Browsing by Author "Dawson, Karl"

Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen Access
    Analysis of combined static load and low temperature hot corrosion induced cracking in CMSX-4 at 550°C
    (Elsevier, 2019-10-18) Brooking, Laurie; Gray, Simon; Dawson, Karl; Nicholls, John R.; Simms, Nigel J.; Sumner, Joy; Tatlock, G. J.
    A CMSX-4 3-point bend specimen was statically loaded under hot corrosion conditions and SEM, (S)TEM and EDX techniques were used to analyse the cracking generated. Sulphur, chlorine, sodium and oxygen were found at the crack tip, and an influence of loading on the corrosion mechanism’s preference to interact with either the γ or γʹ was observed. The microscopy analysis is in support of the corrosive mechanism being a combined stress and electrochemical corrosion linked with low temperature hot corrosion, where crack propagation occurs as a result of localised corrosion enhanced material degradation. High magnification EDX mapping identified W as segregating to the γʹ at room temperature.
  • Thumbnail Image
    ItemOpen Access
    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.
  • No Thumbnail Available
    ItemOpen 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, Karl
    Presentation containing figures within the paper
  • Thumbnail Image
    ItemOpen Access
    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.
  • Thumbnail Image
    ItemOpen Access
    Effects of surface hardening by laser shock peening and shot peening on a nickel-based single-crystal superalloy CMSX-4
    (IOP Publishing, 2024-07-31) Hakeem, Aabid Husen; Morar, Nicolau I; Dawson, Karl; Tatlock, Gordon J; Gibson, Grant J; Gray, Simon
    Improving the expected life of nickel-based single-crystal superalloy turbine components by surface hardening treatments including laser shock peening (LSP) and mechanical shot peening (MSP) are of particular interest for mitigation of life limiting damage such as environmental assisted cracking in hot section components of gas turbines. In the present study the effects of LSP and MSP on the surface roughness, microhardness and work hardening of a nickel-based single crystal superalloy CMSX-4® have been assessed. Surface roughness was measured using laser profilometry. The degree of work hardening was measured using electron backscattered diffraction with local misorientation analysis. The analysis showed evidence for a work hardening layer in the MSP sample to a depth of approximately 70 μm. Sets of slip bands extending far into the bulk of the sample were observed in the LSP-treated sample, without any evidence of a work hardening layer. Microhardness measurements used to gauge the depth of residual stress showed that LSP produced a much deeper hardness profile than MSP, with compressive residual stress depths of 1000 μm and 200 μm in LSP and MSP respectively. The retention of hardness after a heat treatment of 50 h at 700 °C was more prominent in the LSP sample than in the MSP sample. LSP and MSP have therefore been shown to be at the opposite ends of the spectrum of surface hardening treatments of CMSX-4, with LSP giving milder hardening, but to a greater depth.
  • Thumbnail Image
    ItemOpen 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.