Cold Spraying at TWI Yorkshire

Cold Spraying, or more precisely Cold Gas Dynamic Spraying (CGDS), is a high-rate material deposition process in which powder particles (typically 1 to 50 µm) are accelerated to velocities in the range 200 to 1000 m s-1 in a supersonic jet of compressed gas at a temperature much below the melting point of the feedstock powder (ambient temperature to 700°C). Upon impact with a target surface, the solid particles experience plastic deformation that disrupts thin surface films (such as metal oxides) and provides intimate conformal contact between the clean metal surfaces under high local pressure. This permits bonding to occur and layers of deposited material to be built up rapidly.

With CGDS, various materials can be sprayed without exposing them (or the substrate) to high thermal loads. In comparison to other thermal spraying processes (i.e. plasma spraying or flame spraying), CGDS allows coatings to be made with extremely low porosity and oxygen content. The application efficiency is very high and can reach up to 90%.

TWI uses the latest, highest specification commercial system (CGT GmbH Kinetiks ^® 4000 47kW) that can achieve process gas temperatures of up to 800°C and process gas pressures of up to 40 bar. The feed-stock powder can be heated to over 500°C, resulting in improved adhesion for some specific coating systems. The Active Jet Cold Spray Gun can be operated with or without pre-heating the gas. This enables the system to be configured for the application of tailored coatings.

A number of materials have already been proven to be suitable for cold spraying. These include:

• Metals (Al, Cu, Ni, Ti, Ag, Zn, Ta, Nb)
• Refractory metals (Zr, W, Ta)
• Alloys (steels, Ni alloys, MCrAlYs)
• Composites (Cu-W, Al-SiC, Al-Al ₂ O ₃ )

With these materials in mind, a wide range of applications can be explored, with possible end uses in a number of industry sectors, such as aerospace, automotive, oil and gas, power generation, motorsport, medical, petrochemical and electronics.

For more information about the cold spraying process and the TWI's cold spraying facilities, please contact Tiziana Marrocco ( tiziana.marrocco@twi.co.uk).

Download the Cold Spray Services leaflet

A book from Woodhead Publishing Limited: The Cold Spray Materials Deposition Process: Fundamentals and Applications