Microstructure and tensile properties of in situ synthesized (TiBw + TiCp)/Ti6242 composites

Abstract

In the present work, (TiBw+ TiCp)/Ti6242 composites were fabricated via common casting and hot-forging technology utilizing the SHS reaction between titanium and B4C. The XRD technique was used to identify the phases of composites. The microstructures were characterized by means of OM and TEM. Results from DSC and analysis of phase diagram determine solidification paths of in situsynthesized Ti6242 composites as following stages: β-Ti primary phase, monovariant binary eutectic β-Ti + TiB, invariant ternary eutectic β-Ti + TiB + TiC and phase transformation from β-Ti to α-Ti. In situsynthesized reinforcements are distributed uniformly in titanium matrix alloy. Reinforcement TiB grows in whisker shape whereas TiC grows in globular or near-globular shape. TiB whiskers were made to align the hot-forging direction after hot-forging. The interfaces between reinforcements and Ti matrix alloy are very clean. There is no any interfacial reaction. Moreover, the mechanical properties improved with the addition of TiB whiskers and TiC particles although some reduction in ductility was observed. Fractographic analysis indicated that the composites failed in tension due to reinforcements cracking. The improvements in the composite properties were rationalized using simple micromechanics principles. The strengthening mechanisms are attributed to the following factors: undertaking load of TiB whiskers and TiC particles, high-density dislocations and refinement of titanium matrix alloy's grain size.