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Titanium matrix composites were prepared by investment casting in a consumable arc skull casting furnace. With the addition of BC, the average primary β grains are refined, and the morphology of α phase tends to be more equiaxed. The free energy for nucleation consisting of the bulk free energy, orientation-independent interfacial energy, and elastic strain energy is calculated to investigate the role of nucleation sites in determining the shape of critical nucleus. In the current study, the TiB whiskers were found to be arranged in the grain boundary and provide heterogeneous nucleation sites for α precipitates, and the interfacial energy is about 14 % more than that in Ti-64, while its elastic strain energy is reduced to about three quarters of the latter one. [ABSTRACT FROM AUTHOR]

Titanium matrix composites (TMCs) are prepared by investment casting in a vacuum consumable kish furnace. The effects of B 4 C additions on the microstructures and tensile properties of TMCs are investigated. With the addition of B 4 C, the microstructure of TMCs is refined and the strength is improved. The yield strength of TMCs is evaluated by a comprehensive model that combines the strengthening effects of TiB whiskers/TiC particles, grain refinement and solution strengthening of the matrix, which is consistent with the experimental results in the current study. It is found that the yield strength enhancement of TMCs is mainly due to grain refinement and solution strengthening. During tensile deformation, the dislocation piles up at the interface between TiB whisker and matrix, which allows the TiB whiskers to bear extra load and therefore enhances the strength of TMCs. The plastic deformation is localized due to the action of TiB whiskers and this results in the brittle fracture of TMCs. [ABSTRACT FROM AUTHOR]

In this work, (TiB + TiC)/Ti6Al4V composites (TMCs) were prepared by in situ synthesis technology, and were successfully hot indirect extruded at four extrusion temperatures containing below and above β phase transition temperature (T = 1214K, 1259K, 1304K and 1349K). The effect of extrusion temperatures on the matrix, reinforcements and strengthening mechanisms were systematically studied. The results show that the mechanical effects has significantly influence on the microstructures of TMCs below β transformation temperatures, and more elongated α grains are formed. At the temperature of 1214K the α grain refinement mechanisms are controlled by dislocation motion, and there are a large number of dislocations within or between grains, which make the main contribution to the highest yield strength of the TMCs. With the increase of extrusion temperature, the yield strength decreases gradually, while the elongation increases gradually at first and then decreases slightly. This is because the grain refinement mechanism is mainly dynamic recrystallization, and coarser and dislocation-free α grains are formed at the temperature of 1349K. The indirect extrusion temperature should be controlled below the β transus. However, lower or near β transus can result in more fractures of TiB whiskers, which has a negative effect on the mechanical properties of TMCs. [ABSTRACT FROM AUTHOR]