The problems of insufficient holding power and particle shedding in the electroplated diamond tool seriously affect the service life and efficiency of the tool. This paper reviews the methods developed in recent years to improve the performance of electroplated diamond tools, which are summarized into the following three categories: 1. Improve the properties of the coated carcass material and improve the support and bonding of the coating to the diamond; 2. Improve the diamond and The contact area of ​​the carcass eliminates the gap between the diamond and the plating layer; 3. The surface treatment of the diamond particles forms a chemical bond between the diamond and the plating layer. In this paper, various methods are described in detail, and some potential methods are recommended, in order to have a comprehensive and systematic understanding of the improved methods of electroplated diamond tools.
Due to its excellent physical and chemical properties, such as high hardness, high strength, high wear resistance and low coefficient of linear expansion, diamond is used to make diamond tools for the processing of hard and brittle hard-to-machine materials. The diamond tool is prepared by electroplating, and the loose diamond particles are fixed in the plating layer by electrodeposition of the metal, so that the diamond particles have the cutting ability. The diamond tool prepared by electroplating has low manufacturing temperature, avoids heat loss to diamond, and has simple production process, low equipment investment, short manufacturing cycle, convenient molding and repair. Therefore, electroplated diamond products have various tools such as grinding wheels, grinding heads, assorted files, boring cutters, dressing rollers, geological drills, reamers, internal and external circular cutting blades, reamers, wire saws, etc., in machinery, electronics, Industrial applications such as construction, drilling, and optical glass processing are widely used [1-3].
At present, when the diamond tool is prepared by electroplating at home and abroad, the main problem is that the bonding force between the plated carcass metal and the diamond particles is low, and when the diamond particles are subjected to the force in use, the loosening is easy to fall off, resulting in a short service life. The main reason for these phenomena is that the manufacturing temperature is low when the diamond tool is prepared by electroplating, so that the surface of the diamond particles is not easily infiltrated by the general metal, and not only a strong chemical bond is not obtained, but also a gap is often generated. In addition, due to the influence of the electroplating process, diamond tool plating metals are limited in type (only limited to nickel, chromium and other metals and their alloys), unlike the types of metals used in hot pressing tools.
In response to the above problems, various measures have been taken to solve the bonding force between diamond and coated metal. This paper comprehensively introduces the methods developed in recent years to improve the performance of electroplated diamond tools, and summarizes them, hoping to give people a detailed and clear understanding.
1 Improve the carcass material
In the electroplated diamond tool, the coating supports and combines the diamond. It is called the carcass or matrix metal. It determines whether the diamond particles can fully exert the cutting effect. It is generally required to meet high hardness, high wear resistance and high Performance requirements such as toughness, so people first consider improving the diamond tool by improving the performance of the carcass material.
1.1 Alloying of carcass metal
Although a single coating (such as nickel) has a high strength, particularly toughness, it is generally low in hardness, so alloy plating is often used.
1.1.1 Ni-Co binary alloy coating [1-5]
Cobalt can not only improve the strength of nickel metal (the compressive strength of nickel-cobalt alloy is 1600MPa), but also improve the heat resistance of the carcass metal. The strength limit of the Ni Co binary alloy at 800 °C is 500MPa. It can also improve the toughness of the carcass metal. Therefore, the Ni Co binary alloy plating layer has become a widely used carcass material, but sometimes the hardness of the Ni Co binary alloy plating layer is still insufficient, and the carcass is consumed quickly when processing a hard and abrasive material. Moreover, the Ni Co coating can ensure high hardness and wear resistance only when the cobalt content reaches about 30%, and a large amount of expensive metal cobalt increases the cost.
1.1.2 Ni Mn binary alloy coating [6]
Metal manganese can increase the hardness, strength and wear resistance of nickel matrix than cobalt. The nickel-manganese carcass hardness is about 10 degrees higher than the nickel-cobalt carcass hardness. Although the content of manganese in the alloy is small, it has a great influence on the performance of the carcass. When the nickel-manganese carcass diamond drill bit is drilled in a hard and strong abrasive formation, the average life and aging are 55% and 30% higher than that of the nickel-cobalt drill bit, respectively. At the same time, the nickel-manganese carcass bit does not require high speed and pressure. Conducive to reducing material consumption and reducing drilling costs. However, the Ni Mn binary alloy coating has high brittleness and is easy to crack, which makes the working layer easy to be broken.
1.1.3 Ni Co Mn ternary alloy coating [7]
Ni Co Mn ternary alloy coating has higher comprehensive mechanical properties. The hardness is higher than Ni Co, and the brittleness is lower than Ni Mn.
