The deposit does not fuse with the substrate or form a solid solution. The bond is primarily mechanical. Hence, adhesion depends on the molten particle impact velocity as well as the surface condition, which must be clean and roughened by grit blasting or machining prior to spraying. Bond strengths between ca. 10 MPa and >80 MPa can be obtained depending on the thermal spray process and spray parameters used.
Conventional thermal spray techniques include flame spraying and electric arc spraying. These have been used since the mid 1900s and continue to be developed. More advanced thermal spray processes include detonation gun, high velocity oxy-fuel (HVOF), plasma and suspension/precursor spraying. Each process gives different coating characteristics for the same coating material, which determines the coating performance.
Thermal spraying can offer a technically superior and commercially competitive solution to many industrial challenges, including:
- Replacement of chrome or cadmium plating;
- Wear, corrosion and thermal protection, e.g. biomass and waste-to-energy plants, offshore structures, subsea pump internals, impeller wear rings, valve plugs/balls/discs and seats, rock drill internals, compressor blades and vanes, bearing housings, glass plungers, printing rolls, textile guides;
- Biocompatible coatings on orthopaedic and dental implants;
- Dielectric coatings for electrical insulation in power hybrid circuits and heating elements;
- Spray forming e.g. manufacture of thin walled hollow cylindrical objects from pre-shaped cores;
- Component surface restoration after wear or damage
TWI uses a wide range of commercially-available thermal spray equipment, so that technology developments are transferable to industry. The available process technologies are:
- Latest generation cold spray system
- Three different HVOF systems
- Plasma spray (APS)
- Twin wire arc spray
- Flame spray
We offer the following services to our members:
- Applications development
- Coatings research and development
- Consultancy services and materials selection
- Coating failure investigations
- Coating characterisation and testing
Current research projects include the development of improved sacrificial coatings for sea-water corrosion resistance of steel structures, corrosion mitigation of boiler tubes in biomass or waste-to-energy plants, and the development of antifouling coatings for renewable energy applications.
Internal research conducted in the past ten years has resulted in our innovative and versatile proprietary method for applying thick thermal spray coatings to composite materials: CompoSurfTM.
In addition to this, each year we complete dozens of confidential leading-edge projects for individual member companies.
See further information about Materials and Corrosion Management or please email contactus@twi.co.uk.