickel - copper - based binder phase has a high absorption rate for the electron beam, and the electron beam additive manufacturing can realize the steps of substrate preheating and powder bed pre - sintering, reducing the cracking phenomenon of the diamond composite material. Coupled with the fact that the electron beam additive manufacturing has a higher vacuum environment and faster printing characteristics compared with the laser additive manufacturing process, on the one hand, it can effectively avoid the introduction of contamination into the composite material, and on the other hand, it can also avoid the graphitization of diamond to a certain extent, thereby obtaining a dense nickel - copper - based diamond composite material. In addition, compared with the conventional pressure sintering process, the use of the electron beam additive manufacturing process in the present invention can not only reduce the contamination introduced by the mold, but also realize the near - net - shape forming of diamond composite materials with complex configurations, greatly simplifying the process flow.

[0011] As a preferred embodiment, the temperature of the substrate used in the preheating process is 500 - 600 °C. Compared with other technologies, the electron beam additive manufacturing process adopted in the present invention has a wide range and high temperature of substrate preheating, which can reduce the cracking caused by the too - fast solidification speed of the composite material to a certain extent. When the substrate preheating temperature is too high, the nickel - copper alloy powder is severely agglomerated. During the process of spreading powder with a doctor blade, the agglomerated metal powder will affect the uniform spreading of the doctor blade, resulting in the powder being unable to be evenly spread onto the substrate surface. When the substrate preheating temperature is too low, the too - fast cooling speed of the nickel - copper alloy will cause cracks in the composite material, reducing the formability, and there will be a serious powder - blowing phenomenon during the printing process, disturbing the stability of the powder bed, and even clogging the viewing window, generating potential safety hazards.

[0012] As a preferred solution, the conditions for pre-sintering are as follows: the current is 18 - 25 mA, and the time is 4 - 6 s. When the pre-sintering current is too low or the time is too short, during the actual forming process, it will be impossible to maintain the preheating temperature of the substrate continuously within the above suitable range, which will increase the risk of cracking and powder blowing in the subsequent forming process. When the pre-sintering current is too high or the time is too long, it will cause large-area caking of the powder, affecting selective melting and subsequent powder spreading, and restricting the formability of the composite material.

[0013] As a preferred solution, the forming treatment uses an electron beam, where the electron beam current is 1 - 19 mA, and the ratio of the electron beam current value to the electron beam scanning speed value is 1.6 - 4.7. The electron beam additive manufacturing process adopted in the present invention has the characteristics of flexible adjustment of the electron beam current and scanning speed, giving the nickel-copper-based diamond composite material a large forming window. The inventor found that when the current exceeds the range of 1 - 19 mA, obvious instability of the electron beam current will occur, which is not conducive to the stability of the process. When the ratio of the electron beam current value to the scanning speed value is greater than 4.7, the energy density input by the electron beam to the powder bed is too high, and obvious over-melting phenomenon occurs in the nickel-copper-based diamond composite material sample, serious burning loss of diamond, and large macroscopic defects on the surface of the composite material. When the ratio of the electron beam current value to the scanning speed value is less than 1.6, the energy density input by the electron beam is too low, and obvious under-melting phenomenon occurs in the composite material sample, and the metal binder phase and diamond cannot be tightly combined, and even the formability is not available.

[0014] Further preferably, when the ratio of the electron beam current value to the scanning speed value adopted in the nickel-copper-based diamond composite material preparation process is controlled between 2.1 and 3.7, the composite material has better formability and performance. When the ratio of the electron beam current value to the scanning speed value is increased to 2.1, the nickel-copper-based binder phase melts and flows relatively sufficiently and combines well with the diamond. The formed composite material has a macroscopic structure with a relatively flat surface and a relatively uniform microstructure. However, when the ratio of the electron beam current value to the scanning speed value continues to increase above 3.7, graphitization and thermal damage of diamond are found in the scanning electron microscope characterization of the microstructure of the composite material. The inventor found during the research process that when the ratio of the electron beam current value to the scanning speed value is controlled below 3.7, the graphitization phenomenon of diamond can be effectively inhibited.

[0015] Even more preferably, when the ratio of the electron beam current value to the scanning speed value is adjusted between 2.4 and 3, the composite material obtains better comprehensive properties of strength and toughness and wear resistance. This is because the electron beam energy input is sufficient to fully melt the metal binder phase, the interface combination is good, and it can effectively inhibit diamond graphitization and thermal damage, and minimize the generation of defects.

[0016] As a preferred solution, the electron beam scanning direction is parallel to the long side or the short side of the substrate (the substrate is a 120 mm × 120 mm square), and is rotated 90° relative to the scanning direction of the previous layer. The inventors found that the scanning direction and angle of the electron beam also have a certain influence on the surface morphology of the diamond composite material. For example, when the electron beam scanning direction is parallel to the diagonal direction of the substrate, although the macroscopic forming of the diamond composite material can also be achieved, since the length of each scanning path is different from the previous one, it is easy to cause energy to concentrate at the short side (especially the sharp corners) of the composite material, resulting in serious diamond graphitization and thermal damage phenomena. Moreover, the energy concentration causes a small amount of evaporation of the nickel-copper alloy, thus forming an obvious wavy stripe surface structure.

