KINETICS OF METAL-CERAMIC COMPOSITE FORMATION BY REACTIVE PENETRATIONOF SILICATES WITH MOLTEN ALUMINUM

Wetting and reactions between molten Al and silicate substrates (parti cularly mullite) are studied to determine both how substrate density a nd p(O-2) influence wetting behavior, reaction rates, composition, and reaction product microstructure and what key steps control penetratio n kinetics. Guidelines are provided for using reactive penetration or infiltration when fabricating metal/ceramic composites. For dense subs trates, a reactive penetration process occurs. For a certain range, th e chemical reaction between Al and the ceramic is a limiting kinetic s tep resulting in fast reaction rates. Maximum dense mullite substrate reaction rates are between 1000 degrees and 1200 degrees C independent of p(O-2), unlike fused silica, which has faster penetration rates at higher temperatures. For mullite, reaction layer microstructure evolu tion halts reaction at higher temperatures, For porous substrates, rea ctive infiltration alone occurs. Either a critical temperature or p(O- 2) must be reached before infiltration starts.