Browsing by Author "Zhuk, Yuri"

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    Data supporting: 'Surface finishing and residual stress improvement of chemical vapour deposited tungsten carbide hard coatings by vibratory polishing'
    (Cranfield University, 2022-08-31 15:44) Micallef, Christian; Aria, Indrat; Walton, Karl; Zhuk, Yuri
    The images and graphs here include SEM images, AFM scans, plotted surface roughness and residual stress data, schematic diagrams and images of the experimental setup which was used.
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    ItemOpen Access
    Data supporting: 'Surface finishing and tool wear in single point diamond turning of chemical vapour deposited tungsten carbide hard coatings'
    (Cranfield University, 2022-09-15 12:26) Micallef, Christian; Zhuk, Yuri; Aria, Indrat
    The data attached in this dataset include photographs of the experimental setup used to carry out this work, SEM imaging for studying changes to the surface topography of the coating, images outlining changes to the diamond tool tips, 3D optical interferometry images and schematic diagrams.
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    Rapid surface finishing of chemical vapour deposited tungsten carbide hard coatings by electropolishing
    (Elsevier, 2021-11-15) Micallef, Christian; Chiu, Cheng-Wei; Zhuk, Yuri; Aria, Adrianus Indrat
    Tungsten/tungsten carbide (W/WC) coatings deposited through chemical vapour deposition (CVD) exhibit favourable mechanical properties and are widely used to extend the working life and performance of engineering parts which operate in high wear and corrosive environments. Following the coating deposition process, the coated parts must adhere to low surface roughness and geometrical tolerance specifications necessitating the need of a machining or surface finishing operation. Unlike monolithic materials, hard W/WC coatings have low machinability due to their high hardness and superior mechanical properties. In this study, electropolishing, which is independent of the material's hardness and capable of processing parts with complex geometries has been studied as a prospective noncontact machining and surface finishing technique for CVD W/WC coatings. Here we report the electropolishing behaviour of W/WC coatings with an average thickness of 50 ± 15 μm and 1300 ± 50 HV hardness. Optimal electropolishing parameters using 5 wt% sodium hydroxide (NaOH) electrolyte concentration at 21 °C allow a mirror-like surface finish with Ra of less than 50 nm and a change in coating thickness of up to 18 μm to be achieved within 5 min. The change in electrolyte temperature from 21 °C to 40 °C was found to have a significant effect on the electropolishing behaviour due to the formation of a thin and unstable viscous film. The electrolyte concertation of 5 wt% was more stable when compare to 3 wt%, giving an overall better surface finish. EBSD analysis revealed that grains with a {111} orientation were preferentially etched in NaOH.
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    Recent progress in precision machining and surface finishing of tungsten carbide hard composite coatings
    (MDPI, 2020-07-25) Micallef, Christian; Zhuk, Yuri; Aria, Adrianus Indrat
    Owing to their high hardness, fracture toughness and oxidation resistance, tungsten carbide (WC) coatings are extensively deposited on parts that operate in demanding applications, necessitating wear, erosion, and corrosion resistance. The application of thick and hard WC coatings has an inevitable effect on the original dimensions of the parts, affecting the geometrical tolerances and surface roughness. The capability of achieving a sub-micron surface finish and adhere to tight geometrical tolerances accurately and repeatably is an important requirement, particularly with components that operate in high-precision sliding motion. Meeting such requirements through conventional surface finishing methods, however, can be challenging due to the superior mechanical and tribological properties of WC coatings. A brief review into the synthesis techniques of cemented and binderless WC coatings is presented together with a comprehensive review into the available techniques which are used to surface finish WC-based coatings with reference to their fundamental mechanisms and capabilities to process parts with intricate and internal features. The binderless WC/W coating considered in this work is deposited through chemical vapour deposition (CVD) and unlike traditional cemented carbide coatings, it has a homogenous coating structure. This distinctive characteristic has the potential of eliminating key issues commonly encountered with machining and finishing of WC-based coatings. Here, six contact and non-contact surface finishing techniques, include diamond turning, precision grinding, superfinishing, vibratory polishing, electrical discharge machining, and electropolishing are discussed along with their current use in industry and limitations. Key challenges in the field are highlighted and potential directions for future investigation, particularly on binderless WC coatings, are proposed herein
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    Surface finishing and residual stress improvement of chemical vapour deposited tungsten carbide hard coatings by vibratory polishing
    (Elsevier, 2022-04-21) Micallef, Christian; Walton, Karl; Zhuk, Yuri; Aria, Adrianus Indrat
    Hard coatings are widely used in several industries to improve the service life of engineering components. W/WC coatings deposited through chemical vapour deposition (CVD) have the capability of providing the required protection on parts with complex geometries, commonly used in high wear and corrosive environments. Despite the improvement in service life, a key important factor is the adherence to low roughness and tolerance specifications, necessitating the need of a post-coating finishing process. In this work the impact of vibratory polishing on W/WC coating was studied using a vibratory barrel setup and two types of ceramic-based media. An improvement in average Ra of 0.2–0.3 μm was achieved over a duration of 4 h with abrasive wear being the predominant polishing mechanism. Insignificant weight loss (<0.017 g) and hardness changes (−2 < ΔHV < 8) were confirmed while the compressive residual stresses of the coating were found to increase with process time (max Δσ = −1058.3 MPa)
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    Surface finishing and tool wear in single point diamond turning of chemical vapour deposited tungsten carbide hard coatings
    (Elsevier, 2022-09-09) Micallef, Christian; Zhuk, Yuri; Aria, Adrianus Indrat
    Precision-engineered components which operate in demanding conditions often require the application of hard coatings such as tungsten carbide (WC) to improve their functional properties. Following the coating deposition process, a surface finishing or machining operation is often required to correct the sizing or achieve adherence to geometrical tolerancing and surface finish requirements. Single point diamond turning (SPDT) is a widely used ultraprecision machining technique for the fabrication of high-end engineering components made up of ductile materials, making it a desirable technique as a post-coating machining or finishing process. In this study the machinability of hard CVD W/WC coatings with a hardness of 1120 ± 15 HV and a thickness of 100 μm using SPDT was investigated. Here we report the results of axial and transverse turning using a cutting speed of 600 rpm and feed rates of 1 and 5 μm respectively. Experimental results show that an Ra of 0.2 μm is achieved with a diamond tool having a 0.5 mm nose radius. Significant tool wear was observed at the rake/flank edge of the diamond tool due to the coating's hardness. Surface and cross-sectional analysis of the samples' machined areas revealed presence of adhesive and abrasive wear. The occurrence of material pile-up due to tool loading on the surface of the coating was investigated through the indentation technique which demonstrated the occurrence of material deformation contributing to the overall surface roughness.