Application of Metal Matrix Composites to Diesel Engine Pistons

Abstract

Aluminum based FRMs : Fiber Reinforced Metals (MMCs : Metal Matrix Composites) have been in use for the top ring groove of Toyota's diesel engine pistons since 1982.
At first, "KAOWOOL® " (alumina-silica short fiber) FRM as a standard grade and "SAFFIL®" (alumina short fiber) FRM as an upper grade were developed. These FRMs showed good wear resistance, well as higher thermal conductivity and lower thermal expansion than conventional "Niresist" cast iron as the piston ring groove.
In the next step, corresponding to the demands for lower cost with higher strength and superior wear resistance, "ALSILON®" FRM was developed in 1987. The "ALSILON® " (crystalized alumina-silica short fiber) FRM gives both as good performance as "SAFFILL® " FRM and as low cost as "KAOWOOL® " FRM.
In the 3rd step, a new type of MMC has been developed in 1988 to improve higher temperature durability. The MMC is composed of hybrid reinforcements of the "ALSILON® " and NiAl₃ intermetallic compound particulates uniformly dispersed in the aluminum matrix. The NiAl₃ particulates are formed by in-situ procesing and exhibits excellent adhesive wear resistance.
Thus, the MMC pistons have made a steady progress in the field of material and processing technology and their mass, production scale has successfully increased up to more than 200 000 pieces/month (2.4 million pistons/year).