Abstract
The microstructure, mechanical properties, and high-temperature oxidation resistance of AlN/SiO2 nanomultilayer coatings with various SiO2 layer thicknesses were investigated using X-ray diffractometry, high-resolution transmission electron microscopy, scanning electron microscopy, and nanoindentation. The results revealed that SiO2 formed wurtzite-typed hexagonal pseudo-crystal structures and grew epitaxially with AlN when its thickness was less than 0.6 nm. Meanwhile, the multilayer coatings yielded superhardness effect with a maximum hardness of 29.0 GPa. A minute increase in SiO2 thickness from 0.6 to 0.9 nm would decrease the hardness of the nanomultilayer coatings due to the formation of amorphous SiO2 and destruction of epitaxial structure. The high hardness of superhard coatings was sustained after high-temperature annealing treatment of up to 800°C. However, a further increase in annealing temperature to 900°C caused severe oxidation of AlN and thus degradation of coating’s hardness.
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