Ytterbium disilicate-based glass-ceramic as joining material for ceramic matrix composites

A key aspect of ceramic matrix composites integration is related to a reliable joining technique. An ytterbium disilicate based glass-ceramic material is processed by reactive viscous flow sintering between a barium aluminium borosilicate glass and ytterbium oxide and it is used to join SiC/SiC and C/SiC composites. The joining temperature and the in situ formation of the Yb2Si2O7 is optimised at 1200°C without pressure, on the basis of the sintering and crystallisation mechanisms. The mechanical characterization of SiC/SiC and C/SiC joined with the ytterbium disilicate-based glass-ceramic, tested by single-lap offset at RT, exhibits an apparent shear strength of 35 MPa, similar to their interlaminar shear strength. The proposed system displays self-healing behaviour at 1000 °C and 1150 °C, as demonstrated by the partial and complete sealing of induced cracks by Vickers indentation on its surface at different loads, thus suggesting that it can effectively be used as promising joining material for CMCs

Surface machining of Ti6Al4V by means of Micro-Electrical Discharging to improve adhesive joining

The Micro-Electrical Discharge Machining (Micro-EDM) technique has been employed to machine micro-patterns with shaped micro-slots on Ti6Al4V surfaces. Ti6Al4V substrates, with and without micro-slots, were bonded using a commercial epoxy adhesive. Optical microscopy and SEM were used to observe the micro-patterned Ti6Al4V surfaces before and after joining and to analyse the fracture surfaces after mechanical tests. The joints were mechanically characterised, with and without micro-patterns, by means of Single Lap Offset (SLO) shear tests under compression to understand the effect of differently shaped micro-slots. The effects of the shape of the micro-slots, their interlocking or overlapping, and their orientation, with respect to the applied load, are presented and discussed in terms of mechanical performance of the joints

BZ Cam during its 1999/2000 optical low state

We report optical observations of the VY Scl star BZ Cam during its previous optical low state in 1999/2000. We find drastic variations in the line profiles. Narrow-band imaging observations show that its nebula extends farther than previously known and seems to be composed of two components. We determine the [OIII] line intensity of BZ Cam's nebula to 4.8 * 10^-13 erg/cm^2/s. We discover a proper motion of BZ Cam of 25+-2 mas/yr which together with the systemic radial velocity yields a space velocity of 125 km/s. We re-interpret the nebula as being photo-ionized by hypothesized transient, luminous, supersoft X-ray emission during optical low states, and shaped by the transverse motion of BZ Cam.Comment: 8 pages with aa.sty, 8 figures, to appear in A&

Thermal characterisation of ceramic/metal joining techniques for fusion applications using X-ray tomography

This work investigates the thermal performance of four novel CFC–Cu joining techniques. Two involve direct casting and brazing of Cu onto a chromium modified CFC surface, the other two pre-coat a brazing alloy with chromium using galvanisation and sputtering processes. The chromium carbide layer at the interface has been shown to improve adhesion. Thermal conductivity across the join interface was measured by laser flash analysis. X-ray tomography was performed to investigate micro-structures that might influence the thermal behaviour. It was found that thermal conductivity varied by up to 72%. Quantification of the X-ray tomography data showed that the dominant feature in reducing thermal conductivity was the lateral spread of voids at the interface. Correlations were made to estimate the extent of this effect

Evaluation of Residual Stresses in Carbon/Carbon Composites Components Joined to Copper before and after Pulse Electromagnetic Treatment

Приведены результаты расчетно-экспериментальной оценки остаточных напряжений в компонентах, полученных соединениемкомпозита (углерод, упрочненный углеродными волокнами) с медью. Установлено, что импульсная электромагнитная обработка соединения уменьшает уровень остаточных напряжений.Наведено результати розрахунково-експериментальної оцінки залишкових напружень у компонентах, що отримані з’єднуванням композита (вуглець, зміцнений вуглецевими волокнами) з міддю. Установлено, що імпульсна електромагнітна обробка з’єднання зменшує рівень залишкових напружень

Experimental evaluation of pulse electric current effect on residual stresses in composite-to-copper joints

Experimental method for evaluation of residual stress distribution in carbon fiber reinforced car­bon composite jointed to copper is presented. Pulse electric current passed through composite-to-copper joint essentially reduces the level of residual stresses.Представлено експериментальну методику щодо оцінки розподілу залишко­ вих напружень у з’єднанні композита (вуглець, зміцнений вуглецевими волокнами) з міддю. Установлено, що імпульс електричного струму, що пропущений через з’єднання композит-мідь, суттєво зменшує рівень залиш­ кових напружень.Представлена экспериментальная методика оценки распределения остаточных напряжений в соединении композита (углерод, упрочненный углеродными волокнами) с медью. Уста­новлено, что импульс электрического тока, пропущенный через соединение композит-медь, существенно снижает уровень остаточных напряжений