Engineering a new class of thermal spray nano-based microstructures from agglomerated nanostructured particles, suspensions and solutions: An invited review

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Journal titleJournal of Physics D: Applied Physics
Article number93001
SubjectAlumina coating; Average diameter; Bimodal structures; Coating structures; Complex mechanisms; Conventional coatings; Diagnostic tools; Feedstock particles; Hot gas; Hot gas flow; Industrial communities; Liquid drop; Liquid precursors; Measurement device; Micrometre-sized particles; Mixed precursors; Nanometres; Nanostructured coatings; Nanostructured particles; Oxide powder; Parameter variation; Processing Route; Research and development; Size ranges; Solid oxide; Solution precursor; Spray process; Spray technique; Sprayed particles; Thermal barrier; Thermal flows; Thermal plasma; Thermal spray; Thermal spray coatings; Thermal spray process; Thermal spray techniques; Wear-resistant; Agglomeration; Feedstocks; Fuel cells; Industrial applications; Ion beams; Liquids; Manufacture; Network architecture; Powders; Research and development management; Solid electrolytes; Spray guns; Sprayed coatings; Suspensions (fluids); Thermal barrier coatings; Thermal spraying; HVOF thermal spraying
AbstractFrom the pioneering works of McPherson in 1973 who identified nanometre-sized features in thermal spray conventional alumina coatings (using sprayed particles in the tens of micrometres size range) to the most recent and most advanced work aimed at manufacturing nanostructured coatings from nanometre-sized feedstock particles, the thermal spray community has been involved with nanometre-sized features and feedstock for more than 30 years. Both the development of feedstock (especially through cryo-milling, and processes able to manufacture coatings structured at the sub-micrometre or nanometre sizes, such as micrometre-sized agglomerates made of nanometre-sized particles for feedstock) and the emergence of thermal spray processes such as suspension and liquid precursor thermal spray techniques have been driven by the need to manufacture coatings with enhanced properties. These techniques result in two different types of coatings: on the one hand, those with a so-called bimodal structure having nanometre-sized zones embedded within micrometre ones, for which the spray process is similar to that of conventional coatings and on the other hand, sub-micrometre or nanostructured coatings achieved by suspension or solution spraying. Compared with suspension spraying, solution precursor spraying uses molecularly mixed precursors as liquids, avoiding a separate processing route for the preparation of powders and enabling the synthesis of a wide range of oxide powders and coatings. Such coatings are intended for use in various applications ranging from improved thermal barrier layers and wear-resistant surfaces to thin solid electrolytes for solid oxide fuel cell systems, among other numerous applications. Meanwhile these processes are more complex to operate since they are more sensitive to parameter variations compared with conventional thermal spray processes. Progress in this area has resulted from the unique combination of modelling activities, the evolution of diagnostic tools and strategies, and experimental advances that have enabled the development of a wide range of coating structures exhibiting in numerous cases unique properties. Several examples are detailed. In this paper the following aspects are presented successively (i) the two spray techniques used for manufacturing such coatings: thermal plasma and HVOF, (ii) sensors developed for in-flight diagnostics of micrometre-sized particles and the interaction of a liquid and hot gas flow, (iii) three spray processes: conventional spraying using micrometre-sized agglomerates of nanometre-sized particles, suspension spraying and solution spraying and (iv) the emerging issues resulting from the specific structures of these materials, particularly the characterization of these coatings and (v) the potential industrial applications. Further advances require the scientific and industrial communities to undertake new research and development activities to address, understand and control the complex mechanisms occurring, in particular, thermal flow-liquid drops or stream interactions when considering suspension and liquid precursor thermal spray techniques. Work is still needed to develop new measurement devices to diagnose in-flight droplets or particles below 2μm average diameter and to validate that the assumptions made for liquid-hot gas interactions. Efforts are also required to further develop some of the characterization protocols suitable to address the specificities of such nanostructured coatings, as some existing 'conventional' protocols usually implemented on thermal spray coatings are not suitable anymore, in particular to address the void network architectures from which numerous coatings properties are derived. © 2011 IOP Publishing Ltd.
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AffiliationNational Research Council Canada (NRC-CNRC); NRC Industrial Materials Institute (IMI-IMI)
Peer reviewedYes
NPARC number21271316
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Record identifier11f430c3-b553-4253-911d-101d7be2b2f7
Record created2014-03-24
Record modified2016-05-09
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