Centrifugal casting of aluminium containing in situ formed TiB₂

Abstract

A method of producing micrometre sized TiB₂ particles within an aluminium matrix is the salt reaction method, using KBF₄ and K₂TiF₆ salts. The advantages of this in situ reactive process are a small particle size and good particle/matrix interfacial bonding. However, this method is limited to producing low particulate volume percentage material (< 6 vol.-%). To overcome this limitation, centrifugal casting has been investigated. A series of casts was made to observe the influence of centrifugal acceleration g on final TiB₂distribution. This was done by casting at four different rotational speeds (rev min^-1). The TiB₂ particulate content was concentrated towards the outer radius with a clear interface between this region and the remaining unreinforced aluminium matrix. The final concentration of TiB₂ particles increased with inreasing rotational speed and particle clustering was found to influence the settling behaviour of the TiB₂ particles.The present paper demonstrates that centrifugal casting may be employed to yield a higher volume percentage (> 10 vol.-%)TiB₂ reinforced particulate metal matrix composite. Particle volume fraction is a weak function of g, and the final volume fraction may be controlled by the rotational speed. A model has been developed to describe development of the concentration profile of TiB₂ particles as a function of rotational speed.