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The degree of bonding between particles within cold-sprayed deposits is of great importance as it affects their mechanical and physical properties. This article describes a method for characterizing the bonding between aluminum and copper particles following deposition by cold spraying. Aluminum and copper powders were blended in the ratio 1:1 by volume, deposited onto a copper substrate and subsequently heat treated at 400°C for 15 min. An intermetallic layer formed along some regions of the aluminumcopper boundaries, believed to be where true metal to metal contact had occurred. In other regions, metal to metal contact was inhibited by the presence of oxide films. Image analysis was employed to measure the fraction of the aluminum-copper interface covered with intermetallic phases and to estimate intermetallic thicknesses. By increasing the primary gas pressure in the cold-spray process, an increase in the degree of inter-particle bond formation was observed.

Cold gas dynamic spraying is a relatively new spray coating technique capable of depositing a variety of materials without extensive heating. As a result the inherent degradation of the powder particles found during traditional thermal spraying can be avoided. The simplicity of this technique is its most salient feature. High pressure gas is accelerated through a convergent-divergent nozzle up to supersonic velocity. The powder particles are carried to the substrate by the gas and on impact the particles deform at temperatures below their melting point. Computational modeling of thermal spray systems can provide thorough descriptions of the complex, compressible, particle-laden flow, and therefore can be utilized to strengthen understanding and allow technological progress to be made in a more systematic fashion. The computational fluid dynamic approach is adopted in this study to examine the effects of changing the nozzle cross-section shape, particle size and process gas type on the gas flow characteristics through a cold spray nozzle, as well as the spray distribution and particle velocity variation at the exit.

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