Statistics – Applications
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.522f&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Statistics
Applications
Scientific paper
Ceramics are brittle because of their strong covalent or ionic bonds. Brittleness is not the only limitation of ceramics, also the presence of generally up to 20% porosity and the presence of microcracks (c.a. 25%) make ceramics rarely used for advanced applications. Often metals and composites are preferred for certain applications because of its higher fracture toughness. Nevertheless, there are also many advantages in using ceramics if compared to metals and composites such as high hardness, strength retention over a broad temperature range, wear and acid resistance, thermal shock resistance, possibility to be ground with a very smooth surface to high tolerances and low cost. Hence, during the last years, the ceramics market for engineering applications is to be considered in expansion. By keeping into consideration that today a values of KIC25 MPa m1/2 can be attained for some types of ceramics, one of the main factors that influences the utilisation of ceramics for engineering structures is the strong difficulty in joining its together. Most of the modern "Advanced Ceramics" are, in fact, highly-reactive so that its manufacturing and sintering procedures must be carried out only under controlled atmosphere. All that make the possibility to join advanced ceramics by any heat treatment basically impossible under normal conditions. Today, uses of that kind of ceramics are generally restricted to advanced small structural shapes. Starting from the consideration that a future possibility to join ceramics with a safe joint would be really important for structural applications especially where high wear and acid resistance is necessary, the aim of this paper is to show as, according to our theory, a first step of laser welding of reactive ceramics is possible under microgravity and oxigen deficiency conditions. It is enough to think about a satellite or a part of the ISS made from absolutely fire, chemical and wear proof ceramic parts assembled directly on space by laser welding and also the possibility to repair and replace a damaged component without incur in the risk to obtain a less resistant structure. According to our studies, microgravity will avoid the directional grains nucleation and growth; also sedimentation of heavier particles can be avoided. Moreover, microgravity will lead to a homogeneous interface by reducing the thermal convection and by avoiding the buoyancy effect. Furthermore passive oxidation and porosity can also be better controlled by the absence of oxigen. We deem necessary to underline that due to economic and technical troubles in carrying out a defined experimental testing procedure, no trials could be yet performed so, in this instance, we just would like to attract the experts' attention in order to possibly go further with our studies.
Camiolo F.
Favuzza M.
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