[0017] As a preferred solution, the content of the diamond powder is (10-20) vol.% of the mixed powder of the nickel-copper-based binder phase powder and the diamond powder. When the diamond volume fraction is increased to the above range, the comprehensive properties of the composite material, such as strength, toughness and wear resistance, are better.

[0018] As a preferred solution, the nickel-copper-based binder phase powder is prepared by gas atomization method, and the particle size is 53-150 μm. By the gas atomization method, a large number of spherical powders can be quickly prepared, and the selection of coarser particle size atomized powders helps to further improve the fluidity of the powder to ensure the uniformity during the powder spreading process and improve the safety.

[0019] As a preferred solution, the nickel-copper-based binder phase powder is composed of the following components by mass percentage: Cu 27-28%, Si 3-4%, Mn 0.5-1.5%, B 1.5-2.0%, Cu / (Ni + Cu) is 29-30%, and the balance is Ni. Compared with the traditional copper-based binder phase, the introduction of Ni improves the wettability of the binder phase to diamond and increases the hardness and corrosion resistance of the matrix alloy. The addition of alloying elements Si, Mn, and B reduces the melting point of the binder phase to prevent serious graphitization or burning of diamond caused by the high energy input required during the preparation of the high melting point binder phase. The addition of alloying elements Si and B also helps to further improve the hardness and wear resistance of the matrix alloy to meet the requirements of the diamond tool for the hardness and wear resistance of the binder phase during service. The mass fraction of element B is controlled at 1.5-2.0%, which can further improve the corrosion resistance of the binder phase and meet the requirement of the binder phase having a certain toughness. Under the selected composition ratio of the nickel-copper-based binder phase powder in the present invention, the composite material has low melting point, high corrosion resistance, high hardness and high wear resistance, and can be fully melted to achieve densification of the composite material only by using low energy density electron beam energy input, effectively suppressing diamond graphitization and thermal damage caused by increasing the electron beam energy density.

[0020] As a preferred solution, the particle size of the diamond powder is 75-90 μm. If the diamond particle size is too large, the bonding area between the diamond and the metal bonding phase in the composite material is small, the interfacial bonding force is weak, the diamond is easy to fall off, and the toughness of the composite material is low. However, a smaller diamond particle size inhibits the removal efficiency of the composite material against the counter-material, resulting in poor wear resistance of the composite material. Within this particle size range, it is beneficial to improve the comprehensive properties of toughness and wear resistance of the diamond composite material.

[0021] As a preferred solution, the surface of the diamond powder is coated with a tungsten coating with a thickness of 100-200 nm. Any coating preparation process that can be uniform, dense and reach the required thickness range can be applied to the preparation of the tungsten coating on the surface of the diamond powder of the present invention, including but not limited to physical vapor deposition, chemical vapor deposition, electroless plating, etc. The inventors found that bare diamond and nickel-copper bonding phase are not easily mixed evenly, and under electron beam irradiation, the diamond splashes severely, which is mainly due to the too large density difference between the diamond and the nickel-copper bonding phase. As the metal with the highest density, tungsten can quickly increase the weight of the diamond to improve the uniformity of the metal powder and the diamond powder in powder mixing and powder spreading, and inhibit the splashing and floating of the diamond during the melting process of the molten pool, realizing a relatively uniform distribution of the diamond in the composite material.

[0022] Compared with the widely used electroless nickel plating process on the diamond surface, a thinner tungsten coating can achieve the weight gain effect of a thicker nickel coating, thereby reducing the dilution rate of the bonding phase matrix. In addition, in addition to laser-induced diamond graphitization, the catalysis of transition metal elements such as nickel is also an important reason for inducing diamond graphitization. The tungsten coating encapsulation method adopted in the present invention can effectively inhibit the graphitization and burning loss of the diamond, which helps to improve the toughness and wear resistance of the composite material, and the introduction of the tungsten coating can improve the material removal efficiency of the grinding tool and extend the service life, and has the potential to apply this excellent performance to the fields of drill tools and cutting tools.

[0023] The thickness of the tungsten coating on the diamond surface adopted in the present invention is 100-200 nm. If the thickness of the tungsten coating is too thin, that is, the weight gain of the tungsten coating is too low, it cannot effectively inhibit the segregation of the diamond in powder mixing and the splashing under electron beam irradiation, nor can it ensure the complete encapsulation and protection of the diamond by the tungsten coating, increasing the risk of local graphitization of the diamond. If the thickness of the tungsten coating is too thick, it will cause obvious bonding gaps between the tungsten coating and the diamond and the metal bonding phase, further causing cracking and interfacial peeling of the nickel-copper-based diamond composite material.

