The cold gas-dynamic process spray method or simply cold-spray is a high-rate material deposition process in which small, unmelted powder particles (typically 1–50mm in diameter) are accelerated to velocities on the order of 600–1000 mys in a supersonic jet of compressed gas. Upon impact against a substrate, the solid particles deform and bond together, rapidly building up a layer of deposited material.
Cold-spray was developed in the former Soviet Union in the mid-1980s. While performing supersonic wind tunnel tests with flows containing small tracer particles,scientists observed that above a critical particle velocity (which varies for different materials) there was a transition from particle erosion of a target surface to rapidly increasing deposition . Based on these phenomena,a spray system was created and an US patent was issued in 1994.
The nanostructured WC–Co cold-sprayed coating has a high density and microhardness when compared to those of the nanostructured feedstock. The coating microhardness enhancement is much more dependent on the impact velocity than the nanostructured particle
microhardness itself. The impact of the particles against the substrate at supersonic velocities, promotes a densification in each nanostructured particle. There is no significant difference between the average grain size of the nanostructured feedstock and coating. It is possible to produce pure and well bonded nanostructured WC–Co coatings via cold-spray processing.
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