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Investigation into the Effects of Salt Chemistry and SO2 on the Crack Initiation of CMSX-4 in Static Loading Conditions

Martinez, D., Morar, N. ORCID: 0000-0001-9109-8864, Khotari, M. & Gray, S. (2020). Investigation into the Effects of Salt Chemistry and SO2 on the Crack Initiation of CMSX-4 in Static Loading Conditions. In: Superalloys 2020. 14th International Symposium on Superalloys, 13-16 Sep 2021, Virtual. doi: 10.1007/978-3-030-51834-9_73


Although evidence exists of the potential impact of stress, co-incident with corrosive environments at high temperature, for single-crystal turbine blades, the mechanism responsible is not fully understood. This work explores the effect of CaSO4, Na2SO4 and sea salt on the scale formation and crack initiation of CMSX-4 at 550 °C in 50 ppm of SO2 and synthetic air under a static stress of 800 MPa. The cross-sectional analysis showed that the CaSO4 and the Na2SO4 salted specimens did not undergo a significant degree of corrosion degradation, and no cracks were detected after 400 h of exposure. However, sea salt caused significant degradation to the scale and cracks were detected by X-ray CT scanning after 400 h of exposure. The findings from this study suggest that the sulphation of chlorine-containing species in sea salt led to the formation, vaporisation, and re-oxidation of metal chlorides, and this mechanism was found to play a key role in the formation of a non-protective scale. An active oxidation mechanism has been proposed to interpret the results. In conclusion, it is hypothesised that due to the synergistic effect of stress and the formation of a non-protective scale, fast diffusion paths for sulphur, oxygen, and chlorine ingress were formed. Further work is currently being undertaken to understand the effect of these species on the local embrittlement of CMSX-4 that ultimately led to the initiation of cracks in the specimen.

Publication Type: Conference or Workshop Item (Paper)
Additional Information: © 2020 The Minerals, Metals & Materials Society. his version of the article has been accepted for publication, after peer review (when applicable) and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at:
Subjects: Q Science > QD Chemistry
T Technology > TA Engineering (General). Civil engineering (General)
Departments: School of Science & Technology > Engineering
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