Carbide and nitride nanocomposite coatings: development and application of analytic bond-order potentials

The goal of this project is to combine the expertise of two scientific groups in the United Kingdom and Germany in order to advance the fundamental understanding of nanocomposite hard coatings at the atomic scale.In industry, carbide and nitride compounds are widely used as coatings of metal-shaping tools for cutting, milling, lathing, or wire-drawing. These coatings have polycrystalline structures on the micrometer scale (where one micrometer corresponds to one in a thousand parts of a millimeter). They must be sufficiently hard, tough, heat and wear resistant for economical and reliable use in industrial production.Recently, materials research has been focusing on the improvement of the functional performance of these materials by structuring them on a scale that is a thousand times finer than before. Superhard or supertough nanocomposites are composed of nanometer-sized crystalline grains (where one nanometer is one in a thousand parts of a micrometer) seperated by an amorphous phase.Hitherto, most of the technological achievements for nanocomposites have been obtained through experimental research and a large amount of trial and error. The scientific understanding of microscopic mechanisms and processes, which relate the microscopic structural properties of interfaces to the macroscopic mechanical properties, is still mostly empirical and not yet very detailed. However, this understanding is an important prerequisite for the control and optimisation of the synthesis of nanocomposite materials for improved performance. Nowadays, atomistic computer simulations have become well recognised in materials science and technology as valuable and predictive means which augment experimental characterisation and analysis.The atomistic computer simulations require a knowledge of the forces which act between the atoms in the coatings. Whereas these interatomic forces are well-known for ionic systems such as rock salt, they are less well characterized for covalent carbide and nitride systems thatcomprise the cyrstalline and amorphous phases of coatings.The Oxford-based proposal will develop a novel class of interatomic potentials, the so-called bond-order potentials (BOPs), which will be capable of describing and analysing the structures and properties of nanocomposites. We will parameterize the BOPs using a database of veryaccurate but computationally very demanding reference calculations for a wide range of different crystal structures. With the potentials developed at Oxford, atomistic simulations of nanocomposites will then be carried out in close collaboration with IWM and compared to experimental work.