Abstract
Abstract : In this study, duplex stainless steel (DSS) micro-powders and titanium nitride (TiN) nanopowders were blended in a tubular mixer. The motivation for choosing to incorporate TiN into duplex stainless steel is develop DSS with improved wear and mechanical properties. The Characterization of the mixed powders was performed using X-ray Diffraction, Transmission Electron Microscopy and Scanning Electron Microscopy. The mixed powders were consolidated using automated spark plasma sintering machine (model HHPD-25, FCT GmbH Germany). Characterization of sintered TiN nanoparticle reinforced DSS was performed using X-ray Diffraction (XRD) and Scanning Electron Microscopy equipped with Energy-dispersive X-ray spectroscopy (EDS), Electron backscattered diffractions (EBSD) and Transmission kikuchi diffraction (TKD). Densities and hardness of the developed composite were investigated. The mechanical properties and tribological properties of the DSS strengthened with varied amounts of TiN nanoparticles were evaluated using nanoindentation system and tribometers respectively. This study produced seven (7) papers, each of the paper respectively investigated (1) the past works that have been conducted on mechanical alloying and SPS of stainless steels and composites (2) the optimization of SPS process parameters in terms of in terms of sintering temperature, holding time and heating rate for the development of a nanostructured duplex stainless steel reinforced with titanium nitride (TiN), (3) the effect of sintering parameters (sintering temperature and holding time) on the microstructure, corrosion and wear behaviour of the nano-strutured stainless steel composite (4) the effects of TiN nanoparticles addition on displacement and shrinkage rate, microstructure, density, hardness and fracture surface of the duplex stainless steels composite (5) phase transformations and grain boundary interactions associated with the dispersion of TiN nanoparticles into DSS (6) the influence of TiN nanoparticle addition on mechanical properties such as elastic, plastic, strain-to-break (H/Er) and plastic deformation (H3 /Er2 ) parameters of the stainless steel composites (7) the effects of TiN reinforcement on wear properties of coefficient of friction, wear loss, wear and specific wear rates under dry sliding conditions and varying loads and worn surface. The following results were obtained. During optimization of SPS parameters, the XRD result showed the evolution of iron nitride phase while the EDS analysis revealed the presence of nano ranged nitride particles segregated at the grain boundaries of the duplex matrix. A decrease in hardness and densification was observed when sintering temperature and heating rate were 1200...
Ph.D. (Metallurgy)