Due to its high hardness, high strength, high wear resistance and low linear expansion coefficient, diamond tools are suitable for processing hard and brittle hard-to-machine materials such as cemented carbide, optical glass and advanced ceramics. Materials such as stone, semiconductor, ferrite and boron carbide and corundum sintered body are widely used in industrial fields such as machinery, electronics, construction, drilling, medical optical glass processing. However, there are still problems in the use of diamond tools, which are manifested in the fact that the diamond particles are easily detached during work, which reduces the service life and performance level of the diamond tools. According to reports, the utilization rate of diamond in the majority of the diamond tools is only about 60%.
Diamond is non-metallic and has no good affinity with metals, resulting in a high interfacial energy between diamond and common metals or alloys. In particular, when the diamond tool is prepared by electroplating, the manufacturing temperature is low, and the carbon atoms on the diamond surface cannot be interfacially reacted to form carbides to be chemically bonded to the carcass metal, and the diamond particles are only mechanically embedded in the plating substrate. In addition, due to the particularity of the diamond surface, the wettability of the plating solution to the diamond surface is not good, resulting in a gap between the plating layer and the particles. Although the diamond has experienced high temperatures during the preparation of the diamond tool by hot pressing, providing the possibility of forming chemical affinity, when the diamond tool is prepared by hot pressing, the sintering temperature is generally as high as 900 ° C, and the diamond is heated to 700 in air. When the temperature is around °C, the weight loss of oxidation begins, and the pressure resistance decreases. At 1000 °C, the diamond will be graphitized, which greatly affects the strength and use effect of the diamond.
In response to the above problems, various measures have been taken to improve the bonding force between diamond and carcass. In this paper, the surface metallization and surface roughening method are used to improve the mechanical inlay force between diamond and carcass. The chemical bonding between diamond and metal is formed by vapor deposition, electroless plating and post-heat treatment. By implementing the above method, the problem of the bonding force of the particles in the diamond tool can be effectively solved.
1 Improve mechanical setting force
The surface treatment of the diamond is carried out by surface metallization and surface roughening, so that the diamond can be well infiltrated and embedded by the carcass metal, thereby enhancing the bond between the carcass and the diamond particles in the diamond tool.
1.1 Surface metallization
After the surface of the diamond is metallized, the surface of the diamond has metallic properties. The surface layer not only fills the micropores and cracks of the diamond itself, but also promotes the wetting ability between the diamond and the carcass metal, and can improve the tight bonding between the diamond particles and the metal.
1.1.1 continuous metal film
The use of diamond with a continuous metal film to prepare a hot-pressed diamond tool can improve the oxidation resistance of the diamond, prevent the graphite from being graphitized at high temperatures and fall off during use.
A continuous metal film on the diamond surface can be prepared by electroless plating. After electroless plating, the diamond and the carcass metal are tightly bonded, and there is no obvious groove in the interface between the diamond and the carcass except for small cracks. In addition, the mechanical properties of un-plated and electroless Ni-Fe-B diamonds show that the carcass has an uncoated diamond-coated ability of 96.1 MPa, and the inclusion of electroless Ni-Fe-B diamond is 105.4 MPa.
1.1.2 Dispersed metal dots
A diamond surface with a continuous metal film has good electrical conductivity and is not suitable for electroplating to prepare diamond tools. Because in the process of burying sand, the plated diamond and the steel substrate and the plating layer together form a cathode, a phenomenon in which a large number of diamond particles are bonded to each other to form agglomerates. Dispersing the metal dots is to partially metallize the diamond surface. When an electroplated diamond tool is fabricated using diamond having a dispersed metal dot on the surface, the diamond does not form a cathode with the steel substrate and the plating layer, and the diamond particles do not stick to each other during the sanding process.
Electroless plating can be used to form scattered metal dots on the surface of diamond. The main purpose is to control the degree of electroless plating. The concentration of sensitizing solution and activation solution and the time of sensitization and activation treatment, especially the time of electroless plating, must be strictly controlled. The number of metal dots on the diamond surface is kept within a suitable range. Although the number of metal dots on the surface of the diamond is increased, 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 connected into a sheet is formed.
In the electroplated diamond tool prepared by the treated diamond, the obvious boundary between the diamond and the nickel-cobalt plating layer disappears, and some dispersed nickel-cobalt joints are grown on the bonding surface of the diamond and the plating layer. There is a clear boundary between the untreated diamond particles and the nickel-cobalt coating. The plating and the diamond are simply mechanically contained and do not form a strong bond. The electroplated diamond tool was prepared from the treated diamond, and the material removal amount was 1.5 times that of the untreated material when grinding the Al2O3 ceramic workpiece.
1.2 Surface roughening
The roughening method is used to form some tiny pits and cracks on the diamond surface, which increases the surface roughness of the diamond to improve the mechanical integration force of the diamond and the metal and enhance the “mechanical anchor chain” effect. There are two other aspects to increase the roughness of the diamond surface: First, the roughened diamond surface forms some tiny concave surfaces. Because of the large adsorption force on the diamond surface, it is beneficial to the adsorption of metal ions in the surface. Subsequent electroless plating and electroplating; the second is to connect some of the original concave surface and dislocation on the diamond surface, forming a step on the diamond surface, which provides favorable conditions for the growth of electroless plating or electroplated metal deposition layer.
1.2.1 Strong roughening
The diamond is heated to cause the chlorine-based salt melt to erode the diamond to produce graphitization, which causes the surface to form minute rough pits and cracks. Specifically, the chlorine base salt (mainly NaCl + BaCl2) and a small amount of deoxidizer are covered on the diamond, covered with ceramic crucible, heated to 1000 ° C to 1100 ° C in a box type electric resistance furnace, and then kept for 10 min, then The chlorine base salt is removed with boiling water.
