A Method for Characterizing the Degree of Inter-particle Bond Formation in Cold Sprayed Coatings
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JTTEE5 16:566–570 DOI: 10.1007/s11666-007-9070-3 1059-9630/$19.00 ASM International
A Method for Characterizing the Degree of Inter-particle Bond Formation in Cold Sprayed Coatings T.S. Price, P.H. Shipway, D.G. McCartney, E. Calla, and D. Zhang (Submitted June 15, 2007; in revised form July 23, 2007) 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.
Keywords
bonding, CGDS, cold spraying, particle impact
1. Introduction Cold gas dynamic spraying (CGDS) involves the acceleration and impact of solid particles with a substrate to form a coating; typically, deposit thicknesses range between 100 and 1500 lm. The particles are accelerated in a supersonic gas jet which can be produced by the use of a converging-diverging de Laval nozzle (Ref 1). Particles impinging on a substrate will either rebound from the substrate (with or without causing erosion) or bond with the substrate (Ref 2, 3), depending on the material type and particle velocity on impact with the substrate. It has been observed that for a range of metals, particle deposition occurs when the particle velocity exceeds a critical velocity (typically in excess of 500 m/s for materials such as aluminum, copper, and titanium) (Ref 2, 4). The mechanism of coating build up is believed to involve initial impact-damage to the substrate which removes the oxide layer and allows impinging particles to bond with the newly exposed metal surface (Ref 5). A continued flux of impinging particles leads to further deposit build up through high velocity impacts between particles arriving at the substrate and those already deposited. The occurrence of bonding on particle impact is widely regarded to be related to the occurrence of shear T.S. Price, P.H. Shipway, D.G. McCartney, E. Calla, and D. Zhang, School of Mechanical, Materials and Manufacturing Engineering, University of Nottingham, Nottingham, UK. Contact e-mail: [email protected].
566—Volume 16(4) December 2007
instabilities at the interparticle boundaries, due to high strain rate deformation. Much effort has been devoted to improving our understanding of the mechanisms of coating build up t
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