Hard nickel deposits

Hard nickel deposits When the plating variables are adjusted to give deposits with a hardness much above 200 Hy with a Watts solution, internal stress is usually too high and ductility too low for the deposits to be fully satisfactory. Higher hardness coupled with reasonable ductility can be achieved by addition of ammonium salts and operation at higher solution pH. A solution used for this purpose and some deposit properties are as follows ... 

Decomposition products of the above-mentioned organic additives may have an adverse effect in the individual case. Thus, the maximum temperature resistance for hard nickel deposits from sulfate baths is 300 °C. For the galvanic designer, it is therefore important to know for which processing method the electroplating process is required, so that the benefits of nickel, together with the electroplating, can be used for specific applications. 

Tin—Nickel. AHoy deposits having 65% fin have been commercially plated siace about 1951 (135). The 65% fin alloy exhibits good resistance to chemical attack, staining, and atmospheric corrosion, especially when plated copper or bron2e undercoats are used. This alloy has a low coefficient of friction. Deposits are solderable, hard (650—710 HV ), act as etch resists, and find use ia pfinted circuit boards, watch parts, and as a substitute for chromium ia some apphcafions. The rose-pink color of 65% fin is attractive. In marine exposure, tin—nickel is about equal to nickel—chromium deposits, but has been found to be superior ia some iadustfial exposure sites. Chromium topcoats iacrease the protection further. Tia-nickel deposits are bfitde and difficult to strip from steel. Temperature of deposits should be kept below 300°C. 

The effect of ultrasound has been extremely beneficial in improving the hardness of nickel deposits (Tab. 6.11). Using a variety of plating solutions it has been shown that the presence of ultrasound improves the hardness of the coating with the magnitude dependent on the particular bath composition employed [9,12]. 

Sulfur impurities can be detrimental to nickel deposits. Specifically, an increase in sulfur couteut is known to reduce the fracture resistance of electroformed nickel. Since sulfur has a direct influence on the properties of electrodeposited nickel, if no other impurities are present in the deposit, hardness by itself can be used as an indicator of sulfur impurity content. 

The autocatalytic nickel deposition can also be used for alloy deposition (Ni-Co, Ni-Fe) and for the deposition of nickel dispersion coatings (Ni/SiC). The nickel film can be heat-treated, below or well above 280 °C, the transition temperature amorphous/crystalline. The hardness increases up to 400 °C (1000-1200 HV) and then decreases again. Especially the corrosion protection... 

Nickel deposits are most widely used as a base for chromium plating the thicker the deposit (typically 20 xm), the greater the corrosion resistance. Nickel plating is used in engineering where wear resistance, hardness and corrosion resistance are required, e.g. oil valves, rotors, drive shafts and in printed circuit board manufacturer. It is also used for its decorative properties, e.g. doorknobs. 

The deposit of nickel, which itself has good corrosion resistance, gives protection to the base metal and is itself protected from surface oxidation by the chromium. As a decorative finish, chrome plate can also be applied to plastics, usually acrylonitrile-butadiene-styrene (ABS). Hard chrome deposits, typically 150-500 m, are used to build up rollers, hydraulic rams, valves, etc., as a hard, abrasive-resistant wearing surface which is subsequently ground to give a highly accurate surface finish. 

Another important function of metallic coatings is to provide wear resistance. Hard chromium, electroless nickel, composites of nickel and diamond, or diffusion or vapor-phase deposits of sUicon carbide [409-21-2], SiC , SiC tungsten carbide [56780-56-4], WC and boron carbide [12069-32-8], B4C, are examples. Chemical resistance at high temperatures is provided by aUoys of aluminum and platinum [7440-06-4] or other precious metals (10—14). 

Electrodeposition of Metals. Citric acid and its salts are used as sequestrants to control deposition rates in both electroplating and electroless plating of metals (153—171). The addition of citric acid to an electroless nickel plating bath results in a smooth, hard, nonporous metal finish. 

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