Study Of ZrN/TiAlN And CN_x/TiAlN Nanoscale Multilayered Coatings Synthesized Using Ion Beam Assisted Deposition

This paper reported the design and synthesis of ZrN/TiAIN and CN_x/TiAlN multilayered coatings with nanoscale bilayer period on Si(100) by ultrahigh vacuum ion 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, auger electron spectrozcopy 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.The influence of ZrN/TiAIN nanoscale multilayered coatings modulation periods, thickness ratio, ion bombarding energy and ion beam flux on microstructure and properties of the coatings was obvious. A well-defined nanoscale multilayered modulation structure and sharp interfaces were confirmed by AES, SEM and low-angle XRD. High-angle XRD patterns showed that both ZrN and TiAIN monolayers exhibit fcc structure. ZrN monolithic layer had strong (220) and (111) orientation. Strong TiAIN (111) as well as weak TiAIN (200), (220) textures was observed in TiAIN monolayer. The sharp ZrN (111), TiAIN (111) and A1N (111) preferred orientations were found in both mulitlayered coatings. It proved multilayered coatings possessed well modulation structure and integrated crystal structure. Sharp and strong (111) diffraction peak of face-centered-cubic structure can be observed, which may cause a positive effect on its hardness and modulus. Nano Indenter XP system showed that all multilayered coatings possessed higher hardness, elastic modulus and fracture load than the rule-of-mixtures value of monolithic ZrN and TiAIN coatings. The multilayer with modulation period of 6.5 nm, t_ZrN= t_TiAlN=2:3, bombarding energy of 200 eV and N⁺ beam flux of 5 mA displays the highest hardness (>30 GPa), modulus(361 GPa) and critical fracture load (53.3 mN). Increasing substrate temperature can release residual stress build in coatings obviously, although no apparent change can be observed in hardness and friction coefficient. A series of CN_x/TiAlN nanometer multilayered coatings with different periods and ratio of CN_x within each period were prepared by ion beam assisted deposition (IBAD) at room temperature indicated a well-defined composition modulation and layer structure. Experiment reveals that although CN_x and TiAlN monolithic coatings form amorphous and nanocrystalline structures, respectively, the CN_x/TiAlN multilayers exhibit coherent epitaxial growth due to the mutual growth-promoting effect at small CN_x layer thickness (< 0.6 nm). At A= 2.83 nm and the ratio of CN_x is 10%, the multilayers exhibit (111) preferred orientation and show abnormal enhancement of hardness and elastic modulus with maximum values of 32.1 and 408.6 GPa respectively. Its residual stress, tribological properties also obtained the best result. These results above indicated that periodic insertion of CN_x to TiAlN layers, when CN_x layer was thin extremely (0.3-0.5 nm), multilayered coatings with a very strong (111) texture due to CN_x layer crystallization and growth coherently and epitaxially with TiAlN layer exhibited a high hardness. When CN_x layer was thick, it became amorphous, and the coherent interfaces and epitaxial growth were blocked. Therefore, a sharp decrease in hardness and modulus was observed for multilayers.Little studies on relationship between microstructure and properties of nanoscale ZrN/TiAlN and CN_x/TiAlN multilayered coatings can be reported in recent literatures. All results above demonstrated that ion beam assisted deposition can produce nanoscale ZrN/TiAlN and CN_x/TiAlN multilayered coatings with high hardness, high elastic modulus, high adhesion and low compressive stress by controlling process parameters during deposition. Therefore, these studies have great potential as protective coatings on cutting tools, increasing cutting rate, extending lifetime, exploring super-hardness materials and expanding application of industry on nanoscale multilayered coatings.