Ludosław Stobierski

Solid combustion synthesis of Ti3SiC2

Abstract Using powders of Ti and Si and carbon black as reactants, a material composed mainly of the ternary compound Ti 3 SiC 2 and of minor amounts of TiC was synthesized by the method of solid combustion. Following ignition at 1050°C, complete conversion of the reactants to the products was observed in a time of 2 to 5 s. The product obtained from the molar composition 3Ti:Si:2C has properties similar to the CVD-derived polycrystalline Ti 3 SiC 2 , which is a ‘soft’ ceramic material capable of being shaped by metalworking methods and shows a high resistance to oxidation and to aggressive environments.

Hot pressed hydroxyapatite–carbon fibre composites

Abstract Composite samples were obtained from hydroxyapatite powder and carbon fibres by hot pressing at 1100°C and 25 MPa for 15 min in argon atmosphere. Two types of cut carbon fibres produced in a carbonisation process of polyacrylonitrile (PAN) precursor were used both in non-coated or coated form. The coatings of calcium phosphate were applied by sol–gel technique. The highly sintered composite with the best strength properties was obtained from coated carbon fibres with basic character of the surface. The existence of hydroxyl groups on fibre surface makes possible formation of bonds with the calcium phosphate layer formed as a result of polycondensation following the sol–gel procedure.

Solid combustion synthesis of refractory carbides: (A review)

Abstract The specific mechanisms of heterogeneous reactions which are likely to occur during solid combustion synthesis in the TiSiC system are reviewed. Also discussed are the properties of some products of solid combustion as compared with these from other advanced methods of synthesis and the competitiveness of this process with other advanced methods of production of ceramic carbide powders.

Effect of carbon content on the microstructure and properties of silicon carbide-based sinters

The paper presents the results of investigations of the influence of carbon activator content on the microstructure and mechanical properties of silicon carbide sinters with 1, 3, and 6 wt.% of carbon.

Supersaturated solid solutions of boron in SiC by SHS

Abstract Sintering of dense silicon carbide products requires specially prepared starting powders with a small grain size, high purity, and appropriate contents of sintering activators. A method for the preparation of such powders with boron dopant by self-propagating high-temperature synthesis (SHS) is described. Supersaturated solid solutions of boron in βSiC with a boron content of up to 20 wt% were synthesized. Such powders were sintered to high densities by pressureless sintering at relatively low temperatures in a range of 2050–2150°C.

Dihedral angles in silicon carbide

The commonly accepted hypothesis says that the role of sintering activators such as carbon and boron consists in modifying the relation between the energy of surface and that of grain boundaries in SiC. This means that dihedral angles in samples containing one of the activators, both of them or none should be different. To verify this hypothesis we measured dihedral angles in all the mentioned cases. The observed values of dihedral angles were always much bigger than the limiting one of 60°. Moreover, they did not differ significantly and, according to the statistical analysis could be treated as constant. As a consequence our results contradict the opinion saying that the activators modify the energy of surface and grain boundaries.

Molybdenum Silicides as a Bonding Phase in Diamond Composites

Molybdenum silicides were obtained by the self-propagating synthesis (SHS) method. Diamond composites containing 30 mass% of MoSi2 or Mo5Si3 bonding phase had been prepared using HT-HP Bridgman type apparatus. Sintering of the diamond composites were carried out at 2073±50 K and 8±0.2 GPa. The interactions in diamond-silicide composites were studied by means of X-ray diffractometry and transmission electron microscopy (TEM). Results of both mechanical properties and thermal resistance measurements are reported. Hardness HV1 for the composite with the predominantly MoSi2 bonding phase was found to be around 42 GPa. After heat treatment in 1200 °C for 30 min. in vacuum HV1 decreases to 29 GPa. In the second composite containing the Mo5Si3 bonding phase the HV1 of 28.0 GPa after thermal exposure changes to 21.0 GPa.

Mechanical and thermal properties of tungsten carbide – graphite nanoparticles nanocomposites

Abstract Previous studies concerning pure tungsten carbide polycrystalline materials revealed that nanolayers of graphite located between WC grains improve its thermal properties. What is more, pressure-induced orientation of graphene nano platelets (GNP) in hot pressed silicon nitride-graphene composites results in anisotropy of thermal conductivity. Aim of this study was to investigate if addition of GNP to WC will improve its thermal properties. For this purpose, tungsten carbide with 0.5–6 wt.% of GNP(12)-additive underwent hot pressing. The microstructure observations performed by SEM microscopy. The anisotropy was determined via ultrasonic measurements. The following mechanical properties were evaluated: Vickers hardness, bending strength, fracture toughness KIc. The influence of GNP(12) addition on oxidation resistance and thermal conductivity was examined. It was possible to manufacture hot-pressed WC-graphene composites with oriented GNP(12) particles, however, the addition of graphene decreased both thermal and mechanical properties of the material.

Effect of Processing Conditions on Microstructure of SiC-TiB2 Composite

The objective of the study as described in this paper is to analyse the effect of processing conditions as: volumetric content of TiB2 powders and the time of milling them on the parameters of microstructure of particulate composite with a SiC matrix and 10 or 20 vol.% of the TiB2 as dispersed phase. From the initial research conducted by the authors, as well as from the data contained in the reference literature, it is known that the SiC-TiB2 composite is a potential material to be applied in the manufacture of cutting tool inserts. To manufacture composites, SiC powders (Starck, UF-15) and TiB2 powders (Momentive, HCT-30) were used; they were milled for 15 or 30 h in a vibrating-rotating mill with silicon carbide balls as grinding media. The SiC-TiB2 composite was manufactured using a hot pressing method under the following conditions: temperature: 2120 oC; pressure: 25 MPa; and sintering time: 30 min. Under the stereological analysis of SiC-TiB2 some selected microstructural parameters were measured, i.e.: volume fraction of TiB2, average size of TiB2 particles, mean diameter of particles (D), shape factor of TiB2 particles, α, as well as NA and NV parameters that determine the quantity of TiB2 particles contained in the composite. Computer-aided analysis of microstructure of the SiC-TiB2 composites and analysis of results of measurements of mechanical properties of these composites prove their the microstructure and properties depend on the volumetric content of TiB2 dispersed phase, and this dependence is significant.

Phase, Structural and Microstructural Changes in the TiC1-x – Cr3C2 Materials

The earlier studies showed that addition of different chromium carbides to nonstoichiometric fine titanium carbide improve sintering in the similar way. The phase, structural and microstructural changes for addition of various chromium carbides were also similar. In the present work the composite materials were made of various carbon quantity saturated titanium carbide (as matrix) and commercial chromium carbide Cr3C2 (as additive). The titanium carbide powders with variable content of carbon in structure were synthesized by the SHS method. The chromium carbide in quantity of 7.5 % by volume was added to the initial mixture. The influence of various stoichiometry of titanium carbide on onset temperature of sintering was examined by use of high temperature dilatometer. The phase and structural changes of examined materials during sintering were made using XRD and Rietveld method. The evolution of microstructure, versus of different stoichiometry titanium carbides, was observed by use of scanning electron microscopy.