It is in line with the requirements of the electroplated diamond products for the carcass. Stone tools made with Ni Co Mn ternary alloy coatings are sharper and more durable than Ni Co binary alloy coatings, especially for hard stone. The Ni Co Mn ternary alloy coating is low in cost due to the saving of a large amount of expensive material cobalt. The mechanical properties of the Ni Co Mn ternary alloy coating can be adjusted over a wide range to meet the needs of a wider range of applications. However, when the Ni Co Mn ternary alloy plating layer is obtained, the composition of the plating solution is complicated and the stability is not easily controlled.
1.2 Composite of carcass metal
The composite plating layer is a special plating layer formed by uniformly interposing one or several insoluble solid particles and fibers into a metal plating layer by a co-deposition method. Since the composite coating uniformly disperses a large amount of solid particles, these hard particles can greatly hinder the slip between the crystal grains, and the metal can be effectively strengthened.
1.2.1 Ni Co fine-grained diamond composite coating [8 10]
Adding an appropriate amount of nano-diamond powder to the plating solution, the hardness of the obtained Ni Co diamond composite coating is obviously improved, the hardness can reach 601.53 HV [8], and the friction and wear performance is remarkably improved: the friction coefficient of the nickel-cobalt alloy coating is about 0.35, and the life is When the friction radius is 14mm, the average is 0.022km; the friction coefficient of Ni Co diamond composite coating containing nano-diamond powder is about 0.3, and the coating life is 0.15km when the friction radius is 14mm [9]. The Ni Co diamond composite coating is used as the diamond bit matrix, and the prepared diamond bit is drilled in a hard and strong abrasive layer, which has good wear resistance, fast drill bit length, long service life and can prevent hole inclination [10]. Since the ultrafine diamond powder is extremely easy to agglomerate and its performance cannot be fully exerted, measures should be taken to disperse the diamond powder. This inevitably restricts the use value and application prospect of ultrafine powder.
1.2.2 Ni Co rare earth element composite coating [11]
The addition of a small amount of rare earth compound can improve the performance of the plating solution and the coating layer. In the electrodeposition process, the cation is mainly adsorbed on the surface of the metal deposit, and the rare earth metal ion exhibits strong adsorption on the electrode. The rare earth metal ions are easily adsorbed on the active point of crystal growth, that is, adsorbed on the growth point of the crystal plane, and the crystal growth is effectively suppressed. Therefore, after the rare earth element is added to the plating solution, a fine grain plating layer can be obtained. Using the universal cylindrical grinding machine M1420E through the grinding test of bright nickel plating and bright nickel plating diamond tool grinding with rare earth elements, it was found that the addition of rare earth elements improved the grinding ratio of the diamond tool. Bright nickel-plated diamond tools have poor wear resistance, fast consumption of the carcass, can not guarantee the high edge of diamond, and the diamonds fall off quickly; the bright nickel bond tool with rare earth added improves the wear resistance of the carcass, and the diamond package is better, the height of the diamond blade is high. Large, so the efficiency of the tool is improved.
1.2.3 Ni Co carbon nanotube composite coating [12-14]
Carbon nanotubes (CNTs) have superior strength and toughness and can be used as reinforcements for advanced composites to greatly improve the strength and toughness of composites. In addition, CNTs have the characteristics of good chemical stability and low friction factor, and it is expected to prepare a new type of composite coating with high wear resistance, wear reduction and corrosion resistance [13]. Observing the SEM morphology of the composite coating, the surface of the substrate is covered by a thick layer of carbon nanotubes. One end of these carbon nanotubes is deeply embedded in the matrix, and the other end is exposed to the outside of the substrate, which can obviously act on the substrate. Protection [14]. The laboratory is working on the preparation of electroplated diamond tools using this composite coating.
1.3 Grain refinement of carcass metal
The crystallization process of the coating is governed by the nucleation rate and grain growth rate. The faster the rate of nucleation is formed, the slower the grain growth rate, and the finer the crystallization, the denser the coating and the better the hardness and toughness. According to the electrochemical theory, the larger the cathode electrochemical polarization overpotential, the easier it is to form crystal nuclei, and the finer the crystal, the denser the coating. Therefore, people have adopted the objective of improving the electrochemical polarization overpotential and refining the crystal grains to improve the carcass material.
1.3.1 Refined additives [1-3]
After the additive is added to the electrolyte, due to its adsorption on the electrode surface, the electrochemical polarization is increased, the covered crystal grains stop growing, and new crystal nuclei are generated; the new crystal grains are soon covered again, and a new nodule center is generated. So, you can get fine crystals. Secondly, the adsorption of the additive on the surface of the crystal can reduce the surface energy of the crystal, thereby reducing the formation of crystallites, which is favorable for forming a new crystal nucleus. The refining additives are mainly sulfonic acids, sulfinic acids, sulfonamides, disulfonic acids, etc., for example, saccharin, p-toluenesulfonamide, benzenesulfinic acid, benzenesulfonic acid, sodium naphthalenesulfonate, and the like. It can be found from the morphology of the surface of the coating before and after the addition of the aromatic ketone additive that the grain particles before the addition of the additive are large, and the crystallinity of the particles is poor, the crystal grains are loose, and after the addition of the additive, the grain particles are significantly smaller and crystallized. Dense.
