TiN coated

The gap between laboratory wear testing and industrial appHcation trials is extremely difficult to bridge, since there is often Httie or no control over testing in the industrial environment. Despite these limitations, several examples of industrial successes involving ion implanted tools have been reported and blind tests of nitrogen-implanted machine tools have been performed, including tool taps, dies, punches, and TiN coated WC cutting inserts (106). 

Hot Dip Tin Coating of Steel and Cast Iron. Hot dipping of tin [7440-31 -5] has been largely superseded by electrolytic coating techniques, especially for sheet. However, hot dipping can be the method of choice for complex and shaped parts. Very thin layers of tin are extensively used to passivate steel used for canned goods. Tin is essentially nontoxic, is nearly insoluble in almost all foods, and easily wets and completely covers steel with a pinhole-free coating. 

Standard 0.25 or 0.50 lb (227 g) tin coated cans are used for packaging Hquid with neutral and mildly alkaline base formulas polypropylene is used for acid—base removers. Steel and polypropylene dmms are used for industrial removers. Viscous removers are packaged in removable top containers. Dry caustic removers are packaged in bag-lined boxes or fiber dmms. 

Another familiar commercial method is the immersion or hot-dipping process. The article to be coated is immersed in a molten metal bath. Usually httie else is done to change the properties of the coating, which adheres to the surface upon removal of the article from the bath. For a successful coating, an alloying action must take place between the components to some extent. Zinc and tin coatings are appHed to sheet steel by hot-dipping. 

Molten tin wets and adheres readily to clean iron, steel, copper, and copper-base alloys, and the coating is bright. It provides protection against oxidation of the coated metal and aids in subsequent fabrication because it is ductile and solderable. Tin coatings can be appHed to most metals by electro deposition (see Electroplating). 

A reversal of potential of the tin—iron couple occurs when tin-coated steel (tin-plate) is in contact with acid solutions in the absence of air. The tin coating acts as an anode it is the tin that is slowly attacked and not the steel. This unique property is the keystone of the canning industry because dissolved iron affects the flavor and appearance of the product. Thus, the presence of tin protects the appearance and flavor of the product. 

Tin is used in various industrial appHcations as cast and wrought forms obtained by rolling, drawing, extmsion, atomizing, and casting tinplate, ie, low carbon steel sheet or strip roUed to 0.15—0.25 mm thick and thinly coated with pure tin tin coatings and tin alloy coatings appHed to fabricated articles (as opposed to sheet or strip) of steel, cast iron, copper, copper-base alloys, and aluminum tin alloys and tin compounds. 

The coating thickness may range from 0.0025 to 0.05 mm, depending on the type of protection required. Pure tin coatings are used on food-processing equipment, milk cans, kitchen implements, electronic and electrical components, fasteners, steel and copper wire, pins, automotive bearings, and pistons. 

For articles that require only a very thin film of tin, seldom exceeding 0.8 p.m immersion tin coatings are appHed. The process is based on chemical displacement by immersion in a solution of tin salts. Recently, a new autocatalytic tin-deposition process was developed at the research level. It promises to be useful to coat any base material including plastics, in addition to providing coatings of any thickness desired (21). 

Fig. 4. Multilayer coatings on cemented carbide substrates, (a) 73% WC—19%(Ta,Ti,Nb)C—8%Co alloy with a TiC—TiCN—TiN coating of about 10 )J.m total thickness, (b) 85%WC—9%(Ti,Ta,Nb)C—6%Co with a TiC—AI2O2—TiN coating about 9 lm thick, (c) 86%WC—8%(Ta,Ti,Nb)C—6%Co with TiCN...

Fig. 5. Microstructure of a cemented carbide alloy, 86%WC—8%(Ti,Ta,Nb)C—6%Co, with a cobalt-enriched periphery and a TiC—TiCN—TiN coating.

Copper and copper alloys resist corrosion by most food products. Traces of copper may be dissolved and affect taste or metals are often tin coated. 

Solders are cathodic to steel, zinc and cadmium, and anodic to Monel metal. Although tin or tin-coated metals may be used safely in contact with aluminium when they are not fused with it, a joint in aluminium made with a tin-lead solder is liable to destructive corrosion. The formation, on fusion, of the grain-boundary state, which, as already mentioned, makes aluminium so dangerous an impurity in tin, is responsible. Tin-zinc solders may be used the zinc gives a useful degree of protection. 

Thwaites, C.J., The Flow Melting of Electrodeposited Tin Coatings, Tin Research Institute, Greenford... 

Hot dipped tin coatings, like galvanised coatings, have practical thickness limits and possess an under-layer of intermetallic compound, usually described as the alloy layer. 

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