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Titanium diboride (TiB2) is a hard, refractory material, attractive for a number of applications, including wear-resistant machine parts and tools, but it is difficult to densify. The spark plasma sintering (SPS) method allows producing TiB2-based composites of high density with different sintering aids, among them titanium silicides. In this paper, Ti5Si3 is used as a sintering aid for the sintering of TiB2/10 wt % Ti5Si3 and TiB2/20 wt % Ti5Si3 composites at 1600 °C and 1700 °C for 10 min. The phase composition of the initial powders and produced composites was analyzed by the X-ray diffraction method using CuKα radiation. The microstructure was examined using scanning electron microscopy, accompanied by energy-dispersive spectroscopy (EDS). The hardness was determined using a diamond indenter of Vickers geometry loaded at 9.81 N. Friction–wear properties were tested in the dry sliding test in a ball-on-disc configuration, using WC as a counterpart material. The major phases present in the TiB2/Ti5Si3 composites were TiB2 and Ti5Si3. Traces of TiC were also identified. The hardness of the TiB2/Ti5Si3 composites was in the range of 1860–2056 HV1 and decreased with Ti5Si3 content, as well as the specific wear rate Wv. The coefficient of friction for the composites was in the range of 0.5–0.54, almost the same as for TiB2 sinters. The main mechanism of wear was abrasive. [ABSTRACT FROM AUTHOR]

• A novel composite ablator based on silicone resin and B 4 C ceramics is shown. • Methylpolysiloxane ablation rates significantly reduced by formed B 2 O 3 on surface. • Methylpolysiloxane pyrolyses to SiOC and SiO 2. • The presence of B 4 C promotes β-SiC crystallisation during pyrolysis and ablation. Before siloxane resin matrix composites could be successfully used as ablative materials, their mechanism of high-temperature degradation must be investigated in depth. In this study, degradation mechanism, ablation resistance and degradation kinetics of both methylpolysiloxane and the methylpolysiloxane - B 4 C (10 wt%) composite were investigated.. The presence of B 4 C resulted in a higher final sample mass in thermogravimetric tests in synthetic air up to 1500C (85% vs 81%), while during ablation tests it reduced linear and mass ablation rates by 45% and 54%, respectively. The XRD and SEM/EDS studies provided an estimate of the phase contributions formed as a result of exposure to corrosive conditions. The effect of the presence of powders on the amount of SiO 2 glassy phase, β-SiC crystalline phase and free carbon precipitates formed is apparent. [ABSTRACT FROM AUTHOR]

The research concerns the optimisation of sintering zirconium by spark plasma sintering (SPS) and modification of microstructures by introducing the manganese component. The problems of preparing mixtures for sintering were investigated. An additive of 2.5 wt% and 5 wt% manganese micropowders and 1 wt% and 2.5 wt% manganese nanopowders were utilized. An increase in the oxygen content in sintered mixtures made of zirconium and manganese along with an increase in their milling time in water was found. 100 rpm was determined as a safe mixing speed. The introduction of manganese nanopowders into zirconium did not significantly improved the homogeneity of the material. Manganese in larger quantities accumulates at the grain boundaries. The material is very difficult to machining, which is indicated by difficulties in sample preparation. • The conditions of high-speed mixing and sintering by the SPS method did not cause the entire manganese content to react to form ZrMn 2. • Due to the explosiveness of the mixture, 200 rpm was adopted as the optimal speed of homogenization of mixtures. • Mechanical milled Zr–Mn mixtures tend to oxidize. [ABSTRACT FROM AUTHOR]

The sintering behaviours, phase compositions, microstructures, and mechanical properties of Al 2 O 3 -based matrix composites reinforced with up to 20 vol% of cubic boron nitride (cBN, super-hard phase) were investigated. The materials were prepared via the method of spark plasma sintering (SPS). Additionally, pure cBN powder was treated under identical SPS conditions for the purpose of comparison. The temperatures at which hexagonal boron nitride (hBN, graphite-like phase) was detected in pure cBN and in cBN dispersed in the Al 2 O 3 + 10 TiN matrix were 1600 °C and 1300 °C, respectively. The presence of additives in the Al 2 O 3 matrix had a pronounced influence on the formation of hBN, with TiN > ZrO 2 > pure Al 2 O 3. All the composites exhibited quite good improvements in fracture toughness, of about 1.5 MPa·m1/2 on average over that of Al 2 O 3. Crack deflection on cBN grains was identified as the main toughening mechanism of the ceramics investigated. Unlabelled Image • Composites containing cubic boron nitride (cBN) have been sintered at low pressure. • Spark plasma sintering (SPS) method allows to obtain full dense composite at 1300 °C. • Al 2 O 3 -based composites with cBN have better fracture toughness than pure Al 2 O 3. • During SPS pure cBN is more stable then cBN dispersed in ceramic matrix. • TiN promotes of graphite-like, hexagonal boron nitride formation most extensively. [ABSTRACT FROM AUTHOR]