Cold-Spraying Coupled to Nano-Pulsed Nd-YaG Laser Surface Pre-treatment
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JTTEE5 19:1062–1073 DOI: 10.1007/s11666-010-9500-5 1059-9630/$19.00 ASM International
Cold-Spraying Coupled to Nano-Pulsed Nd-YaG Laser Surface Pre-treatment D.K. Christoulis, S. Guetta, E. Irissou, V. Guipont, M.H. Berger, M. Jeandin, J.-G. Legoux, C. Moreau, S. Costil, M. Boustie, Y. Ichikawa, and K. Ogawa (Submitted December 22, 2009; in revised form February 25, 2010) The effect of Al2017 substrate pre-treatment using pulsed laser ablation on adhesion strength of coldsprayed Al coating is examined. A high energy pulsed laser beam was coupled with a cold-spray gun to result in laser ablation of the substrate surface a few milliseconds prior to the deposition. The influence of the laser fluence and repetition rate on substrate surface morphology and physico-chemical properties are investigated. Coating-substrate interfaces were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of thin foils which were prepared using focused ion beam (FIB). Adhesion strength was evaluated by means of finite element method (FEM) of LAser Shock Adhesion Tests (LASAT). The results are compared to samples prepared on as received substrate, and pre-treated by two conventional methods, namely polishing and grit-blasting. It is shown that the coatingsubstrate interface is significantly improved when pulsed laser ablation is performed at optimized parameters. No oxide layer was found at the coating-substrate interface on laser ablated sample while two oxide layers were found on the as-received sample indicating that particle impingement transformed the native alumina layer in an amorphous Al oxide phase. The observations allow concluding that bonding of cold spray Al particles on Al2017 substrate requires either the removal of the native oxide layer or its transformation in an amorphous Al oxide phase.
Keywords
adhesion, aluminum, bond strength, cold-spray, LASAT, pulsed laser ablation, substrate pre-treatment
1. Introduction In thermal spray, coating adhesion strength is paramount since advanced coatings must remain bonded to the substrate under various and severe conditions. Many studies are devoted to the bonding mechanisms and to the optimization and improvement of coating bond strength in thermal spray (Ref 1-6). The same requirements of high coating adhesion hold true for cold spray coatings. However, the cold spray process differs from other thermal spray processes in its bonding mechanisms since there is no melting of the feedstock powder (Ref 7-13). Indeed, powder particles are accelerated in their solid state by a low temperature supersonic gas stream (Ref 14) and are D.K. Christoulis, S. Guetta, V. Guipont, M.H. Berger, and M. Jeandin, Mines-ParisTech, C2P-Competence Center for Spray Processing, CNRS UMR 7633, Evry, France; E. Irissou, J.-G. Legoux, and C. Moreau, National Research Council Canada, Industrial Materials Institute, Montreal, QC, Canada; S. Costil, Universite´ de Technologie de Belfort-Montbe´liard, LERMPS, Belfort, France; M. Boustie, Laboratoire de Combustion et de
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