Shielding Gas Influence On AA5086 Welded Joints: Residual Stresses Analysis, Microstructural Characterisation and Mechanical Properties

Samples of AA5086 aluminium alloy were welded by gas tungsten arc welding (GTAW) with alternating current using three different shielding gases. The samples were welded with pure argon (Ar), a mixture of argon and helium (Ar + He) and a new mixture composed of argon, nitrous oxide and oxygen (Ar + N2O + O2). The effect of the shielding gas on the residual stresses and on the mechanical and microstructural properties of the welded joints was evaluated and compared with the base metal. The new gas mixture produced compressive residual stresses in the longitudinal and transverse directions in the weld metal. Tensile test of welded joints indicated similar values for yield strength and ultimate tensile strength; however, these values were lower compared to the base metal. The new gas mixture provided a welded joint with hardness values in the weld metal and heat affected zone close to the base metal values and with greater magnitude compared to samples welded using pure argon and mixture of argon and helium. Microstructural characterisation performed by optical and scanning electron microscopy showed that the new mixture produced welded joints with lower porosity.

Photocatalytic Degradation of Methylene Blue Dye by Electrospun Binary and Ternary Zinc and Titanium Oxide Nanofibers

Synthetic dyes, dispersed in water, have harmful effects on human health and the environment. In this work, Ti and/or Zn oxide nanofibers (NFs) with engineered architecture and surface were produced via electrospinning followed by calcination. Calcination and subsequent cooling were operated at fast rates to generate porous NFs with capture centers to reduce the recombination rate of the photogenerated charges. After morphological and microstructural characterisation, the NFs were comparatively evaluated as photocatalysts for the removal of methylene blue from water under UV irradiation. The higher band gap and lower crystallinity were responsible for the lower photocatalytic activity of the ternary oxides (ZnTiO3 and Zn2TiO4) towards the degradation of the dye. The optimal loads of the highly performing binary oxides were determined. By using 0.66 mg mL−1 wurtzite ZnO for the discoloration of an aqueous solution with a dye concentration of 15 µM, a higher rate constant (7.94 × 10−2 min−1) than previously reported was obtained. The optimal load for anatase TiO2 was lower (0.33 mg mL−1). The corresponding rate constant (1.12 × 10−1 min−1) exceeds the values reported for the commonly used P25–TiO2 benchmark. The catalyst can be reused twice without any regeneration treatment, with 5.2% and 18.7% activity decrease after the second and third use, respectively.

Method for the Microstructural Characterisation of Unidirectional Composite Tapes

The outstanding properties of carbon fibre-reinforced polymer composites are affected by the development of its microstructure during processing. This work presents a novel approach to identify microstructural features both along the tape thickness and through the thickness. Voronoi tessellation-based evaluation of the fibre volume content on cross-sectional micrographs, with consideration of the matrix boundary, is performed. The method is shown to be robust and is suitable to be automated. It has the potential to discriminate specific microstructural features and to relate them to processing behaviour removing the need for manufacturing trials.

Design, Development and Evaluation of Thermal Properties of Polysulphone–CNT/GNP Nanocomposites

Polysulphone (PSU) composites with carbon nanotubes (PSU-CNT) and graphene nanoplatelets (PSU-GNP) were developed through the solution casting process, using various weight load percentages of 1, 3, 5, and 10 wt% of CNT and GNP nanofillers. The microstructural and thermal properties of the PSU-based composites were compared. The microstructural characterisation of both composites (PSU-CNTs and PSU-GNPs) showed a strong matrix–filler interfacial interaction and uniform dispersion of CNTs and GNPs in the PSU matrix. The analysis demonstrated that both the thermal conductivity and effusivity improved with the increase in the weight percentage (wt%) of CNTs and GNPs because of the percolation effect. The polysulphone-based composite containing 10 wt% CNTs showed a remarkably high thermal conductivity value of 1.13 (W/m·K), which is 163% times higher than pure PSU. While the glass transition temperature (Tg) was shifted to a higher temperature, the thermal expansion was reduced in all the PSU-CNT and PSU-GNP composites. Interestingly, the CNTs allowed homogeneous distribution and a reasonably good interfacial network of interaction with the PSU matrix, leading to better microstructural characteristics and thermal properties than those of the PSU-GNP composites. The findings highlight the importance of controlling the nature, distribution, and content of fillers within the polymeric matrix.