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Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
Surface treatment   an overview
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Surface treatment an overview

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briefly discusses various surface treatment processes

briefly discusses various surface treatment processes

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  • 1. ahmadkhan_99@hotmail.com 1
  • 2. Major Surface Treatments Finishing and Polishing Coatings  Conversion Coatings (oxidation, anodizing)  Metal Coatings (electrochemical, electroless)  Thermal Coatings (carburizing – flame spraying)  Deposition  Physical Vapor Deposition  Chemical Vapor Deposition  Organic Coatings
  • 3. Finishing and Polishing Blast Finishing Shot Peening Tumbling Buffing Chemical Polishing
  • 4. Conversion Coatings A conversion coating is a coating produced by chemical treatment of a metallic surface that gives a superficial layer containing a compound of the metal  Oxidation  Phosphate Coatings  Chromate Coating  Various Coloring Processes
  • 5. Conversion Coatings - Oxidation Oxidation  Not all oxides are detrimental – many are tightly adhering leading to passivation and hardening of surface
  • 6. Conversion Coatings - Oxidation Black Oxide – chemical application  Typically applied to steel, copper and stainless steel Anodizing – electrochemical conversion  Usually done to Aluminum  2-25 mm thick typically  Multiple colors possible  Improved Corrosion and Wear Resistance
  • 7. Conversion Coatings – Phosphate Coating Immersion in a Zn-P bath with Phosphoric acid causes growth of a crystalline zinc phosphate layer  Iron, Zinc or Manganese Phosphate layer  Primarily this is used as a base for subsequent painting and it also serves as corrosion protection coating Typically applied to C-steel, low alloy steel and cast irons Sometimes applied to Zinc, Cadmium, Aluminum and Tin Typically very thin ~ 2.5 micron
  • 8. Metal Coatings Electroplating Electroless Plating Immersion Plating Metallizing of Plastics and Ceramics
  • 9. Metal Coatings - Electroplating  Used to increase wear and corrosion resistance  Electrochemical process used to create a thin coating bonding to substrate  Process is slow so coating thickness can be closely controlled (10-500 mm)
  • 10. Metal Coatings - Electroplating  Applications  Tin and Zinc are deposited on steel for further working  Zinc and Cadmium are deposited on parts for corrosion resistance  Copper is deposited for electrical contacts  Nickel for corrosion resistance  Chromium can be used to impart wear resistance  Precious metals for decoration or electronic devices
  • 11. Metal Coatings – Electroless Coatings Part is submerged into an aqueous bath filled with metal salts, reducing agents and catalysts  Catalysts reduce metal to ions to form the coating Excellent for complex geometries as deposition is uniform across surface regardless of geometry (except very sharp corners (0.4 mm radii))
  • 12. Metal Coatings – Immersion Plating Deposition of a metallic coating on a substrate by chemical replacement from a solution of a salt of the coating metal It differs from electroless plating in not requiring a chemical reducing agent; the substrate metal itself act as a reducing agent,
  • 13. Thermal Treatments Surface Heat Treatment Diffusion Coating Hot-Dip Coatings Weld Overlay Coatings
  • 14. Thermal Treatments – Surface Heat Treatment  Basic concept is to heat the surface to austenitic range, then quench it to form surface martensite - workpiece is steel  Heating Methods  Flame Treatment  Induction Heating  Copper coil wraps around part to heat by induction  Electron Beam or Laser Beam Hardening  Typically heat small area and allow the bulk solid heat capacity to quench the small heated area
  • 15. Thermal Treatments – Diffusion Coating  With low carbon steel, the surface can be enriched by diffusion of C or N into surface  Carburizing  Nitriding  Metal Diffusion  Chromizing – Chromium diffuses into surface to form corrosion resistant layer.  Take care with carbon steels as surface will decarburize  Aluminizing – Used to increase the high temperature corrosion resistance of steels and superalloys
  • 16. Thermal Treatments – Hot-Dip Coatings  These coatings are used for corrosion protection  Galvanizing  Parts are dipped into a molten zinc bath  Galv-annealing  Galvanized parts are then heat treated to ~500 ºC to form Fe-Zn inter-metallic  Used for metals that need spot welded to protect copper electrode from alloying with zinc and reducing its life
  • 17. Vapor Deposition Chemical Vapor Deposition (CVD) Physical Vapor Deposition (PVD)  Thermal PVD  Sputter Deposition  Ion plating
  • 18. Chemical Vapor Deposition  Deposition of a compound (or element) produced by a vapor-phase reduction between a reactive element and gas  Process typically done at elevated temps (~900ºC)  Coating will crack upon cooling if large difference in thermal coefficients of expansion
  • 19. Chemical Vapor Deposition  Applications  Diamond Coating, Carburizing, Nitriding, Aluminizing and Siliconizing processes  Semiconductor manufacturing
  • 20. Organic Coatings - paint  Enamels  Lacquers  Water-base paints  Powder Coating

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