1.3.2 Ultrasonic method [15-16]
The use of ultrasonic waves can cause intense mechanical vibration of the material and can also produce a one-way force. When a certain frequency of ultrasonic waves passes through the liquid, small bubbles of appropriate size resonate. In the sparse phase of the ultrasound, the vesicles rapidly expand and become larger; in the dense phase, the vesicles are suddenly compressed until they collapse. When the vesicle is suddenly compressed, the surrounding liquid fills the cavity at a great speed, and the nearby liquid or solid is subjected to high pressure of thousands of atmospheres, which is cavitation or cavitation [15].
Electroplating using high current density under ultrasonic conditions makes the coating more compact, smooth, uniform in thickness, non-porous, well bonded to the substrate, and has high strength and hardness. Nickel plating in an ultrasonic field with a frequency of 16 kHz increases the hardness by 30 to 5 [15]. Under appropriate process conditions, the internal stress of the coating can also be made lower than that of the coating without ultrasonic plating. The reason is that when the cathode current density is high to a certain value, the cathode polarization is sharply increased, resulting in an increase in hydrogen evolution, a rise in pH, and a nickel hydroxide solution in the cathode, and the cavitation of the ultrasonic wave refines the sol. And dispersion and stabilization to prevent sol condensation and precipitation. Ultrasonic waves should not be used in the whole process of diamond sand [16]. It is only used in the thickening period. When the diamond abrasive grains are buried in a certain thickness of the coating, ultrasonic waves are used, and the diamond abrasive grains will not be shaken, which will not affect the diamond tools. The number of sands.
1.3.3 Pulse plating and nano-tire material [17-18]
Pulse plating is a new type of plating technology developed in the 1960s. The electrochemical principle is based on: in one pulse period, when the current is turned on, the electrochemical polarization increases, the metal ions in the vicinity of the cathode region are fully deposited, and the crystal of the plating layer is fine and bright; when the current is turned off, near the cathode region The discharge ions return to the initial concentration and the concentration polarization is eliminated. Therefore, pulse plating is a new type of power application. The relaxation of the current or voltage pulse is used to reduce the concentration polarization of the cathode, thereby allowing a higher current density to achieve higher electrode polarization and ultimately achieving grain refinement. At present, electrodeposition technology has become an important preparation method for nanomaterials. These materials have high hardness and good toughness [17]. When used to prepare diamond tools, the wear resistance of diamond tools can be significantly improved. Li Zhaomei [18] and Others prepared the nano-nickel diamond tool by pulse electrodeposition method, and carried out the wear destructive test. The results show that the average life of the pulsed nano-nickel diamond tool is significantly higher than that of the conventional nickel-cobalt diamond tool, which is about 1.5 times. .
2 Improve the contact area between diamond and carcass
2.1 Using surface roughened diamond particles
The roughening method is used to form some tiny pits and cracks on the diamond surface, and the surface of the diamond in contact with the carcass is increased to improve the mechanical integration force of the diamond and the metal, and enhance the "mechanical anchor chain" effect. A strong roughening method is: covering the diamond with a chlorine base salt (mainly NaCl + BaCl2) and a small amount of deoxidizing agent, covering with a ceramic crucible, heating in the furnace to 1000 ° C to 1100 ° C, and then holding the heat, and then The chlorine base salt is removed with boiling water. The diamond is heated, and the chlorine-based salt is melted to cause graphitization of the diamond corrosion, so that the surface forms minute rough pits and cracks. Another weakening method is to etch the diamond in a roughening solution (nitric acid + sulfuric acid or nitric acid + hydrogen peroxide) at room temperature or under heating, stirring constantly, and then washing it with distilled water. Diamonds form defects such as pits and cracks and slight graphitization under the corrosion of strong oxidizing acids.
2.2 Eliminate the gap between the diamond particles and the carcass in the tool
Since diamond is a non-metal, it has no good affinity with metals, resulting in a high interfacial energy between diamond and common metals or alloys, often creating voids, which reduce the bonding between diamond particles and the substrate of the coating. In this case, the particle surface modification method, the CVD method, the ultrasonic method, or the electroless plating method can be utilized to avoid or compensate for such voids.
