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Coating off
2012-12-07 by seoer10

Electroplated diamond tools multi-channel processes involved in the manufacturing process, any process inadequate, will cause the coating off.

 plating pretreatment

Steel substrate in the treatment step before entering the plating tank is referred to as pre-plating treatment. Pre-treatment: mechanical polishing, degreasing, etching and activation steps. The purpose of the pre-plating processing is to remove the surface of the base of the burr, grease, oxide film, rust and oxide scale, normal growth, the formation of the binding force between the molecules to expose the base metal of the metal lattice. If handled properly, before plating the surface of the substrate has a thin oil film and the oxide film, the metal lattice of the base metal can not be sufficiently exposed, it will hinder the binding force between the metal coating  of the bath

Formulations of the bath directly affect the kind of plating metal, hardness, wear resistance, with different process parameters also control the thickness of the plating metal crystals, caused by the density and the size of the plating internal stress. For the production of electroplated diamond tools,abrasive tools, most of the nickel or nickel - cobalt alloy, fails to consider the impact of bath impurities, and the factors that affect the coating off:

1) affect the coating of the internal stress of the internal stress is generated in the electro-deposition process, the solution of the additives and their decomposition products and hydroxides will increase the internal stress. Such stress is in the plating process, plating layer by some deposition factors, caused due to lattice defects. In particular the role of certain metal ions and organic additives, will significantly increase the internal stress of the coating. Macroeconomic stress and micro-stress two types of coating internal stress. Macroscopic stress is manifested in a sheet metal plating on one side, bending flakes impact of stress within the coating. Microscopic stress is manifested mainly by increasing the hardness of the coating.

Macroscopic stress can cause the coating to produce bubbles, cracking, loss and other phenomena in the storage, grinding wheel,use process.

Different plating bath for electroless nickel or nickel - cobalt alloy composition, internal stress are significant differences between the higher chloride content, the greater the internal stress. For the main salt of nickel sulfate plating bath, bath internal stress watt class were less than other types of plating solution. By adding an organic brightener, or stress relieving agent the macro internal stress of the coating may be significantly reduced while increasing its microscopic internal stresses. Different process combinations, such as current density, pH value, temperature, and can make the same kinds of bath of the coating have different internal stress. Therefore, to reduce the influence of the internal stress must strictly control the scope of the process of the bath, so as to ensure that the internal stress of the coating in the range of the process requirements.

2) the impact of hydrogen evolution in any plating solution, regardless of how the PH value, due to the water molecule dissociation, always present a certain amount of hydrogen ions. Accordingly, under appropriate conditions, both in acidic, neutral or alkaline electrolyte solution for electroplating with a metal precipitated on the cathode, while often hydrogen precipitated. Hydrogen ions in the cathodic reduction, part of the formation of hydrogen gas to escape, the part of the state of atomic hydrogen to penetrate the base metal and coating. So that the lattice distortion causing great stress, but also the coating significantly deformed. At this point, no defects from the appearance point of view, but it's mechanical performance is substandard. Adsorbed hydrogen will swell so the tool during use, when the temperature of the surrounding medium is increased, aggregation in the matrix metal or plating metal plating bubbled off phenomenon.

The electroless nickel cathode current efficiency of 95%, only 5% of the hydrogen evolution reaction. However, if the temperature is too high, the PH value is too low, the components improper causes the hydrogen evolution exacerbate. Therefore, how to control the plating hydrogen evolution reaction control coating internal stress is a problem worth exploring.

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