1. Production of carbide-coated diamond
The principle of mixing metal powder with diamond, heating to a fixed temperature and insulation for a certain time under vacuum. At this temperature, the vapor pressure of the metal is sufficient for covering, and at the same time, the metal is adsorbed on the diamond surface to form a coated diamond.
2. Selection of coated metal
In order to make the diamond coating firm and reliable, and to better understand the influence of the coating composition on the coating force, the coating metal must be selected. We know that diamond is an alloomorphism of C, and its lattice is a regular tetrahedron, so the principle of coating the metal composition is that the metal has a good affinity for carbon. In this way, under certain conditions, chemical interaction occurs at the interface, forming a firm chemical bond, and a Me-C membrane is formed. The infiltration and adhesion theory in the diamond-metal system points out that the chemical interaction occurs only when the adhesion work AW> 0 and reaches a certain value. The short periodic group B metal elements in the periodic table, such as Cu, Sn, Ag, Zn, Ge, etc. have poor affinity for C and low adhesion work, and the bonds formed are molecular bonds that are not strong and should not be selected; the transition metals in the long periodic table, such as Ti, V, Cr, Mn, Fe, etc., have large adhesion work with the system of C. The interaction strength of C and transition metals increases with the number of d layer electrons, so Ti and Cr are more suitable for covering metals.
3. Lamp experiment
At the temperature of 8500C, diamond can not reach the free energy of activated carbon atoms on the diamond surface and metal powder to form metal carbide, and at least 9000C to achieve the energy needed for the formation of metal carbide. However, if the temperature is too high, it will produce thermal burning loss to the diamond. Considering the influence of temperature measurement error and other factors, the coating test temperature is set at 9500C. As can be seen from the relationship between insulation time and reaction speed (below),? After reaching the free energy of metal carbide generation, the reaction proceeds quickly, and with the generation of carbide, the reaction rate will gradually slow down. There is no doubt that with the extension of insulation time, the density and quality of the layer will be improved, but after 60 minutes, the quality of the layer is not greatly affected, so we set the insulation time as 1 hour; the higher the vacuum, the better, but limited to the test conditions, we generally use 10-3mmHg.
Package inset ability enhancement principle
The experimental results show that the fetal body is stronger to the coated diamond than the uncoated diamond. The reason for the strong inclusion ability of the fetal body to the coated diamond is that, personally, there are surface defects and micro-cracks on the surface or inside of any uncoated artificial diamond. Due to the presence of these microcracks, the strength of the diamond decreases, on the other hand, the C element of the diamond rarely reacts with the fetal body components. Therefore, the tire body of uncoated diamond is purely a mechanical extrusion package, and this kind of package insert is extremely weak. Once the load, the above microcracks will lead to the concentration of stress, resulting in the decline of the package insert ability. The case of overburden diamond is different, due to the plating of a metal film, the diamond lattice defects and micro cracks are filled out, on the one hand, the strength of the coated diamond is increased, on the other hand, filled with micro cracks, there is no longer stress concentration phenomenon. More importantly, the infiltration of the bonded metal in the tire body is converted into the carbon on the diamond surfaceThe infiltration of compounds. The result is the bonding metal on diamond wetting angle from more than 100 o to less than 500, greatly improved the bonding metal for diamond wetting, make the tire body of the covering diamond package set by the original extrusion mechanical package into bonding package, namely the covering diamond and tire body bond, thus significantly improve the fetal body
Package insetting ability. At the same time, we also believe that other factors such as sintering parameters, coated diamond particle size, grade, fetal body particle size and so on have a certain impact on the package insert force. The appropriate sintering pressure can increase the pressing density and improve the hardness of the fetal body. Appropriate sintering temperature and insulation time can promote the high temperature chemical reaction of the tire body composition and the coated metal and diamond, so that the bond package is firmly set, the diamond grade is good, the crystal structure is similar, the similar phase is soluble, and the package set is better.
Excerpt from Liu Xiaohui
Post time: Mar-13-2025
