Study On Preparation Of CNTs/TiAl Alloy Composites By Hot Pressed Sintering

CNTs/TiAl Composite materials were prepared by using mechanical milling to refine the TiAl powder and mix with CNTs,and adopting vacuum hot pressed sintering method. The optical microscope(OM), X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) were used for microstructure observation and phase analysis of samples. And their micro hardness and density were measured. The ball milling process and powder mixing process were studied by observing the morphology change of the powder after ball milling and the distribution of the carbon nanotubes. Then the hot press sintering process of the composites was studied. Based on the successful preparation of composite materials, the effects of CNTs content, ball milling in hydrogen and Mg element on the microstructure and mechanical properties of the composites were studied.The results show that CNTs/Ti/Al composite powders with small size and uniform CNTs were prepared by the method of stage milling and ultrasonic dispersing and moist milling. During hot pressing sintering at 900?, the micro hardness and density of the composites reached the maximum value of 644.3HV and 3.764g/cm3 respectively, and the XRD analysis showed that the main components were ?-TiAl. When insulation 5h, microhardness and density of the composites increased to 738.3HV and 3.987 g /cm3. When adding 0.5wt.% CNTs, the microstructure of the composite material is refined and the fracture changes from intergranular fracture to intergranular fracture. The CNTs at fracture presents the state of pull out or bridging, serving as the purpose of bridge strengthening and load transfer mechanism. When the CNTs content is 1.0wt.%, the micro hardness of the composite reaches the maximum value of 764.1HV, which is improved by 27.9% compared to the matrix.After ball milling in hydrogen, the microstructure of Ti/Al composite powders and composite materials were further refined. Fracture morphology is quasi cleavage in the CNTs content of 0.5wt.% and the micro hardness and density of the composites reach the maximum 782.3HV and 3.914 g/cm3 respectively in the CNTs content of 1.5wt.%, which show that the ball milling in hydrogen was helpful to the homogeneous dispersion of CNTs base on the morphology analysis of the fracture.After adding 1.0at.% Mg elements, the microstructure of the composite was small and uniform and the micro hardness reached the maximum 814.7HV. When the Mg content is 2.0at.%, the lamellar structure appeared in the micro morphology and the hardness was significantly reduced to 554.5HV. CNTs at fracture show tear shape. From the above, it can be known that the Mg element improves the brittleness of the composite material and improves the bond strength between CNTs and the matrix.