Progression of Hot Corrosion in Ni-base Superalloys for Industrial Gas Turbines
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Advanced engineering materials, MSc
Publicerad
2019
Författare
Medina Viramontes, Camilo
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Siemens Industrial Turbomachinery AB is a world leading company that is dedicated to the manufacture of industrial gas turbines for energy generation. Industrial gas turbines are one of the most efficient and popular methods for providing energy to various sectors. Over the years, the use of these turbines has been extended due to the development of new materials and manufacturing methods that have improved their high temperature performance allowing them to operate at higher temperatures and leading to an increase in efficiency. Aircraft engines have benefited from these advances since they operate in a similar form as industrial gas turbines. Due to the larger market size of the aircraft engine sector in comparison to that of the gas turbine sector and the perception that both applications operate under similar conditions, the development of new materials for industrial gas turbine applications has been neglected in favour of the development of materials for the aircraft engine market. However, the current environmental issues have led to a diversification of fuels used in the gas turbines making them more susceptible to corrosion damage at their current working temperatures (1350°C) in addition to working in salt-containing environments like coasts, offshore and desserts. Therefore, it is imperative that gas turbine manufacturers develop alloys that can withstand such hazardous conditions. In this project, the progression of hot corrosion in Ni-base superalloys is evaluated in six different materials. Three of them are commercial alloys: CM247, CMSX-4 and Inconel 792; while the other three are alloys developed by Siemens, two of which are polycrystalline and the other one is a single crystal. Samples of all of the six alloys were exposed to a mixed-sulphur atmosphere at two different temperatures (700 and 850°C) for several cycles and their corrosion products were analysed using stereomicroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. At 700°C, the alloys underwent type II hot corrosion, and at 850°, they underwent type I hot corrosion. Based on a literature study and the results of the experiment, a reaction mechanism was proposed for each case. In terms of performance, alloys CM247 and CMSX-4 suffered the most damage, followed by a polycrystalline variation of a Siemens alloy. Inconel 792 and the single crystal variation of the Siemens alloys performed better.
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Ämne/nyckelord
Materialvetenskap , Produktion , Maskinteknik , Materialteknik , Materials Science , Production , Mechanical Engineering , Materials Engineering