Microstructure and mechanical properties of as-deposited and annealed TiB2/BN superlattice coatings

TiB2/BN multilayers with the modulation ratios (tTiB2:tBN) ranging from 1:1 to 16:1 and a constant modulation period of 24nm were prepared by magnetron sputtering. The TiB2/BN multilayers were subsequently annealed in a vacuum environment at temperatures of 500–700°C for 30min, then characterized by extensive measurements. All multilayers exhibited small grain sizes and stable layer structures with polycrystalline with TiB2(001), TiB2(101), TiB2(002) textures or amorphous BN, resulting in higher hardness and elastic modulus than that of individual monolithic TiB2 or BN coatings. The hardness of as-deposited multilayer can reach as high as 39.34GPa at tTiB2:tBN=13:1, meanwhile the friction coefficient got to 0.028, which was also the lowest. The hardness and friction were almost unchanged after annealing at 500–700°C, which was attributed to good thermal stability in the layer structure and the existence of stable TiBxNy phases. ► TiB2/BN multilayers have potential as protective coating in dry machining. ► Annealing is found to be beneficial for thermal stability. ► The highest hardness of 39.34GPa appears at tTiB2:tBN=13:1. ► Good thermal stability of the properties of annealed layers is observed. ► Thermally stable TiBxNy phases contributes to stable layer structure and properties.