Papers by Author: Štefan Kavecký

Abstract: Cu/ZrB₂ composite was prepared by gas pressure infiltration of molten metal into ceramic preform. Microstructure and erosion resistance of composite was investigated. The microstructure was analysed by light microscopy and scanning electron microscopy. The chemical compositions were analysed using energy dispersive X-ray spectroscopy. Good penetration of copper along the grain boundaries of the 60% porosity sintered ceramics was analysed in the whole volume of composite. The interfacial morphology shows the regular interfaces without any macroscopic reactions [1]. Cu/ZrB₂ composite was subjected to 60 spark discharges to investigate the ablation resistance. Linear dependence of the amount of loss material on the number of electrical discharge analytical cycles for Cu/ZrB₂ composite was determined.

Abstract: Tungsten as refractory material and high thermal conductive carbon fibres are promising candidates for production of copper matrix composites for high temperature applications. Three types of rod-like samples were prepared by gas pressure infiltration of different carbon/tungsten fibre preforms with copper and/or copper alloy (Cu-0.5Cr) respectively. The fibres are aligned parallel to rod axis and were combined with the tungsten wire cloth. The microstructure of prepared hybrid composites was examined. The samples were thermally cycled 3 times up to 550 °C at a relatively high heating/cooling rate (10 K/min) to touch real condition in applications where high heat is formed during short time. The thermal expansion behaviour in radial direction was also analysed. Results show that a combination of both types of reinforcements in rod-shapes samples insures good protection against composite disintegration during high temperature thermal loading.

Abstract: In this paper, two different technologies for preparation of the composite are presented: vacuum diffusion bonding and gas pressure infiltration. Samples contained different volume fractions of tungsten fibres (10%, 50% and 78%) that were arranged in unidirectional, cross-ply and circular architecture. The coefficient of thermal expansion (CTE) of Cu/W MMC samples was measured in the longitudinal and transverse direction to the fibre orientation and it strongly depended on arrangement of reinforcing phase and direction of measurement. For the unidirectional material the CTE was 4 - 6 ppm.K-1 and 11-12 ppm.K-1 in directions parallel and transverse to the fibre orientation, respectively. Samples in a shape of a ring contained reinforcement that was wounded around the sample centre (circumferential winding) or was cut-out from the Cu/W MMC plate. In the second case, the reinforced fibres had the woven arrangement. The CTE of ring measured in radial direction showed values from 5 ppm.K-1 to 20 ppm.K-1 for composites containing 72 and 10 vol. % of W-fibres, respectively.

Abstract: Carbon nanotubes have been prepared by CVD from acetylene-argon gaseous system in tubular flow reactor. Acetylene gas was used as the carbon source needed for carbon nanotube growth. Several types of high porosity foam-like Ni substrate were used as catalyst material at pyrolysis temperatures from 673 to 973 K. Influence of the surface morphology of the foam-like Ni substrates on the carbon nanotubes morphology and growth have been studied.