2.2.1 Particle surface modification method [19]
The diamond particles are oxidized to form a hydrophilic chemical group on the surface, thereby improving the hydrophilicity of the diamond surface and tightly bonding the diamond particles to the plating layer. If the hydrophilic groups on the diamond surface are replaced by some more hydrophilic organic genes by chemical means, the effect can be further improved.
2.2.2 Electroless plating method [20]
Electroless plating deposits metal on the surface of diamond by an oxidation-reduction reaction of an autocatalytic process without an applied current, thereby forming a uniform and dense film coating. It has been found that when a diamond tool is obtained by chemical composite plating, there is no gap between the diamond and the metal carcass. In addition, ultrasonic vibration will expand around the diamond particles, completely eliminating the gap. The particulate diamond can be directly electrolessly plated to obtain a tool which can be uniformly suspended in the plating solution. For large-grain diamonds, we recommend that you first perform electroplating and sanding to allow the diamond to be pre-embedded in the coating. The thickening process can be electroless.
3 Improve chemical bonding between particles and carcass
By treating the diamond, the carbon atoms on the surface form metal/carbon chemical bonds with the metal atoms, which can completely solve the problem that the diamond and the carcass bond strength in the diamond tool is not strong.
3.1 Surface metallization [21]
The surface treatment of the diamond particles by electroless plating can form a firm and tight connection between the diamond and the coating. However, if the diamond surface is completely metallized, the surface of the diamond particles has good electrical conductivity and is not suitable for electroplating to prepare diamond tools. In the process of burying sand, the plated diamond and the steel substrate and the plating layer together form a cathode, and a phenomenon in which a plurality of diamond particles are bonded to each other to form a block is formed. Therefore, the researchers used diamonds with dispersed conductive dots to make electroplated diamond tools [21]. The method is to control the degree of electroless plating on the diamond surface, strictly control the concentration of the sensitizing solution and the activating solution, and the time of sensitization and activation treatment, so that the number of metal dots on the diamond surface is kept within a suitable range. Although the number of conductive dots on the surface of the diamond increases, the connection point with the plated metal can be increased, and the bonding property between the plating layer and the diamond can be improved. However, when the metal dots are too dense, a thin layer of metal joined into a sheet is formed.
After the electroless plating of diamond, the obvious boundary between the diamond and the nickel-cobalt-based coating disappeared, and some scattered nickel-cobalt joints were grown on the bonding surface of the diamond and the coating [21]. The electroplated diamond tool was prepared from the activated diamond, and the material removal amount was 1.5 times that of the unactivated treatment when grinding the Al2O3 ceramic workpiece [21]. However, with this method, the diamond particles and the coating may be chemically combined in the original sense, and the true chemical bond is not achieved, and the intermolecular force may account for a larger proportion.
3.2 CVD method [22]
Using diamond CVD deposition technology to repair the prepared diamond tools, not only can the newly formed diamonds be deposited in the gaps in the tool, but also the diamond particles in the tool can be regenerated, and the surface is further developed and improved. Particle properties. The MPCVD method has been successfully used for void repair occurring between diamond particles and carcass metal after electroplating. Observation of the surface topography of an electroplated diamond tool prepared using diamond particles having an average size of 16 μm under SEM revealed irregularities and irregularities in the surface, and concave and voids between the diamond particles and the carcass metal. The tool was placed in an MPCVD system and the average size of the diamond particles was increased to 25 μm. The gap between the diamond particles and the carcass metal was compensated by SEM and the surface of the diamond particles was regular and full [22]. This method is used to repair the electroplated diamond tool, which has higher cutting force, wear resistance and particle bonding than the unrepaired electroplated diamond tool. At high temperatures during the MPCVD process, carbon-metal bonds are formed between the diamond and the carcass, creating a strong bond between the diamond particles and the carcass metal [22].
references
[1] Guo Hetong, Zhang Sanyuan. Composite coating [M]. Tianjin: Tianjin University Press, 1991.
[2] Li Dabo. Electroplated diamond bit technology [M]. Beijing: Geological Publishing House, 1995.
[3] Wang Qinsheng. Electroplating Technology of Superhard Materials [M]. Zhengzhou: China Abrasives Industry Co., Ltd., 1989.
