Papers by Author: Christian Kronholz

Abstract: Due to their better mechanical and physical properties diamond tools have largely replaced cemented carbide tools for machining of mineral materials like concrete and rocks. The decomposition tendency of diamond has to be taken into consideration during the manufacturing process as well as during their employment in machining tools. By using water cooling the diamond decomposition is reduced, but the contamination of occupied buildings by concrete/rock-watermixture and the need of water supply units on building sites are unfavourable. However, absence of water cooling lead to an increased tribological and thermal wear of conventional diamond tools. Due to the heat development the diamonds in direct contact with mineral materials as well as the diamonds in deeper layers are deteriorated. The Institute of Materials Engineering pursues a novel thermal protection shield concept, in which thermal insulating materials such as Al2O3, ZrO2 or glass in diamond impregnated composite structures act as heat shield, which protects diamonds in deeper layers against high temperature and graphitisation. Before the effectiveness of this concept could be investigated suitable composites have to be manufactured. In this paper the powder metallurgical production processes of diamondalumina- cobalt-composites with varying alumina and cobalt particle sizes, their microstructures and porosities are described. In comparison to composites with larger alumina particle sizes it could be observed that the distribution of alumina particles with particle sizes below 70 ,m in the cobalt matrix is uniform and the porosity of the composite decrease.

Abstract: Manufacturing diamond-cobalt composites by sintering results in residual stresses due to the mismatch of thermal expansion coefficients mainly. To understand the influence of manufacturing process parameters on residual stresses of sintered diamond-cobalt composites samples are produced by different process parameters. The investigated diamond composites are pressureless sintered as well as pressureless sintered combined with hot isostatically pressing. Here the influence of powder characteristics and process parameters like compaction pressure and sintering temperature on the residual stresses and microstructure was analysed by X-ray diffraction, microscopy and tomography. The aim of this study is to correlate residual stresses with manufacturing parameters and to give hints for optimising the residual stress state and for improving the lifetime of diamond-cobalt composites.