In the last decade, ultra-high temperature ceramics raised renewed interest after the first studies in the 60's. Thanks to their high melting point, superior to any group of materials, and to their set of interesting physical and engineering properties, they find application in aerospace industry, propulsion field, as cladding materials in generation IV nuclear reactors and solar absorbers in novel HT CSP systems. Recent efforts were devoted to the achievement of high strength and toughness materials, or to the optimization of high temperature stability under oxidative environment. Critical issues rose during the study of each property and are still under continuous investigation. However, to fully exploit the potential of UHTCs in the widest possible range of applications, effective processes for joining these materials to themselves, other ceramics, or metals must be developed. Conventional solid-state diffusion bonding and brazing approaches have complementary strengths and weaknesses, the major drawbacks being high processing temperatures and pressures, long processing times and the need for meticulous surface preparation. Considerations of these issues and the desire to exploit the high-temperature capabilities of UHTCs encouraged exploration of transient-liquid-phase (TLP) bonding methods. In this work, for the first time, joining tests are conducted on pure and doped carbides and borides using transient-liquid-phase (TLP) joining. Bonding is performed under controlled atmosphere using refractory-metal based multilayer metallic interlayers. These interlayers are designed to develop transient-liquid films that enable rapid, reliable, and low-temperature bonding of a wide range of ceramics. It will be shown that the type and amount of sintering aid are key issues affecting the integrity of the joint because fragile secondary phases may form as a result of their interaction and reaction with the metal interlayer. On successful joints, preliminary results of nanoindentation tests are shown.
Joining of ultra-high temperature ceramics
L Silvestroni;D Sciti;L Esposito;
2012
Abstract
In the last decade, ultra-high temperature ceramics raised renewed interest after the first studies in the 60's. Thanks to their high melting point, superior to any group of materials, and to their set of interesting physical and engineering properties, they find application in aerospace industry, propulsion field, as cladding materials in generation IV nuclear reactors and solar absorbers in novel HT CSP systems. Recent efforts were devoted to the achievement of high strength and toughness materials, or to the optimization of high temperature stability under oxidative environment. Critical issues rose during the study of each property and are still under continuous investigation. However, to fully exploit the potential of UHTCs in the widest possible range of applications, effective processes for joining these materials to themselves, other ceramics, or metals must be developed. Conventional solid-state diffusion bonding and brazing approaches have complementary strengths and weaknesses, the major drawbacks being high processing temperatures and pressures, long processing times and the need for meticulous surface preparation. Considerations of these issues and the desire to exploit the high-temperature capabilities of UHTCs encouraged exploration of transient-liquid-phase (TLP) bonding methods. In this work, for the first time, joining tests are conducted on pure and doped carbides and borides using transient-liquid-phase (TLP) joining. Bonding is performed under controlled atmosphere using refractory-metal based multilayer metallic interlayers. These interlayers are designed to develop transient-liquid films that enable rapid, reliable, and low-temperature bonding of a wide range of ceramics. It will be shown that the type and amount of sintering aid are key issues affecting the integrity of the joint because fragile secondary phases may form as a result of their interaction and reaction with the metal interlayer. On successful joints, preliminary results of nanoindentation tests are shown.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