[4] Li Chaoqun. Selection of carcass material for electroplated diamond bit [J]. Superhard Materials and Engineering, 1999(2): 19~23
[5] Li Dabo et al. Research and Application of Electroplated Diamond Bits in China[J]. Prospecting Engineering, 1996(4): 41~43
[6] Li Chaoqun. Application of Electroplated Nickel-Manganese Carcass Diamond Bits[J]. Prospecting Engineering, 1998(2): 36~38
[7] Li Yundong et al. Study on New Coatings in Electroplated Diamond Tools[J]. ææ–™ä¿æŠ¤,2002,35(12):12～13
[8] Bao Xuejin et al. Study on nickel-cobalt composite coating containing nano-diamond powder[J].Diamond & Abrasives Engineering,2006(1):39～42
[9] Li Chengming et al. Friction and wear properties of metal-nano-diamond composite coatings [J]. Diamond and Abrasives Engineering, 2004(1): 39~42
[10] Li Chaoqun. Diamond Drill Bits in Composite Plating Process[J]. Geology and Prospecting, 1995, 31(1): 63~64
[11] Gao Hongyu et al. Effect of rare earth lanthanum on the performance of electroplated diamond tools [J]. Diamond and Abrasives Engineering, 2006 (5): 66 ~ 68
[12] Chen Xiaohua et al.Study on the Process of Electrodeposited Nickel-carbon Sodium Tube Composite Coating[J].Surface Technology,2004,31(2):36～39
[13] Wang Qinsheng. Mechanism of Ultrasonic Strengthening Electroplating Process and Improving Coating Quality [J]. Industrial Diamond, 2003 (4 ~ 5): 69 ~ 72
[14] Wang Xiuzhi et al. Effect of Ultrasound on Preparation Process of Electroplated Diamond Tools[J]. Abrasives Communication, 2006(3): 11~12
[15] Wang Liping.Effect of Pulse Current Density on Texture and Hardness of Electrodeposited Nanocrystalline Nickel[J].Plating & Finishing,2005,27(3):40～42
[16] Li Zhaomei et al. Application of Pulse Electrodeposition of Nanocrystalline Nickel in the Manufacturing of Diamond Tools[J]. China Surface Engineering, 2005, 18(5): 43~46
Due to its excellent physical and chemical properties, such as high hardness, high strength, high wear resistance and low coefficient of linear expansion, diamond is used to make diamond tools for the processing of hard and brittle hard-to-machine materials. The diamond tool is prepared by electroplating, and the loose diamond particles are fixed in the plating layer by electrodeposition of the metal, so that the diamond particles have the cutting ability. The diamond tool prepared by electroplating has low manufacturing temperature, avoids heat loss to diamond, and has simple production process, low equipment investment, short manufacturing cycle, convenient molding and repair. Therefore, electroplated diamond products have various tools such as grinding wheels, grinding heads, assorted files, boring cutters, dressing rollers, geological drills, reamers, internal and external circular cutting blades, reamers, wire saws, etc., in machinery, electronics, Industrial applications such as construction, drilling, and optical glass processing are widely used [1-3].
At present, when the diamond tool is prepared by electroplating at home and abroad, the main problem is that the bonding force between the plated carcass metal and the diamond particles is low, and when the diamond particles are subjected to the force in use, the loosening is easy to fall off, resulting in a short service life. The main reason for these phenomena is that the manufacturing temperature is low when the diamond tool is prepared by electroplating, so that the surface of the diamond particles is not easily infiltrated by the general metal, and not only a strong chemical bond is not obtained, but also a gap is often generated. In addition, due to the influence of the electroplating process, diamond tool plating metals are limited in type (only limited to nickel, chromium and other metals and their alloys), unlike the types of metals used in hot pressing tools.
In response to the above problems, various measures have been taken to solve the bonding force between diamond and coated metal. This paper comprehensively introduces the methods developed in recent years to improve the performance of electroplated diamond tools, and summarizes them, hoping to give people a detailed and clear understanding.
1 Improve the carcass material
In the electroplated diamond tool, the coating supports and combines the diamond. It is called the carcass or matrix metal. It determines whether the diamond particles can fully exert the cutting effect. It is generally required to meet high hardness, high wear resistance and high Performance requirements such as toughness, so people first consider improving the diamond tool by improving the performance of the carcass material.
1.1 Alloying of carcass metal
Although a single coating (such as nickel) has a high strength, particularly toughness, it is generally low in hardness, so alloy plating is often used.
1.1.1 Ni-Co binary alloy coating [1-5]
Cobalt can not only improve the strength of nickel metal (the compressive strength of nickel-cobalt alloy is 1600MPa), but also improve the heat resistance of the carcass metal. The strength limit of the Ni Co binary alloy at 800 °C is 500MPa. It can also improve the toughness of the carcass metal. Therefore, the Ni Co binary alloy plating layer has become a widely used carcass material, but sometimes the hardness of the Ni Co binary alloy plating layer is still insufficient, and the carcass is consumed quickly when processing a hard and abrasive material. Moreover, the Ni Co coating can ensure high hardness and wear resistance only when the cobalt content reaches about 30%, and a large amount of expensive metal cobalt increases the cost.
