Surface Treatment, Coating, Cleaning

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A brief knowledge about surface treatment, which is a process applied to the surface of a material to make it better in some way, for example by making it more resistant to corrosion or wear. Shot peening is a surface treatment in which small hard pellets are shot against the surface of a metal to make it more resistant to fatigue.
  • 1. By AKANKSHA MISHRA
  • 2. Introduction Surface modification of materials- • Act of modifying the surface of a material by bringing physical, chemical or biological characteristics different from the ones originally found on the surface of a material. • Simply, this process, affect either a thin layer on the surface of the part itself, or add a thin layer on top of the surface of the part. Why we use surface treatment? • Improves hardness and durability • Rebuild surface • Controls friction, reduces, adhesion, improves lubrication • Improves corrosion resistance • Improves aesthetics(beauty)
  • 3. Surface modification of material- Types- 1) Mechanical hardening of the surface 2) Case Hardening 3) Thermal spraying 4) Vapor deposition 5) Electroplating 6) Electroless plating 7) Anodizing 8) Painting
  • 4. Mechanical hardening of the surface-  Mechanical hardening of the surface is a surface treatment which creates a plastically deformed strain hardened layer of material itself, by the application mechanical impulses(e.g.- light hammering).  This process include:- a) Shot peening b) Water peening c) Laser peening d) Explosive hardening
  • 5. a) Shot peening- (Uses tiny balls of metal or ceramic) • The surface get plastically deformed. • Make the surface harder.
  • 6. b) Water jet peening- (uses a jet of water at high pressures e.g.- 400MPa) • Uses cavitation impacts in the same way as shot peening. • Used to improve fatigue strength and/or to introduce compressive residual stress. • In the case of cavitation peening, cavitation is generated by cavitating jet.
  • 7. c) Laser peening- (surface is hit by tiny impulses from a laser) • The surface of the work piece is subjected to laser shocks. • As a result of which compressive stress is induced in the component, thus improving the fatigue life. • Specification- Laser intensity- 100 to 300 J/cm2 Pulse duration- 30 sec
  • 8. Laser hardening application- An expensive process used to improve fatigue strength of jet fan blades and turbine impellers.
  • 9. d) Explosive hardening- (Layer of explosive roated on the surface is blasted) • The explosion hardening technique can obviously increases the hardness of metals by several plastic deformation caused by the shock wave. Explosive hardening application- The most common application of explosive shock hardening is to cost high-mega steel rail frogs and switching.
  • 10. Case Hardening- • Basically, the component is heated in an atmosphere containing elements (such as C/N/B) that alter the component, microstructure and properties of surface. (Doping) • The duration and temperature control the concentration and depth of the doping. • Mostly this process is used to harden steel and other iron alloys, including low carbon steels, alloy steels, tool steels.
  • 11. Types of case hardening-
  • 12. Thermal Spraying- • Metal is melted in a specially designed spray gun. (using oxy-fuel, plasma, or other means to heat the sprayed metal till it melts) • High pressure gas then sprays the liquid metal • depositing a layer on top the part (similar to a painting process).
  • 13. Types of thermal spraying- A. Thermal wire spray B. Thermal metal powder spray C. Plasma spray
  • 14. Thermal wire spray- • The feed stock is in wire or rod form. • Metal droplets atomized by air jets using acetylene or hydrogen, which mixed with oxygen and burned at the nozzle's face. • Coating texture- 200micro inch to 800micro inch • Commonly sprayed materials- Zn, Al
  • 15. Thermal metal powder spray- • Powder feed instead of wire • Oxyacetylene torch modified for powder feed • No high pressure air to assist atomization: low deposition rate • Easy method for materials that cannot be made into wire.
  • 16. Plasma spray- • The material to be deposited(feedstock) is introduced into the plasma jet, emanating from a plasma torch. • In the jet, where the temperature is of the order of 10,000K, the material is melted and propelled towards a substrate. • There, the molten droplets flatten, rapidly solidify and form a deposit.
