Browsing by Author "Duarte Martinez, Fabian"
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Item Open Access Data for the paper "Molecular dynamics simulation of the elliptical vibration assisted machining (EVAM) of pure iron"(Cranfield University, 2018-07-31 16:20) Goel, Saurav; Duarte martinez, Fabian; Giusca, ClaudiuData files used for figures 3 and 5 in the associated article from the Journal of Micromanufacturing. These need to be opened in the Origin software (https://www.originlab.com/).Item Open 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, K.; 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.Item 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 Investigation into the environmental assisted crack initiation mechanism of CMSX-4 in simulated aero engine environments at 450 - 550°C.(Cranfield University, 2023-03) Duarte Martinez, Fabian; Nicholls, J. R.; Gray, Simon; Castelluccio, Gustavo M.The aviation industry has continued to increase the efficiency of gas turbine engines, which are now designed to operate on a wide variety of flight routes. In general, the efficiency drive has led to components spending longer times at temperatures, where accelerated corrosion can occur. This has led to a complex degradation mechanism being identified in the lower shank region under the platform of single-crystal turbine blades. This research aims to understand the mechanism of crack initiation due to the synergistic effect of stress and high temperature corrosion environments on CMSX-4 in the lower operating temperature range, 450°C - 550°C, of an aero gas turbine blade. The first part of the investigation consisted in comparing the effect of different salt deposits in a 50 ppm SO₂ - air environment at 550°C. A 50 ppm SO₂ – air concentration was considered because the air going through the lower shank is fed directly from the compressor, and not from the combustor (which is the main source of sulphur). Characterisation of the resulting scales were carried out using scanning electron microscopy, energy dispersive spectroscopy and X- ray diffraction. Results from thermodynamic modelling are also presented. The first part of the investigation showed that CMSX-4 sample under an applied stress and no applied salt did not experience accelerated corrosion attack or crack formation when exposed to 50 ppm SO₂ - air in a 400-hour period. The same observation was made for a CMSX-4 sample under an applied stress and salted with CaSO₄. Sea salt caused accelerated corrosion attack with cracks up to 1.3 mm through the substrate formed after 400 hours of exposure. Further tests using NaCl salt in 50 ppm SO₂ – air showed that cracks can initiate after just 10 minutes of exposure at 550°C. Crack growth rates are significantly reduced after two hours of exposure within a 50-hour salt cycle. Cracks with NaCl in 50 ppm SO₂ – air have also been observed at temperatures as low as 450°C. When NaCl salt was applied to CMSX-4 and exposed to air only for 50 hours, the corrosion attack was reduced considerably, and the initiation of cracks is either suppressed or significantly delayed beyond a 50-hour period. Although this PhD has only focused on a 50-hour period, longer exposure times should be carried out to determine if air exposures delay crack initiation time, or if crack initiation is completely supressed. This thesis has therefore shown that the interaction of stress, NaCl and a sulphur- containing environment are critical to cause early crack initiation in single crystal nickel-based superalloys in the temperature range 450 - 550°C. The effect of having small concentrations of moisture in the gaseous environment or as inclusions retained in the salt are still to be investigated. A working hypothesis is that 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 leads to high amounts of H₂ formed at the scale/alloy interface. Potentially, the H₂ formed at the alloy/scale interface may dissociate into atomic hydrogen, and lead to hydrogen embrittlement. For further verification of this hypothesis, a set of tests have been suggested.Item Open Access A microscopy study of nickel-based superalloys performance in type I hot corrosion conditions(Taylor and Francis, 2023-03-10) Waeytens, Manon; Syed, Adnan U.; Roberts, Tracey; Duarte Martinez, Fabian; Gray, Simon; Nicholls, John R.Alloy material selection for sustainable, efficient, and cost-effective use in components is a key requirement for both power generation and aerospace sectors. Superalloys are manufactured using a combination of different elements, selected carefully to balance mechanical performance and environmental resistance to be used in a variety of different service conditions. Therefore, a fundamental understanding of each element is critical to alloy design. In this paper, the interaction of alloy chemistry, particularly chromium as a corrosion-resistant element along with titanium and molybdenum, and their effect on alloys performance for the relevant gas turbine industries were discussed. Based on the findings, the single-crystal alloy is found to be a better corrosion resistant alloy exhibited higher corrosion resistance in comparison to polycrystal alloys and proved that microstructure has a significant impact on alloy performance. This study also established that molybdenum level in chromia former alloys can significantly enhance the corrosion damage.