Superhard ceramic composites: Influence of interfaces on properties of low pres-sure sintered composites

• Applicant: Dr.-Ing. Anne-Kathrin Wolfrum
• Subject Area: Glass, Ceramics and Derived Composites ; Synthesis and Properties of Functional Materials
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 429418801

Cost-effective, wear-resistant materials are of great importance for a wide range of applications in a variety of industrial and social sectors. Extremely wear resistant materials are based on diamond and cubic boron nitride (cBN). However, these materials must be produced by high-pressure and high-temperature processes and are therefore limited in size, geometry and cost. These extreme conditions are necessary because diamond and cBN are metastable at normal pressure and convert into their hexagonal phases hBN and graphite during sintering. Literature and own investigations have shown that the wear of the composites is determined by the diamond or cBN even at low volume percentages of the hard materials, if these grains are strongly bonded. A new extremely wear-resistant material class could thus be created by strongly bonding the hard particles. So far, this was only successful with SiC-bonded diamond materials produced by reactive infiltration. For other matrix materials and for composites containing cBN, this has so far not been reproducible despite the use of fast sintering processes such as Spark Plasma Sintering (SPS). An essential approach to solve this problem, which has not been systematically investigated so far, is the use of coated diamond and cBN particles. As a result of the applicant's PhD, requirements for such coatings could be worked out. Based on this preliminary work, the interaction of coated diamond and cBN particles with the matrix during sintering and the emerging structure and properties of the interface between cBN/ diamond and the ceramic matrices (Al2O3; Si3N4) will be systematically investigated. On the one hand, newly developed dense TiN, TiC and SiC coatings and technologies for sintering (SPS) are available for this purpose. On the other hand, methods of artefact-free preparation and analysis of such materials (FESEM; EBSD; XRD micro-Raman; TEM) have been developed in preliminary work and methods for the quantification of interface properties, residual stresses, mechanical and wear properties have been tested. As a result, it should be clarified whether the transformation of metastable phases can be suppressed by such coatings. The interaction of uncoated and coated particles with the matrices and the resulting structures and properties of the interfaces will be explained and the consequences for wear behaviour understood. On the one hand, the results are important for understanding the stabilization of metastable phases. On the other hand, they form a basis for future developments of cost-effective superhard wear-resistant materials.

• DFG Programme: Research Grants