Research Development of Hard Ceramic Nano-multilayer Films

Ceramic nanomultilayers are becoming hot research because of superhardness effect. Recent progresses and limitations in the research of these artificial hard materials is reviewed, and possible future work is highlighted. Over the past two decades, numerous experimental studies have been conducted leading to significant progress in the exploring of new superhard nanomultilayer systems and understanding of their microstructures. In the aspect of microstructure, it is now commonly accepted that the formation of coherent interface between modulation layers is a critical microstructure prerequisite for nanomultilayers to obtain superhardness. In the aspect of developing new nanomultilayer systems, owing to the template effect, coherent epitaxial growth can be easily realized between two modulation layers even if they naturally have different crystalline structures or one of them exists in amorphous, and material combination that is able to achieve superhardness are thus greatly expanded. On the other hand, in contrast to experimental studies, relatively slow progress has been achieved in theoretical studies aimed in explaining the hardening mechanism of these ceramic nanomultilayers. The mainstream theory currently employed is still the one that was proposed twenty years ago to explain the hardness anomaly enhancement in nanomultilayers formed by metal components, with emphasis on impediment to dislocation motion by interfaces. Therefore, future works should involve in building up new hardening mechanisms and design principles that can be applied to ceramic nanomultilayers, and exploring new multilayer material combinations such as carbides, borides, and even oxides.