[0024] The present invention also provides a nickel-copper-based diamond composite material obtained by the above preparation method. This material has the advantages of high density, high wear resistance and toughness. At the same time, the configuration of this material can be precisely controlled by the electron beam additive manufacturing process.

[0025] The present invention also provides an application of a nickel - copper - based diamond composite material prepared by an electron beam additive manufacturing process. When it is applied to the near - net - shape forming of drilling tools, grinding tools or industrial molds, it can achieve the integrated forming of the structure - function of diamond tools, reducing the subsequent processing cost and time of the industrial production of complex components.

[0026] Compared with the prior art, the beneficial technical effects brought by the technical solution of the present invention are as follows:

[0027] 1) The present invention uses an electron beam additive manufacturing process to prepare a nickel - copper - based diamond composite material, introducing a new preparation method into the field of metal - based diamond composite materials. The additive manufacturing process can achieve the near - net - shape forming of complex structures and the integrated preparation of structure - function. Using an electron beam as the energy source can achieve the stable forming of diamond brittle materials. The nickel - copper - based diamond composite material prepared by the electron beam additive manufacturing process has a wide process window and good macroscopic formability. In particular, the substrate of electron beam additive manufacturing can be pre - heated at a higher temperature, reducing the cracking phenomenon caused by the too - fast solidification rate of the composite material to a certain extent. Through further process optimization, the densification of the diamond composite material can be achieved, effectively suppressing the graphitization of diamond, and obtaining a nickel - copper - based diamond composite material with excellent comprehensive performance.

[0028] 2) The present invention uses a nickel - copper alloy as the bonding - phase matrix of the diamond composite material, improving the wettability to diamond. Doping Si, Mn, B alloying elements in the nickel - copper alloy bonding phase, through enhancing the solid - solution strengthening, fine - grain strengthening and second - phase strengthening effects, improves the hardness and wear resistance of the bonding phase, reduces the melting point of the nickel - copper alloy, improves the fluidity, and helps to improve the formability and mechanical properties of the composite material.

[0029] 3) The preparation method selected by the present invention is carried out under normal pressure throughout the process and does not involve dangerous steps such as fine - powder transfer and mechanical ball - milling method, being suitable for industrial production.

[0030] 4) When the nickel - copper - based diamond composite material prepared by the present invention is used as diamond tools such as drilling tools, grinding tools, and industrial molds, it can achieve the near - net - shape forming and rapid manufacturing of tools with specific complex configurations, improving the production efficiency. Description of the Drawings

[0031] Figure 1 It is a secondary - electron scanning image of the surface morphology of the nickel - copper - based diamond composite material prepared in Example 1.

[0032] Figure 2 It is a back - scattered electron scanning image of the cross - section microstructure of the nickel - copper - based diamond composite material prepared in Example 1.

[0033] Figure 3Secondary electron scanning image of the surface morphology of the nickel-copper-based diamond composite prepared in Example 2.

[0034] Figure 4 Backscattered electron scanning image of the cross-sectional microstructure of the nickel-copper-based diamond composite prepared in Example 2.

[0035] Figure 5 Secondary electron scanning image of the surface morphology of the nickel-copper-based diamond composite prepared in Example 3.

[0036] Figure 6 Backscattered electron scanning image of the cross-sectional microstructure of the nickel-copper-based diamond composite prepared in Example 3.

[0037] Figure 7 Secondary electron scanning image of the surface morphology of the nickel-copper-based diamond composite prepared in Example 4.

[0038] Figure 8 Backscattered electron scanning image of the cross-sectional microstructure of the nickel-copper-based diamond composite prepared in Example 4.

[0039] Figure 9 Secondary electron scanning image of the surface morphology of the nickel-copper-based diamond composite prepared in Example 5.

[0040] Figure 10 Backscattered electron scanning image of the cross-sectional microstructure of the nickel-copper-based diamond composite prepared in Example 5.

[0041] Figure 11 Macroscopic photograph of the nickel-copper-based diamond composite prepared in Comparative Example 1.

[0042] Figure 12 Secondary electron scanning image of the surface morphology of the nickel-copper-based diamond composite prepared in Comparative Example 4.

[0043] Figure 13 Backscattered electron scanning image of the cross-sectional microstructure of the nickel-copper-based diamond composite prepared in Comparative Example 4.

[0044] Figure 1 、 2 Surface and cross-section scanning pictures of the nickel-copper-based diamond composite prepared in Example 1. It can be seen that in Example 1, the surface morphology is relatively flat, the densification degree is relatively high, the diamond distribution is relatively uniform, the interface is straight, and there is no obvious graphitization and thermal damage of the diamond.

[0045] Figure 3 、 4The surface and cross-section scanning pictures of the nickel-copper-based diamond composite material prepared in Example 2 are shown. It can be seen that the surface morphology, diamond distribution characteristics, and interfacial microstructure of Example 2 are quite similar to those of Example 1, indicating that when the ratio of the electron beam current value to the scanning speed value is the same, the surface morphology and tissue characteristics of the composite material are similar. Within the range provided by the present invention, changing the powder mixing, preheating, and pre-sintering parameters has almost no obvious effect on the formability of the composite material.

