Investigations into the Phase Segregation, Formation of nanostructure with a high thermal stability and origin of the hardness enhancement in Superhard Nanocomposites consisting of a stable, hard, transition metal nitride and Si3N4 or BN as interfacial phase by means of Thermodynamic and ab initio DFT Calculations

• Applicant: Professor Dr. Stan Veprek
• Subject Area: Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: from 2007 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 52425726

Theoretical investigation into the phase stability and segregation in nitride systems, such as Ti-Si-N and Ti-B-N, Ti-Al-N, Cr-Al-N, which form superhard nanocomposites and coatings. Ab initio DFT calculations will provide the lattice stability of metastable phases and the interaction parameters which will be used to calculate the Gibbs free energy of the mixed stoichiometric nitrides in wide range of nitrogen pressure and temperature that are relevant for the deposition and application of the nanocomposites. If, as expected, these calculations will yield the chemical spinodal, the effect of the interfacial energy will be considered in order to elucidate if, and under which conditions the system will remain also coherently spinodal. Later on, the calculations will be extended to more complex systems, such as nc-(TiAl)N/a- Si3N4, nc-(AlCr)N/a-Si3N4, and - if the time will allow us - also to selected oxide systems which may be of great interests for industrial applications. The reliability of the results will be tested by calculating the materials parameters for pure substances, such as TiN, Si3N4 ... (energy of formation, lattice constant, elastic moduli, decohesion energy) and their comparison with available experimental data. In order to understand the origin of the hardness enhancement, the strain - stress curves will be calculated using the ab initio DFT method, and than used in a construction of realistic mechanical models of both, the nanocomposites and of the recently prepared heterostructures.

• DFG Programme: Research Grants