Effect of Heat Treatment on the Microstructure and Mechanical Properties of Stainless Steel 316L Coatings Produced by Co
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Bandar AL-Mangour, Phuong Vo, Rosaire Mongrain, Eric Irissou, and Stephen Yue (Submitted July 25, 2013; in revised form October 31, 2013) In this study, the effects of heat treatment on the microstructure and mechanical properties of cold sprayed stainless steel 316L coatings using N2 and He as propellant gases were investigated. Powder and coating characterizations, including coating microhardness, coating porosity, and XRD phase analysis were performed. It was found that heat treatment reduced porosity, improved inter-particle bonding, and increased ductility. XRD results confirmed that no phase transformation occurred during deposition. Significant increase in UTS and ductility was observed for the annealed specimens obtained with nitrogen propellant, whereas little changes were observed for the helium propellant produced specimen.
Keywords
cold gas dynamic spray, fractography, inter-particle bonding, mechanical properties, stent
1. Introduction Cold gas dynamic spray is an emerging coating technique in which micron size powder particles are accelerated by a supersonic gas jet generated through a converging-diverging nozzle and sprayed onto a substrate where they impact, deform, and bond to create a dense coating (Ref 1-5). The technology has become of worldwide interest for its numerous advantages over current thermal spray processes with a prominent advantage being that powder particles remain predominately in the solid state during the entire deposition process, thereby minimizing thermal stresses, oxidation, phase transformation, and grain growth. Due to its benefits, cold spray processing is envisioned for medical devices such as hydroxyapatite coatings for orthopedic implants (Ref 6). Because failure and fractures in coronary stents seem to be attributed to high cycle fatigue (Ref 7, 8), which can be adversely affected by increasing grain size, the use of cold spray coating material has been proposed as an alternative manufacturing choice to the conventional casting and hot Bandar AL-Mangour and Stephen Yue, Department of Mining and Materials Engineering, McGill University, 3610 University St., Montreal, QC H3A 2B2, Canada; Phuong Vo and Eric Irissou, National Research Council Canada, 75 de Mortagne Blvd., Boucherville, QC J4B 6Y4, Canada; and Rosaire Mongrain, Department of Mechanical Engineering, McGill University, 817 Sherbrooke St. West, Montreal, QC H3A 2K6, Canada. Contact e-mails: [email protected] and [email protected].
Journal of Thermal Spray Technology
and cold forming route for manufacturing coronary stents (Ref 9). The vast majority of coronary stents are manufactured from 316L stainless steel for its superior corrosion resistance and well-suited mechanical properties (Ref 10-12). Many medical devices, including stents, are primary processed via casting and subsequent thermo-mechanical processing to achieve the required shape and mechanical properties (Ref 13). In the case of stent material, selection of melt source is important to ensure the homogeneity, porosity and micro-clea
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