New Materials

RST Bond Goat: The key to a successful ceramic coating on Al-alloys is development of an Al-Si bond coat with a modulus of elasticity and thermal characteristics that can tolerate engine stresses. Oomputer aided analyses at IKE indicated that conventional metallurgical methods would not produce these bond coats with the necessary characteristics. The developed Rapid Solidification Technology (RST) allows an intimate mixing of elements in levels otherwise unobtainable.

excellent potential for meeting the high temperature engine operational requirements.

It is generally agreed that a pure monolithic ceramic diesel engine will not be available for many years. This is because of cost and reliability of current ceramics. The use of monolithic ceramic materials in the future'will be focused on specific parts where the use of ceramics is cost-effective. That is in particular parts where temperature-stable heat insulation and wear resistant materials are needed; in addition, they are needed in part ignition automobiles engines, where the exhaust gas should be kept at high temperature until it reaches the catalyst. The catalytic converter cast-in-place aluminium titariate inserts are being used in production by Porsche.

The properties to be improved are as follows:

Due to the rapid quenching, the Al-Si alloy can be produced with more than twice the amounts of Si than with other methods. The overeutectic addition of Si (>30%) to AI reduces the thermal expansion coefficient of the bond coat to the range of steels. Carbon-carbon composite for cylinder liners (high and medium speed engines): Raising cylinder working pressures and temperatures to increase engine cylinder power has reached a limit in the development of the modern diesel engine. A group at RWTH Aachen has recently developed a carbon-carbon composite cylinder with a wear/corrosion resistant plasma sprayed coating on the inside. This concept has the potential of retaining cylinder concentricity during engine operation at high temperatures and pressures. Conventional cylinder liners under these conditions are thereby increasing both blow-by and friction.

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