[0046] Figure 5 、 6 The surface and cross-section scanning pictures of the nickel-copper-based diamond composite material prepared in Example 3 are shown. It can be seen that the surface morphology of Example 3 is rough, the diamond distribution is uneven, the interface is distorted, and there is an obvious graphitization phenomenon of the diamond. This shows that when the ratio of the electron beam current value to the scanning speed value is relatively high, the electron beam with a higher energy density leads to unstable fluctuations in the molten pool and the graphitization phenomenon of the diamond. To obtain a high-performance composite material, this ratio should be appropriately reduced.

[0047] Figure 7 、 8 The surface and cross-section scanning pictures of the nickel-copper-based diamond composite material prepared in Example 4 are shown. It can be seen that there are a large number of holes in the surface morphology of Example 4, the interface is straight, but there are microcracks at the interface between the diamond edges and the nickel-copper-based bonding phase. The tissue around the cracks is extremely fine. This is because when the ratio of the electron beam current value to the scanning speed value is relatively low, the electron beam with a lower energy density cannot fully melt and make the metal bonding phase flow, resulting in some incompletely melted areas. This area retains the original fine tissue of the atomized powder, but due to incomplete melting, the bonding phase has a low strength and cannot provide a high binding force and holding force for the diamond, resulting in cracks at the tip. To obtain a high-performance composite material, this ratio should be increased.

[0048] Figure 9 、 10 The surface and cross-section scanning pictures of the nickel-copper-based diamond composite material prepared in Example 5 are shown. It can be seen that the morphology and tissue characteristics are similar to those of Example 1 and Example 2, indicating that the electron beam additive manufacturing forming process of the nickel-copper-based diamond composite material has a large process window. By changing the ratio of the electron beam current value to the scanning speed value within a certain range, samples with good formability can be obtained. Therefore, it is necessary to finely adjust this ratio and detect and compare the performance indicators such as strength, toughness, and wear resistance of the composite material under different energy density inputs.

[0049] Figure 11It is a macroscopic photograph of the nickel - copper - based diamond composite material prepared in Comparative Example 1. It can be seen that a large - area region is missing in the composite material, which is caused by severe fluctuations in the molten pool and severe evaporation of the metal bonding phase due to excessive energy density. It shows that when the ratio of the electron beam current value to the scanning speed value exceeds the range provided by the present invention, it is impossible to form a nickel - copper - based diamond composite material.

[0050] Figure 12 , 13 It is the surface and cross - section scanning pictures of the nickel - copper - based diamond composite material prepared in Comparative Example 4. It can be seen that the surface of the diamond is rough and stepped, the edges are blurred and distorted, showing obvious diamond graphitization and thermal damage phenomena. It shows that when the scanning method is changed, the energy concentration phenomenon of the electron beam at the short side or sharp corner is not conducive to simultaneously realizing the densification forming of the composite material and the weak damage or non - damage of the diamond. Specific Embodiments

[0051] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution will be described completely and in detail below in conjunction with the drawings of the present invention. It should be understood that based on the embodiments shown in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0052] Unless otherwise specifically stated, the raw materials, reagents, instrument equipment, etc. in the present invention can be purchased from the market or obtained by existing preparation methods. The preparation and testing methods without specifying specific conditions are usually implemented according to conventional conditions or the conditions recommended by the equipment manufacturers.

[0053] Example 1

[0054] 1. Material Preparation

[0055] (1) Prepare nickel - copper - based bonding phase powder: The alloy powder with the composition of Ni 65.3 Cu 28 Si4Mn1B 1.7 (wt.%) is prepared by gas atomization method, and spherical powder with a particle size range of 53 - 150 μm is selected.

[0056] (2) Prepare diamond powder: Select artificial diamond with a particle size range of 75 - 90 μm. After degreasing the diamond surface, tungsten is plated by physical vapor deposition method, and the tungsten coating thickness is 200 nm.

[0057] (3) Mix the powders: Weigh the nickel - copper - based bonding phase powder and diamond powder so that, by volume fraction, the diamond content accounts for 10%. Mix them by mechanical stirring until evenly mixed.

[0058] 2. Electron Beam Additive Manufacturing

[0059] (1) Preheating: Use a 316L stainless steel substrate, and the substrate preheating temperature is 550 °C.

[0060] (2) Powder spreading and pre-sintering: The powder spreading layer thickness is 0.05 mm. After powder spreading, pre-sintering is carried out using a pre-scanning process of 22 mA and 5 s.

[0061] (3) Forming: Use an electron beam with a current of 18 mA and a scanning speed of 6 m / s (the ratio is 3) for forming. The electron beam scanning direction is parallel to the substrate edge and rotates 90° compared to the scanning direction of the previous layer.

