The processing of nanomaterials and nanocomposites has advanced since the 1990s. The growth and opportunities afforded by this technological domain is evident through the trends of research and development (R&D) funding, Science Citation Index (SCI) publications, and patent applications presented in this paper. This article reviews the current state for the development of thermal sprayed nanocomposite coatings. The types of nanocomposite thermal spray feedstock materials that are available commercially, as well as those currently in the development phase, are critically assessed. The thermal spray approaches to deposit nanocomposite coatings are discussed, including the conventional plasma spray and high velocity oxygen fuel (HVOF) processes and the more recently developed cold spray, suspension thermal spray (STS), and solution precursor thermal spray (SPTS) processes. These processes are assessed in relation to their deposition mechanisms and the specific nanocomposite materials associated with each technique. The unique microstructure of the coatings deposited by each method is highlighted in relation to process and compositional control. The exceptional attributes of nanocomposite coatings, such as mechanical strength and toughness, wear resistance, thermophysical, and electrical properties, are also presented together with specific applications.

Thermal spray fabrication of rare-earth permanent magnetic coatings (PMCs) presents potential manufacturing routes for micro-magnetic devices. Despite this potential, thermal spray of PMCs is still not widely explored due to oxidation concerns. It was established that oxidation leads to the loss of ferromagnetic phases in these materials and results in deterioration of magnetic performance. Although this review focuses on a specific class of material, i.e., magnetic materials, there is significant technical crossover to all classes of feedstocks that are employed in thermal spray processing. The oxidation mechanisms and the associated influencing factors are explored in this work to implement effective processing techniques during the deposition process. This paper reviews the various stages and mechanisms of oxidation in thermal spray processes. The factors that influence the extent of oxidation depend on the type of oxidation that is dominant and rely on the type of spray system, powder injection position, and the particle size of feedstock. Among the aspects that are reviewed include the oxygen-fuel ratio for high velocity oxygen-fuel (HVOF), current intensity, gas flow rate, particle size, spray distance, and substrate temperature. Protection strategies to minimize oxidation in thermal spray processes, such as gas shrouding and shielding, are presented.

No abstract

No abstract