Microstructure and mechanical properties of in situ Ti-TiB based composite materials produced by casting and subjected to hot workingTuesday (27.09.2016) 11:15 - 11:30 Part of:
Light weight titanium alloys having a high specific strength and excellent corrosion resistance are important structural materials for aircraft, space and other engineering applications. While the pace of conventional titanium alloy development has slowed down, alternative alloy designing ideas for improving major properties, such as creep resistance, strength and stiffness, are being explored. In the present study, discontinuously reinforced composite materials based on Ti-TiB have been manufactured in situ by common casting using different titanium alloys as matrix materials. The produced composites were reinforced with TiB whiskers and jointly with TiB whiskers and oxides of a rare-earth element. Multiple 2-D hot forging (hot drawing) was applied to align the boride whiskers along the drawing direction and to retain a high aspect ratio of the whiskers. The efficiency of the boride alignment depended on the flow stress of the matrix material under the hot forging conditions. Higher flow stresses led to less effective boride alignment and more intensive breaking of the TiB whiskers. The hot forged composite materials with preferably oriented boride whiskers were used to prepare the specimens for mechanical testing. The strength properties depended on the volume fraction, the aspect ratio of TiB whiskers, the texture sharpness of the TiB phase (predominant orientation of the whiskers along the tensile axis), and the presence of the rare-earth element oxides. The composite materials showed much higher strength in a wide temperature range without drastic ductility and fracture toughness reduction in comparison with the matrix material. The presence of the TiB whiskers having predominant orientation along creep loading and the rare-earth oxides led to appreciable improvement in the creep resistance as compared to that of the matrix material. The effect of the TiB whiskers on the mechanical properties is discussed in terms of a shear-lag model for discontinuously reinforced metal matrix composite materials.