FABRICATION OF FUNCTIONALLY GRADED Al/B4C COMPOSITE MATERIALS VIA GRAVITY SEDIMENTATION METHOD

Functionally graded materials (FGMs) are a new class of advanced materials, which are characterized by continuous and smooth variation in the microstructure and/or composition in one or more dimensions of the component. Therefore, sharp local stress concentration along dissimilar phases with distinct properties,which are present in the conventional materials, is avoided resulting in improved thermal and mechanical properties. In the present investigation, functionally graded Al-B4C composites have been fabricated via gravity sedimentation of Al and B4C powders in a viscous liquid. The sedimentation liquid was prepared by dissolving Poly Methyl Methacrylate (PMMA) in toluene. At first, the settling velocities of different sized constituent powders in the sedimentation media were measured experimentally and the results were compared to those calculated by the Stokes law. These results were used for optimization the gravity sedimentation method for fabricating Al-B4C composites. The resultant deposits with graded concentration of B4C in Al matrix were heated to burn out the binder and consolidated via standard powder metallurgy procedures for making bulk FGMs. It was concluded that by using the proper size of the constituent powders, FGM composites with a smooth concentration gradient of B4C in the Al matrix can be produced

Keywords:

Al-B4C composites , Functionally graded materials (FGMs) , Sedimentation method , Stokes law , Powder metallurgy