Study On Microstructure And Mechnical Properties Of Ti_f/Al Composites

Of all the metal matrix composites which have been developed and applied currently, the research on aluminum matrix is deepest. Metal matrix composites have the advantages of low density, high specific strength, high specific stiffness, high specific elastic modulus, high electrical and thermal conductivity, high temperature resistance, oxidation resistance, erosion resistance, creeping resistance and fatigue resistance. Titanium fibers have the priority of high specific strength, good ductility and corrosion resistance. Therefore, in this article Ti_f/Al composites were fabricated in pursue of combination of the advantages of both matrix and reinforcement, in order to obtain a kind of aerospace material with the advantages of lightweight, high strength, high chemical stability and wide application.In this article unidirectional and bidirectional Titanium fiber reinforced 5A06 composite materials were fabricated by pressure infiltration method. In order to suppress too strong Ti-Al interfacial reaction and reduce the formation of brittle TiAl₃, TiN films were prepared on the surface of titanium fiber using vacuum ion plating. Optical microscopy, precise analytical balance, transmission electron microscopy, scanning electron microscopy and X-ray diffraction were used for investigation on composite microstructure and interface morphology. The mechanical properties of unidirectional and bidirectional Titanium fiber reinforced 5A06 composite materials were studied, to obtain changes of mechanical properties at different fiber directions, different volume fractions and different ambient temperatures, and analyze the impact of fiber coating on the mechanical properties of composites.The average thickness of TiN coating is about 2μm with ununiform distribution. The surface of non-coated titanium fibers had generated reaction products, while there was no obvious product on the surface of coated titanium fibers. And after coating treatment, there is no existence of TiAl₃, thus TiN coating effectively prevented the appearance of the interface diffusion, and controlled interfacial reaction.Through the coating process, mechanical properties of Ti_f/Al composite have been improved to some extent. The tensile strength increased nearly 15%, which could prove coating effectively optimized interfacial situation. On the other hand, the elongation ratio decreased slightly. The tensile strength of unidirectional Ti_f/Al is 806MPa, and the composite has good plasticity and ductility. With the increasing of angle between the stress direction and fiber axis, the mechanical properties of composite materials have a significant change. By way of the fracture of composite materials is seen in the 0°-30°direction it is the fracture mode that composite axial tensile stress caused the pull-out of fiber. The fracture mode of 30°-45°direction is common failure action for the axial tensile stress and interfacial shear stress. At 45°-90°direction due to the high volume fraction interface increases, for the tensile stress in the interface controlled fracture damage. The bending strength is 1350MPa, showing high strength and toughness. Two-dimensional Titanium fiber mesh reinforced Aluminium composites have good isotropic characteristics and have high tensile strength and elongation rate at the 45°direction.Ti_f/Al and 2D-Ti_f/Al composites have high temperature strength. As the temperature increased, the bonding strength of interface decreased, and the elongation rate of the material was further improved. The bending strength of Ti_f/Al is up to 650MP at 500℃, and the bending strength of 2D-Ti_f/Al composites at 300℃can be more than 300MPa.