Preparation and characterization of ZrB2/AlN multilayers by N+ beam assisted deposition

ZrB2/AlN multilayers with modulation periods (Λ) ranging from 4 to 18 nm and modulation ratios (tZrB2:tAlN) ranging from 1:2 to 4:1 were manufactured by ion beam assisted deposition at different N+ bombarding energies from 100 to 500 eV. The multilayers are characterized by various techniques including X-ray reflection (XRR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and their mechanical properties were measured by nano-indentation and surface profilometry. The multilayers showed small grain sizes and polycrystalline with ZrB2[001], [100], and AlN[100] textures at proper ion beam bombarding energies. The maximum hardness and critical load of ZrB2/AlN multilayers were over 31 GPa and 57 mN, respectively. These values are 1.6 and 10.6 times higher than the rule-of-mixtures values of monolithic ZrB2 and AlN coatings (19.8 GPa and 5.4 mN). The hardest multilayer also showed an improved fracture resistance and residual stress. These enhancement effects in multilayers should be related to the resistance to dislocation glide and grain growth across coherent interface between the ZrB2 and AlN layers. The formation of proper stress field in multilayers owing to the mismatch between two materials was also one of the main reasons for hard enhancement.