Superhardness Effect and High Temperature Oxidation Resistance of AlN/SiO_2 Nano-multilayers

A series of AlN/SiO_2 nano-multilayers with different individual SiO_2 layer thicknesses were prepared by reactive magnetron sputtering.The microstructure and mechanical properties of these mul- tilayers were studied by X-ray diffraction,high-resolution transmission electron microscope,scanning electron microscope and nanoindentation.The influence of SiO_2 layer thickness on the microstructure and mechanical properties of AlN/SiO_2 nano-multilayers was studied,and the high temperature oxi- dation resistance was investigated.The SiO_2 layer is usually amorphous under sputtering condition. Results show that when its thickness is less than 0.6nm,the SiO_2 layer is forced to crystallize into hexag- onal pseudoerystal structure and grows epitaxially with AlN,and the multilayers exhibit superhardness effect.With a further increase in its layer thickness,SiO_2 layer transforms into amorphous structure and blocks the coherent growth of multilayers,accompanied with a decline in the film hardness.The results of high temperature annealing test indicate that the oxidation resistance temperature for AlN/SiO_2 nano-multilayers with high hardness is up to 800℃,equivalent to that for the AlN monolayer.The addition of SiO_2 layer can improve the hardness of multilayers,but it will not remarkably improve the high temperature oxidation resistance of films.