Surface Engineering By Israa Faisal University of Al-Qadisiyah College of Engineering Material Engineering Department

cladding Clad metals are bonded metal-to-metal laminar composite systems that can be fabricated by a number of processes. The principal cladding techniques include hot-roll bonding, cold-roll bonding, explosive bonding, and weld cladding (including laser cladding), although centrifugal casting, adhesive bonding, extrusion, and hot isostatic pressing have also been used to produce clad metals.

cladding Clad metals can be provided in plate, sheet, tube, rod, and wire forms. Most engineering metals and alloys can be clad. Cladding combinations that have been commercially produced on a large scale. The cladding of steel with stainless steel, copper, nickel alloys, titanium, and tantalum has become increasingly popular in the chemical processing industries. Applications include pressure vessels, reactors, heat exchangers, and storage tanks.

cladding Clad metal systems designed for corrosion control can be categorized as follows: Corrosion barrier systems Transition metal systems Noble metal clad systems Sacrificial metal systems

Cladding/ Corrosion-Barrier Systems The combination of two or more metals to form a corrosion-barrier system is most widely used where perforation caused by corrosion must be avoided. This is shown schematically in Low-carbon steel and stainless steel are susceptible to localized corrosion in chloride-containing environments and can perforate rapidly. When steel is clad with a stainless steel layer, the corrosion-barrier mechanism prevents perforation. Localized corrosion of the stainless steel is prevented; the stainless steel is protected galvanically by the sacrificial corrosion of the carbon steel in the metal laminate. Therefore, only a thin pore-free layer is required.

Clad transition metal systems Clad transition metal systems provide an interface between two incompatible metals. They not only reduce galvanic corrosion where dissimilar metals are joined, but they also allow welding techniques to be used when direct joining is not possible. Clad metals provide an ideal solution to the materials problem of dual environments. For example, in the application of small battery cans and caps, copper-clad, stainless steel clad nickel (Cu/SS/Ni) is used where the external nickel layer provides atmospheric corrosion resistance and low contact resistance. The copper layer on the inside provides the electrode contact surface as well as compatible cell chemistry. The stainless steel layer provides strength and resistance to perforation corrosion.

Chemical vapor deposition (CVD) Chemical vapor deposition (CVD) involves the formation of a coating by the reaction of the coating substance with the substrate. The coating species can come from a gas or gases or from contact with a solid . The process is more precisely defined as the deposition of a solid on a heated surface by a chemical reaction from the vapor or gas phase .In general, three processing steps are involved in any CVD reaction: (1) the production of a volatile carrier compound, (2) the transport of the gas to the deposition site without decomposition, and (3) the chemical reaction necessary to produce the coating on the substrate.

Chemical vapor deposition

Chemical vapor deposition (CVD) Chemical vapor deposition processes can be classified as either open reactor systems, including thermal CVD and plasma CVD, or as a closed reactor system, as in pack cementation. In thermal CVD, reactions usually take place above 900 °C (1650 ° F), whereas plasma CD usually operates at temperatures between 300 and 700 ° C (570 and 1290 ° F) . Using the lower-reaction-temperature plasma CVD enables coatings to be produced on substrates with low melting points or that otherwise would undergo solid-state transformations over the range of deposition temperatures. Furthermore, the low deposition temperature of plasma CVD coatings limits the stresses due to the large mismatches in thermal expansion that can lead to cracking and delamination of the coating.

Chemical vapor deposition (CVD) Materials that cannot ordinarily be deposited by electrodeposition-for example, the refractory metals tungsten, molybdenum, rhenium, niobium, tantalum, zirconium, hafnium, and so forth-are deposited using CVD processes. These refractory metals are deposited at temperatures far below their melting points or sintering temperatures, and coatings can be produced with a preferred grain size and grain orientation. For example, tungsten that is deposited by the hydrogen reduction of the halide and deposition at a lower temperature (500 °C,) gives a finer grain size with higher strength (83 Mpa,) than deposition at a higher temperature (700 ° C)

Ex. Of Chemical vapor deposition (CVD) Diamond films grown by CVD exhibit outstanding properties approaching natural diamond, such as high electrical resistivity, high optical transparency, extreme hardness, high refractive index, and chemical inertness. Different film-deposition techniques and system configurations result in films with different characteristics. Diamond films can be grown using processing variables of different concentrations of methane in methane-hydrogen gas mixtures and flow rates .The CVD of diamond requires the presence of atomic hydrogen, which selectively removes graphite and activates and stabilizes the diamond structure. The basic reaction involves the decomposition of methane, which can be activated by microwave plasma, thermal means (hot filament), plasma arc, or laser.

Physical Vapor Deposition (PVD) Physical vapor deposition (PVD) processes involve the formation of a coating on a substrate by physical deposition of atoms, ions, or molecules of the coating species. There are three main techniques for applying PVD coatings: thermal evaporation, sputtering, and ion plating. Thermal evaporation involves heating of the material until it forms a vapor that condenses on a substrate to form a coating. Sputtering involves the electrical generation of a plasma between the coating species and the substrate. Ion plating is essentially a combination of these two processes.

Physical Vapor Deposition

Physical Vapor Deposition (PVD) Originally PVD was used to deposit single metal elements by transport of a vapor in a vacuum without involving a chemical reaction. Today, PVD technology has evolved so that a wide array of inorganic materials (including metals, alloys, compounds, or their mixtures) and organic compounds can be deposited. The PVD process occurs in a vacuum chamber and involves a vapor source and the substrate on which deposition occurs. Different techniques arise because of variations in atmospheres, vapor source heating method, and electrical voltage of the substrate, all of which contribute to the structure, properties, and deposition rate of the coating.

Physical Vapor Deposition (PVD) The steps in deposition occur as follows: 1. Synthesis of the material deposited (transition from a condensed state, solid or liquid, to the vapor phase, or, for deposition of compounds, reaction between the components of the compound, some of which may be introduced into the chamber as a gas or vapor) 2. Vapor transport from the source to the substrate 3. Condensation of the vapors followed by film nucleation and growth