Based on the principles of cold spray, Cold Gas Dynamic Manufacturing (CGDM) is a high-velocity metal spraying process capable of the high-rate deposition of dissimilar materials under cold conditions. However, unlike many cold-spraying techniques that have focussed primarily on surface coatings, the CGDM process has been tailored for solid free-form fabrication. Central to the needs of the process is the ability to accelerate the feedstock powder – through entrainment into a high-velocity gas flow – to speeds in excess of its critical deposition velocity. The critical factor here is not the gas velocity but rather the ultimate particle velocity; and it is the drag force experienced by the individual powder particles that affect their velocity. This paper documents the methods used to predict, model and validate nozzle performance – in terms of particle acceleration and ultimate velocity – via Computational Fluid Dynamics (CFD) and Particle Image Velocimetry (PIV). Results are presented and discussed pertaining to the effects of nozzle type (de Laval, MLN etc.) and geometry, as well as gas type (Helium and Nitrogen), composition and temperature. Abstract only; no full-text paper available.

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