Browsing by Author "Nkosi, Nompumelelo Venessa"

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    Development of Ti6Al4V-Cr3C2 metal matrix composites using selective laser melting
    (Stellenbosch : Stellenbosch University, 2024-03) Nkosi, Nompumelelo Venessa; Sacks, Natasha; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.
    ENGLISH ABSTRACT: The manufacturing of titanium alloys and metal matrix composites (MMCs) using selective laser melting (SLM) has seen a rapid growing trend over the years. This is due to the developing manufacturing technologies and the demand of attractive and improved engineering components for industrial use in aerospace, medical, and automotive sectors. The dual α-β phase titanium alloy; Ti6Al4V has found its great application in the manufacturing of turbine blades and engine components in aerospace due to its high lightweight-to-strength ratio and good combination of properties. There is always a need to further improve these mechanical properties and performance, hence the concept of the addition of metal carbides to the Ti6Al4V matrix which studies have found to have a great strength hardening effect and results in an increase in the specific strength of the composite, thus increasing the component’s life span. This study focuses on the feasibility of manufacturing metal matrix composites of the Ti6Al4V matrix reinforced with chromium carbide (Cr3C2) using selective laser melting. A scoping review was conducted to evaluate the status of SLM and its application in the manufacturing of titanium MMCs using metal carbides and it was found that the most used carbide was TiC due to its compatibility with Ti6Al4V and its attractive properties. It was also reported that the main influential SLM processing parameters were the laser power, hatch distance, scan speed and the scanning strategies which all played key roles in determining the quality of the parts. These studies were then used to choose Cr3C2 as a reinforcing material due to the high hardness, corrosion and wear resistance and comparable low density as compared to other commonly used carbides. In addition to this, Cr3C2 is a grain refiner, therefore this property aids in improving the Ti6Al4V properties using grain refinement mechanisms and since chromium is a beta stabilizer, it’s addition to Ti6Al4V will lead to the improvement of the ductility and toughness of the final MMC. The design thinking problem solving approach was used to carry out the experimental methodology. Powder characterisation for the feedstock powders was conducted to determine the flowability, apparent density, morphology, particle size and composition. The Ti6Al4V alloy samples were initially printed using the SLM machine optimised parameters, characterised and the mechanical properties were used as benchmark for the addition of the Cr3C2. Two compositions of Cr3C2 (5 wt% & 10 wt%) powders were added to the Ti6Al4V powder to make individual mixtures that were used as feedstock for SLM. The design of experiment planning was used for SLM parameter optimization of Ti6Al4V-Cr3C2 whereby the parameters were tailored, and the response of the prints was evaluated. The effect of the scanning strategy, laser power, scanning speed and hatch distance on the density, microstructure, hardness, and tensile behaviour was studied, and the optimal conditions were determined for the compositions to obtain crack-free Ti6Al4V-Cr3C2 composites. The optimal composites were heat treated and the hardness, microstructure and tensile properties were compared with as-built Ti6Al4V properties to evaluate the effect of the annealing heat treatment.