[0062] 3. Sample characterization and analysis

[0063] The obtained samples have good macroscopic formability. The surface and cross-section microstructure pictures of the samples observed by scanning electron microscopy are as shown in Figure 1 and 2 . The surface of the composite material is flat, the diamond is evenly distributed in the metal binder phase, the interface is straight, the combination is good, and there is no obvious graphitization and thermal burn-out phenomenon.

[0064] Example 2

[0065] 1. Material preparation: The material preparation in this example is the same as that in Example 1.

[0066] 2. Electron beam additive manufacturing

[0067] (1) Preheating: Use a 316L stainless steel substrate, and the substrate preheating temperature is 530 °C.

[0068] (2) Powder spreading and pre-sintering: The powder spreading layer thickness is 0.05 mm. After powder spreading, pre-sintering is carried out using a pre-scanning process of 21 mA and 6 s.

[0069] (3) Forming: Use an electron beam with a current of 12 mA and a scanning speed of 4 m / s (the ratio is 3) for forming. The electron beam scanning direction is parallel to the substrate edge and rotates 90° compared to the scanning direction of the previous layer.

[0070] 3. Sample characterization and analysis

[0071] The obtained samples have good macroscopic formability. The surface and cross-section microstructure pictures of the samples observed by scanning electron microscopy are as shown in Figure 3 and 4 . The initial surface is flat, the microstructure is uniform and dense, and the diamond has no obvious damage. Comparing the samples of Example 1 and Example 2, the macroscopic morphology and microstructure are highly similar, indicating that when the ratio of the electron beam current value to the scanning speed value is the same, the formability of the samples is similar. This is because when this ratio is the same, the energy density input by the electron beam is consistent. In addition, it can also be shown that within the scope described in the present invention, changing the preheating and pre-sintering parameters has little effect on the formability of the samples.

[0072] Example 3

[0073] 1. Material preparation: The material preparation in this example is the same as that in Example 1.

[0074] 2. Electron beam additive manufacturing: The difference in the electron beam additive manufacturing process in this example from that in Example 1 is only that an electron beam with a current of 18 mA and a scanning speed of 4 m / s (ratio of 4.5) is used for forming.

[0075] 3. Sample characterization and analysis

[0076] The obtained sample has good macroscopic formability. The surface and cross-section microstructure pictures of the sample further observed by scanning electron microscope are as shown in Figure 5 and 6 . Through scanning electron microscope observation, it is found that there are large protrusions, depressions and other defects on the surface of the sample, the distribution of diamond is relatively uneven, and the interface is not straight, indicating that obvious graphitization phenomenon appears in the local area of the diamond surface. It shows that when the ratio of the electron beam current value to the scanning speed value is large, although the forming of the metal matrix diamond composite material is also realized, due to the high input energy density, the molten pool is unstable, resulting in more obvious micro-defects and obvious damage to the diamond. It shows that the process with a large ratio of the electron beam current value to the scanning speed value has an obvious thermal damage effect on the diamond while realizing the densification of the composite material.

[0077] Example 4

[0078] 1. Material preparation: The material preparation in this example is the same as that in Example 1.

[0079] 2. Electron beam additive manufacturing: The difference in the electron beam additive manufacturing process in this example from that in Example 1 is only that an electron beam with a current of 12 mA and a scanning speed of 6 m / s (ratio of 2) is used for forming.

[0080] 3. Sample characterization and analysis

[0081] The obtained sample has good macroscopic formability. The surface and cross-section microstructure pictures of the sample further observed by scanning electron microscope are as shown in Figure 7 and 8As shown. Through scanning electron microscopy observation, it was found that there were many unfused holes on the surface of the sample, the distribution of diamond was relatively uneven, the nickel-copper bonding phase-diamond interface was flat, but microcracks appeared at the edges of the diamond, the metal structure around the microcracks was extremely fine, and there were a small number of unfused pores. It shows that when the ratio of the electron beam current value to the scanning speed value is small, although the forming of the metal-based diamond composite material is achieved and the thermal damage of the diamond is inhibited, due to the low input energy density, the metal is not fully melted or there is not enough time for the melted metal to flow after melting, resulting in more obvious microdefects, reducing the density, and weakening the holding effect of the metal-based bonding phase on the diamond. It shows that the process with a small ratio of the electron beam current value to the scanning speed value can effectively inhibit the thermal damage of the diamond, but is not conducive to the densification of the nickel-copper-based bonding phase.

[0082] Examples 1 to 4 illustrate that the ratio of the electron beam current value to the scanning speed value seriously affects the microstructure and formability of the nickel-copper-based diamond composite material. Therefore, the subsequent examples mainly explored the influence of this ratio on the properties of the composite material (including strength and toughness and wear resistance).

[0083] Example 5

[0084] 1. Material preparation: The material preparation in this example is the same as that in Example 1.

[0085] 2. Electron beam additive manufacturing

[0086] (1) Preheating: A 316L stainless steel substrate was used, and the preheating temperature of the substrate was 570 °C.