1.1.2 Ni Mn binary alloy coating [6]
Metal manganese can increase the hardness, strength and wear resistance of nickel matrix than cobalt. The nickel-manganese carcass hardness is about 10 degrees higher than the nickel-cobalt carcass hardness. Although the content of manganese in the alloy is small, it has a great influence on the performance of the carcass. When the nickel-manganese carcass diamond drill bit is drilled in a hard and strong abrasive formation, the average life and aging are 55% and 30% higher than that of the nickel-cobalt drill bit, respectively. At the same time, the nickel-manganese carcass bit does not require high speed and pressure. Conducive to reducing material consumption and reducing drilling costs. However, the Ni Mn binary alloy coating has high brittleness and is easy to crack, which makes the working layer easy to be broken.
1.1.3 Ni Co Mn ternary alloy coating [7]
Ni Co Mn ternary alloy coating has higher comprehensive mechanical properties. The hardness is higher than Ni Co, and the brittleness is lower than Ni Mn.
It is in line with the requirements of the electroplated diamond products for the carcass. Stone tools made with Ni Co Mn ternary alloy coatings are sharper and more durable than Ni Co binary alloy coatings, especially for hard stone. The Ni Co Mn ternary alloy coating is low in cost due to the saving of a large amount of expensive material cobalt. The mechanical properties of the Ni Co Mn ternary alloy coating can be adjusted over a wide range to meet the needs of a wider range of applications. However, when the Ni Co Mn ternary alloy plating layer is obtained, the composition of the plating solution is complicated and the stability is not easily controlled.
1.2 Composite of carcass metal
The composite plating layer is a special plating layer formed by uniformly interposing one or several insoluble solid particles and fibers into a metal plating layer by a co-deposition method. Since the composite coating uniformly disperses a large amount of solid particles, these hard particles can greatly hinder the slip between the crystal grains, and the metal can be effectively strengthened.
1.2.1 Ni Co fine-grained diamond composite coating [8 10]
Adding an appropriate amount of nano-diamond powder to the plating solution, the hardness of the obtained Ni Co diamond composite coating is obviously improved, the hardness can reach 601.53 HV [8], and the friction and wear performance is remarkably improved: the friction coefficient of the nickel-cobalt alloy coating is about 0.35, and the life is When the friction radius is 14mm, the average is 0.022km; the friction coefficient of Ni Co diamond composite coating containing nano-diamond powder is about 0.3, and the coating life is 0.15km when the friction radius is 14mm [9]. The Ni Co diamond composite coating is used as the diamond bit matrix, and the prepared diamond bit is drilled in a hard and strong abrasive layer, which has good wear resistance, fast drill bit length, long service life and can prevent hole inclination [10]. Since the ultrafine diamond powder is extremely easy to agglomerate and its performance cannot be fully exerted, measures should be taken to disperse the diamond powder. This inevitably restricts the use value and application prospect of ultrafine powder.
1.2.2 Ni Co rare earth element composite coating [11]
The addition of a small amount of rare earth compound can improve the performance of the plating solution and the coating layer. In the electrodeposition process, the cation is mainly adsorbed on the surface of the metal deposit, and the rare earth metal ion exhibits strong adsorption on the electrode. The rare earth metal ions are easily adsorbed on the active point of crystal growth, that is, adsorbed on the growth point of the crystal plane, and the crystal growth is effectively suppressed. Therefore, after the rare earth element is added to the plating solution, a fine grain plating layer can be obtained. Using the universal cylindrical grinding machine M1420E through the grinding test of bright nickel plating and bright nickel plating diamond tool grinding with rare earth elements, it was found that the addition of rare earth elements improved the grinding ratio of the diamond tool. Bright nickel-plated diamond tools have poor wear resistance, fast consumption of the carcass, can not guarantee the high edge of diamond, and the diamonds fall off quickly; the bright nickel bond tool with rare earth added improves the wear resistance of the carcass, and the diamond package is better, the height of the diamond blade is high. Large, so the efficiency of the tool is improved.
1.2.3 Ni Co carbon nanotube composite coating [12-14]
Carbon nanotubes (CNTs) have superior strength and toughness and can be used as reinforcements for advanced composites to greatly improve the strength and toughness of composites. In addition, CNTs have the characteristics of good chemical stability and low friction factor, and it is expected to prepare a new type of composite coating with high wear resistance, wear reduction and corrosion resistance [13]. Observing the SEM morphology of the composite coating, the surface of the substrate is covered by a thick layer of carbon nanotubes. One end of these carbon nanotubes is deeply embedded in the matrix, and the other end is exposed to the outside of the substrate, which can obviously act on the substrate. Protection [14]. The laboratory is working on the preparation of electroplated diamond tools using this composite coating.
