Ceramic and Cermet Coatings
A Research Update
Researchers at the NRC Industrial Materials Institute (NRC-IMI) in Longueuil, Quebec, are continuing to explore and develop new possibilities for high-performance coatings. Coatings, in this case using ceramic and ceramic-metallic (cermet) materials, are an important and valuable area of research in the field of industrial materials. New coatings being developed have applications in areas as diverse as aerospace parts and biomedical implants.
 Researchers begin with a process called thermal spraying, a widely-used technology for applying coatings. As the term implies, thermal spraying involves the use of high temperatures to heat particles that will make up the coating. Meanwhile, the heated particles are accelerated to an extremely high velocity. When sprayed onto a cold (in relative terms) surface, the particles deform and quickly "freeze" on the substrate. The resulting coating comes about from millions upon millions of particles accumulating on the surface.
By incorporating nanostructured materials into the "feedstock" used to produce the coatings, researchers have succeeding in creating coatings containing nanostructured zones. Such coatings have been shown to have significant advantages in terms of both production and performance when compared to the thermal spray processing of conventional microstructured materials. The new nanostructured coatings are targeted mainly for demanding applications in the biomedical and aerospace fields and on components subjected to wear for which performance and durability are key requirements and premature failure can have serious consequences.
Research has shown that hydroxyapatite coatings produced at NRC-IMI using a nanostructured powder and a carefully controlled thermal spray process exhibited a higher degree of crystallinity, improved bonding to the substrate, and greater bioactivity when compared to conventional coatings produced using more traditional thermal spray processes. These three attributes are important when such coatings are being employed on biomedical implants, such as might be the case on components used for hip replacement.
Other work has demonstrated that improved wear resistance can be achieved with the introduction of a nanostructured phase. Such results have been obtained in working with tungsten-cobalt cermets and titania. In the latter case, nanostructured zones within the coating appear to play an important role in improving the performance.
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