[0087] (2) Powder spreading and pre-sintering: The powder spreading layer thickness was 0.05 mm, and after powder spreading, pre-sintering was carried out using a pre-scanning process of 20 mA and 5 s.

[0088] (3) Forming: An electron beam with a current of 16 mA and a scanning speed of 5 m / s (the ratio was 3.2) was used for forming. The electron beam scanning direction was parallel to the edge of the substrate and rotated 90° compared with the scanning direction of the previous layer.

[0089] 3. Sample characterization and analysis

[0090] The sample obtained in this example had good macroscopic formability. The microstructure pictures of the surface and cross-section of the sample further observed by scanning electron microscopy are as Figure 9 、 10 shown. It can be seen that the surface of the sample was relatively flat, the density was relatively high, the distribution of diamond was relatively uniform and there was no obvious damage. Therefore, the density, flexural strength, fracture toughness and wear ratio of this sample were further tested, and the test results are shown in Table 1.

[0091] Table 1 Test results of density and mechanical properties of Example 5

[0092]

[0093] Example 6

[0094] 1. Material preparation: The material preparation for this example is the same as that in Example 5.

[0095] 2. Electron beam additive manufacturing

[0096] (1) Preheating: Use a 316L stainless steel substrate, and the preheating temperature of the substrate is 555 °C.

[0097] (2) Powder spreading and pre-sintering: The powder spreading layer thickness is 0.05 mm, and after powder spreading, pre-sintering is carried out using a pre-scanning process of 22 mA and 6 s.

[0098] (3) Forming: Use an electron beam with a current of 18 mA and a scanning speed of 5 m / s (ratio is 3.6) for forming. The electron beam scanning direction is parallel to the substrate edge and rotates 90° compared to the scanning direction of the previous layer.

[0099] 3. Sample characterization and analysis

[0100] The samples of Example 6 were tested for density, flexural strength, fracture toughness, and wear ratio. The test results are shown in Table 2. Comparing Example 5 and Example 6, it can be seen that when the ratio of the electron beam current value to the scanning speed value increases, the fracture toughness increases slightly, but the flexural strength and wear ratio decrease. This may be due to the slight graphitization on the diamond surface when the energy density increases slightly.

[0101] Table 2 Test results of density and mechanical properties of Example 6

[0102]

[0103] Example 7

[0104] 1. Material preparation: The material preparation for this example is the same as that in Example 5.

[0105] 2. Electron beam additive manufacturing

[0106] (1) Preheating: Use a 316L stainless steel substrate, and the preheating temperature of the substrate is 545 °C.

[0107] (2) Powder spreading and pre-sintering: The powder spreading layer thickness is 0.05 mm, and after powder spreading, pre-sintering is carried out using a pre-scanning process of 21 mA and 5 s.

[0108] (3) Forming: Use an electron beam with a current of 15 mA and a scanning speed of 5 m / s (ratio is 3) for forming. The electron beam scanning direction is parallel to the substrate edge and rotates 90° compared to the scanning direction of the previous layer.

[0109] 3. Sample characterization and analysis

[0110] The sample of Example 7 was tested for density, flexural strength, fracture toughness and wear ratio, and the test results are shown in Table 3. Comparing Example 5 and Example 7, it can be seen that when the ratio of the electron beam current value to the scanning speed value decreases, the fracture toughness decreases slightly, but the flexural strength and wear ratio increase. This may be due to the reduction of microdefects caused by high-energy beam impact when the energy density decreases slightly.

[0111] Table 3 Test Results of Density and Mechanical Properties of Example 7

[0112]

[0113] Example 8

[0114] 1. Material preparation: The material preparation of this example is the same as that of Example 7.

[0115] 2. Electron beam additive manufacturing

[0116] (1) Preheating: A 316L stainless steel substrate was used, and the substrate preheating temperature was 570 °C.

[0117] (2) Powder spreading and pre-sintering: The powder spreading layer thickness was 0.05 mm, and pre-sintering was carried out after powder spreading using a pre-scanning process of 22 mA and 4 s.

[0118] (3) Forming: An electron beam with a current of 14 mA and a scanning speed of 5 m / s (ratio of 2.8) was used for forming. The electron beam scanning direction was parallel to the substrate edge and rotated 90° compared with the scanning direction of the previous layer.

[0119] 3. Sample characterization and analysis

[0120] The sample of Example 8 was tested for density, flexural strength, fracture toughness and wear ratio, and the test results are shown in Table 4. Comparing Example 7 and Example 8, it can be seen that when the ratio of the electron beam current value to the scanning speed value further decreases, the fracture toughness increases slightly, but the flexural strength and wear ratio decrease. This may be due to the increase of microdefects caused by insufficient flow of the bonding phase when the energy density decreases slightly.

[0121] Table 4 Test Results of Density and Mechanical Properties of Example 8

[0122]

[0123] Example 9

[0124] 1. Material preparation: The material preparation of this example is the same as that of Example 8.

