Chromium coatings electrodeposition

A.STM B650, Std. Spec, for Electrodeposited Engineering Chromium Coatings of Ferrous Substrates, American Society for Testing and Materials, Philadelphia,... 

Chromium is also a very hard metal with excellent wear resistance, and so is widely used as a coating material for engineering applications. For these purposes, coatings are applied by electrodeposition which may be several millimetres thick. These hard engineering chromium coatings invariably contain fine cracks and fissures which can allow corrodents to attack the... 

Electrodeposited chromium coatings. Electrolytic corrosion testing Coatings cathodic to the substrate-rating of electroplated test specimens subjected to corrosion tests... 

Aluminum alloys with chromium The electrodeposition of Cr has been investigated in acidic chloroaluminates by Ali et al. [27]. They report that the Cr content in the AlCr deposit can vary from 0 to 94 mol%, depending on the deposition parameters. The deposit consists both of Cr-rich and Al-rich solid solutions as well as intermetaUic compounds. An interesting feature of these deposits is their high-temperature oxidation resistance the layers seem to withstand temperatures up to 800 °C, so that coatings with such an alloy could be interesting for applications in engines. 

Until the 1970s, most chromium coatings had been applied (Table 10.11) by either electrodeposition or chemical vapor deposition. In the strip coating field vacuum [136] aud powder [137] coating and electrodeposition have been investigated extensively [138] since steel, having a thin flash coating of chromium, can compete successfully with tinplate. 

Where the corrosion resistance of a coating depends upon its passivity, it is common to follow plating with a conversion coating process to strengthen the passive film. Zinc, cadmium and tin in particular are treated with chromate solutions which thicken their protective oxides and also incorporate in it complex chromates (see Section 1S.3). There are many proprietary processes, especially for zinc and cadmium. Simple immersion processes are used for all three coatings, while electrolytic passivation is us on tinplate lines. Chromate immersion processes are known to benefit copper, brass and silver electrodeposits, and electrolytic chromate treatments improve the performance of nickel and chromium coatings, but they are not used to the extent common for the three first named. 

Electrodeposited chromium coatings—Electrolytic corrosion testing (EC test)... 

As mentioned earlier, a thin overlay of chromium is applied on nickel coating to prevent the corrosion of nickel coatings. Chromium is generally applied in the form of electrodeposit. As chromium coating is resistant to corrosion and has a bright luster, it is used as a decorating coating. Chromium is more active than iron (E° = -0.76 V) and has a tendency to become passive. 

Special care should be taken to prevent or retard the diffusion of substrate metals (silver, copper, chromium) into electrodeposited gold under high-temperature conditions. A suitable barrier to prevent diffusion is a thin nickel or palladium coating between the gold plating and the substrate. 

Brooman E. W. (2005), Compliant electrodeposited and electroless nanostructured and nanocomposite coatings to replace chromium coatings , Galvanotechnik, 12,103. 

Nickel, chromium and zinc are commonly used as electrodeposits. Chromium, the hardest of these coatings, is applied for abrasion resistance... 

Nickel is also widely used as an electrodeposited underlay to chromium on chromium-plated articles, reinforcing the protection against corrosion provided by the thin chromium surface layer. Additionally the production of articles of complex shape to close dimensional tolerances in nickel by electroforming —a high-speed electrodeposition process —has attracted considerable interest. Electrodeposition of nickel and the properties of electro-deposited coatings containing nickel are dealt with in greater detail in Section 14.7. 

Gold coatings on separable electric contacts and slip rings make use of the high hardness possible with electrodeposition to resist wear. Rhodium is another metal which can be exceptionally hard. Thick coatings have a cracked-sealed structure similar to that of chromium. 

Wearmouth has described the production of nickel-cobalt, nickel-manganese, and nickel-chromium alloy coatings for non-decorative uses. The nickel-cobalt and nickel-manganese are electrodeposited direct from sulphamate-based solutions, the nickel-cobalt alloys offering higher hardness than the nickel-manganese alloys, which are restricted to a relatively... 

A wide range of applications for hard, wear-resistant coatings of electroless nickel containing silicon carbide particles have been discussed by Weissenberger . The solution is basically for nickel-phosphorus coatings, but contains an addition of 5-15 g/1 silicon carbide. Hiibner and Ostermann have published a comparison between electroless nickel-silicon carbide, electrodeposited nickel-silicon carbide, and hard chromium engineering coatings. 

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