Nanocomposite coatings: thermal spray processing, microstructure and performance

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.