Oxidation of MCrAlY coatings on Ni based superalloys

Abstract

i AcknowledgementsFirstly I would like to thank the Department of Materials for the use of their materials and facilities. The range of equipment available and people have made working there a pleasure, but also allowed the use of several techniques that proved invaluable.I am grateful to my project supervisor, Professor R. C. Thomson; firstly for offering me such an interesting project and secondly, for her guidance and support, which have been invaluable during this project.I would also like to thank Dr G. West for the continued support he has given me throughout my PhD. His help and guidance on many aspects (especially on FIBSEM and TEM related matters) have been immeasurable, but more than that I am extremely grateful for his moral support and his friendship; working with him is something I will miss. I would also like to thank my fellow office mates, especially Juan Sanchez-Hanton and Kate Burke for helping to create such an enjoyable office atmosphere.I am also extremely grateful to RWE npower for part funding this project and giving me the opportunity to look at such an interesting area of metallurgy. I am especially grateful to Dr Jon Wells from RWE npower, not only for providing a raft of samples but for his advice and support throughout.Finally, I would like to thank my friends and family for their support and encouragement throughout, especially my parents for having always been there to offer help and support, and Anne for always cheering me up and supporting me through the difficult times.ii AbstractEnsuring a sustainable power generation supply into the future is of worldwide importance. A combination of power generation methods to meet this (including both fossil plant and renewables) is a certainty. Therefore, the maintenance of conventional fossil-fired plants is required to provide a low cost, flexible and reliable electricity supply, and in order to conserve fuel resources it is important to ensure they operate as efficiently as possible. Lifetime predictions of important components (such as turbine blades in industrial gas turbine engines) are essential in order to avoid failures and unnecessary downtime, improve the ability to schedule routine maintenance work and to help develop new coating systems to meet the ever more demanding requirements. Better models would allow improved predictions and mean that service schedules could be set with better accuracy thereby, limiting downtime and reducing costs as well as being better able to predict coating performance and thus increase engine efficiency.Ni-based superalloys are a common material utilised for turbine blades due to their high temperature strength. Coupled with MCrAlY coating systems and thermal barrier coatings (TBC) they are able to withstand both the high temperatures and arduous environments they will encounter during service. In order to effectively predict the lifetime of components such as turbine blades it is vital to understand the oxidation behaviour of these systems and how factors such as the MCrAlY composition, processing f...

High temperature oxidation of NiCrAlY coated Alloy 625 manufactured by selective laser melting

“…A γ-Ni/γ′-Ni 3 Al matrix with well dispersed α-Cr precipitates (bulky and lamellar) and (Ni,Y)-rich intermetallic precipitates were identified in the bulk NiCrAlY variant (Fig. 4(b, e)), consistent with the expected phases for Ni-22Cr-10Al-1Y [47].…”

Microstructure and lifetime of Hf or Zr doped sputtered NiAlCr bond coat/7YSZ EB-PVD TBC systems

“…However, diffusion processes of Ta from NiCoCrAlYTa commercial bond coats and its interaction with other elements from different superalloys have been barely reported. Previous reports have been focused on oxidation effects (e.g., weight gain, lifetime under furnace cycling tests) as well as oxide scales and bond coat characteristics [14,[22][23][24]. Moreover, few investigations have been conducted to understand the interplay of Ta with Ti, Hf, Re, among other elements from the used superalloys, and the way it affects the microstructure and diffusion phenomena between the bond coat and the substrate, especially at their interface [25][26][27].…”