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Materials, Coatings, and Platings
Published in Paul G. Slade, Electrical Contacts, 2017
Claddings are made by compressing two or more metals at a very high force which creates metallurgical bonds at their interfaces and elongates the composite. The top layers are usually a noble metal on a nickel liner, and most substrates are copper alloy spring metals such as 98.1 wt% Cu, 1.9 wt% Be (Unified Numbering System [UNS] designation 17200); 94.8 wt% Cu, 5.0 wt% Sn, 0.19 wt% P (phosphor bronze, C51000) and 88.2 wt% Cu, 9.5 wt% Ni, 2.3 wt% Sn (C72500); see Chapter 24, Table 24.9. With a flat stock, the cladding is obtained by squeezing between rolls (see Chapter 17, Section 17.5). Clad inlays are produced by first skiving a groove in the substrate into which a strip of the precious contact metal on the nickel liner is placed and then rolled. For clad wires of circular or other shapes, the substrate in the form of a rod is pressed into the hollow tubes of nickel and the noble metal, which then is drawn through a die. Heat is released during reduction which facilitates interdiffusion at the layer interfaces. Work-hardening occurs, and so annealing in an inert atmosphere, followed by further reduction, may be needed to obtain the desired thickness. Sheet clad metal is, then, slit to width and is the raw material for stamping and forming the contact. The amount of required precious metal is minimized by selectively locating it on the substrate so to achieve the ideal “contact engineering surface.” Excess material, cut away in the stamping, is reclaimed. Thicknesses of the noble metal in the inlay for contacts typically range at 0.75–5 μm. Multilayer inlays can also be obtained. The nickel liner is usually several micrometers thick.
Galvanic corrosion behaviour and mechanism of skin effect heat tracing pipes
Published in Corrosion Engineering, Science and Technology, 2020
Fei Xie, Zeqi Wang, Dan Wang, Ming Wu, Tan Zou, Ke Gong
Microstructure observation of X52 steel and 20# steel samples by Leica DM2500 material microscope. The XQ2B type metallographic mosaic machine is used to inlay them, then the samples were abraded with a series of grit papers (80# to 2000#), and W2.5 diamond grinding paste for mechanical polishing respectively. After being etched by 4% nitric acid solution, rinse with water and alcohol, and blow dry with a hair dryer.