Microstructures and mechanical properties of hot indirect extruded in situ (TiB + TiC)/Ti6Al4V composites: Effect of extrusion temperature

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.