1.2.2 weak roughening
The diamond is eroded in a roughening solution (nitric acid + sulfuric acid or nitric acid + hydrogen peroxide) at room temperature or under heating, and is continuously stirred, and then washed with distilled water. Diamonds have some defects (such as pits, cracks) and slight graphitization on the surface under strong oxidative corrosion of acid.
2 improve chemical bonding force
By treating the diamond at a high temperature, the carbon atoms on the surface form metal/carbon chemical bonds with the metal atoms, thereby forming a strong bond between the diamond particles and the tool carcass metal through the bridge function of the bond.
2.1 Vapor deposition method
The vapor deposition method is divided into physical vapor deposition and chemical vapor deposition according to the action mechanism. Under vacuum, the metal is vaporized into atoms, molecules or ions and deposited directly onto the surface of the plated part, called vacuum physical vapor deposition (PVD). Depending on the gasification method of the film-forming material, the PVD method can be further divided into vacuum evaporation plating, vacuum micro-evaporation plating, vacuum sputtering plating, and vacuum ion plating. Chemical vapor deposition (CVD) is a method in which a gaseous compound (such as a halide) is introduced into a reaction chamber in which a plated member is placed under a certain pressure, temperature and time under a certain pressure, temperature and time, and is thermally decomposed or chemically contacted with the workpiece. Synthesize to form a plating layer.
The bonding strength between vacuum micro-evaporation coating and diamond surface is the highest among various plating methods. After micro-evaporation of titanium with large-grain diamond, the interface bonding strength of the side is 140 MPa, while the conventional PVD is heat-treated at 800 °C after titanium plating. The highest strength is 80 MPa. After the titanium is vacuum-evaporated, it is used for frame sawing to cut soft stone saw blades, and the resection rate is increased by 90% to 120%.
X-ray diffraction analysis (XRD) of vacuum-plated Ti-Cr diamond revealed that carbides (films) such as TiC and Cr2C3 were formed on the surface of the diamond, and this carbide formed a strong chemical bond with the diamond surface. On the other hand, it can be well infiltrated by the carcass metal or alloy. Scanning electron microscopy analysis of the bonding state of vacuum-plated Ti-Cr diamond in the carcass shows that the vacuum-plated Ti-Cr diamond and the carcass interface have obvious carbide transition layer formation, and the carcass is vacuum-plated Ti-Cr diamond. For chemical bonding.
2.2 Electroless plating and subsequent heat treatment
The surface of the diamond is plated with a metal which is chemically bonded to carbon by the electroless plating method mentioned above, and then the plated diamond is placed in a vacuum furnace for heat treatment to form a desired carbide on the surface of the diamond, thereby making it easy to form Infiltrated by ordinary metals. Through the bending strength test of the diamond saw blade, it is proved that the diamond obtained by the heat treatment after electroless plating has higher bending strength than ordinary diamond, from 75MPa to 95MPa, and the increase is more than 20%. The microporosity and crack of the diamond itself can also be It is filled and its compressive strength is increased by more than 30%.
2.3 Salt bath method
Under high temperature conditions, the diamond-active metal or alloy is heated to melt into the diamond surface, and penetrates into the micropores and cracks under the action of capillary force to form a layer of metal or alloy on the diamond surface. Compound film. The specific method is that the surface-cleaned diamond is mixed with the required metal powder, placed in a high-temperature snail, covered with a chlorine-based salt and a small amount of deoxidizing agent, and heated to 900 ° C to 1000 ° C through a box-type electric resistance furnace. Keep warm, then cool to room temperature with the resistance furnace, and finally take out the water and boil it to remove the salt residue. X-ray diffraction pattern analysis (XRD) of the diamond after plating on the salt bath showed obvious diffraction peaks of WC, indicating that WC was formed on the diamond surface, and the diffraction peak of W was the strongest, and the diamond surface after plating treatment The structure should be diamond (inner layer) + WC + W (outer layer).
It is worth mentioning that the argon-shielded brazing, vacuum induction brazing and laser brazing techniques can be used to achieve the Ti-plated diamond and steel matrix at the brazing temperature of 790 °C using Ag-Cu-Ni alloy brazing filler metal. The firm connection, after grinding, the diamond shedding rate is 11%. At the brazing temperature of 800 ° C, the Ag-Cu-Cr alloy brazing filler metal can be used to achieve a firm connection between the coated Ni film diamond and the steel substrate. After grinding, the diamond shedding rate is only 8%.
By enhancing the mechanical bonding force between diamond and metal and forming a chemical bond between diamond and metal, the bonding force between diamond and carcass in diamond tools can be improved to varying degrees. However, in contrast, increasing chemical affinity is a powerful and effective method to completely solve the problem of insufficient bonding between diamond and carcass in diamond tools.
However, all current methods involve high temperature treatment, even reaching above 1000 ° C. Such high temperature will cause oxidation loss or graphitization of diamond, so we suggest that low temperature chemical treatment technology can be used to form such metal/carbon chemical bonds. Hehe. For example, using a strong oxidant to boil the diamond to oxidize the surface carbon atoms to form a C-OH bond, and then chemically treating the metal atom to replace the hydrogen atom in the carboxyl group, or even replacing the entire carboxyl group, thereby obtaining diamond carbon atoms at normal temperature. Chemical bonding of metal atoms. The laboratory is conducting research in this area and hopes that colleagues can work together to solve the key problem of poor bonding between diamond and carcass in the preparation of diamond tools.