Abstract
M.Tech. (Chemical Engineering)
Recent development in nanoindentation techniques has enabled investigations on the mechanical properties of materials under dynamic conditions as the technique offers unique capabilities for direct measurement of hardness, modulus of elasticity and contact stiffness among other properties. In this study, ultra nanoindentation (UNHT) technique was used to investigate the mechanical properties of spark plasma sintered Ti-6Al-4V reinforced with 1 to 4 vol% TiN nanoparticles. The morphology and microstructure of the as-sintered samples were examined using field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDS) and Electron Backscattered Diffraction (EBSD). The hardness, modulus of elasticity and creep properties were examined using Berkovich diamond indenter which is equipped with a three-sided pyramid. Microstructural results indicated that sintered samples containing 1 vol % of TiN nanoparticles was fully transformed from lamellar to bimodal and duplex structures. It was also observed that TiN nanoparticles segregated at the grain boundaries of the Ti-6Al-4V matrix. Results obtained from the EBSD revealed that α phase, hexagonal close packed (HCP) was stabilised at the expense of β phase Body centered cubic crystal structure (BCC). The nanoindentation results showed that both hardness and modulus of elasticity depend on the presence of volume fraction of TiN in Ti-6Al-4V matrix. There was significant increase in bulk hardness, modulus of elasticity while subsequently decreasing the contact depth and maximum depth of the indentation with increase in volume fraction of TiN. The mechanical properties (hardness and modulus of elasticity) of each phase (α and β) were derived from the grid indentation technique, where the β phase exhibited the highest hardness against α phase and the grain boundary, which may be due to uniform distribution of TiN along the grain boundary and β phases were found along the grain boundary. Optimum properties were obtained with the addition of 2 vol % of TiN which had highest creep resistance compared with that of Ti base alloy.