1.3 Grain refinement of carcass metal
The crystallization process of the coating is governed by the nucleation rate and grain growth rate. The faster the rate of nucleation is formed, the slower the grain growth rate, and the finer the crystallization, the denser the coating and the better the hardness and toughness. According to the electrochemical theory, the larger the cathode electrochemical polarization overpotential, the easier it is to form crystal nuclei, and the finer the crystal, the denser the coating. Therefore, people have adopted the objective of improving the electrochemical polarization overpotential and refining the crystal grains to improve the carcass material.
1.3.1 Refined additives [1-3]
After the additive is added to the electrolyte, due to its adsorption on the electrode surface, the electrochemical polarization is increased, the covered crystal grains stop growing, and new crystal nuclei are generated; the new crystal grains are soon covered again, and a new nodule center is generated. So, you can get fine crystals. Secondly, the adsorption of the additive on the surface of the crystal can reduce the surface energy of the crystal, thereby reducing the formation of crystallites, which is favorable for forming a new crystal nucleus. The refining additives are mainly sulfonic acids, sulfinic acids, sulfonamides, disulfonic acids, etc., for example, saccharin, p-toluenesulfonamide, benzenesulfinic acid, benzenesulfonic acid, sodium naphthalenesulfonate, and the like. It can be found from the morphology of the surface of the coating before and after the addition of the aromatic ketone additive that the grain particles before the addition of the additive are large, and the crystallinity of the particles is poor, the crystal grains are loose, and after the addition of the additive, the grain particles are significantly smaller and crystallized. Dense.
1.3.2 Ultrasonic method [15-16]
The use of ultrasonic waves can cause intense mechanical vibration of the material and can also produce a one-way force. When a certain frequency of ultrasonic waves passes through the liquid, small bubbles of appropriate size resonate. In the sparse phase of the ultrasound, the vesicles rapidly expand and become larger; in the dense phase, the vesicles are suddenly compressed until they collapse. When the vesicle is suddenly compressed, the surrounding liquid fills the cavity at a great speed, and the nearby liquid or solid is subjected to high pressure of thousands of atmospheres, which is cavitation or cavitation [15].
Electroplating using high current density under ultrasonic conditions makes the coating more compact, smooth, uniform in thickness, non-porous, well bonded to the substrate, and has high strength and hardness. Nickel plating in an ultrasonic field with a frequency of 16 kHz increases the hardness by 30 to 5 [15]. Under appropriate process conditions, the internal stress of the coating can also be made lower than that of the coating without ultrasonic plating. The reason is that when the cathode current density is high to a certain value, the cathode polarization is sharply increased, resulting in an increase in hydrogen evolution, a rise in pH, and a nickel hydroxide solution in the cathode, and the cavitation of the ultrasonic wave refines the sol. And dispersion and stabilization to prevent sol condensation and precipitation. Ultrasonic waves should not be used in the whole process of diamond sand [16]. It is only used in the thickening period. When the diamond abrasive grains are buried in a certain thickness of the coating, ultrasonic waves are used, and the diamond abrasive grains will not be shaken, which will not affect the diamond tools. The number of sands.
1.3.3 Pulse plating and nano-tire material [17-18]
Pulse plating is a new type of plating technology developed in the 1960s. The electrochemical principle is based on: in one pulse period, when the current is turned on, the electrochemical polarization increases, the metal ions in the vicinity of the cathode region are fully deposited, and the crystal of the plating layer is fine and bright; when the current is turned off, near the cathode region The discharge ions return to the initial concentration and the concentration polarization is eliminated. Therefore, pulse plating is a new type of power application. The relaxation of the current or voltage pulse is used to reduce the concentration polarization of the cathode, thereby allowing a higher current density to achieve higher electrode polarization and ultimately achieving grain refinement. At present, electrodeposition technology has become an important preparation method for nanomaterials. These materials have high hardness and good toughness [17]. When used to prepare diamond tools, the wear resistance of diamond tools can be significantly improved. Li Zhaomei [18] and Others prepared the nano-nickel diamond tool by pulse electrodeposition method, and carried out the wear destructive test. The results show that the average life of the pulsed nano-nickel diamond tool is significantly higher than that of the conventional nickel-cobalt diamond tool, which is about 1.5 times. .
2 Improve the contact area between diamond and carcass
2.1 Using surface roughened diamond particles
The roughening method is used to form some tiny pits and cracks on the diamond surface, and the surface of the diamond in contact with the carcass is increased to improve the mechanical integration force of the diamond and the metal, and enhance the "mechanical anchor chain" effect. A strong roughening method is: covering the diamond with a chlorine base salt (mainly NaCl + BaCl2) and a small amount of deoxidizing agent, covering with a ceramic crucible, heating in the furnace to 1000 ° C to 1100 ° C, and then holding the heat, and then The chlorine base salt is removed with boiling water. The diamond is heated, and the chlorine-based salt is melted to cause graphitization of the diamond corrosion, so that the surface forms minute rough pits and cracks. Another weakening method is to etch the diamond in a roughening solution (nitric acid + sulfuric acid or nitric acid + hydrogen peroxide) at room temperature or under heating, stirring constantly, and then washing it with distilled water. Diamonds form defects such as pits and cracks and slight graphitization under the corrosion of strong oxidizing acids.
