On the formation and distribution of in situ synthesized TiB2 reinforcements in cast aluminium matrix composites

Introduction of TiB2 reinforcements into aluminium matrices allows composites to be obtained that exhibit excellent mechanical properties and good wear and corrosion resistance. These composites find applications in the automotive, aerospace and marine industries. In the present work, the in situ synthesis of ultrafine TiB2 particulates in an aluminium matrix was accomplished by reaction synthesis of TiB2 using K2TiF6 and KBF4 (in 120% excess to the stoichiometrically needed) fluxes in pre-melted aluminium. Composites were prepared with different concentrations of TiB2 in (2.5, 5 and 10 wt %) in an aluminium matrix. The holding time of the molten composite in an induction furnace was varied from 10 min to 50 min. The in situ formation of TiB2 reinforcement and its distribution in cast aluminiummatrix composites was analyzed based on microstructural studies, microhardness measurements and wear tests. The exothermic reaction between the halide fluxes starts after 10 min of holding time and completes before 20 min of holding time. The dominant phase was TiB2 after 20 min of holding time, while the formation of Ti3B4 was observed as the holding time was extended. The distribution of the reinforcing phases was studied by analyzing the scanning electron microscopy (SEM) images. An optimum holding time (20 min) of the composite melt was determined based on the dominant wear mechanism, microhardness, and phase composition of the composites