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

Microstructural design of hard coatings

Different approaches to superhard coatings and nanocomposites

Thermal stability of nitride thin films

This article presents an attempt to explain in a simple way, understandable to a broad spectrum of readers, the unusual combination of the mechanical properties of the recently developed new class of superhard nanocomposites, such as high hardness which significantly exceeds that of the rule of mixtures, enhancement of the elastic modulus as measured by the indentation technique, very high elastic recovery which is observed upon the indentation and the absence of crack formation even under elastic deformation corresponding to a strain of more than 10%. Future experimental work is suggested which should bring further progress towards the understanding of these materials.

https://mediatum.ub.tum.de/doc/958922/file.pdf

Towards the understanding of mechanical properties of super- and ultrahard nanocomposites

The aim of this paper was to examine correlations between deposition parameters and the coating properties of RF-sputtered films in deposition conditions and after heat treatment at temperatures up to 700 °C. The investigations deal with titanium-, chromium- and hafnium-based nitrides, borides and ternary alloys. Different materials such as SAE 52100 steel, ASP 23 high-speed steel and Ti6A14V titanium alloy, which are commonly used in the aerospace industry, were coated to analyse the influence of the substrate material. The coatings were tested with respect to their phase composition, microstructure, residual stress, thickness, microhardness and adhesion. It is shown that the deposition parameters, as well as heat treatment at a temperature as low as 400 °C, can change considerably the coating properties.

The influence of a heat treatment on the microstructure and mechanical properties of sputtered coatings

This paper describes the influence of vacuum heat treatments up to 700 °C on the mechanical and tribological properties of sputtered PVD-coatings. We have deposited titanium, hafnium and chromium based nitride and boride layers on different substrate materials such as steel SAE 52100, ASP 23 high speed steel and titanium alloy Ti6A14V. It is shown, that hardness, adhesion as well as the brittleness of the coating varied strongly depending on the residual stresses of the film. The highest wear resistance could be achieved with hexagonal chromium nitride films. The annealing process could lead to a significant change of the wear properties, depending strongly on the layer composition. Titanium and chromium nitride coatings were hardly influenced by the heat treatment, whereas titanium and hafnium borides and ternary boron nitrides showed a remarkable increase of wear, when deposited with a thin titanium intermediate layer.

W. Herr

Papers

The influence of a heat treatment on the microstructure and mechanical properties of sputtered coatings

Effect of an annealing process on the tribological properties of sputtered hard coatings