  • 17. Vapor Deposition- They are of two types- 1) Physical vapor deposition(PVD) 2) Chemical vapor deposition(CVD) Physical vapor deposition(PVD) Family of processes in which a material is converted to its vapor phase in a vacuum chamber and condensed onto substrate surface as a very thin film. • Coating materials: metals, alloys, ceramics and other inorganic compounds, even some polymers • Substrates: metals, glass, and plastics • Very versatile coating technology o Applicable to an almost unlimited combination of coatings and substrate materials
  • 18. Applications of PVD- • Antireflection coatings of magnesium fluoride (MgF2) onto optical lenses • Depositing metal to form electrical connections in integrated circuits • Coating titanium nitride (TiN) onto cutting tools and plastic injection molds for wear resistance
  • 19. Chemical vapor deposition(CVD) Involves interaction between a mixture of gases and the surface of a heated substrate, causing chemical decomposition of some of the gas constituents and formation of a solid film on the substrate. • Reactions occur in enclosed reaction chamber • Reaction product nucleates and grows on substrate surface to form the coating • Most CVD reactions require heat • Variety of coating and substrate materials
  • 20. Application of CVD- • Industrial metallurgical processes • Coated carbide tools • Solar cells • Refractory metals on jet engine turbine blades • Integrated circuit fabrication Photomicrograph of cross section of a coated carbide cutting tool using CVD and PVD
  • 21. Sputtering- • An electrical field ionizes an inert gas(Ar). • Ions are generated and directed at a target. • The ions sputter target atoms. • The ejected atoms are transported to the substrate. • Atoms condense and form a thin film.
  • 22. Electroplating- • Electroplating is the process of depositing one metal onto another metal. • Electrons travel from the negative end of the battery through the cathode, through the solution, up through the anode, and into the positive end of the battery. • The positively charged ion form the solution are attracted to the negatively charged cathode. • These ions attached themselves to the cathode.  Electroplating can enhances- Chemical properties- increase corrosion resistance Physical properties- increase thickness of part Mechanical properties- increase tensile strength & hardness
  • 23. Electroless plating- • Part is submerged into an aqueous bath filled with metal salts , reducing agents and catalysts. • Catalysts reduce metal to ions to form the coating. • This process can be used to plate non conducting parts with a layer of metal. • Excellent for complex geometries as deposition is uniform across surface regardless of geometry (except very sharp corners ( 0.4 mm radii)
  • 24. Anodizing- • The process uses the metal as an anode, by electrolytic process a layer of hard metal oxide is formed at the anode i.e. on the surface of the part. • The coating provided on the metal surface may be of different colors (usually black, red, blue) • Electrolytic treatment produces a stable oxide layer on the metallic surface • Applications: Aluminium, Magnesium, zinc, titanium, and other metals • Dyes can be incorporated into anodizing process to create a wide variety of colors • Especially common in aluminium anodizing • Functions: primarily decorative; also corrosion protection
  • 25. INTRODUCTION • PAINT is a solution of a pigment in water, oil, or organic solvent, used to cover wood or metal articles either for protection from moisture and termites etc. • For different surfaces different types of paints from different companies are used. Some of the leading companies of India are Asian paints, Nerolac, berger, nippon etc.
  • 26. Paints are of three types: A. Enamel: oil-based paints that produce a smooth surface and glossy appearance B. Lacquers: these are resin based paints that dry to a thin coat after the solvent evaporates out. Common examples are varnish used in painting wood. C. Water-based paints: common examples include several wall paints and home-interior paints. Lacquers Water-based
  • 27. The most common methods of paint application include: I. Dip coating: Part is dipped into a container of paint, and pulled out. II. Spray coating: One or more spray guns move along the surface of the part to give a uniform coat of paint; this is the method most commonly used in painting auto bodies, home appliances, e.g. fridge doors, etc. III. Electrostatic spraying: Here the paint particles are given an electrostatic charge and the spray is achieved by applying a voltage difference across the paint particles and the part. IV. Silk-screening: This is the most common method of painting patterns, text, etc on top of most products. Tine holes are made in a thin (silk-like) sheet, corresponding to the pattern that needs to be painted. The screen is kept on top of the part in the correct position, and the paint is poured n top of the screen. A roller (or squeegee brush) is used to squeeze the paint out through the holes in the silk screen and onto the part. The screen is removed and the part is sent to dry in an oven.
  • 28. Silk screening has several very important uses: 1. It is used extensively in the textile industry to create colored patterns on textiles (e.g. logos on T-shirts). 2. It is used to paint almost all text and patterns on all electronics products – e.g. all numbers, text and symbols on your mobile phone. 3. It is used to deposit patterns of solder-paste on top of printed circuit boards. Lead-less electronic chips are placed on top of these patterns, and a process called wave-soldering then solders the chip to the circuit board. We will see this process in detail later.
  • 29. Silk screening process-
  • 30. ACKNOWLEDGEMENT I wish to express my sincere gratitude to Dr. Jyoti Pandey for providing me an opportunity to give my presentation on “Surface Modification” I sincerely thank Dr. Jyoti Pandey for their guidance and encouragement in carrying out this presentation work. I also wish to express my gratitude to my class friends of BBAU, who rendered their help during the period of my presentation work.
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