Synthesis of ductile titanium-titanium boride (Ti-TiB) composites with a beta-titanium matrix: The nature of TiB formation and composite properties

The study focused on the in-situ synthesis of titanium (Ti)-titanium boride (TiB) composites with [beta] phase in the matrix by reaction sintering of TiB^sub 2^ with Ti and alloying element powders. The goal was to examine the nature of TiB whisker formation in three different kinds of powder mixtures: (1) [beta]-Ti alloy powders and TiB^sub 2^; (2) [alpha]-Ti powder, a master alloy (Fe-Mo) powder containing the [beta]-stabilizing elements, and TiB^sub 2^; and (3) [alpha]-Ti powder, a [beta]-stabilizing elemental powder (Mo or Nb), and TiB^sub 2^. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker formation and their growth were studied at processing temperatures ranging from 1100 [degrees]C to 1300 [degrees]C. The morphology, size, and distribution of whiskers were found to be influenced by the powder-packing conditions. A large particle-size ratio in bimodally packed mixtures led to the formation of a TiB monolithic layer around [beta] grains. With a relatively finer starting powder, smaller size ratio, and trimodal packing arrangement, the TiB whiskers were found to be distributed more homogeneously in the matrix. The study also used the X-ray direct comparison method and the structure factor for the [beta] phase to determine the volume fraction of TiB phase from X-ray data. Tensile tests and fractographic investigations were carried out on selected composites. The evolution of the composite microstructure, the influence of powder-packing variables, and the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed. [PUBLICATION ABSTRACT]