Wave-actuated Preform Infiltration Routines in MMC Production

University dissertation from Dept. of Production and Materials Engineering, Box 118, S-221 00 Lund, Sweden, tel+46 46 2228595, fax+46 46 2224529

Abstract: The implementation of highly magnetostrictive wave-actuator techniques in preform infiltration processes for metal-matrix composite production is described. Metal matrix materials require additional methods to handle the content, shape and position of the ceramic reinforcements, which are not required for metal alloy casting. Commercial fabrication of advanced metal matrix composite products has hitherto been marginal. One approach is the use of manageable substructures, preforms, of reinforcement elements bonded by a secondary ceramic phase, which can be infiltrated through their open porosity by the metal-matrix when molten. Infiltration of high density ceramic preforms is troublesome due to the dimensional fineness of channel geometry and poor wetting conditions. Present work examines the possibility of using highly magnetostrictive actuators to improve infiltration mainly of aluminium alloys into alumina short-fibre structures at low pressure differences. Models are derived to describe the coupling between infiltration and actuation properties. Experimental wave-actuated infiltration equipment have been designed, built and evaluated. The mechanical properties of MMC materials which have been manufactured are evaluated. An application of MMC-materials has been studied. The theory and the models are formulated from established fundamental principles. The influence of preform fiber microgeometry on infiltration pressures has been studied using the concept of contact angles. Preform elasticity has been modeled for the determination of the properties of elastic wave propagation. Finite element analysis has been used as a tool to model the dynamic behaviour of wave-actuated crucibles containing matrix-melt. A novel routine has been developed in this work, applying wave energy to a resonant crucible containing molten matrix alloy. An evacuated preform is immersed in the melt and the infiltration is then carried out at applied pressure differences of 2 MPa or less. The infiltrated preform is removed from the melt before cooling is started. This routine works without needing special tools for the MMC geometry, the MMC will attain the same geometry as the geometry of the initial preform structure. This method is found to have a higher industrial potential than the other researched concepts of this work. The best results of infiltration of high volume fraction preforms are achieved when the preform is actuated directly by a solid wave-guide.

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