Microstructural characterisation of in situ TiB/Ti matrix composites prepared by mechanical alloying and hot pressing

Abstract

Various TiB whisker reinforced Ti – 4.0Fe – 7.3Mo composites were prepared by mechanical alloying followed by hot pressing using titanium, boron and FeMo alloy powders as starting materials. X-ray diffraction, SEM and TEM were used to characterise the microstructure of the composites which consisted of TiB, α-Ti and β-Ti. The β-Ti was formed owing to the solid solution of FeMo elements in the titanium matrix, and TiB was synthesised by chemical reaction between titanium and boron. The TiB whiskers were distributed along α-Ti or β-Ti grain boundaries or within these grains, and those distributed along the grain boundaries were coarser than those in the interior of α-Ti or β-Ti grains. The cross-section of the TiB whisker was hexagonal, and the interface between TiB and the titanium matrix was faceted, with no precipitation phase being found. The starting boron content did not influence the dimensions of the TiB whiskers.