2.2 Eliminate the gap between the diamond particles and the carcass in the tool
Since diamond is a non-metal, it has no good affinity with metals, resulting in a high interfacial energy between diamond and common metals or alloys, often creating voids, which reduce the bonding between diamond particles and the substrate of the coating. In this case, the particle surface modification method, the CVD method, the ultrasonic method, or the electroless plating method can be utilized to avoid or compensate for such voids.
2.2.1 Particle surface modification method [19]
The diamond particles are oxidized to form a hydrophilic chemical group on the surface, thereby improving the hydrophilicity of the diamond surface and tightly bonding the diamond particles to the plating layer. If the hydrophilic groups on the diamond surface are replaced by some more hydrophilic organic genes by chemical means, the effect can be further improved.
2.2.2 Electroless plating method [20]
Electroless plating deposits metal on the surface of diamond by an oxidation-reduction reaction of an autocatalytic process without an applied current, thereby forming a uniform and dense film coating. It has been found that when a diamond tool is obtained by chemical composite plating, there is no gap between the diamond and the metal carcass. In addition, ultrasonic vibration will expand around the diamond particles, completely eliminating the gap. The particulate diamond can be directly electrolessly plated to obtain a tool which can be uniformly suspended in the plating solution. For large-grain diamonds, we recommend that you first perform electroplating and sanding to allow the diamond to be pre-embedded in the coating. The thickening process can be electroless.
3 Improve chemical bonding between particles and carcass
By treating the diamond, the carbon atoms on the surface form metal/carbon chemical bonds with the metal atoms, which can completely solve the problem that the diamond and the carcass bond strength in the diamond tool is not strong.
3.1 Surface metallization [21]
The surface treatment of the diamond particles by electroless plating can form a firm and tight connection between the diamond and the coating. However, if the diamond surface is completely metallized, the surface of the diamond particles has good electrical conductivity and is not suitable for electroplating to prepare diamond tools. In the process of burying sand, the plated diamond and the steel substrate and the plating layer together form a cathode, and a phenomenon in which a plurality of diamond particles are bonded to each other to form a block is formed. Therefore, the researchers used diamonds with dispersed conductive dots to make electroplated diamond tools [21]. The method is to control the degree of electroless plating on the diamond surface, strictly control the concentration of the sensitizing solution and the activating solution, and the time of sensitization and activation treatment, so that the number of metal dots on the diamond surface is kept within a suitable range. Although the number of conductive dots on the surface of the diamond increases, the connection point with the plated metal can be increased, and the bonding property between the plating layer and the diamond can be improved. However, when the metal dots are too dense, a thin layer of metal joined into a sheet is formed.
After the electroless plating of diamond, the obvious boundary between the diamond and the nickel-cobalt-based coating disappeared, and some scattered nickel-cobalt joints were grown on the bonding surface of the diamond and the coating [21]. The electroplated diamond tool was prepared from the activated diamond, and the material removal amount was 1.5 times that of the unactivated treatment when grinding the Al2O3 ceramic workpiece [21]. However, with this method, the diamond particles and the coating may be chemically combined in the original sense, and the true chemical bond is not achieved, and the intermolecular force may account for a larger proportion.
3.2 CVD method [22]
Using diamond CVD deposition technology to repair the prepared diamond tools, not only can the newly formed diamonds be deposited in the gaps in the tool, but also the diamond particles in the tool can be regenerated, and the surface is further developed and improved. Particle properties. The MPCVD method has been successfully used for void repair occurring between diamond particles and carcass metal after electroplating. Observation of the surface topography of an electroplated diamond tool prepared using diamond particles having an average size of 16 μm under SEM revealed irregularities and irregularities in the surface, and concave and voids between the diamond particles and the carcass metal. The tool was placed in an MPCVD system and the average size of the diamond particles was increased to 25 μm. The gap between the diamond particles and the carcass metal was compensated by SEM and the surface of the diamond particles was regular and full [22]. This method is used to repair the electroplated diamond tool, which has higher cutting force, wear resistance and particle bonding than the unrepaired electroplated diamond tool. At high temperatures during the MPCVD process, carbon-metal bonds are formed between the diamond and the carcass, creating a strong bond between the diamond particles and the carcass metal [22].
references
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