The recent development in the field of superhard materials with Vickers hardness of ⩾40 GPa is reviewed. Two basic approaches are outlined including the intrinsic superhard materials, such as diamond, cubic boron nitride, C3N4, carbonitrides, etc. and extrinsic, nanostructured materials for which superhardness is achieved by an appropriate design of their microstructure. The theoretically predicted high hardness of C3N4 has not been experimentally documented so far. Ceramics made of cubic boron nitride prepared at high pressure and temperature find many applications whereas thin films prepared by activated deposition from the gas phase are still in the stage of fundamental development. The greatest progress has been achieved in the field of nanostructured materials including superlattices and nanocomposites where superhardness of ⩾50 GPa was reported for several systems. More recently, nc-TiN/SiNx nanocomposites with hardness of 105 GPa were prepared, reaching the hardness of diamond. The principles of de...

https://mediatum.ub.tum.de/doc/958917/file.pdf

The search for novel, superhard materials

In recent years, near-nano (submicron) and nanostructured materials have attracted increasingly more attention from the materials community. Nanocrystalline materials are characterized by a microstructural length or grain size of up to about 100 nm. Materials having grain size of ∼0.1 to 0.3 μm are classified as submicron materials. Nanocrystalline materials exhibit various shapes or forms, and possess unique chemical, physical or mechanical properties. When the grain size is below a critical value (∼10–20 nm), more than 50 vol.% of atoms is associated with grain boundaries or interfacial boundaries. In this respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid. Therefore, grain boundaries play a major role in the deformation of nanocrystalline materials. Nanocrystalline materials exhibit creep and super plasticity at lower temperatures than conventional micro-grained counterparts. Similarly, plastic deformation of nanocrystalline coatings is considered to be associated with grain boundary sliding assisted by grain boundary diffusion or rotation. In this review paper, current developments in fabrication, microstructure, physical and mechanical properties of nanocrystalline materials and coatings will be addressed. Particular attention is paid to the properties of transition metal nitride nanocrystalline films formed by ion beam assisted deposition process.

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Nanocrystalline materials and coatings

Electrochemical processes have been extensively investigated for the removal of a range of organic and inorganic contaminants. The great majority of these studies were conducted using nitrate-, perchlorate-, sulfate-, and chloride-based electrolyte solutions. In actual treatment applications, organic and inorganic constituents may have substantial effects on the performance of electrochemical treatment. In particular, the outcome of electrochemical oxidation will depend on the concentration of chloride and bromide. Formation of chlorate, perchlorate, chlorinated, and brominated organics may compromise the quality of the treated effluent. A critical review of recent research identifies future opportunities and research needed to overcome major challenges that currently limit the application of electrochemical water treatment systems for industrial and municipal water and wastewater treatment. Given the increasing interest in decentralized wastewater treatment, applications of electrolytic systems for treat...

Challenges and Opportunities for Electrochemical Processes as Next-Generation Technologies for the Treatment of Contaminated Water

Thermal stability of nitride thin films

Provided is a surface-coated cutting tool combining superior heat resistance, superior wear resistance, and superior lubricity. A surface-coated cutting tool of the present invention includes a substrate and a coating formed on the substrate, and the coating is characterized in that the coating is formed by physical vapor deposition and includes one or more layers, that at least one of the one or more layers is a first coating layer, and that the first coating layer contains aluminum and nitrogen, has a thermal effusivity of 2,000 to 5,000 J·sec −1/2 ·m −2 ·K −1 , has a thickness of 0.2 to 5 μm, and has a crystal structure including a hexagonal structure.

Surface coated cutting tool

Ceramic superlattice is one of approaches for new ceramic film development. We deposited TiN/A1N superlattice films by arc ion-plating process, and evaluated the crystal structure of these films by transmission electron diffraction and X-ray diffraction. It was revealed that the crystal structure of A1N changes from Wurtzite type to NaCl type for superlattice periods ≤ 3 nm. The film hardness increased to about twice that of the TiN single layer film at a period = 2.5 nm. NaCl phase of A1N is one of the phases that exists under high pressure and it is expected that there will be a high bulk modulus.

Formation of cubic-A1N in TiN/A1N superlattice

There can be provided a novel and useful process for the synthesis of hard boron nitride consisting essentially of single phase cubic boron nitride by a gaseous phase synthesis technique, which comprises adding a F atom-containing gas to the gaseous phase or adding a F atom-containing gas and H atom-containing gas to the gaseous phase, whereby the codeposited hexagonal boron nitride can selectively be etched and hard boron nitride of substantially single phase can finally be synthesized.

Process for the synthesis of hard boron nitride

PURPOSE:To provide surface coating member suitable for employing as cutting tool and the like, which can be formed by PVD method on the surface of base metal under the condition that the characteristics of the base metal are maintained and has rigid film having not only wear resistance but also toughness. CONSTITUTION:The rigid film provided on base metal is produced by laminating one or more compounds selected from the group consisting of the nitride, oxide, carbide, carbonitride and boride of group IVa, Va and VIa metal elements or Al and Si elements and the nitride, oxide, carbide, carbonitride and/or boride of the alloy of two kinds of metal elements selected from the group consisting of IVa, Va and VIa elements and Al and Si elements to each other by the laminating period of 0.4-50nm so as to form the film having the above-mentioned structure with the whole thickness of 0.5-10mum.

Surface coating member excellent in wear resistance

A highly pure cubic boron nitride film is formed on a substrate by a method which comprises irradiating an excimer laser on a target comprising boron atoms and optionally nitrogen atom and depositing cubic boron nitride on a substrate which is placed to face the target.

Production of cubic boron nitride films by laser deposition

To control bromate (BrO 3 − ) contamination in the water supply, it is necessary to develop a rapid BrO 3 − removal technology without a post-treatment. In this study, rapid removal of BrO 3 − from water streams was examined using an electrolytic flow cell. Copper was selected as a working electrode for BrO 3 − reduction by cyclic voltammetry. The electrolytic flow cell with a layered copper mesh cathode successfully reduced BrO 3 − to Br − at around neutral pH. BrO 3 − removal followed the pseudo-first order reaction of BrO 3 − concentration, and the reaction rate constant based on common logarithm was evaluated to be 0.00224 s −1 . Only 3.6 min of contact time was required to decrease BrO 3 − concentration in tap water from 30 to 10 μg/L without pH control. Thus, the electrochemical process is feasible for rapid removal of BrO 3 − without post-treatment.

Akira Nakayama

Papers

Formation of cubic-A1N in TiN/A1N superlattice

Process for the synthesis of hard boron nitride

Surface coating member excellent in wear resistance

Production of cubic boron nitride films by laser deposition

Rapid removal of bromate ion from water streams with an electrolytic flow cell