E-Thesis 328 views
High-temperature corrosion resistance and microstructural transitions of polycrystalline nickel-based superalloys / DARREN KAPPALA-RAMSAMY
Swansea University Author: DARREN KAPPALA-RAMSAMY
DOI (Published version): 10.23889/SUThesis.69354
Abstract
Inconel 601 is a commercially available nickel-based superalloy used as a wire belt in the petrochemical, chemical and thermal processing industries. These industries can contain chlorine-baring gases such as HCl at high-temperatures, which exposed Inconel 601 to a chlorine-based attack in a steam o...
| Published: |
Swansea University, Wales, UK
2024
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | EngD |
| Supervisor: | Penney, D. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa69354 |
| Abstract: |
Inconel 601 is a commercially available nickel-based superalloy used as a wire belt in the petrochemical, chemical and thermal processing industries. These industries can contain chlorine-baring gases such as HCl at high-temperatures, which exposed Inconel 601 to a chlorine-based attack in a steam oxidation environment whilst used in-service. Inconel 601 suffered severe embrittlement because of chromium depletion zones observed in its microstructure, coupled with a reduction of hardness in the material that resulted in failure by belt distortion.Chapter 4 comprised of a failure analysis on the Inconel 601 belts provided from industry. Sample cross-sections were analysed to observe the extent of the corrosion damage on Inconel 601 due to in-service conditions. Inconel 601 belt samples were provided in new condition, after 2 weeks (when the belt was still in usable condition)and after 2 months (when the belt had suffered a failure due to harsh service environment). Understanding how the industrial conditions, which included process variables such as temperature and corrosive gases, affected the morphology and service life of Inconel 601 was an important preliminary step, to facilitate an exploration into new alloys which may offer a benefit in performance, and provide a longer more predictable service life in subsequent chapters.Chapter 5 explored the amount of damage caused by the temperature in industrial conditions without the influence of corrosive species, in dry atmospheric oxidising conditions, with a thermal cycle at 2 fixed temperatures of 850°C and 950°C for 42,100 and 200 hours. Inconel 601 was assessed, with 3 alternative alloys which included Inconel 625, Haynes 214 and Nikrothal PM 58, which were hypothesised as potential candidates to replace Inconel 601, ascertaining if they offered improved performance in such conditions as explored. Within this chapter it was noted that minimal thermomechanical weakening and mass loss occurred for all alloys due to the 850°C and 950°C oxidation exposures, therefore it was ascertained that the influence of such temperatures without corrosive gases was not severely damaging to these alloys.Chapter 6 explored the influence of thermal cycling and corrosive gases to the 4 alloys used in Chapter 5 which were Inconel 601, Inconel 625, Haynes 214 and Nikrothal PM 58. An initial baseline experiment involving steam oxidation ruled out that steam was significantly damaging to the alloys selected, after which 2% HCl was introduced to the experiments. The latter explored the influence of a steam + 2% HCl vapour gas blend, with a 750°C/850°C thermal cycle that mimicked industrial conditions in Chapter 4. Inconel 601’s mechanical properties experienced a significant deterioration, in comparison to other alloys analysed due to the 2% HCl addition. A reduction of tensile performance was observed for Inconel 601 at 138 hours, due to a decline of both maximum elongation from 44% to 16%, and uniform elongation from 36% to 13%, which was the most significant reduction of ductility in comparison to all other alloys. Furthermore, these conditions induced a reduction of ultimate tensile strength in Inconel 601 from 666 to 430 MPa after 138 hours, which was also the most significant reduction in strength compared to other alloys analysed. Inconel 601 also featured the most scale spallation , observed in the macro-images which was quantified through the greatest percentage mass loss relative to other alloys analysed in the HCl-baring test conditions. Inconel 601’s cross-sectional microstructure denoted severe embrittlement through chromium-depletion zones in the backscattered electron images and energy-dispersive spectroscopy analysis, akin to industrial conditions.Furthermore, corrosion cracking was identified in IN 601 due to 2% HCl addition, which was not present in all the other alloys analysed. |
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| Item Description: |
A selection of content is redacted or is partially redacted from this thesis to protect sensitive and personal information. |
| Keywords: |
nickel-based superalloys, high-temperature corrosion, failure-analysis, in-service replication, scanning electron microscopy, energy-dispersive spectroscopy, tensile properties. |
| College: |
Faculty of Science and Engineering |
| Funders: |
UKRI, EPSRC |