Microstructure and tensile properties of in situ (TiB+TiC)/Ti6242 (TiB:TiC=1:1) composites prepared by common casting technique

In the present work, (TiBw + TiCp)/Ti6242 composites with TiB:TiC = 1:1 were produced by common casting and hot-forging technology utilizing the SHS reactions between titanium and B,C, C powder. The microstructures of composites were examined using optical microscopy (OM) and transmission electron microscopy (TEM). The X-ray diffraction (XRD) was used to identify the phases that were present in the composites. There are three phases - TiB, TiC and titanium matrix alloy. TiB grows in short-fiber shape, whereas TiC grows in dendritic, equiaxed or near-equiaxed shape. TiB whiskers were made to align the longitudinal direction and TiC dendritic was broken up after hot-forging. The reinforcements are distributed uniformly in matrix alloy. The interfaces between reinforcements and titanium matrix alloy are very clean. The tensile strength (yield strength and ultimate tensile strength) and the Young's modulus improve with the addition of TIE whiskers and TiC particles although some reduction in ductility is observed. (TiBw + TiCp)/Ti6242 composites with TiB:TiC = 4:1 will fracture on a lower level of applied stain due to deformation restraint of TiB whiskers on titanium matrix alloy. The (TIBw + TiCp)/Ti6242 composites with TiB:TiC = 1:1 show higher tensile strength and ductility. The addition of graphite not only improves the tensile strength and the Young's modulus but also increases the ductility. The improved Young's moduli and increased tensile strengths of the composites are explained using shear lag and rule-of mixtures theories. The Young's moduli of the composites were found in good agreement with that calculated from Tsai-Halpin equation applied for discontinuous-reinforced composites. (C) 2001 Elsevier Science B.V. All rights reserved.