[0125] 2. Electron beam additive manufacturing

[0126] (1) Preheating: Use a 316L stainless steel substrate, and the preheating temperature of the substrate is 560 °C.

[0127] (2) Powder spreading and pre-sintering: The powder spreading layer thickness is 0.05 mm. After powder spreading, pre-sintering is carried out using a pre-scanning process of 22 mA and 5 s.

[0128] (3) Forming: Use an electron beam with a current of 12 mA and a scanning speed of 5 m / s (ratio is 2.4) for forming. The electron beam scanning direction is parallel to the substrate edge and rotates 90° compared to the scanning direction of the previous layer.

[0129] 3. Sample characterization and analysis

[0130] The samples of Example 9 were tested for density, flexural strength, fracture toughness, and wear ratio. The test results are shown in Table 5. Comparing Example 8 and Example 9, it can be seen that when the ratio of the electron beam current value to the scanning speed value is 2.4, the flexural strength, fracture toughness, and wear ratio of the composite material are all improved. This shows that when the ratio of the electron beam current value to the scanning speed value is 2.4, while the composite material achieves densification, fine grain strengthening of the metal bonding phase is realized, and the graphitization and thermal damage of diamond are inhibited. This example achieves the optimal comprehensive performance.

[0131] Table 5 Test results of density and mechanical properties of Example 9

[0132]

[0133] Comparative Example 1

[0134] 1. Material preparation: The material preparation of this comparative example is the same as that of Example 1.

[0135] 2. Electron beam additive manufacturing

[0136] The difference between this comparative example and Example 1 is only that during the forming process, an electron beam with a current of 18 mA and a scanning speed of 3 m / s (ratio is 6) is used for forming. The electron beam scanning direction is parallel to the substrate edge and rotates 90° compared to the scanning direction of the previous layer.

[0137] 3. Sample characterization and analysis

[0138] The macroscopic morphology photo of the sample of Comparative Example 1 is as Figure 11 shown. It can be clearly seen from Figure 11 that although forming is achieved in some areas of the composite material, due to the extremely high electron beam energy density, a large number of macroscopic deep pits appear in the sample, and uniform and stable forming can no longer be achieved.

[0139] Comparative Example 2

[0140] 1. Material preparation: The material preparation of this comparative example is the same as that of Example 1.

[0141] 2. Electron beam additive manufacturing

[0142] The difference between this comparative example and Example 1 is only that during the forming process, an electron beam with a current of 3.5 mA and a scanning speed of 7 m / s (ratio of 0.5) is used for forming. The electron beam scanning direction is parallel to the substrate edge and rotates 90° relative to the scanning direction of the previous layer.

[0143] 3. Sample characterization and analysis

[0144] In Comparative Example 2, no formed sample could be obtained for characterization and analysis. It shows that when the electron beam energy density is too low, the preparation of nickel-copper-based composite materials cannot be achieved by this process.

[0145] Comparative Example 3

[0146] 1. Material preparation: The difference in material preparation between this comparative example and Example 1 is only that when preparing diamond powder, after selecting synthetic diamonds with a particle size range of 75 - 90 μm, physical vapor deposition tungsten coating treatment is not performed, and the other conditions are the same.

[0147] 2. Electron beam additive manufacturing: The electron beam additive manufacturing process of this comparative example is the same as that of Example 1.

[0148] 3. Sample characterization and analysis

[0149] In Comparative Example 3, serious powder splashing occurred during printing. This may be because the diamond was not coated with tungsten, and the irradiation of the electron beam caused negative charges to accumulate on the surface of the diamond with poor conductivity. The mutual repulsion between like charges caused the lighter diamond to splash severely, restricting the forming of nickel-copper-based diamond composite materials.

[0150] Comparative Example 4

[0151] 1. Material preparation: The material preparation of this comparative example is the same as that of Example 7.

[0152] 2. Electron beam additive manufacturing: The difference in the electron beam additive manufacturing process between this comparative example and Example 7 is only that the electron beam scanning direction is parallel to the substrate diagonal direction, that is, inclined at 45° to the substrate edge, and the other conditions are the same.

[0153] 3. Material characterization and analysis

[0154] The surface of the composite material in Comparative Example 4 is uneven, and obvious graphitization and thermal ablation of the diamond occurred during printing, as Figure 12 、 13As shown, the diamond surface is rough and stepped, showing obvious wavy stripes, the interface is tortuous, showing obvious graphitization and thermal ablation phenomena, and there are a small number of pores in the bonding phase. This is because when the electron beam scanning method is changed, the length of each scanning path is different from the previous one, which easily leads to energy concentration at the short sides (especially sharp corners), resulting in serious diamond graphitization and thermal damage phenomena, and the energy concentration causes a small amount of evaporation of the nickel-copper alloy, leaving pores in the composite material. Therefore, the electron beam scanning direction should be parallel to the substrate edge and rotated 90° compared with the scanning direction of the previous layer to reduce the energy concentration in the local area, so as to achieve weak damage or no damage to the diamond during the uniform and dense forming process of the diamond composite material.

