The high load-bearing ability of cylindrical roller bearing made its usage in rotating machinery popular. However, the performance of this bearing is impeded by the contact stress, stiffness and the temperature rise experienced operation. In this study, the thermomechanical behaviour of martensitic stainless steel (X20) fabricated roller bearing with polyamide pin type cage subjected to different rotating/operating speeds was simulated using finite element analysis software, Abaqus. The outcome of the analyses shows that the temperature, heat flux, contact or Hertzian stress and frictional energy developed in the bearing during operation increases with a corresponding increase in speed. It was further observed that a slight increase in the operating speed of the bearing leads to a significant rise in the temperature and frictional energy developed in the bearing. Also, the maximum Hertzian/contact stress was observed to developed on the outer ring of the roller bearing assembly (at the point of contact between the outer ring and the balls) in all the operational speeds considered. Thus, making this outer ring more susceptible to failure during operation as compared to the other components of the bearing.

The industrial application of the spheroidization process using high-temperature plasma is regarded as a good method for the conversion of irregularly shaped particles into a spherica shape. High temperature and controlled plasma conditions are required to obtain satisfactory results. Given this, a 3D model was used to simulate heat transfer from a source term to titanium-alloy particles using ANSYS Fluent software. Such models consider the effects of particle treatment on thermodynamic and transport properties of the plasma. This present study aims to investigate the impact of heat transfer on the particles and the effect of radiation energy loss on the particles, using numerical analysis. The results showed that the operating condition such mass flow was inversely proportional to the rate of heat transfer between plasma particles and the characteristics of the plasma gas, which was due to significant variation in radiation energy losses.

Copper alloys are typically produced by conventional casting processes, including spark plasma sintering (SPS), which often produce inhomogeneous mixtures of Cu or Al precipitates and unwanted intermetallic phases in solid products. Induction melting should provide good mixing, controlled heating and melt stirring, potentially improving homogeneity. Homogeneous melts should produce homogeneous powders, giving better properties in additive manufacturing (AM). To ascertain homogeneity, a density test was developed. After comminution, homogeneous powders can be used to produce high quality components. To manufacture dense AM components, spheroidised powders are needed because they increase particle packing and powder flow. An Al-50Cu (at.%) button was produced by high-frequency (HF) induction melting, to give better mixing and hence phase distributions. To identify the phases and their distributions, the as-cast sample was studied using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD), as well as absolute density using helium pycnometry. Results indicated inhomogeneity in the samples, due to Al loss, complex solidification and the densest phase settling at the bottom of the button.

This work reports on a simple approach to improving the optoelectronic properties of Wurtzite ZnO nanoripples by means of incorporating hydrothermally synthesised ZnO nanoparticles under controlled synthesis temperature. Initially, ZnO nanoparticles were investigated and subsequently utilised as seeds to induce ripple growth in spin-coated ZnO thin films. TEM images illustrated the development of nanospheres at 140°C. The yield of ZnO NPs at 180°C increased and consisted of a combination of nanorods and nanospheres. Morphologically, seedless ZnO nanoripples showed rugged ends of the nanoripple structures. The SEM images illustrated that the layers uniformly formed on the substrates, and seeding the ZnO nanoripples caused the nanoripples to elongate. The thickness of the nanoripples thin films showed a decrease with the incorporation of hydrothermally synthesised ZnO seeds from 134 nm for unseeded ZnO nanoripples to 96 nm at 180°C. The incorporation of ZnO NPs seeding treatment increased the transmission of ZnO nanoripples from 82% to 92%, leading to untreated ZnO nanoripples exhibiting a direct band gap of 3.19 eV that increased after seeding to 3.36 eV. The change in the band gap to a higher value(s) and increased transparency confirms the progressive improvement of the thin films due to incorporating ZnO seeding for optoelectronic and photovoltaic applications.

