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respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid.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

Microstructural design of hard coatings

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

Ultrafine particle-layered film for coating cutting tools. The film has more than two layers of at least two compounds consisting mainly of carbide, nitride, carbonitride or oxide of at least one element selected from a group consisting of IVa group elements, Va group elements, VIa group elements, Al, Si and B, and that each layer is made of ultrafine particles. Ultrafine particle-layered film improves hardness, strength, wear-resistance and heat-resistance of the tools.

Layered film made of ultrafine particles and a hard composite material for tools possessing the film

Super hard composite material for tools, comprising a substrate of CBN sintered body containing more than 20 % by volume of cubic boron nitride (CBN), improved in strength of base material, wear-resistance, hardness at high temperatures and acid-resistance usable in cutting work of steels which are difficult to be machined. The substrate (2) has a laminated film (1) consisting of super thin films (a) and (b) each deposited alternatively on the substrate (2), the super thin film (a) being made of nitride and/or carbide of at least one element selected from a group comprising IVa group elements, Va group elements, VIa group elements, A1 and B and possessing a crystal structure of cubic system and metallic bond property, the super thin film (b) being made of at least one compound possessing a crystal structure other than cubic system and covalent bond property under equilibrium condition at ambient temperature and pressure, each unit layer of the super thin films (a) and (b) having a thickness of 0.2 nm to 20 nm, and the laminated film (1) on the whole possessing a crystal structure of cubic system.

Super hard composite material for tools

Hard composite material for tools, comprising a substrate of CBN sintered body containing more than 20% by volume of cubic boron nitride or diamond sintered body containing more than 40% by volume of diamond. The substrate has at least one layer of hard heat-resisting film consisting mainly of Ti, Al and at least one element selected from a group comprising C, N and O on a portion or portions of said substrate where cutting participate. Improved in strength of base material, wear-resistance and oxidation-resistance, less reactive with iron and showing longer tool life comparing to known cutting tools and usable in wider applications such as hardened steel, cast ion and simultaneous cutting of cast ion and aluminum alloy.

Makoto Setoyama

Papers

Formation of cubic-A1N in TiN/A1N superlattice

Layered film made of ultrafine particles and a hard composite material for tools possessing the film

Super hard composite material for tools

Hard Composite Material for Tools

Thermal stability of TiN/AlN superlattices