Formation of discrete periodic nanolayered coatings through tailoring of nanointerfaces-Toward zero macroscale wear.

Notwithstanding the success of nanolayered coatings in the reduction of wear at nano-/microscales, the improvement of the wear resistance at the macroscale remains an issue. Moreover, the effects of nanointerfaces in nanolayered coatings on their macrotribological properties are not understood well. This paper reports on the engineering of nanointerfaces in diamond-like C/Cr nanolayered coatings to tailor their characteristics including the degree of intermixing, defects, and Cr growth mode. The result was the fabrication of a coating with subnanometer-thick periodic albeit discrete Cr interlayers. This was achieved using our patented deposition technique. This coating contained less interfacial defects compared to classic nanolayered coatings with continuous nanolayers and presented record-breaking wear rates at the macroscale. Finite Element analysis was performed and micropatterning strategy was used to reduce the wear rate further. Last, we report on discovery of a dimensionless parameter that can be used to predict the wear resistance of carbon-based nanolayered coatings.

Hard, Flexible, and Transparent Nanolayered SiN x/BN Periodical Coatings.

In this study, SiN x/BN periodical nanolayered coatings (PNCs) are developed. PNCs were deposited at the room temperature on plastic and glass substrates. They demonstrate the excellent mechanical durability of inorganic materials and optical transparency and flexibility of organic ones. The 150 nm thick PNC shows optical transparency, sapphire-like hardness, high wear protection, and flexibility. Such a coating with a superior combination of optical and mechanical properties has not been reported previously.

Increased elasticity and damping capacity of diamond-like carbon coatings by immobilized C60 fullerene clusters.

Material loss and plastic deformation induced by frictional interactions at moving mechanical interfaces continue to be major issues responsible for efficiency and performance degradation of systems. Establishment of fully elastic interactions in the contact region without compromising the structural rigidity and integrity of materials represents a promising solution. In this study, we report on improving the elasticity, damping properties, ductility and wear resistance of diamond-like carbon (DLC) coatings through introducing an immobilized C60 cluster layer. The C60 clusters were immobilized using cysteamine (HS(CH2)2NH2) self-assembled monolayers (SAMs) attached to a pre-sputtered Au layer. A Ni adhesive layer was deposited onto plasma cleaned Si (100) substrates prior to Au, SAM-C60, and DLC deposition. Precise dynamic ultra nano-indentation tests indicated a drastic improvement in elasticity and damping capacity of the C60-DLC hybrid (Ni-Au-SAM/C60-DLC) multilayer coating compared to those of the C60-free (Ni-Au-DLC) multilayer. The behavior of the coatings under reciprocating contact conditions was evaluated. Quantification of the resistance of the coatings against wear and permanent deformation revealed a significant improvement in the wear rate from ∼3.38 × 10-8 to ∼5.14 × 10-10 mm3 N-1 mm-1 upon incorporation of the immobilized C60 clusters. The corresponding mechanisms were assessed through experiments and finite element (FE) simulations.

Highly durable and biocompatible periodical Si/DLC nanocomposite coatings.

Functional nanocomposite coatings comprised of periodically stacked nanolayers of diamond-like carbon (DLC) and amorphous silicon were developed for biomedical applications. The periodical nanocomposite structure provided high surface durability while silicon aided in reducing the residual stress. The structural, mechanical, tribological, and biomedical properties of the Si/DLC coatings deposited by magnetron sputtering were investigated systematically. The effect of the negative substrate bias on the structure and properties of the coatings was also assessed. The coatings demonstrated high durability and high biocompatibility. The bias voltage and bias mode affected both the hardness and residual stress of the Si/DLC coatings. Particularly, application of 60 V negative bias during the DLC layer deposition resulted in the lowest wear rate. FEM simulations showed that the wear resistance of the coatings was dictated by the hardness as well as the adhesion between the coatings and a chromium sub-layer. The periodical alternation of Si and DLC nanolayers led to a significant improvement of MC3T3 cell adhesion compared to the previously published data for Si-DLC composites.

Highly wear-resistant and biocompatible carbon nanocomposite coatings for dental implants.

Diamond-like carbon coatings are increasingly used as wear-protective coatings for dental implants, artificial joints, etc. Despite their advantages, they may have several weak points such as high internal stress, poor adhesive properties or high sensitivity to ambient conditions. These weak points could be overcome in the case of a new carbon nanocomposite coating (CNC) deposited by using a C60 ion beam on a Co/Cr alloy. The structure of the coatings was investigated by Raman and XPS spectroscopy. The wear resistance was assessed by using a reciprocating tribotester under the loads up to 0.4 N in both dry and wet sliding conditions. Biocompatibility of the dental implants was tested in vivo on rabbits. Biocompatibility, bioactivity and mechanical durability of the CNC deposited on a Co/Cr alloy were investigated and compared with those of bulk Co/Cr and Ti alloys. The wear resistance of the CNC was found to be 250-650 fold higher compared to the Co/Cr and Ti alloys. Also, the CNC demonstrated much better biological properties with respect to formation of new tissues and absence of negative morphological parameters such as necrosis and demineralization. Development of the CNC is expected to aid in significant improvement of lifetime and quality of implants for dental applications.

Toward Zero Micro/Macro-Scale Wear Using Periodic Nano-Layered Coatings.

Wear is an important phenomenon that affects the efficiency and life of all moving machines. In this regard, extensive efforts have been devoted to achieve the lowest possible wear in sliding systems. With the advent of novel materials in recent years, technology is moving toward realization of zero wear. Here, we report on the development of new functional coatings comprising periodically stacked nanolayers of amorphous carbon and cobalt that are extremely wear resistant at the micro and macro scale. Because of their unique structure, these coatings simultaneously provide high elasticity and ultrahigh shear strength. As a result, almost zero wear was observed even after one million sliding cycles without any lubrication. The wear rate was reduced by 8-10-fold compared with the best previously reported data on extremely low wear materials.