Electroplating Improvement Research Diamond Tool (3)

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. .

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