Evolution of microstructure and phases in in situ processed Ti-TiB composites containing high volume fractions of TiB whiskers

A series of titanium composites, with varying volume fractions of titanium monoboride (TiB) whiskers, were made by mixing various proportions of titanium (Ti) and titanium diboride (TiB2) powders followed by hot pressing. The phases present were identified by x-ray diffraction. Microstructural examination revealed three different types of TiB whisker morphologies: (i) long and needle-shaped TiB whiskers that are isolated and randomly oriented in the Ti matrix at relatively low volume fractions (0.3), (ii) colonies of refined and densely packed TiB whiskers from intermediate-volume (0.55) to high volume (0.73 and 0.86) fractions, and (iii) coarse and elongated TiB particles with a few needle-shaped whiskers at the highest volume fraction (0.92). Ln all the composites, TiB was found to be the predominant reinforcement. However, in Ti-TiB composites with 0.86 and 0.92 volume fractions of TiB? a significant amount of TiB, was also present. The relative volume fractions of Ti, TiB, and TiB2 phases were estimated from the integrated intensities of diffraction peaks by the direct comparison method employing the calculated structure factors and Lorentz polarization factors. The composite microstructure, as well as the evolution of different morphologies, of TiB whiskers is discussed.