Development of magnesium based hybrid nanocomposite

摘要

This thesis focused on development of magnesium based composite with enhanced mechanical properties. Near dense monolithic magnesium, micron sized nickel particle reinforced magnesium composite and TiO2 nanoparticle reinforced magnesium nanocomposite were successfully developed using the cost effective powder metallurgy process of blend-press-sinter followed by hot extrusion. Hybrid nanocomposite consisting of 1.5 volume% nickel and 0.33volume% TiO2 was also developed using similar technique.;The developed monolithic and reinforced magnesium composites were characterized to determine the microstructural evolution, particle distribution and grain morphology using appropriate characterization techniques such as XRD, SEM and FE-SEM. The samples were also subjected to microhardness, macrohardness, tensile and compressive tests to determine the effect of the reinforcements on the mechanical properties of magnesium.;The nickel reinforcement particles dispersion was reasonably uniform with good matrix-reinforcement interfacial integrity. The small volume fraction of elemental nickel particle reinforcement refined grain morphology and significantly improved the hardness and tensile strength of the magnesium matrix without affecting the yield strength. However, ductility was adversely affected. The tensile strength was increased by ∼21% with a ∼26% decrease in the fracture strain, the reinforcement changed the tensile fracture mode of magnesium matrix from pseudo-ductile to brittle mode dominated by nickel particle fracture. The room temperature compression properties of the synthesized nanocomposites reveal an increase in the 0.2% compressive yield strength and ultimate compressive strength of pure magnesium up to ∼81% and ∼23% respectively with a ∼18% decrease in the fracture strain.;In the TiO2 reinforced magnesium nanocomposites, microstructural characterization of the nanocomposites reveal significant reduction in grain size of pure magnesium with addition of titanium oxide nanoparticles. The room temperature tensile properties of the synthesized nanocomposites revealed no significant improvement in the strength characteristics of magnesium with the addition of TiO2 nanoparticles, the tensile fracture strain of the synthesized nanocomposites was found to marginally surpass that of pure magnesium and a maximum fracture strain of ∼17% with the addition of 0.33 vol.% TiO2 was obtained. The room temperature compression properties of the synthesized nanocomposites reveal an increase in the 0.2% compressive yield strength and ultimate compressive strength of pure magnesium with no significant change in the fracture strain. With addition of 1.00 vol.% TiO2, the 0.2% compressive yield strength and the fracture strain of pure magnesium increased by ∼65%% and ∼37% respectively. With the addition of TiO2 nanoparticles, the level of anisotropy/asymmetry of pure magnesium measured using tensile compression asymmetry values was found to be lower than that of the synthesized pure magnesium and a minimum of ∼1 for Mg-1.00vol.% TiO2 nanocomposite was observed.;The microstructural characterization of the magnesium hybrid nanocomposite reveals significant grain refinement beyond that of individual nickel and TiO2 particle reinforcements. The simultaneous addition of 1.5vol.% nickel and 0.33vol% TiO2 significantly improved the hardness, tensile strength and fracture strain of the magnesium matrix but with adverse effect on its the yield strength. The room temperature compression properties of the hybrid nanocomposites reveal an increase in the 0.2% compressive yield strength and ultimate compressive strength of pure magnesium up to ∼112% and ∼29% respectively with a ∼12 % decrease in the fracture strain.