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Thermal spraying techniques

At IEK-1, a variety of highly innovative production methods are used in the area of thermal spraying.

Two key thermal spraying technology methods are plasma spraying (PS) and high velocity oxy-fuel spraying (HVOF). These are highly efficient methods for the deposition of metallic or ceramic layers.

Flammenbild A3000

With plasma spraying, particle-shaped starting materials are melted in a plasma jet created by ionization of a gas stream and are accelerated towards the substrate. A variety of process parameters such as the gas composition, the gas flow, the current, the spraying distance, the distribution of particle size, the gas flow of the substrate, and the ambient pressure influence the melting and the velocity of the particles and thus have a significant impact on the resulting microstructure.

The plasma and particle properties during flight can be analysed in order to obtain better understanding of the processes and to ensure quality.

Processes

Atmospheric plasma spraying

Atmospheric plasma spraying (APS) is particularly well suited for the deposition of ceramics, especially oxide ceramics for thermal barrier coatings.

Plasma burners: Triplex II, Triplex Pro, F4, 9MB, F100 Connex

Figure: Atmospheric plasma sprayingFigure: Sulzer Metco F4 plasma spray gun

Diagram: Atmospheric plasma sprayingDiagram: Sulzer Metco F4 plasma spray gun

Suspension plasma spraying

Suspension plasma spraying (SPS) is an APS process in which a suspension is used as a precursor. This allows particles to be processed on a submicrometre scale and as a result, new microstructured layers.

Suspension plasma sprayingFigure: Suspension plasma spraying


Vacuum plasma spraying

With vacuum plasma spraying (VPS), ceramic and in particular, metallic coatings can be fabricated. With this method, oxygen uptake can be largely avoided.
Plasma burners: F4 (55 kW), TriplexPro-200 (65 kW)

Facility: Vacuum plasma sprayingFacility: Vacuum plasma spraying and low-pressure thin-film plasma spraying


Low pressure plasma spraying–thin film

Low pressure plasma spraying–thin film (LPPS-TF) is a refinement of vacuum plasma spraying at low pressure. This allows the deposition of thin, gas-tight layers. It even enables the deposition of innovative, columnar structures from the vapour phase.

Plasma burners: F4 (55 kW), TriplexPro-200 (65 kW)

Picture: Low pressure plasma spraying–thin filmLow pressure plasma spraying–thin film: plasma jet at different pressing pressures.

Structure: Low pressure plasma spraying–thin filmLow pressure plasma spraying–thin film: columnar layer structure



High velocity oxy-fuel spraying

Picture: High velocity oxy-fuel sprayingBurner for high velocity oxy-fuel spraying (HVOF) in operation.

In contrast to plasma spraying, high velocity oxy-fuel spraying allows significantly higher particle velocities at comparatively moderate temperatures of the fuel gas flame. This makes this process particularly well suited for wear-resistant alloys and (Co,Ni)CrAlY bond coats.

Burners: DJ2600, DJ2700, hybrid aircap hydrogen-/methane-oxygen process with Air/N2 shroud gas.


Process diagnostics

Plasma properties

TEKNA ENP-04-CS enthalpy probe

Calorimetric/mass-spectrometric measurement of plasma enthalpy, temperature, and composition, as well as plasma velocity

Image: Enthalpy probeEnthalpy probe for determining plasma properties (image: TEKNA)

Optical emission spectroscopy
Determination of plasma gas composition and temperature

Abbildung: Optical emission spectroscopyExample of optical emission spectroscopy


Particle properties

Tecnar DPV-2000

Two-colour pyrometry for measuring particle temperature, time measurement for determining particle velocity, measurement of particle diameter and the particle stream

System for measuring particle propertiesSystem for measuring particle properties: DPV 2000

Tecnar Accuraspray-g3

Two-colour pyrometry for measuring particle temperature, correlation-based measurement of of particle velocity, plume-intensity profiles by means of digital image analysis

System for measuring particle propertiesSystem for measuring particle properties: Accuraspray-g3 (photo: Tecnar)


Coating materials (selection)

  • Alloys
    e.g. (Ni,Co)CrAlY, NiCr, corrosion-resistant steel
  • Metals
    e.g. tungsten, copper
  • Oxide ceramics
    e.g. ZrO2, Al2O3, TiO2, Al-Mg-spinel, pyrochlore structures (e.g. La2Zr2O7), perovskites
  • Other
    e.g. B4C, WC/Co


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