Home     Team Capabilities Publications Directions
 

Induction-Coupled Plasma

 
  • Commercially available torches, [Tekna Plasma Systems, Inc.]

  • Can be used for plasma spraying, spheroidizing, plasma chemistry, waste destruction and plasma synthesis of materials

  • Can produce dense coatings, using coarser powders than DC plasma spray
  • No electrodes…coil + electromagnetic induction [400 kHz - 4 MHz
  • Toroidal plasma region @ ~10,000 K
  • Central powder injection via water-cooled probe
  • Low gas jet & particle velocities [<30 m/s]…longer dwell times, larger heating zone
  • More complex than DC plasma systems
  • Used for spraying monotapes...continuous fiber reinforced metal matrix composites
     

The CPPM's lab.-scale RF/ICP reactor used for depolymerization, plasma treatment and plasma chemistry

 
Wire Arc Spray (Twin Wire Arc)

 
  • The only direct heating/melting process
  • D.C. arc between conducting/consumable wires
  • Air, Ar, N2 atomizing gases
  • Direct melting + gas atomization...high thermal efficiency
  • Limited to metals [Al, Al-Si, Zn, Steels, Ti, Sn] & cored cermet, carbide, nitride etc. wires
  • Wire feedstocks [typically 1/16 -1/8" in diameter]
  • Higher deposition rates than HVOF, plasma

     


Process Characteristics

  • Arc Temperature: >25,000 °C
  • Jet Speeds: typically 50-100 m/s
  • Atomizing Gas Flow: 500-3000 slm
  •  Particle Speeds: 50-100 m/s
  • Wire Feed Rate: 150-2000 gm/min
     


Deposit Characteristics

  • Density: 80-95 %...depending on particle velocity/size

  • Droplet size: sub-micron to ~200 µm...increased porosity

  • Bond Strength: ~10-40 MPa

  • Low heat input to substrate/part

  • Microstructures:...coarser...thicker splats, wider size range than with powders. Improved by using smaller diameter wires

  • Relatively low oxide contents
Vacuum Plasma Spray [LPPS®]

 
  • APS --> oxide inclusions or "stringers" due to hot particle/air interactions
  • Late 1960's/early 70's...R&D on controlled atmosphere plasma spray...
  • E. Muehlberger [1974]...1st paper on VPS/LPPS®
  • Showed v. low oxide contents and >99 % density
  • Modified plasma torch --> insulation + nozzles
  • Remote torch/part manipulation, transfer/load-locks, etc.

 

 

Process Characteristics

  • Broader/longer spray jets --> extension of jet isotherms

  • Longer spray distances...e.g.. for MCrAlY, 3-4" in APS; 16" in LPPS®

  • Cleaner interfaces with reverse transferred-arc [RTA] cleaning

  • Virtual elimination of oxide inclusions

  • High coating densities possible

  • Ability to spray thick [>1"] deposits

  • Substrate preheating to >1000 °C possible
High Velocity Oxy-Fuel [HVOF] Spray

 
  • Invented in 1958 by Union Carbide [now Praxair]
  • Introduced commercially c.1974; now ~5-8 different designs
  • Carbides [WC/Co, Cr3C2/NiCr], metals [SS], polymers
  • Pressurized internal combustion + supersonic jet expansion
  •  to atm.

  • Fuel [H2, C3H6, C3H8, MAPP, kerosene] + oxygen

  • Improved gas heating and acceleration --> improved heat & momentum transfer to particles
  • Powder feedstocks, typically [-45, +10 µm]

Process Characteristics

  • Jet Temperature: generally >2500 °C

  • Jet Speeds: typically >1000 m/s

  • Gas Flow Rate: 400-1100 slm

  • Particle Speeds: 200-1000 m/s

  • Powder Feed Rate: 15-50 gm/min

     

 Deposit Characteristics
  • Density: >95 %...due to longer dwell time + high particle velocity
  • Bond Strength: ~70-80 MPa
  • Microstructures...similar to D-Gun®. Fine oxide dispersion
  • Density, oxide etc. comparable to plasma spray
  • Reduced decarburization due to lower jet temperature…important when spraying materials such as WC/Co
Air Plasma Spray (APS)

 
  • D.C. arc between central thoriated W cathode [emits e- ]
    & water-cooled, concentric Cu nozzle anode
  • Electron + ion recombination...releases energy
    => used to heat gases & powder
  • Ar, Ar/H, Ar/He, N2 plasma gases --> govern jet enthalpy
  • Plasma/arc gas stabilizes the arc...vortex stabilization.

