Influence of Particle Velocity on Adhesion of Cold-Sprayed Splats
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. Guetta, M.H. Berger, F. Borit, V. Guipont, M. Jeandin, M. Boustie, Y. Ichikawa, K. Sakaguchi, and K. Ogawa (Submitted August 8, 2008; in revised form April 8, 2009) In cold spray, innovative coating process, powder particles are accelerated by a supersonic gas flow above a certain critical velocity. Particles adhesion onto the substrate is influenced by particle impact velocity, which can change dramatically depending on particle position from the core of the jet. In the present work, an original experimental set-up was designed to discriminate the particles as a function of the levels of velocity to investigate the influence of this parameter on adhesion. Particles at given positions could therefore be observed using scanning electron microscope, which showed different morphologies as a function of impact velocity. High pressure and temperature at the interface during impact were calculated from numerical simulations using ABAQUSÒ. Transmission electron microscope analyses of thin foils were carried out to investigate into resulting local interface phenomena. These were correlated to particle impact velocity and corresponding adhesion strength which was obtained from LAser Shock Adhesion Test.
Keywords
adhesion, cold spray, high-velocity LASAT, numerical simulation, splat
impact,
1. Introduction Cold-sprayed coatings can be achieved only when the velocity of in-flight particles exceeds a certain critical velocity (Ref 1, 2). Therefore, the velocity prior to impinge on the substrate is the most important parameter in cold spray (Ref 3). However, this in-flight velocity is not uniform in the jet flow, particularly when particles go through the shock wave area termed as the ‘‘bow shock’’ area (Ref 4). In this area, the smallest particles can be decelerated dramatically or deflected away from the substrate (Ref 5). This work focused therefore on particle impact velocity. A good coating-substrate adhesion is essential. However, to investigate into coating adhesion and cohesion, the study of adhesion of elementary particles, namely splats, onto the substrate is required. Even though particle adhesion mechanisms have not been yet elucidated, it can be assumed they are influenced S. Guetta, F. Borit, V. Guipont, and M. Jeandin, Ecole des Mines de Paris (ENSMP), Competence Centre for Spray Processing (C2P), Evry Cedex, France; M.H. Berger, Ecole des Mines de Paris (ENSMP), Centre des Mate´riaux P.M. Fourt, Evry Cedex, France; M. Boustie, Ecole Nationale Supe´rieure de Me´canique et dÕAe´rotechnique (ENSMA), Laboratoire de Combustion et De´tonique (LCD), Poitiers, France; and Y. Ichikawa, K. Sakaguchi, and K. Ogawa, Graduate School of Engineering, Fracture and Reliability Research Institute (FRI), Tohoku University, Sendai, Japan. Contact e-mail: serge.guetta@ ensmp.fr.
Journal of Thermal Spray Technology
by particle impact velocity, which results from spraying conditions (Ref 6, 7), particle diameter (Ref 8), and particle position from the center of the jet (Ref 9). Different splat morphologies observed by scanning e
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