Abstract
Binderless ultra–tough titanium carbonitride (TiCN) was successfully consolidated by spark plasma sintering. The impact of blending and milling parameters on the formation of titanium carbonitride from milled titanium nitride, graphite and multiwalled carbon nanotube (MWCNTs) admixture were investigated. The effect of wet milling and dry milling on the phases and morphology of the developed composites were also studied. The morphology, microstructure and the chemical composition of as – received powders, admilled powders and the sintered compact were characterized by using energy dispersive Xray spectroscopy (EDS), X-ray diffractometer, and scanning electron microscopy respectively. The varying compositions of the ad-milled powders were sintered at 100 oC/min (heating rate), 10 mins (holding time), 50 MPa sintering pressure and 2000 oC (sintering temperature). Vickers hardness test, fracture toughness and modulus of elasticity were carried out on the sintered sample to evaluate the mechanical properties. The sintered TiN-based composites were completely formed without cracks, however with very fewer pores, an indication of a good metallurgical bonding quality achieved at the composite grain boundary interface. The structure of the grains has completely transformed to bimodal grains within the composites at 1 wt.% graphite in TiN for 40 h of milling, and subsequent composites developed was based on the result obtained at 1 wt.% graphite in TiN for 24 and 40 h of milling at different compositions. Much increment was observed in microindentation hardness and fracture toughness values of the sintered compact as the percentage graphite increased. The results show that grain size of the sintered sample decreases as the percentage composition of graphite/MWCNTs particles and milling time increases. Based on the results of the analysis, it was concluded that the incorporation of graphite/MWCNTs enhances the microstructures which ultimately are crucial to the mechanical behaviour of the sintered compacts.
D.Phil. (Metallurgical Engineering)