Browsing by Author "Bishop, Alex"

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    Atmospheric pressure plasma etching of Ti-6Al-4Vusing SF₆
    (Cranfield University, 2023-06) Bishop, Alex; Huang, Zhaorong; Giusca, Claudiu; Long See, Tian
    Atmospheric pressure plasma (APP) etching using SF₆ has been shown to etch Ti- 6Al-4V (Ti64). Operating parameters for input power, SF₆ concentration and standoff distance were determined through previous work as 1.2 kW, 0.8 L min⁻¹ and 6mm respectively as the optimum values for etching using the Helios 1200 machine. By using various surface characterisation techniques, information over a broad range of spatial frequencies was obtained. By conducting stationary, dynamic and areal etching, the process has been shown a high degree of precision and material removal rates varying from 0.5 mm3 min⁻¹ to 2 mm³ min⁻¹ . This process preferentially etches the BCC β phase of Ti64 over the HPC α phase by∼50 %. It is proposed that this preferential etching of the β phase is due to both the crystal structure strength being weaker than the α phase and the BCC crystal structure being less dense than HPC, making it easier to remove more volume of material. The etching process is highly temperature dependent and preheating of the samples is required to achieve a clean trench. Significant amounts of redeposition also remain on the surface <2 µm which comprise of mostly fluorine and oxygen, but this is easily removed. The surface remains optically opaque after etching due to significant roughening of the surface, however negligible contamination remains. The proposed material removal mechanism is through the formation of volatile VFₓ and TiF₄ compounds.
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    Effect of plasma processing parameters on the surface modification of fibre reinforced composites by atmospheric pressure plasma treatment
    (euspen, 2021-06-10) Frumosu, Lydia; Bishop, Alex; Castelli, Marco; Bennett, Adam; Nicholls, John R.; Huang, Zhaorong
    This report presents a study on the effect of microwave plasma sources on the surface modification of carbon fibre reinforced composites. The adhesion property of polymer composites is an important consideration in manufacturing processes. A key challenge in polymer adhesion is the need for adhesive pre-treatment to improve the wettability properties of the surface. Often three sequential steps are needed: contaminant removal, physically induced surface modification and chemical treatment. Atmospheric plasma treatment (APT) has been shown to either achieve, or eliminate the need for, one or more of these steps. The effects of APT on the surface properties of thermoplastics and thermosetting polymers have been reported recently, but the report on the effect of different plasma sources on the APT of polymers is limited. 50% carbon fibre epoxy samples were subjected to a microwave plasma source with varied flow rate, power, and samples’ distance from source, under atmospheric conditions. The surface energy of the composites was determined using liquid contact angle analysis. A coherence scanning interferometer was used to characterise the surface changes. The underlying mechanisms for the observed change of surface properties will be discussed.
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    Large-scale manufacturing route to metamaterial coatings using thermal spray techniques and their response to solar radiation
    (Springer, 2021-07-04) Faisal, Nadimul Haque; Sellami, Nazmi; Venturi, Federico; Hussain, Tanvir; Mallick, Tapas; Muhammad-Sukki, Firdaus; Bishop, Alex; Upadhyaya, Hari; Katiyar, Nirmal Kumar; Goel, Saurav
    Metamaterials, an artificial periodic two- or three-dimensional configuration can change propagation characteristics of electromagnetic waves (i.e., reflection, transmission, absorption). The current challenges in the field of metamaterial coatings are their manufacturing in large scale and large length scale. There is a clear need to enhance process technologies and scalability of these. Thermal spraying is a method used to deposit small to large scale coatings where the sprayed layer is typically formed by successive impact of fully or partially molten particles of a material exposed to various process conditions. This work aims to investigate the feasibility to manufacture large scale metamaterial coatings using the thermal spray technique and examine their response to solar radiation. Two types of coatings namely, Cr2O3 and TiO2 were deposited onto various substrates (e.g., steel, aluminium, glass, indium tin oxide (ITO) coated glass) with a fine wire mesh (143 µm and 1 mm aperture sizes) as the masking sheet to manipulate the surface pattern using suspension high-velocity oxy-fuel thermal spraying (S-HVOF) and atmospheric plasma-sprayed (APS) methods, respectively. Post deposition, their responses subjected to electromagnetic wave (between 250 nm to 2500 nm or Ultraviolet (UV)-Visible (Vis)-Infrared (IR) region) were characterised. The additional microstructural characterisation was performed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), three-dimensional profilometry and optical spectroscopy. It is demonstrated that through novel application of thermal spray techniques, large scale manufacturing of metamaterial coating is possible, and such material can affect the electromagnetic wave propagation. Comparison between Cr2O3 and TiO2 coatings on aluminium substrates showed reduced three orders of reduced reflectance for Cr2O3 coatings (for 1 mm aperture size) throughout the spectrum. It was concluded that for a similar bandgap, Cr2O3 coatings on aluminium substrate will yield improved optical performance than TiO2 coating, and hence more useful to fabricate opto-electronic devices.