Plasma Spraying of Thick Stainless Steel Coating of a Stereolithography Resin

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Abstract The use of plasma spraying can be very beneficial in a rapid prototyping/manufacturing route for producing industrial metallic parts, e.g. tools and molds. Compared to the most recent and advanced laser-based or flame/arc spray-based methods, plasma spray basically shows a higher efficiency and process control in addition to a wider range of coating materials and better coating properties. This work deals with plasma spraying of AISI 316 stainless steel onto conventional MVA 200 acrylate resin as the second stage of a rapid prototyping route involving stereolithography plus plasma spray. This resulted in a 3 key issues : - Achieving a good coating/substrate adhesion, notwithstanding the preventing from previous grit blasting of the resin and poor physico-chemical bonding between the organic substrate and stainless steel ; - Good building-up of the sprayed particles up to a rather high thickness (i.e. of a few mm) through adequate plasma spray conditions, which limits the residual stress level; - Coating conforming closely to the substrate geometry, which precludes from surface damaging under spraying. The work showed that the process can meet all the previously-mentioned requirements combined with the achievement of high-quality coatings (i.e. with a low porosity in particular). A major part consisted in optimizing the plasma spray conditions using a CAPSATC ("Controlled Atmosphere/Temperature Plasma Spraying") unit. This included the development of an original thermal pre-treatment of the substrate (patented), namely "PINPRO", to promote coating/substrate adhesion. SEM, EDS, EPMA, FTIR, QIA (Quantitative Image Analysis), ... were particularly employed to study microstructures and interfaces. Phenomenological approaches to the involved adhesion mechanisms and coating build-up are discussed. For the latter, the first steps in the application of Lattice-Gas Modeling (LGM) of stainless steel layer build-up were made. LGM is a new and powerful simulation tool for the spray operator or user.