Browsing by Author "Nicholls, John"
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Item Open Access Data for the paper titled Analysis of Combined Static Load and Low Temperature Hot Corrosion Induced Cracking in CMSX-4 at 550°C(Cranfield University, 2020-02-03 08:09) Gray, Simon; Brooking, Laurie; Nicholls, John; Sumner, Joy; Simms, Nigel; J. Tatlock, Gordon; Dawson, KarlPresentation containing figures within the paperItem Open Access Environmentally assisted cracking of a single crystal nickel-based superalloy(Taylor and Francis, 2023-03-03) Dawson, Karl; Duarte Martinez, Fabian; Gray, Simon; Nicholls, John; Gibson, G.; Leggett, J.; Tatlock, G. J.Single crystal material, of CMSX-4® alloy composition, was cast and secondary orientation was controlled at the machining stage, to produce c-ring cross-section tubes with known crystallographic orientations. The c-ring tubes were coated with NaCl before being subject to loading up to 700MPa and heated for durations of up to 2 hrs at 550°C in flowing environments containing air and SO2. No cracking was observed in short term tests that were run in the absence of either NaCl, or SO2, indicating a symbiotic interaction is required to initiate cracking. Experiments confirm the presence of oxygen, chlorine and sulphur at the crack tips, formed along {001} crystallographic planes, however, they were distributed discretely, with several oxide and sulphide phases observed. In this work, we image, analyse and identify the phases formed during the cracking and corrosion of CMSX-4® superalloy and hypothesise on the complex chemical interactions that take place during crack initiation.Item Open Access High temperature corrosion of HVOF coatings in laboratory-simulated biomass combustion superheater environments(Springer, 2022-12-26) Pidcock, Andy; Mori, Stefano; Sumner, Joy; Simms, Nigel; Nicholls, John; Oakey, JohnThis study examines the fireside corrosion of FeCrAl, NiCr, NiCrAlY and A625 coatings applied by ‘high velocity oxy fuel’(HVOF) and exposed to simulated biomass firing conditions (gas composition CO2, N2, SO2 and HCl). The coatings and a typical base steel alloy (T92) were exposed to simulated conditions at 600 °C for 1000 h in a laboratory scale furnace. Samples were coated with a potassium chloride deposit. Samples were then cold mounted in a low-shrinkage epoxy resin and then cross-sectioned. Corrosion was assessed by dimensional metrology comparing the coating thickness change of the samples. The cross-sections of the ‘worst’ and ‘best’ coatings were examined. Results show that all but one coating (HVOF NiCr) outperformed the T92 alloy. No coating composition or method was conclusively better. Evidence of Cr depletion as well as the formation of a sulphidation layer have been found in the exposed samples with coatings. The formation of a K2SO4 layer has also been observed on all coated specimens.Item Open Access Pseudo-code: Modelling evaporation in electron-beam physical vapour deposition of thermal barrier coatings(Cranfield University, 2023-08-11 15:26) Chevalier, Julie; Isern arrom, Luis; Almandoz Forcen, Koldo; Chalk, Christine; Nicholls, JohnPseudo-code for EBPVD ingot evaporation computational modelItem Embargo 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, PingThe 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).Item Open Access Thermal Diffusivity Changes of EB-PVD Thermal Barrier Coatings Undergoing Oxidation Ageing.(Cranfield University, 2020-03-13 09:59) Tinsley, Lawrence; Roy, Rajkumar; Mehnen, Jorn; Chalk, Christine; Nicholls, JohnNormalized (apparent) thermal diffusivity values for yttria-stabilised zirconia (7YSZ) Thermal Barrier Coatings undergoing isothermal oxidation ageing with data captured at 16-hour intervals.