Browsing by Author "Syed, Adnan"

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    Chlorine-induced stress corrosion cracking of single crystal superalloys at 550 °C
    (Springer, 2024-08-05) Duarte Martinez, Fabian; Dawson, Karl; Tatlock, Gordon; Leggett, J.; Gibson, G.; Mason-Flucke, J. C.; Nicholls, John; Syed, Adnan; Morar, N.; Gray, Simon
    This study has investigated the effect of NaCl and different gaseous environments on the stress corrosion cracking susceptibility of CMSX-4 at 550 °C. The presence of SOx leads to the rapid dissociation of NaCl into Na2SO4 and the release Cl2 and HCl, which then trigger an active oxidation mechanism and stress corrosion cracking. The incubation time for crack initiation at 690 MPa and in the presence of a sulphur containing environment is 10 min. A working hypothesis is that stress corrosion cracking occurs due to the hydrogen released at the oxide/alloy interface when metal chlorides are formed; however, this hypothesis needs to be further explored.
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    Effect of NaCl and SO2 on the stress corrosion cracking of CMSX-4 at 550°C
    (Taylor and Francis, 2023-05-01) Duarte Martinez, Fabian; Syed, Adnan; Dawson, Karl; Tatlock, G. J.; Morar, N. I.; Kothari, M.; Tang, C.; Leggett, J.; Mason-Flucke, J. C.; Gibson, G.; Nicholls, Nicholls, John R.; Gray, Simon; Castelluccio, Gustavo M.
    In the pursuit of more efficient gas turbine engines, components are required to operate for longer times at elevated temperatures. This increased time in service, together with a complex loading regime, can expose the material to environmental attack. This work has demonstrated that the interaction of stress, NaCl and a sulphur-containing environment is critical to cause crack initiation in the early stages of the exposure and accelerated corrosion rates in CMSX-4 at 550°C. The effect of having small concentrations of moisture in the gaseous environment or as water crystallisation in the salt is still to be investigated. A working hypothesis is that the interaction of alkali chlorides with a sulphur-containing atmosphere is the trigger to a self-sustaining cycle where metal chloride formation, vaporisation and oxidation lead to high amounts of hydrogen injection in a rapid manner and, therefore, hydrogen embrittlement.
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    Fireside corrosion study of superheater materials in advanced power plants
    (Cranfield University, 2011-10) Syed, Adnan; Simms, Nigel J.; Oakey, John
    Conventional power plants are major emitters of CO2 gases, which are believed to be contributing to global warming. An efficient, co-firing biomass-coal power plant with oxy-firing combustion system (running at high steam temperature and pressure), can play a vital role in CO2 emission reduction. However, these techniques will further worsen the issue of fireside corrosion of heat exchangers. An increase in fireside corrosion rates can cause short component lives and unexpected failures if not dealt with appropriately. The aim of this PhD study was to use laboratory-based testing to assess the performance of alloy materials under superheater conditions in simulated co-fired (biomass and coal) air and oxy-fired combustion. In this PhD project five different alloys were used. Synthetic deposits were also prepared to simulate superheater deposit compositions. Tests were carried out at temperatures appropriate for metal temperatures in superheaters/reheaters of future power plants. The performance of samples was determined using: mass change data, advanced microscopy techniques, x-ray diffraction and dimensional metrology. Additional tests were carried out to investigate deposit stability and the effect of high concentrations of salts. The results achieved have confirmed the hypothesis that increased fireside corrosion rates are due to the combined effect of extreme environment: high temperatures, SO2 and HCl gases, aggressive deposits. Corrosion damage follows trends that resembles ‘bell-shaped’ curve in both air and oxy-fired conditions. Alloy corrosion damage in novel oxy-firing compared to air-firing conditions was significantly higher at 700C. The peak of the curve shifts from 650 to 700C in oxy-fired conditions. The alloys with higher chromium content clearly showed better corrosion resistance. The work on deposit chemistry and exposure to high salt concentrations has improved the understanding of corrosion reaction mechanisms. Corrosion damage data have been used to produce basic fireside corrosion mathematical model; which can be used as a stepping stone towards further development of fireside corrosion models.
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    Medium entropy alloys for biomedical applications
    (Cranfield University, 2024-06-07) Zhang, Jiacheng; Stiehler, Martin; Syed, Adnan; Jorge Jr, Alberto Moreira; Jolly, Mark R.; Georgarakis, Konstantinos
    High entropy alloys (HEAs) is a rapidly emerging class of metallic materials consisting of four or more elements in equimolar or quasi-equimolar compositions. These alloys often have simple crystal structures and tailorable properties attracting significant interest for different applications. Common metallic materials for orthopaedic and dental implants include stainless steel, Co-Cr and Ti- alloys. Although these materials are widely in use, issues relevant to biocompatibility and suspected toxicity and the elastic modulus mismatch compared to that of hard tissue have been raised in recent years. High entropy alloys specifically designed for bio-medical applications can offer solutions to overcome these limitations. Bio-HEAs have emerged in the last couple of years and currently receive increasing scientific attention. In this work, we discuss on the design of new entropic alloys using only non-toxic elements such as Ti, Zr, Nb, Ta and Mo. We use a systematic approach to investigate the effect of additional elements on the microstructure and properties of the alloys starting from the binary Ti-Nb and extending to the ternary Ti-Zr-Nb, the quaternary Ti-Zr-Nb-Ta and the Ti-Zr-Nb-Ta-Mo alloy. The alloy design is building on previous work on beta Ti- alloys which has shown promising trends for reducing the elastic modulus of implant materials. The alloys were produced by arc-melting and suction casting under Ar inert atmosphere. X-ray diffraction, and scanning electron microscopy were employed to reveal their crystal structure and microstructure. respectively. The developed alloys exhibit BCC crystal structure and a dendritic microstructure in their as-cast condition. The addition of Zr and Mo was found to increase the hardness of the alloys.