Advanced Materials & Processes

NOV-DEC 2013

Covers developments in engineering materials selection, processing, fabrication, testing/characterization, materials engineering trends, and emerging technologies, industrial and consumer applications, as well as business and management trends

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i T S S e The the official journal of the ASM Thermal Spray Society, publishes contributions on all aspects—fundamental and practical—of thermal spray science, including processes, feedstock manufacture, testing, and characterization. As the primary vehicle for thermal spray information transfer, its mission is to synergize the rapidly advancing thermal spray industry and related industries by presenting research and development efforts leading to advancements in implementable engineering applications of the technology. Articles from the October and December issues, as selected by Editor-in-Chief Christian Moreau, are highlighted. The December issue features papers from the 2012 Asian Thermal Spray Conference, organized by guest editor Dr. Seiji Kuroda. The last two articles highlighted below are from this special issue. In addition to the print publication, is available online through For more information, please visit JTST HIGHLIGHTS 12 "Review on the Oxidation of Metallic Thermal Sprayed Coatings: A Case Study with Reference to Rare-Earth Permanent Magnetic Coatings" Jo Ann Gan and Christopher C. Berndt Thermal spray fabrication of rare-earth permanent magnetic coatings (PMCs) presents potential manufacturing routes for micro-magnetic devices but is not widely explored because of oxidation concerns. Oxidation leads to the loss of ferromagnetic phases and deterioration of magnetic performance. Although this review focuses on magnetic materials, there is significant technical crossover to all classes of feedstocks used in thermal spray. Oxidation mechanisms and the associated influencing factors to implement effective processing techniques during the deposition process are explored while various stages and mechanisms of oxidation in thermal spray processes are reviewed. Factors that influence the extent of oxidation depend on the dominant oxidation type and rely on the type of spray system, powder injection position, and feedstock particle size. "Net Shape Fins for Compact Heat Exchanger Produced by Cold Spray" Yannick Cormier, Philippe Dupuis, Bertrand Jodoin, and Antoine Corbeil Near-net-shaped pyramidal fin arrays of various sizes and fin densities were manufactured using masks made of commercially available steel wire mesh. The feedstock powders that produce the fins were characterized using scanning electron microscopy. Mask obstruction was investigated and the standoff distances between the substrate, mesh, and nozzle were empiriUniform heat flux on the fins cally determined. Fin array char- (without flow) resulting in a acterization was performed uniform surface temperature. using digital microscopy. The fin arrays' heat transfer performance was assessed experimentally for a range of Reynolds number relevant to the desired application. Fins produced using the cold spray process outperform traditional straight (rectangular) fins at the same fin density. Researchers hypothesize this is due to increased fluid mixing and turbulence. "Resistance to Corrosion of Zirconia Coatings Deposited by Spray Pyrolysis in Nitrided Steel" G.I. Cubillos, J.J. Olaya, M. Bethencourt, G. Cifredo, and G. Blanco Coatings of zirconium oxide were deposited onto three types of stainless steel, AISI 316L, 2205, and tool steel AISI D2, using the ultrasonic spray pyrolysis method. The effect of the flux ratio on the process and its influence on the structure and morphology of the coatings was investigated. The coatings obtained, 600 nm thick, were characterized using x-ray diffraction, scanning electron microscopy, confocal microscopy, and atomic force microscopy. Corrosion resistance of coatings deposited over steel (not nitrided) and stainless steel nitrided (for 2 h at 823 K) in an ammonia atmosphere was evaluated. The zirconia coating enhances stainless steel's corrosion resistance, with the greatest increase observed for tool steel. When the deposition is performed on previously nitrided stainless steel, the morphology of the surface improves and the coating is more homogeneous, which leads to improved corrosion resistance. Confocal image 2205-ZrO2. "Evolution of Lamellar Interface Cracks During Isothermal Cyclic Test of Plasma-Sprayed 8YSZ Coating with a Columnar-Structured YSZ Interlayer" Schematic of the potential oxidation regions within a generic thermal spray process. 72 Chang-Jiu Li, Yong Li, Guan-Jun Yang, and Cheng-Xin Li The cracks in thermal barrier coatings (TBCs) along the direction of the interface between the ceramic coating and bond coat ADVANCED MATERIALS & PROCESSES • NOVEMBER-DECEMBER 2013

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