Crystallization of amorphous SiC and superhardness effect in CrAlN/SiC nanomultilayered films

A series of CrAlN/SiC nanomultilayers with different SiC layer thickness were synthesized by reactive magnetron sputtering. The microstructure and mechanical properties were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) and nano-indentation techniques. The results indicated that, when SiC layer thickness was less than 0.8 nm, amorphous SiC layers were forced to crystallize under the template effect of CrAlN layers and grew epitaxially with CrAlN layers, resulting in abnormal enhancement of mechanical properties. The maximum hardness and elastic modulus could respectively reach 35.4 GPa and 431 GPa when SiC layer thickness was 0.8 nm. With further increase of SiC layer thickness, SiC layers changed back to amorphous state and broken coherent growth structure of nanomultilayers, leading to the decrease of hardness and elastic modulus.