Repetition: Electrochemistry

Transcription

1 Repetition: Electrochemistry Process types Cathodic deposition Anodic oxidation Electroless deposition

2 Repetition: Cathodic Deposition Basic set up Potential curve - + U(x) - Me + S K 300 nm Cathode fall: cathode screened by positive ions + A x Basic characteristics: Metallic substrates Mostly aqueous solutions Narrow parameter window in T Large parameter window of chemical additives

3 Repetition: Anodic Oxidation Chemistry: kJ 2Al + 3O Al 2 O 3 Alumina grows to thick films, because pores enable contact to the metallic substrate. The initially porous coating can be infiltrated and colored. Afterwards it is densified. The method is extremely shape conserving. No additional coating is deposited, only the substrate material is transformed.

4 Repetition: Electroless Deposition + Reduction of metal ions by electrons which are supplied by a reagens introduced into the solution. + The reaction takes place only at a catalytic surface (metal surface, because electrons can easily be set free). + To sustain the deposition process, the deposited material has to be auto-catalytic. + If there is no catalytic surface (insulator): activation by PdCl 2 or SnCl 2 ; Pd or Sn are directly deposited on the surface. They act catalytically. + Reagences: Natrium-Hypophosphite: Ni, Co Natrium-Boron Hydride: Ni, Au Dimethylaminborane: Ni, Co, Au, Cu, Ag Hydrazine: Ni, Au, Pd Formaldehyde: Cu

5 Thermal Spraying: Process Types Thermal spraying High velocity spraying Detonation spraying Arc discharge spraying Cold gas spraying Further Information: Gesellschaft thermisches Spritzen (Society of Therrmal Spraying, in German)

6 Thermal Spraying With Wire 1. Acetylene/Oxygen 2. Wire or stick 3. Burner nozzle 4. Acetylene/Oxygen flame with spray particles 5. Substrate

7 Thermal Spraying With Powder 1. Acetylene/Oxygen 2. Powder container 3. Burner nozzle 4. Carrier gas+powder 5. Acetylene/Oxygen flame with spray particles 6. Substrate

8 High Velocity Spraying (HVOF) HVOF=High Velocity Oxygen Fuel 1. Burner gas/oxygen 2. Powder 3. Burner nozzle with/without water cooling 5. Burner gas /Oxygen flame with spray particles 6. Substrate

9 Detonation Spraying 1. Acetylene 2. Oxygen 3. Nitrogen 4. Powder 5. Ignition device ("Spark plug") 6. Water cooled exit pipe 7. Substrate

10 Plasma Spraying 1. Inert gas 2. Cooling water 3. DC current 4. Pulverized spray material 5. Cathode 6. Anode 7. Substrate

11 Cold Gas Spraying 1. Carrier gas 2. Heating elements 3. Powder supply 4. Supersonic nozzle 5. Spray stream 6. Coating 7. Substrate

12 Thermal Spraying: Process Characteristics Thermal spraying HVOF High Vel.- spray Detonation spray Arc spray Atmos. Plasmaspr. Vacuum Plasmaspr. Gas Temperature [ C] Particle velocity [m/s] Adhesion [Nmm -2 ] 8 >70 > >70 Oxide content [%] ppm Porosity [%] <0.5 Spray flow [kg/h] Relative costs [1=low]

13 Thermal Spraying: Fundamentals Partially melted droplet hits substrate: d ρ "Sombrero Morphology" D S D d ρ ρ = 1,3 µ S v i 0,2 ρ = Density of melt v i = Impact velocity µ = Viscosity of melt

14 Thermal Spray: Coating Morphology 200 µm 500 µm

15 Thermal Spray: Applications Automotive Medical Industry Home

16 Mechanical Plating Packaging into protective sheets Welding to distance frame 1. Base material (substrate) 2. Coating material 3. Separation layer (Glas wool, MgO or Al 2 O 3 ) 4. Sheet, closed by crimping or welding 5. Welded distance frame 6. Weld seam 7. Evacuation pipe

17 Detonation Plating 1. Base material (Substrate) 2. Distance 3. Coating material 4. Ignition device 5. Explosive material 6. Plated coating material 7. Accelerated coating material 8. Detonation residues 9. Detonation front 10. Unburnt detonation material 11. Wavy transition zone 12. Material stream with high velocity 13. Shock front in air

18 Build Up Welding: Process Types Flame Build Up Welding Arc Build Up Welding Sub Powder (UP) Build Up Welding Plasma Build Up Welding Laser Build Up Welding

19 Flame Build Up Welding Gas-powder-process

20 Arc Build Up Welding Tungsten-Inert gas-process ("WIG") Metal-Inert gas-process ("MIG")

21 Sub Powder (UP) Build Up Welding Band electrode 1. Power supply 2. Band electrode 3. Band feed 4. Contact clamps 5. Loose powder 6. Cinder 7. Coating 8. Substrate Double band

22 Plasma Build Up Welding Powder Wire (Plasma-MIG) Plasma-Hot Wire 1. Tungsten cathode 6. RF generator (for ignition) 2. Argon 7. Coating 3. Welding powder 8. Base Material 4. Welding wire 9. Hot wire-power supply 5. Hot wire 10. Oscillating movement

23 Laser Build Up Welding I Welding powder Laser Low thermal load of substrate Thin, but existing bond zone (some µm) Possibility to create complex shapes

24 Laser- Build Up Welding II WC-particles in Ni-matrix Laser trace Base material Base material is not deformed, but a thin bond zone is clearly visible. The resulting compound has excellent properties.

25 Laser Build Up Welding : 3d-Objects 3d-Pile On Weld powder Laser 3d-shape Finished Object Low thermal load of substrate Thin, but existing bond zone (some µm) Possibility to create complex shapes

26 Melt Dipping Dipping of workpiece through flow agent film Flow agent attatched to workpiece in advance Anti corrosion coatings (e. g.: Zn) Zn is sacrificial layer, i. e. it is consumed with a rate of 2-8µm/year Consumption rate depends on environmental conditions (SO 2 ).