  • Nozzle confines the arc & accelerates heated gases/powders

  • High power [20 to >200 kW]
  • Widest materials capability => polymers to refractory metals
  • Generally use powdered feedstock materials

Process Characteristics

  • Jet Temperature: 10-15,000 °C

  • Jet Speeds: typically 200-1000 m/s

  • Gas Flow: 100-250 slm

  • Particle Speeds: 200-800 m/s

  • Feed Rate: 25-150 gm/min

  • Pressure: atmospheric to ~50 Torr

     

 Deposit Characteristics
  • High degree of particle melting &
    high particle velocity
  • Density: 90-99 %
  • Thin splats + fine microstructure
  • Bond Strength: 34-70 MPa
  • Inert gas plasma jet --> low oxide contents
  • Mixing/entrainment of air --> inter-splat oxidation
  • Inherently some oxide in APS
    VPS/LPPS® developed to eliminate oxidation
Flame Spray

  • 1st process developed... modified oxy-acetylene torches

  • Metallizing, oxides, polymers

  • Uses powder, rod, or wire feedstocks

  • External combustion + jet expansion

  • Generally very simple designs, but can include aircaps/ shrouds to concentrate the jet

  • Controlled by varying fuel:oxygen and gas flow rates
     

Process Characteristics

  • Jet Temperature: generally >2500 °C
  • Jet Speeds: typically <100 m/s
  • Gas Flow: 100-200 slm
  • Particle Speeds: up to ~80 m/s
  • Powder Feed Rate: 30-50 gm/min
     

Deposit Characteristics

  • Density: 85-95 %...due to lower jet temp. & velocity
  • Bond Strength: 5-20 MPa [some of the lowest attainable
  • Powder --> more uniform properties
  • Wire/Rod --> more erratic melting/atomization
  • Microstructures...coarse splats and porosity
  • Relatively high oxide inclusions in metals

CPPM Processing Equipment

 

  • Sulzer Metco [US], Inc., spray booth in an acoustic enclosure for Air Plasma Spray [APS]

  • Controlled atmosphere/low pressure plasma spray deposition chamber

  • Three-axis programmable spray torch/substrate manipulation system

  • Various water-cooled substrate holders/chill-blocks for substrate thermal management

  • Sulzer-Metco [US], Inc., 03-CA, 120 kW DC Plasma Spray System

  • Sulzer-Metco [US], Inc., 9MB, 80 kW DC Plasma Spray System

  • Praxair Surface Technologies, Inc. [formerly Miller Thermal, Inc.] SG-100, 80 kW DC Plasma Spray torch

  • Inert Gas Shrouds for the O3-CA and SG-100 Plasma Spray Torches

  • Plasmadyne™ Volumetric Powder Feeder

  • Miller Thermal, Inc. [2], Volumetric Powder Feeders

  • Stellite Coatings, Inc., Jet Kote II® HVOF Combustion Spray System

  • Praxair Surface Technologies, Inc., HV-2000 HVOF Combustion Spray System

  • Sulzer Metco [US], Inc., Diamond Jet® HVOF Combustion Spray System

  • Praxair/Tafa, Inc., 9000-Series Wire-Arc Spray, with ArcJet™ attachment

  • UTP Welding Technologies, Uni-Spray-Jet™ Flame Spray guns

CPPM Coating Testing and Characterization Equipment
  • AMTI sliding pin-on-disk [POD] wear tester [microprocessor controlled, Room Temperature]

  • Hommelwerke Dektak T-20 stylus-tracing profilometer and PC-based data acquisition system

  • Byk-Gardner balance beam mar and scratch adhesion tester.
  • Complete metallography sample preparation with Struers Abrapol® automated sample polishing.
  • Control Vision, Inc. LaserStrobe™ laser stroboscopy system for measuring particle velocity

The CPPM also has full access to the testing, characterization and diagnostic equipment available within the Department of Materials Science & Engineering at Drexel University

  • Two [2] Amray Model 1830 Scanning Electron Microscopes [SEM] with EDS and OIM.

  • JEOL CX-100 Transmission Electron Microscope [TEM].

  • Olympus PMG3 optical microscope with computerized image analysis.

  • Siemens Model D-500 X-ray Diffraction system.

  • Vacuum hot press furnace [10-5 Torr, up to 1600 °C] and HIP unit [new 1998]. Powder classification and Horiba Model LA-910 laser scattering particle size analyzer.

  • Complete Mechanical Testing Lab. [room and elevated temp. tensile, creep & fatigue.]

  • Thermal Analysis and CTE Measuring Equipment.

  • Solidification and Heat Treatment Laboratory.

  • Complete P/M Laboratory. Composites Laboratory; Metal/Polymeric Matrix with Fibers.

Back to top