Abstract
Abstract : There has been a great consideration in the research and development of carbon nanotubes and its composites due to both their physical and chemical properties which make them desirable for wide uses in the engineering fields such as in catalysts, supercapacitors, nanoelectronic devices, solar energy, aerospace, etc. However, there are still some challenges during the homogenous dispersion of carbon nanotubes (CNTs) in metal and metal oxides without breaking/damaging the nanotube structure. This research focused on the study of dispersion characteristics of multi-walled CNTs (MWCNTs) in Ti-6Al-4V and TiO2 matrix composites, using two methods namely; planetary ball milling and sonication-freeze drying. Efforts were made to understand the relationship between the processing parameters and effect of MWCNTs on the dispersion of MWCNTs in Ti-6Al-4V and TiO2 by studying the microstructures and phases of reinforced Ti-6Al-4V and TiO2 composite powders and sintered composites. Furthermore, the 1 vol. % and 2 vol. % of MWCNTs were dispersed in Ti-6Al-4V and TiO2 respectively by adapted planetary ball milling (in dry condition under vacuum and with no addition of process control agent) and sonication freeze drying. Subsequently, the unreinforced Ti-6Al-4V, TiO2 and mixed composite powders were consolidated by spark plasma sintering (SPS) under vacuum at 850 °C and 1000 °C. Different characterization technique such as scanning electron microscopy and X ray diffraction were used to quantitively analyse the microstructure and nanostructural evolution of the crystalline phases in the MWCNTs/Ti-6Al-4V and MWCNTs/TiO2 powder mixtures after planetary ball milling and of the sintered bulk materials. The density and microhardness of the sintered bulk materials were also measured. The results obtained from this study showed that during planetary ball milling, especially at prolonged milling time (5 hrs) results in better dispersion of MWCNTs in the matrix composite powders than the sonication freeze drying technique. In addition, it was observed that it is difficult to effectively disperse MWCNTs of higher volume fraction in metal matrices. It was also observed that the relative densities of the consolidated MWCNTs/Ti-6Al-4V and MWCNTs/TiO2 composites improved at higher sintering temperature (1000 °C) but decreased with increased volume fraction of MWCNTs. The use of planetary ball milling and SPS technique showed better dispersion of MWCNTs in Ti-6Al-4V and TiO2 no sign of interfacial reactions in the composites.
M.Tech. (Metallurgy)