At present, the commonly used plating methods are as follows:
The method specifically refers to first depositing metals such as Ni, Co, Cu, or Ni-W, Co-W and other composite metals on the surface of diamond abrasive products through oxidation-reduction reactions to make the diamond conductive, and then electroplating it to obtain the required的plating.
Electroless plating + electroplating products of diamond particles are usually only used for resin bond tools, which can increase the surface roughness of diamond particles and improve the physical control of the particles by the bond. At the same time, the coating can compensate for the internal defects of diamond particles and improve their mechanical properties.
It is worth noting that electroless plating or electroplating of Ni, Co, Cu on the surface of diamond abrasive powder is not suitable for metal bond tools. Even products plated with Ni-W and Co-W alloys cannot be used for metal bond tools. The reason is that Ni, Co is a graphitizing element and cannot play a role in metallurgical bonding.
Salt bath plating is to add metal powders such as Ti or Cr to the chloride, and then put diamond abrasive particles into the mixed solution, heat the solution to 850℃~1100℃, and form the corresponding diamond surface after 1~2h salt bath treatment Carbide coating.
The advantage of this method is that the plating layer is firmly bonded to the diamond; the disadvantage is that the plating temperature is high, the process of separating the diamond from the salt bath after plating is complicated, and the plating cost is high.
The surface of diamond abrasive powder used for metal bond diamond tools such as saw blades, geological drill bits, etc. should be coated with strong carbide forming elements, such as Ti, cr, Mo, w, V, etc. These metals are generally vacuum coated It is deposited on the diamond surface, but this method requires vacuum equipment and the process is complicated. At present, the commonly used vacuum plating technologies are as follows:
1. Vacuum physical vapor deposition (PVD)
Vacuum physical vapor deposition refers to the use of vacuum evaporation coating machine, magnetron sputtering coating machine or ion beam coating machine and other equipment and vacuuming it to vaporize the target metal into atoms, molecules or ions and directly depositing on the surface of the plating part. According to the different vaporization methods during film coating, the method can be divided into vacuum evaporation plating, vacuum sputtering plating and vacuum ion plating.
However, this method has some shortcomings, such as low single-time coating, uneven coating, easy to leak plating, only physical adhesion between the coating and diamond abrasive powder, no chemical metallurgical bonding, etc.; in order to obtain the best coating structure, multiple coatings are required. It is difficult to realize industrial application.
2. Vacuum chemical vapor deposition (CVD)
Chemical vapor deposition is the use of gaseous substances under certain pressure, temperature, and time conditions to perform chemical reactions on the solid surface to form a coating. CVD generally introduces the gaseous compound (such as halide, etc.) of the metal to be plated into the reaction chamber where the plated part is placed, and thermal decomposition or chemical synthesis occurs in contact with the workpiece to form a coating.
However, the reaction temperature of this method is generally as high as 900-1200°C, which is easy to damage the diamond; like PVD, it has the problems that the reaction gas phase is difficult to penetrate into the accumulated particles, the single coating amount is low, and the cost is high.
The use of metal powder and diamond contact reaction at high temperature to form a carbide or metal layer on the diamond surface is called powder covering sintering method or solid powder contact reaction method. The formation of the coating is actually that the metal oxides in the powder such as WO3, WO2, MoO3, MoO2 are volatile at high temperatures and undergo a carbon reduction reaction with the carbon atoms on the diamond surface to form carbides.
Although this method can increase the amount of single coating, because the coating temperature is generally higher than 850 ℃, the diamond abrasive powder will be oxidized and the compressive strength will be reduced. The actual use effect shows that the improvement of the performance of diamond tools is not obvious.
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