DEVELOPMENT OF FUNCTIONALLY GRADED MATERIALS BY SOLIDIFICATION PROCESSING ON A ROTATING TABLE

Abstract

Graded structure, although found many a times in ordinary engineering materials, is being : tailored with the intention of attaining gradient of composition and/or microstructure in materials called- Functionally= Graded' Materials (FGM), in. order to achieve the designed functionsand_ properties. In the present work a. centrifugal casting set-up, has been designed and fabricated in order. to develop aluminum-alumina based functionally graded material by melting-aluminum in a graphite crucible inside a muffle furnace at a temperature of 900°C Magnesium has been added to the melt :before _ adding preheated -(200°C) alumina. particles. of an average size of 85 μm, at the rate of 1;66-2.5 gm/s during stirring The-resulting -slurry with the crucible is immediately transferred and mounted on platform rotating at 300 rpm and the melt is solidified in the crucible while rotating in platform, to get cast- FGM ingots Three FGM ingots. with nominal average alumina content of -10,:15 and 20 wt% have been cast The microstructure of the cast specimens_ clearly shows; the decreasing volume fraction of alumina particles from outer radius to the centre in all the cast ingots, showing the influence of centrifugal force pushingthe denser. alumina- particles towards the outer radius .during rotation of the melt in the crucible. The centre of the cast ingot has, a particle free region and the size of this region increases as one moves .towards the bottom of the cast. ingot. At a-give'n radial_ distance from the centre of the ingot, alumina content increases with increasing height'. from the bottom of the cast ingot, indicating a` tendency for flotation which has been attributed to finite life time of bubble-particle combine, often observed' in cast composites. However, the microstructures show, in general, that there is . no voids present at the particle matrix interface and so it is evident: that centrifugal force succeeded' -in detaching the particles from the bubble. The FGM ingots.: with higher nominal average particle content, has a higher alumina content at a given radial -distance at the same height from the bottom.: