Advances in Science and Technology Vol. 64

Abstract: It is recognized that many factors need to be taken into consideration in the successful design and manufacture of high quality glass-ceramic-to-metal seals, particularly if an adequate component lifetime is to be achieved. During their preparation, undesirable reactions may occur between diffusing metal species and glass constituents, and these can lead to the formation of highly localized internal stresses, the presence of which can initiate failure of a seal either during manufacture or, more seriously, whilst in service due to the influence of static fatigue. In the case of high temperature systems, reactions under hostile operating conditions also need to be taken into consideration. A thorough understanding of the relevant glass-ceramic/metal interactions is therefore required in order that steps can be taken to avoid or at least minimize reactions within the interfacial region that may lead to localized modifications of the glass-ceramic microstructure. In this contribution, factors influencing the lifetime behaviour of glass-ceramic/metal systems are reviewed and discussed, with particular reference given to SOFC sealants and also to advanced electrical components developed at AWE including seals to stainless steels and Ni-based superalloys. Fundamental studies on bonding to pure Fe, Ni and Cr are also included.

Abstract: Glass-metal joints are needed for the optical windows in ITER to perform diagnostics. These joints must be leak tight for the safety (presence of tritium in ITER) and to preserve the vacuum. They must also withstand the ITER environment: temperatures around 250 °C and neutron fluxes of 109 n/cm2.s. At the moment, little information is available about glass-metal joints suitable for ITER. Therefore, we set-up a 2D elastic model of prototype Al diffusion bonded optical windows using Abaqus code to model temperature effects on the windows. With this model we analyzed the influence of different parameters like the joint area and the braze thickness on the mechanical properties of the joint. Calculations of the thermal stress created by a temperature field of 150 °C (normal ITER temperature) showed that the Al-bond is the weakest part of the window. To find a way of reducing the thermal stress, the influence of some parameters has been studied. In particular, a specific thickness of the Al layer can result in a minimum of stress in the Al bond while the joint area and the thickness of the glass have only a small influence on the stress in the windows. The calculations allowed to propose an optimized design for the windows prototypes.

Abstract: SiC Ceramic was joined to itself using active brazing Alloys, like Ti in shape of sheet filler of Ag-cu and Ti-6AI-4V. This operation is occurred in an inert gas furnace.Interfacial microstructure studied with Scanning electron microscopy and X-Ray diffraction. Variation of Electrical Specific Resistance measured by 4 pin astute multimeter and strength of these joint was measured by fracture shear loading. This Joint is happened at 900c and upper temperature with 90 minutes and upper time. Electrical specific Resistance goes upper with joint in low temperature & time but this variation is very little. The microstructure showed an excellent bonding at the interfaces. The data showed also that the joining of the SiC decreases with increasing temperature and time.