Microstructure And Properties Of TiB Reinforced Ti Matrix Composites Prepared By Reaction Sintring

In situ reaction synthesized TiB whisker reinforced Ti matrix composites have been fabricated by planetary grinding pretreatment and hot pressing (HP) techniques. XRD, SEM and TEM were used to study the influences of sintering temperature and the volume fraction of in situ TiB in the composites on microstructure to obtain a better understanding on the strengthening mechanisms. A theoretical model for growth of in situ TiB whiskers and the formation mechanisms of defect existed in the in situ synthesized TiB whiskers have been proposed.For the as-prepared composites, TiB whiskes formed by the in situ reaction between B and Ti powders, and no B was retained in Theα-Ti matrix. The average diameter of the in situ TiB_w increases with the increase of sintering temperature and TiB volume fraction. The aspect ratio increase with the increase of sintering temperature, however, the situation is reversed with the increase designed TiB volume fraction.Relative density of the composite is above 90%. Bending strength, Young's modulus and toughness of B20 composites sintered at 1300℃reach maximum values, which are 939MPa, 167GPa and 11.5MPa·m1/2, respectively. Strengthen mechanisms of the composites are attributed to sizes, volume fraction and disturbituion of TiB whiskers, fine-grained microstructure ofα-Ti matrix and crystal defects also have some effects.The in situ TiB whiskers obtained in the composites are generally with a hexagonal shape at the transverse section, and exhibits typical crystallographic planes of the (100), (101) and (101) type, and a growth orientation of [010]. There exist no orientation relationships between TiB_w and theα-Ti matrix.Stacking faults and dislocations exist in the TiB whisker, and the size of TiB whisker become bigger with the increase of sitering temperature, the type and density of crystal defects also change as a result. There only exits stacking faults in the small TiB whiskers, the density of stacking faults decreases with the increases of the TiB whisker size, dislocations appear and then increases with the increases of the TiB whisker size. Based on the above experimental observation, a theoretical model for the formation of defect within TiB whiskers has been proposed.