In situ TiB whisker reinforced Ti-4.0Fe-7.3Mo matrix composites have been fabricated by spark plasma sintering(SPS). The microstructure of the in situ TiB whiskers and interfacial structures in the composites were investigated by scanningelectron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution electron microscopy (HREM). The interfacesbetween in situ TiB and the Ti matrix are clean and faceted along the (100)
TiB plane. However, small lateral growth steps areobserved along the (101) and (10
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) planes of TiB. Because of the characteristics of the TiB crystal structure, the growing velocityof the (100)
TiB plane along the [010]
TiB direction is much faster than that of the [001]
TiB direction, which leads to TiB growth as awhisker shape along the [010]
TiB direction with a hexagonal transverse section. The growth mechanism of TiB whiskers is a stackingprocess of the (100)
TiB plane.