Vapors and Droplets Mixture Deposition of Metallic Coatings by Very Low Pressure Plasma Spraying
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B. Vautherin, M.-P. Planche, R. Bolot, A. Quet, L. Bianchi, and G. Montavon (Submitted May 13, 2013; in revised form November 20, 2013) In recent years, the very low pressure plasma-spraying (VLPPS) process has been intensely developed and implemented to manufacture thin, dense and finely structured ceramic coatings for various applications, such as Y2O3 for diffusion barriers, among other examples. This paper aims at presenting developments carried out on metallic coatings. Aluminum was chosen as a demonstrative material due to its ‘‘moderate’’ vaporization enthalpy (i.e., 38.23 KJ cm23) compared to the one of copper (i.e., 55.33 KJ cm23), cobalt (i.e., 75.03 KJ cm23), or even tantalum (i.e., 87.18 KJ cm23). The objective of this work is primarily to better understand the behavior of a solid precursor injected into the plasma jet leading to the formation of vapors and to better control the factors affecting the coating structure. Nearly dense aluminum coatings were successfully deposited by VLPPS at 100 Pa with an intermediate power plasma torch (i.e., Sulzer Metco F4 type gun with maximum power of 45 kW). Optical emission spectroscopy (OES) was implemented to study and analyze the vapor behavior into the plasma jet. Simplified CFD modeling allowed better understanding of some of the thermo-physical mechanisms. The effect of powder-size distribution, substrate temperature and spray distance were studied. The phase composition and microstructural features of the coatings were characterized by XRD and SEM. Moreover, Vickers microhardness measurements were implemented.
Keywords
aluminum, coating properties, computational fluid dynamic, feedstock powder size, optical emission spectroscopy, very low pressure plasma spraying
1. Introduction The very low pressure plasma spray (VLPPS) process is an emerging process allowing manufacturing ceramic and metallic coatings (Ref 1-19). It is operated in an inert atmosphere (i.e., Ar) at unusually low pressures, between 100 and 1000 Pa, typical values. As a consequence, the deposition mechanisms are different compared to the ones encountered with the atmospheric plasma spray (APS) process, and even low pressure plasma spraying (LPPS), since they result mostly from the condensation of vapors instead of the stacking of flattened particles. Depending upon spray operating parameters, coating structures vary from nearly dense to highly porous. As shown by Von Niessen et al. (Ref 4), Gindrat et al. (Ref 7, 13), Hospach This article is an invited paper selected from presentations at the 2013 International Thermal Spray Conference, held May 13-15, 2013, in Busan, South Korea, and has been expanded from the original presentation. B. Vautherin, M.-P. Planche, R. Bolot, and G. Montavon, IRTESLERMPS, UTBM, Site de Se´venans, 90010 Belfort Cedex, France; and A. Quet and L. Bianchi, CEA Le Ripault, 37260 Mons, France. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
and Mauer (Ref 1, 9, 10, 14), Dorier et al. (Ref 11, 15), Zhu et al. (Ref 2, 5), and Guittienn
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