The effect of annealing on hardness, residual stress, and fracture resistance determined by modulation ratios of TiB2/TiAlN multilayers

Nanostructured multilayers of TiB2/TiAlN at different modulation ratios (tTiB2:tTAlN) ranging from 1:24 to 6:1 were deposited onto Si(100) wafers by ion beam assisted deposition (IBAD). The multilayers were subsequently annealed in a vacuum environment at a temperature of 500 °C for 30 min, and then characterized by extensive measurements including X-ray reflection (XRR), X-ray diffraction (XRD), scanning electron microscopy (SEM), nano-indentation and surface profilometry. It was found that the mechanical properties of the multilayers were closely related to tTiB2:tTAlN. A maximum hardness of 37 GPa was achieved at tTiB2:tTAlN of 1:18 for as-deposited TiB2/TiAlN multilayer. This hardest multilayer also showed the improved residual stress and fracture resistance. The hardness and elastic modulus of the multilayers increased significantly after annealing. The maximum hardness of the multilayer at tTiB2:tTAlN of 1:14 was up to 41 GPa after annealing at 500 °C.

► TiB2/TiAlN multilayer has potential on quality in protective coatings.
► Modulation ratio is a key factor corresponding to its mechanical properties.
► There is a critical modulation ratio for the hardest multilayer.
► Annealing at 500 °C gives a significant contribution to its properties.