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 wer e produced by common casting and hot-forging technology utilizing the SHS r eactions between titanium and B,C, C powder. The microstructures of composi tes were examined using optical microscopy (OM) and transmission electron m icroscopy (TEM). The X-ray diffraction (XRD) was used to identify the phase s that were present in the composites. There are three phases - TiB, TiC an d titanium matrix alloy. TiB grows in short-fiber shape, whereas TiC grows in dendritic, equiaxed or near-equiaxed shape. TiB whiskers were made to al ign the longitudinal direction and TiC dendritic was broken up after hot-fo rging. The reinforcements are distributed uniformly in matrix alloy. The in terfaces between reinforcements and titanium matrix alloy are very clean. T he 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 com posites 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 stre ngth and ductility. The addition of graphite not only improves the tensile strength and the Young's modulus but also increases the ductility. The impr oved Young's moduli and increased tensile strengths of the composites are e xplained using shear lag and rule-of mixtures theories. The Young's moduli of the composites were found in good agreement with that calculated from Ts ai-Halpin equation applied for discontinuous-reinforced composites. (C) 200 1 Elsevier Science B.V. All rights reserved.