While traditional thermal spray processes are widely used in many applications, they rely on thermal energy to melt or soften the feedstock. This can lead to thermal degradation and partial oxidation of the coating material, which may be undesirable. For metal materials that are highly prone to oxidation, thermal spray must be conducted in a protected atmosphere or under a vacuum, which adds extra cost. The heat input from thermal spray processes introduces residual stress into the deposits, which can limit the attainable thickness. Additionally, the thermal balance must be carefully managed through part cooling and precise gun manipulation to avoid excessive internal stresses and potential substrate degradation.
Similarly, fusion-based additive manufacturing processes such as Laser Powder Bed Fusion (LPBF) and Directed Energy Deposition (DED) also use thermal energy to melt or partially melt the feedstock material. These high-temperature processes can induce thermal stresses, distortion, cracking, and residual porosity. Additionally, high temperatures may trigger phase transformations in the material, potentially impacting its mechanical properties. To counteract these issues, these processes often require an inert atmosphere or operation in a vacuum, necessitating precise control of thermal conditions to prevent defects and maintain material integrity.
In contrast, Cold Spray technology enables material deposition in the solid state without high thermal loads. This results in deposits with high density, minimal or no oxidation, and no phase transformation or heat-affected zones, while maintaining manageable levels of residual stress. Cold Spray is particularly advantageous for applications where preserving the properties of both the feedstock and substrate material is critical, working with temperature- and oxygen-sensitive materials, and achieving high deposition rates.
Cold Spray at TWI
TWI conducts research to explore the potential of Cold Spray and optimise the process for specific applications, including:
- Wear and corrosion-resistant coatings for harsh environments
- Improved biocompatible coatings for medical implants
- Thick metallic coatings for thermally sensitive substrates
- Bond coatings for oxide ceramics, such as thermal barrier coatings (TBCs)
- Repair techniques for lightweight aerospace alloys
- Near-net-shape additive manufacturing for various applications, such as ODS alloys for the nuclear industry
- Multi-material builds and functional grading of materials
Explore Our Facilities
TWI uses high-specification commercial systems, including:
- Titomic 523: A manual/portable low-pressure cold spray system that uses compressed air as the process gas, capable of operating at pressures up to 6 bar and temperatures up to 600°C.
- Impact Innovations 5/11, and Titomic TKF-1000: High-pressure cold spray systems offering higher operating temperatures and pressures (with N₂ gas at up to 1100°C and 60 bar), delivering enhanced coating quality. These systems can be operated with or without pre-heating the gas and with a variety of spray nozzles, allowing for configuration based on specific requirements.
A number of materials have already been proven to be suitable for cold spraying. Here is a non-exhaustive list:
- Metals (Al, Cu, Ni, Ti, Ag, Zn, Ta, Nb)
- Refractory metals (Zr, W, Ta)
- Alloys (steels, Ni alloys, MCrAlYs, Al-alloys)
- ODS alloys (PM2000, Eurofer97, YWT variants)
- Composites (Cu-W, Al-SiC, Al-Al2O3)
With these materials in mind, a wide range of applications can be explored, with possible end uses in sectors such as aerospace, automotive, oil and gas, power generation, motorsport, medical, petrochemical and electronics.
To keep up-to-date with our latest developments, please follow our LinkedIn page: TWI Cold Spray Technology Centre. For any enquiries, please email contactus@twi.co.uk.