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New Cold Spray technology, Australian launch

CSIRO : 03 November, 2003  (New Product)
Revolutionary Cold Spray technology, described as the next milestone for the thermal spray industry, has been unveiled to Australian industry for the first time.
At a recent demonstration day funded by the Victorian State Government under its Agenda for New Manufacturing more than 100 organisations saw first hand the advantages of the Cold Spray system, which eliminates the detrimental effects of high temperature on coatings and substrates experienced with thermal spray techniques.
Dr Mahnaz Jahedi of CSIRO Elaborately Transformed Metals (CSIRO Division of Manufacturing & Infrastructure Technology) says, 'Cold Spray technology or cold gas-dynamic spray technology produces coatings with a gas jet temperature, which is lower than thermal spray processes such as powder flame, wire arc, plasma arc and high-velocity oxygen fuel spraying'.

Dr Jahedi says, 'Cold spray might be more appropriately called 'room-temperature spray' technology because particles are applied at temperatures much lower than the melting temperature of not just the coating but the substrate as well'.

'This revolutionary system avoids a raft of high-temperature effects such as oxidation, vaporisation, melting, crystallisation, residual stresses and gas release,' Dr Jahedi says.

'Not surprisingly we say that it is the next milestone for the thermal spray industry'.

CSIRO and Dr Jahedi have made it possible for easy access to the development of cold sprayed, exotic coatings for Australian industry, by importing the first cold spray system to Australia.

There are useful applications for cold spray technology in just about any industry utilising thermal spraying: from the biomedical industry where it can be used for prostheses with improved wear and fatigue characteristics; to the aerospace industry where it offers coatings of greater fatigue resistance, in the chemical and mineral processing and die casting industries and for applications in the electronics, paper, oil, gas and glass industries.

Dr Jahedi says, 'By virtue of its 'low temperature' nature, cold spray technology is also expected to be useful for the 70% of materials which could be spray coated but are ruled out by the high temperatures required by current thermal technology'.

Conventional 'thermal spray' processes require the sprayed materials to be preheated so the particles are in a semi-molten state when they reach the substrate, allowing them to splash across the surface. But as the 'splats' cool, they contract slightly, creating residual (stored) stresses or flaws at the interface and within the coating that can cause defects later.

Another advantage for the Cold Spray System is that cold-sprayed materials are accelerated to high speed slamming into the substrate at supersonic velocities (500-1500 m per second).

Dr Jahedi says, 'This forms a tight bond without the undesirable chemistry changes and stresses associated with conventional thermal processes.

'At this stage, it is believed this high-velocity impact disrupts thin metal-oxide films on the particle and substrate surfaces, pressing their atomic structures into intimate contact with one another under momentarily high interfacial pressures.'

Cold sprayed materials experience little to no defect-causing oxidation during flight, and exhibit remarkably high densities and conductivities once fabricated.

Other possible uses of the Cold Spray system include fabricating layer by layer, manufacturing low-defect small piece parts, joining chemically dissimilar materials with bonds that gradually transition from one material composition to another, and as a low-temperature alternative to welding.

Dr Jahedi says 'Cold spray as a fabrication process also has some significant advantages in developing industrial prototypes and advancing new designs quickly and comparatively inexpensively compared to the usual prototyping processes.'

However utilising the Cold Spray System for specific applications requires tailoring by CSIRO.

Dr Jahedi says, 'To do this we offer customers a development programme to identify the best materials, particle sizes and impact velocities for each application, as well as an examination into gas dynamics, plastic deformation, and spray nozzle configurations for each job'.

Some Other Advantages of cold spray technology:

Retains properties of initial particles
Deposits oxygen-sensitive materials without vacuum
High hardness, cold work microstructure
Corrosion-resistant coatings
Plastic coating without volatile solvents
Intermetallic coatings/repair (phase and compositional stability)
Can apply Metal on ceramic and Metal on glass
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