What Does Low Pressure Plasma Spraying (LPPS) Mean?
Low pressure plasma spraying (LPPS) is a surface processing technique used to impart new functions absent or insufficient in the original material at a low pressure. LPPS coating is a low-velocity, high-temperature spraying process that is performed in a near-vacuum argon atmosphere. This process enables materials that are sensitive to oxidation to be sprayed.
LPPS can improve properties such as:
- Wear resistance
- Corrosion resistance
- Thermal barrier
- Decorative elements
- Electromagnetic effects
Major applications of LPPS include:
- Thermal barrier coatings (corrosion-resistant bond coats)
- Environmental barrier coatings
- Electrical insulating coatings
- Tribological deposits
- Coatings for medical implants
- Functional layers for solid fuel cells
Corrosionpedia Explains Low Pressure Plasma Spraying (LPPS)
Low pressure plasma spraying (LPPS) is a thermal spray technology that consists of a group of processes in which finely divided surfacing materials are deposited in a molten or semi-molten condition on a prepared substrate to form a spray deposit at a low pressure.
The coating is formed by the impingement of particles, heated and accelerated simultaneously using a heat source on the substrate. At the substrate surface the impacting particles flatten and solidify rapidly to form splats. Layers and consolidation of particles leads to deposit formation. When sprayed on substrates of various shapes, free-standing parts can be produced in such forms as:
Deposition may be in the form of:
- Very fine molten droplets
- Vapor phase deposition
- A mixture of vapor and droplet deposition
LPPS systems can be used to produce dense, high-quality coatings in the 1- to 100-micron thickness range with lamellar or columnar microstructures.
The parameters which influence deposit properties include:
- Feedstock type
- Plasma gas composition and flow rate
- Energy input
- Torch offset distance
- Substrate cooling
This technique is mostly used to produce coatings on structural materials. Such coatings provide protection against corrosion & wear. They can change the electrical or tribological properties of the surface and replace worn material.
Contrary to atmospheric plasma spraying, the LPPS process is performed in a vacuum chamber at a pressure of approx. 20 - 100 Torr. This technique is cost effective for the spray forming of specialized materials, refractory metals and reactive materials (like titanium).
LPPS offers the following advantages over conventional atmospheric plasma process:
- Oxide-free metallic coatings
- High adhesive strength of metallic coatings
- Variable coating thickness between 0.05 mm and several millimeters
- High coating densities (close to theoretical)
- Low residual stresses
- Low operational cost