A Study Of ZrB₂/AlN And CrN/AlN Nanoscale Multilayered Coatings Synthesized Using Magnetron Sputtering And Multi-arc Ion Plating

Surface engineering, as a newly synthesis subject, has been progressed rapidly in recent yeas. It was proved that the application of surface engineering can excellently improve surface property of material, which can improve productivity and save resources. There has been an increasing interest in the hard thin film because of their high performance in improving the properties of tools and products, such as cutting properties, wear-resistance, lifetime, or even the appearance. In the past two decades, nano-scale multilayers have attracted a great deal of attention since their superior comprehensive mechanical properties at small modulation periods, and this also makes them promising hard coating materials.This paper reported the deposition of ZrB₂/AlN multilayered coatings with nanoscale bilayer period on Si(100) by ultrahigh vacuum radio frequency magnetron sputtering and the deposition of CrN/AlN multilayered coatings with nanoscale bilayer period on Si(100) and stainless steel by Multi-arc ion plating. 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, was employed to investigate layered and crystal structure of the coatings. Multi-functional tester was employe(?) to investigate the wear resistance 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.1. ZrB₂/AlN coatings synthesized by ultrahigh vacuum radio frequency magnetronsputteringIn the study of ZrB₂/AlN nanolayer coatings, effects of bilayer periods, thickness ratio, working pressure and substrate b(?)as on the structure and mechanical properties of multilayered coatings were analysed and studied. High-angle XRD patterns showed that both ZrB and AlN monolayers exhibit typical hexagonal structure. AlN monolithic layer had strong AlN(100) orientation. Strong ZrB₂(001), ZrB₂(100) as well as weak ZrB₂(002) textures was observed in ZrB₂ monolayer. The sharp AlN(100) and ZrB₂(100) preferred orientations were found in both mulitlayered coatings, producing a mixed polycrystalline in the multilayered stucture. It proved multilayered coatings possessed well modulation structure and integrated crystal structure. Sharp and strong (100) diffraction peak of hexagonal structure can be observed, which may cause a positive effect on its hardness and modulus. A well-defined nanoscale multilayered modulation structure and sharp interfaces were confirmed by low-angle XRD. 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 ZrB₂ and A1N coatings. The multilayer with modulation period of 30 nm, t_AlN:t_ZrB2=1:3, working pressure of 0.4 Pa and substrate bias of-60 V displayed the highest hardness (34.6 GPa), modulus (488.7 GPa) and critical fracture load (40.1 mN). Tribological experiment showed that nanoscale ZrB₂/AlN multilayers exhibited better wear resistance than that of monolithic ZrB₂ and A1N coatings. Multilayer with A=20 nm had the smallest friction coefficient of 0.25.2. CrN/AlN coatings synthesized by Multi-arc ion platingThe nanoscale CrN/AIN multilayered coatings were prepared by multi-arc ion plating. The results of XRD, profiler and Nano indentation indicated that AlN(111), CrN(111) and CrN(200) preferred orientations can be found in almost all CrN/AlN multilayers. AlN has cubic structure at small modulation period due to coherent epitaxial growth on CrN layers, which produced the lattice distortion in CrN/AlN interfaces. This result induced the hardness and elastic modulus of CrN/AlN multilayers increase with the decrease of modulation period. Their values increased quickly as the modulation periods were less than 8 nm and reached the maximum hardness (35.0 GPa) and elastic modulus (405 GPa) at the modulation period of 3.8 nm. The formation of c-AlN and a coherent structure with CrN might be the main reasons for the enhancement of hardness and elastic modulus of CrN/AlN multilayers. With increasing modulation ratio (t_CrN:t_AlN),the hardness and elastic modulus of CrN/AlN multilayered coatings both increased at the same modulation period.All results above demonstrated that iultrahigh vacuum radio frequency magnetron sputtering and Multi-arc ion plating can produce nanoscale ZrB₂/AlN and CrN/AIN 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, exploring super-hardness materials and expanding application of industry on nanoscale multilayered coatings.