HIGH-TEMPERATURE STEAM AND PRESSURISED WATER CORROSION BEHAVIOURS OF NITRIDE CERAMIC COATINGS FOR ACCIDENT TOLERANT FUEL CLADDINGS

  • Xi Yu

Student thesis: Master of Philosophy

Abstract

A new coating design and material selection of accident tolerant fuel (ATF) claddings have been produced using magnetron sputtering (MS) technique. ZrN single layer and Ti(Si)N single layer coatings were successfully deposited with flat and dense morphology and good adhesion with a polished zirconium alloy plate and Si wafer. TiSixN/Ti (x=0.08, 0.13, 0.19) double layer structure coatings were deposited as two flat and dense layers bonded together well with a Zy-4 polished plate. To evaluate the corrosion behaviours of these coatings under accident scenarios and operational conditions, a high-temperature steam test (600°C, 800°C and 1000°C with Ar flow 0.4L/min and H2O 90%) and autoclave immersion test (360°C, 19.7MPa) were conducted. Scanning electron microscopy (SEM) associated with energy-dispersive X-ray spectroscopy (EDS) were used for surface and microstructure analysis. X-ray diffraction (XRD) was conducted to evaluate the phase of coatings before and after corrosion tests. Single layer ZrN coatings demonstrated significant spallation after steam and autoclave tests due to the large differences in thermal expansion coefficient between the ceramic layer and Zr substrate. The TiSixN/Ti double layer structure showed better adhesion with the underneath Zy-4 substrate following steam and autoclave tests. The ZrN layer was fully oxidised after 1-hour 600°C steam test and two-day autoclave immersion. TiSi(0.08, 0.13, 0.19)N/Ti coatings exhibited superior steam resistance up to 4 hours at 1000°C. The corrosion behaviour varied according to the Si content and exposure temperature. However, the corrosion behaviour against pressurised water showed a significant difference compared with water vapour. Only part of TiSi0.08N survived after a seven-day pressurised water immersion test at 360°C, 19.7MPa. Under high-temperature (1000°C) steam, oxidation of TiSiN and Si-volatilization were the degradation mechanisms for the TiSixN layer. However, oxidation of TiSiN and Si-dissolution were the mechanisms of corrosion when under pressurized water
Date of Award1 Aug 2020
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorDavid Hall (Supervisor) & Ping Xiao (Supervisor)

Keywords

  • Corrosion behaviours
  • Nitride ceramic coating
  • Accident tolerant fuel cladding

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