Unit 10 Surface Engineering Two major surface treatmentsCovering the surfacesAltering the surfacesSurface Engineering Requirements(1) control friction and wear;(2) improve corrosion resistance;(3) change physical property,such as conductivity [导电率], resistivity,reflection;(4) alter dimension;(5) vary appearance, e.g., color and roughness;(6) reduce cost;Covering the surfaces The treatments thatcover the surfacesinclude:1. organic coatings2. inorganic coatings.Shown on the right.covering the surfacesorganic coatings inorganic coatingsElectroplatingThin-film coatingsFurnace fusingsHot dippings Thermal sprayings Conversion coatingsElectroplatingIt is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.Anode [正极]: positively charged electrode. The source of the material to be deposited.electrochemistry: the medium through which metal ions are exchanged and transferred to the substrate to be coated.cathode: negatively charged electrode. the substrate to be coated.Plating is done in a plating bath which is usually a non-metallic tank (plastic). The tank is filled with electrolyte which has the metal, to be plated, in ironic form.Procedure [步骤]: As the current is applied, positive metal ions from the solution are attracted to the negatively charged cathode and deposit on tire cathode. As a replenishment for these deposited ions, the metal from the anode is dissolved and goes into the solution and balances the ironic potential.Thermal spraying processThermal sprayed metal coatings are depositions of metal which has been melted immediately prior to projection onto thesubstrate.[1] The metals used and the application systemsused vary but most applications result in thin coatings applied to surfaces requiring improvement to their corrosion orabrasion resistance properties.The process for application of thermal spray metal is relatively simple and consists of the following stages：(1)Melting the metal at the gun.(2)Spraying the liquid metal onto the prepared substrate by meansof compressed air.(3)Molten particles are projected onto the cleaned substrate.Two main types of wire application available：Arc spray：a pair of wires are electrically energized so that an arc is struck across the tips when brought together through apistol. Compressed air is blown across the arc to atomize andpropel the autofed meta wire particles onto the preparedworkpiece.Gas spray：in combustion flame spraying the continuously moving air is passed through a pistol, melted by a conical jet of burning gas. The molten wire tip enters the cone, atomizes and is propelled onto the substrate.Thin-film coatingsTwo methods of thin-film coating：PVD—physical vapor depositioninvolve atom-by-atom, molecule-by-molecule, or ion deposition of various materials on solid substrates in vacuum [真空]systems.CVD—chemical vapor depositionCVD is capable of producing thick, dense, ductile, and good adhesive coatings on metals and non-metals such as glass and plastic. Contrasting to the PVD coating in the “line of sight”, the CVD can coat all surfaces of the substrate.Three CVD coating processConventional CVD coating process：requires a metal compound that will volatilize at a fairly low temperature and decompose to a metal when it contacts with the substrate at higher temperature. Well-knownexample：NiCO(nickel carbonyl).4Diamond CVD coating process：is introduced to increase the surface hardness of cutting tools. The process is done at the temperature higher than 700℃(1300℉) which will not soften most tool steel.Plasma-Assisted CVD coating process：can be performed at lower temperature than diamond CVD coatings. This process is used to apply diamond coatings or silicon barrier coatings on plastic films andsemiconductors [半导体], including the state of the art 0.25 µmsemiconductors.Altering the surfacesHardening treatments High-energy processes Special treatments课间音乐High-energy processesThey are relatively new surface treatment methods.They can alter the properties of the surfaces without changing the dimension of the surfaces. Common high-energy processes including：Electron beam treatmentIon implantationLaser beam treatmentNotes1. Thermal sprayed metal coatings are depositions of metal whichhas been melted immediately prior to projection onto thesubstrate.句意：热喷涂金属涂层是熔融金属立刻喷射到基体上形成的金属沉积层。

2. The plasma is established between the substrate (workpiece) andthe target (donor) and transposesThe sputtered off target atoms to the surface of the substrate.句意：基体（工件）和靶材（杂质）间形成等离子体，将溅射的靶材原子传送到基体表面上。