[0155] Comparative Example 5

[0156] 1. Material preparation: The material preparation of this comparative example is the same as that of Example 1.

[0157] 2. Electron beam additive manufacturing: The difference between the electron beam additive manufacturing process of this comparative example and that of Example 1 is only that the substrate preheating temperature is 100 °C.

[0158] 3. Material characterization and analysis

[0159] In the printing process of Comparative Example 5, macroscopic cracking occurred in the sample, and the stable forming of the nickel-copper-based diamond composite material could not be achieved. It can be seen that the relatively high preheating temperature achievable by the electron beam additive manufacturing process is one of the key factors for the stable forming of the nickel-copper-based diamond composite material.

[0160] Test Example 1 Density test

[0161] Using an MSA324S-000-DU type densitometer, the density test was carried out according to the principle of Archimedes' drainage method. The contaminated layer on the surface of the composite material sample was removed with a diamond grinding wheel, and deionized water was used as the solution medium to measure and calculate the density of the sample.

[0162] Test Example 2 Flexural test

[0163] A three-point flexural test was carried out using an Instron 3369 type electronic universal material testing machine. Samples of 20×4×3 mm were cut from the composite material by laser cutting technology and ground to 180 mesh with a diamond sanding disc. The test span was selected as 13 mm and the loading speed was 1 mm / min.

[0164] Test Example 3 Fracture toughness test

[0165] The fracture toughness test was carried out using an Instron 3369 electronic universal material testing machine. Samples of 20×4×3 mm were cut from the composite material by laser cutting process. A notch with a depth of 2 mm was prefabricated in the middle of the sample and ground to 180 mesh with a diamond sand disc. The test span was selected as 16 mm and the loading speed was 1 mm / min, and the test was carried out with the notch facing downwards.

[0166] Test Example 4 Abrasion Ratio Test

[0167] The abrasion ratio test was carried out according to JB / T 3235-2013. Samples with a side length of not less than 15 mm were cut from the composite material by laser cutting process and ground to 180 mesh with a diamond sand disc. The test conditions were selected as a grinding wheel speed of 25 m / s and a grinding time of 192 s.

[0168] Test Example 5 Microstructure Characterization

[0169] The microstructure of the sample was observed using a MIRA4 LMH scanning electron microscope equipped with an Ultim Max 40 energy spectrometer. Samples with a side length of not less than 8 mm were cut from the composite material by laser cutting process. After grinding to 2000 mesh with a diamond sand disc, they were polished to a mirror surface using W1 diamond spray.

[0170] In summary, the present invention has the following advantages:

[0171] For the first time, the electron beam additive manufacturing process was successfully used to achieve the macroforming of nickel-copper-based diamond composite materials. By regulating the electron beam current and scanning speed, etc., while further ensuring the formability and densification of nickel-copper-based diamond composite materials, the graphitization and thermal ablation of diamond can be inhibited. The preparation process of the present invention is safe, fast, stable, easy to realize industrial production, and can be applied to the near-net forming preparation of complex configuration diamond tools in various fields such as drilling tools, grinding tools, and industrial molds.

[0172] It should be understood that the present invention should not be limited to these embodiments shown in this specification, but should conform to the broadest scope consistent with the innovation disclosed by the present invention.

Claims

1. A method for preparing a nickel-copper-based diamond composite material, characterized in that: It is obtained by mixing nickel-copper-based binder phase powder and diamond powder and then forming through a powder bed electron beam additive manufacturing process; The electron beam additive manufacturing process includes: preheating, powder spreading, pre-sintering and forming treatment; During the preheating process, the substrate temperature used is 500 - 600 °C; The nickel-copper-based binder phase powder is composed of the following components by mass percentage: Cu 27 - 28%, Si 3 - 4%, Mn 0.5 - 1.5%, B 1.5 - 2.0%, the balance is Ni, and Cu / (Ni + Cu) is 29 - 30%; For the forming treatment, an electron beam is used, where the electron beam current is 1 - 19 mA, and the ratio of the electron beam current value to the electron beam scanning speed value is 1.6 - 4.7; The conditions for the pre-sintering are: the current is 18 - 25 mA, and the time is 4 - 6 s; The surface of the diamond powder is coated with a tungsten coating with a thickness of 100 - 200 nm.

2. The nickel-copper-based diamond composite material and its preparation method according to claim 1, characterized in that: The content of the diamond powder is (10 - 20) vol.% of the mixed powder of nickel-copper-based binder phase powder and diamond powder.

3. A nickel-copper-based diamond composite material, characterized in that: Obtained by the preparation method according to claim 1 or 2.

4. Use of a nickel-copper-based diamond composite material according to claim 3, characterized in that: Applied to the near-net shaping of drill tools, grinding tools or industrial molds.

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