Study Of ZrB₂/AlN And ZrB₂/WN_x Nanoscale Multilayered Coatings Synthesized Using Ion Beam Assisted Deposition

This paper reported the design and synthesis of ZrB₂/AlN, ZrB₂/W and ZrB₂/WN_x multilayered coatings with nanoscale bilayer period on Si(100) by ultrahigh vacuum on beam assisted deposition (IBAD). The mechanical properties of the multilayered coatings including hardness, elastic modulus and adhesion were measured by profiler and Nano Indenter XP system. X-ray diffraction and scanning electron microscopy were employed to investigate layered and crystal structure of the coatings. Our aim is to obtain insight into the significance of different process parameters on the structure and mechanical properties of the multilayered coatings. IBAD can produce nanoscale multilayered coatings with high hardness, fracture resistance, and low compressive stress by controlling process parameters during deposition. Therefore, these coatings will have great potential as protective coatings on cutting tools and other mechanical components.ZrB₂/AlN multilayered coatings with nanoscale bilayer periods have been synthesized from ZrB₂ and A1N target on Si(100). The influence of modulation periods, thickness ratio and ion bombarding energy on microstructure and properties of the coatings is obvious. The nanoscale multilayered modulation was confirmed by SEM and low-angle XRD. High-angle XRD patterns show that monolithic A1N and ZrB₂ layers reveal typical hexagonal structure. The ZrB₂(001), (100) and AlN(100) preferred orientation with weak ZrB₂(101) and AlN(101) peak can be found in some multilayered structures. Besides, a weak Zr(110) is found in this monolithic ZrB₂ layer and some multilayered ZrB₂/AlN coatings owing to recombination of B" and Zr²⁺ when sputtering. It can be seen from ZrB₂/AlN coatings that different bombarding energy can result in different crystal structures. The results show that some multilayered coatings possess higher nano hardness and elastic modulus than the rule-of-mixtures value of monolithic ZrB₂ and A1N coatings. The multilayer with modulation period of 7.6 nm, t_ZrB2:t_AlN=3:2, bombarding energy of 300 eV and N⁺ beam flux of 5 mA displays the highest hardness (>31 GPa) and critical fracture load (57 mN). Its residual stress, tribological properties also obtain the best result. Some series of ZrB₂/W and ZrB₂/WN_x nanometer multilayered coatings were prepared by ion beam assisted deposition (IBAD). The effects of modulation periods, thickness ratio, ion bombarding energy and substrate temperature on microstructure and properties of the coatings was studied. The low-angle XRD pattern and SEM indicate a well-defined composition modulation and layer structure of the multilayered coating. High angle XRD patterns of monolithic W coating exhibits cubical structure, WN_x coating with the hexagonal and cubical mixed structure, but ZrB₂ layer reveals typical hexagonal structure. This crystallinity or amorphous structure is found in the multilayered coatings. The multilayer with modulation period of 9.6 nm, t_ZrB2:t_WNx=3:1, bombarding energy of 200 eV displays that the maximum hardness and elastic modulus are over 30 GPa and 406 GPa, respectively. Especially, when proper bombarding energy N^* at 200 eV, substrate temperature at 430°C, ZrB₂/WN_x( multilayered coatings possess the highest hardness (36.6 GPa), Its elastic modulus, residual stress and tribological properties also obtain the best result.All results above demonstrated that IBAD can produce nanoscale ZrB₂/AlN, ZrB₂/W and ZrB₂/WN_x multilayered coatings with high hardness, fractuer resistance, and low compressive stress by controlling process parameters during deposition. Therefore, these coatings have great potential as protective coatings on cutting tools and other mechanical components.