Effects Of CNTs Content And Magnesium Content On Microstructure And Properties Of CNTs/TiMg Composites

CNTs/TiMg Composite materials were adopting vacuum hot pressed sintering method.Carbon nanotubes dispersed in anhydrous ethanol were evenly mixed into Ti/MgH₂ powders by wet milling.And the vacuum hot pressing sintering process was used to prepare the CNTs/TiMg composites.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 composites were prepared by different Hot-pressing Sintering processes.Then the appropriate hot-pressing process was obtained through comparative study.The effects of CNTs content and Mg content on the structure and properties of the composites were studied on the basis of the successful fabrication of the composites.The results show that the maximum microhardness and density of the composites are 512 HV and 4.321 g/cm³ respectively when sintered at 800 ^oC.XRD analysis shows that the main component of the composites is Ti.When the holding time reaches 30 mins,the microhardness increases to 568 HV,and the density is about 4.2g/cm³.The holding time has little effect on the density.With the addition of different magnesium materials,the hardness of the composites has been significantly improved,reaching 573HV,which is 81.9%higher than that of CNTs/pure titanium composites.The analysis of XRD shows that the main phases in the composites were Ti,Mg and C,and a small amount of Ti-Mg solid solution new phases.The cross-section morphology of the composites shows that the melted magnesium fills the grain interface during extrusion,and the composites have better compactness and lower density.The density of the composites with MgH₂ is the lowest,reaching 4.13g/cm³.When 0.5wt.%CNTs were added,the microstructure of the composites was refined to a certain extent.The fracture surface changes from intergranular fracture to transgranular fracture.When the content of CNTs is 1.0wt.%,the microhardness and density of the composites reach 232HV and 4.13g/cm³ respectively,which are 26.1%higher and 8.2%lower than that of the matrix respectively.The fracture morphology of CNTs shows that the uniform dispersion of CNTs has a great influence on the composites.After adding 5.0wt.%MgH₂,the microstructure of the composite is fine and uniform.Its microhardness reaches a maximum of 389HV.When the content of MgH₂is 10.0wt.%,lamellar structure appears in the micro-morphology.Its hardness was significantly reduced to 265HV.Moreover,CNTs were torn at the fracture.It can be concluded that proper addition of Mg can improve the brittleness of composites and the bonding strength between CNTs and matrix.