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 titan ium (Ti) and titanium diboride (TiB2) powders followed by hot pressing. The phases present were identified by x-ray diffraction. Microstructural exami nation 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 re fined and densely packed TiB whiskers from intermediate-volume (0.55) to hi gh volume (0.73 and 0.86) fractions, and (iii) coarse and elongated TiB par ticles with a few needle-shaped whiskers at the highest volume fraction (0. 92). Ln all the composites, TiB was found to be the predominant reinforceme nt. However, in Ti-TiB composites with 0.86 and 0.92 volume fractions of Ti B? a significant amount of TiB, was also present. The relative volume fract ions of Ti, TiB, and TiB2 phases were estimated from the integrated intensi ties of diffraction peaks by the direct comparison method employing the cal culated structure factors and Lorentz polarization factors. The composite m icrostructure, as well as the evolution of different morphologies, of TiB w hiskers is discussed.