Mechanofusion Processing of Metal-Oxide Composite Powders for Plasma Spraying
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Mechanofusion Processing of Metal-Oxide Composite Powders for Plasma Spraying Ricardo Cuenca-Alvarez1, Carmen Monterrubio-Badillo2, Hélêne Ageorges3, Pierre Fauchais3 1 Instituto Politécnico Nacional, CIITEC, México, D.F. 02250, Mexico 2 Instituto Politécnico Nacional, CMP+L, México DF 07430, Mexico. 3 SPCTS-UMR 6638, University of Limoges, 87060, Limoges Cedex, France. ABSTRACT Composite particles destined to build plasma sprayed coatings, are prepared by the mechanofusion process (MF). These particles consist of a stainless steel core particle coated by finer particles of alumina. Changes induced by the MF process are monitored by SEM, DRX, and laser granulometry, revealing that the dry particle coating process is governed by agglomeration and rolling phenomena. Simultaneously, the MF performance is controlled by the operating parameters such as the compression gap, the mass ratio of host to guest particle, and the powder input rate. The mechanical energy input leads to a nearly rounded shape of the final composite particles; however, no formation of new phases or components decomposition is detected by XRD analysis. The resulting composite powder features optimal characteristics, concerning particle shape and phases distribution, to be plasma sprayed in air. INTRODUCTION Production of composite powders is performed from a variety of commercial processes; however powder characteristics depend on the parameters of each process. Examples are ball milling, sol-gel process, atomization, mechanical alloying, sintering, self-propagating hightemperature synthesis (SHS), spray drying, etc. [1]. Since applications such as plasma spraying, need to use particles featuring characteristics such as good flow ability, spherical shape, two or more phases joined with no reaction between each other; powder preparation route must be selected according to these needs. Then, it is not only advantageous, but also necessary to design devices with the ability to modify such materials and thus obtaining composite powders with unique functionality. Some devices are developed to achieve this goal [2]: The Hybridizer©, the Magnetically Assisted Impaction Coater (MAIC), the Rotating Fluidized Bed Coater (RFBC), the Theta Composer, and the Mechanofusion Process©. These techniques are based under the dry particle coating principle with no need for using binder or water [3]. Consequently, economical and environmental benefits are obtained because some stages are avoided, for instance, drying of powder. A special interest is oriented towards the Mechanofusion device, henceforth called MF. It can be used for inducing significant changes in the functionality or properties of the original host particles, and thus creating engineered powders [4]. This technique attaches fine particles (guest) onto the surface of much larger particles (host), via strong mechanical forces; simultaneously, spheroïdization of particles is attained by a rolling effect. Mechanofused powders have been used for different applications. For instance, organic particles type PMM
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