This work investigated the influence of heating temperature (°C) on the microstructure and microhardness of TiB/Ti6Al4V-ELI composite clads that were produced via in-situ alloying using laser metal deposition technique. The samples were produced on a Ti6Al4V base plates which were heated at different temperatures (25°C, 200°C, 300°C, 400°C and 500°C) before they were characterised for microstructure and hardness. It was found that the TiB/Ti6Al4V-ELI sample that was produced on a non-pre-heated base plate was characterized by TiB particles and had the lowest hardness of 511 ± 66 HV. Base plate heating resulted in the formation of TiB whiskers that were dispersed within the titanium matrix. 200°C led to a microstructure with clusters of TiB whiskers hence it had an increased hardness of 651 ± 40 HV. A fine microstructure with homogeneous distribution of the TiB whiskers was obtained at 500°C base plate heating temperature and had hardness of 565 ± 14 HV.

Fe-Co alloys are considered good candidates for high-temperature applications due to their high saturation magnetisation and Curie temperature. However, these alloys show low levels of ductility at room temperature. In this study, cluster expansion was employed to probe the thermodynamic stability of the FeCo1-XVX and Fe1-XCoVX alloys. Ten new stable structures were found from both FeCo1-XVX and Fe1-XCoVX systems. Their stability was observed by deducing the heats of formation, and it was found that VFeCo2 and VFe2Co (P4/mmm) are the most thermodynamically stable phases. The results also showed that vanadium prefers the Co-site rather than the Fe-site substitution. The calculated Pugh’s ratio and Poisson’s ratio confirm that alloying with V effectively improved the ductility. It was also found that VFeCo2, VFe2Co, VFe4Co3 and FeCo showed a positive shear modulus condition of stability for the structures. The ternary addition of V in the FeCo system resulted in enhanced magnetic properties. Thus, ternary systems with vanadium addition enhance the ductility of the Fe-Co systems, and these alloys could be used to develop future magnets.

As South Africa moves towards the production and storage of green energy sources, proton exchange membrane (PEM) fuel cells have been characterized as promising energy sources for transportation, heating, and power sources and have an efficient energy conversion that does not allow greenhouse gas emissions. However, to improve the energy efficiency and to reduce the system cost, and make it suitable for large-scale commercialization, precious metal catalyst needs to be developed with improved catalyst activities for PEM fuel cells. Due to the high cost of platinum, platinum alloy nanostructures have been investigated for use as an electrocatalyst in PEM fuel cells. Platinum-nickel alloy nanostructures in previous research studies have shown 36- and 22-times enhancement in mass and specific activity respectively, towards the cathodic oxygen reduction reaction (ORR) in PEM fuel cells and for the methanol oxidation reaction (MOR) in direct methanol fuel cell (DMFC) than the Pt/C catalyst. Therefore, this research focused on developing rich Pt-skin platinumnickel nanoframes which were synthesized using solvothermal and in-house developed methods. The intermediate products were etched to remove the interior using either a weak acid or an oxidative acid for comparison. The final product was supported by Vulcan XC-72 at a loading of 20 wt. % Pt-Ni. The properties of Pt-Ni/C will be characterized and evaluated to determine if the nanoframes are formed. The preliminary results for the X-ray diffraction pattern showed that the structure of Pt-Ni contracted and affected the catalyst properties. The catalytic activities were determined by electrochemical methods using thin-film RDE measurements, the results indicated that Pt-Ni as-synthesized has higher specific activity at 900 mV versus RHE. The specific and mass activity of the oxygen reduction reaction for Pt-Ni/C will be compared to the activities of the current high-performing Pt/C catalyst.

Recently, laser additive manufacturing (LAM) technologies are increasingly being applied for producing components with excellent physical and mechanical properties in the aerospace, automotive and energy industries. This work is aimed at modelling the fatigue usage factor of γ-TiAl alloy fabricated through LAM. The modelling and simulation were performed using the COMSOL Multiphysics 5.4 software by developing a y-TiAl alloy microstructure. This was modelled to generate the material properties (density, heat capacity at constant pressure and thermal conductivity) from the microstructure of a unit cell as a general representation of the alloy. The computed properties were used in modelling the LAM process to fabricate γ-TiAl alloy part with subsequent fatigue simulation to determine the usage factor (Ke). From the models, the maximum Von Mises stress and transient temperature were 2.88 x108 Nm-2 and 1510 K respectively, for the LAM fabrication process; while the fatigue usage factor model showed a maximum Von Mises stress of 2.91 x108 Nm-2 and a fatigue usage factor of 0.35.