Browsing by Author "Brewster, Gyaneshwara"

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    The effect of volatilisation of refractory metal oxides on the cyclic oxidation of Ni-base superalloys
    (Springer Science Business Media, 2014-04-01T00:00:00Z) Brewster, Gyaneshwara; Edmonds, I. M.; Gray, Simon
    The role of refractory metals on the bare oxidation behaviour of a range of compositionally complex single crystal Ni-base superalloys has been investigated using a range of techniques. It has been shown that this series of fourth generation alloys were borderline alumina formers at 1,100 °C, and their cyclic oxidation performance was detrimentally affected by increased levels of Mo and Co. In addition, there was strong evidence that Re, Ru and Mo were lost through the process of cyclic oxidation, which supports the hypothesis that these elemental additions were lost through volatilisation/sublimation, contributing to their poor cyclic oxidation performance.
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    Strain tolerance evolution of EB-PVD TBCs after thermal exposure or CMAS attack
    (Elsevier, 2023-08-28) Gao, Zhaohe; Zhang, Xun; Chen, Ying; Chalk, Christine; Nicholls, John; Brewster, Gyaneshwara; Xiao, Ping
    The microstructural evolution and Young’s modulus evolution of EB-PVD TBCs upon thermal exposure and separately after CaO-MgO-Al2O3-SiO2 (CMAS) attack have been compared and investigated. Moduli measured by four methods all show an increase due to sintering whereas their rates of increase are different. On finer scale (i.e. nano indentation), modulus increases from 87.3 GPa in as-deposited coatings to 198 GPa after sintering at 1400 °C for 100 h. While on global scale, the modulus increases from below 10 GPa to153 GPa after identical exposure. For the CMAS attacked TBCs at 1300 °C for 0.5 h, modulus values acquired by different methods are much closer. The effect of sintering and CMAS infiltration on coating’s structural integrity is discussed in terms of elastic strain energy available for driving edge delamination. The energy release rate of CMAS attacked TBCs at 1300 °C for 0.5 h is ∼1200 J/m2, which is equivalent to that of TBCs exposed at 1400 °C for 250 h (no CMAS).