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Di Martino S.F.,Loughborough University | Faulkner R.G.,Loughborough University | Hogg S.C.,Loughborough University | Vujic S.,Institute for Materials Science and Welding | Tassa O.,Centro Sviluppo Materiali S.p.A
Materials Science and Engineering A | Year: 2014

Current energy drivers are pushing research in power generation materials towards improved efficiency and improved environmental impact. In the context of new generation ultra-supercritical (USC) power plant, this is represented by increased efficiency, service temperature reaching 750. °C, pressures in the range of 35-37.5. MPa and associated carbon capture technology. Ni base alloys are primary candidate materials for long term high temperature applications such as boilers. The transition from their current applications, which have required lower exposure times and milder corrosive environments, requires the investigation of their microstructural evolution as a function of thermo-mechanical treatment and simulated service conditions, coupled with modelling activities that are able to forecast such microstructural changes. The lack of widespread microstructural data in this context for most nickel base alloys makes this type of investigation necessary and novel. Alloy INCONEL 617 is one of the Ni-base candidate materials. The microstructures of four specimens of this material crept at temperatures in the 650-750. °C range for up to 20,000. h have been characterised and quantified. Grain structure, precipitate type and location, precipitate volume fraction, size and inter-particle spacing have been determined. The data obtained are used both as input for and validation of a microstructurally-based CDM model for forecasting creep properties. © 2014.

Vujic S.,Institute for Materials Science and Welding | Di Martino F.,Institute for Materials Science and Welding | Matera S.,Loughborough University | Tassa O.,Centro Sviluppo Materiali S.p.A | And 4 more authors.
Materials Science Forum | Year: 2014

Due to its high creep strength and oxidation resistance, C-263 is a promising Ni-based alloy for applications in superheater tubes in coal fired thermal power plants. The creep strength is mostly based on finely distributed gamma-prime precipitates. In this work, the microstructural evolution of this material during heat treatment and thermal ageing has been investigated. The investigations were carried out by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Diffraction Pattern (SADP) and Energy Dispersive Spectroscopy (EDS). Besides, equilibrium and Scheil calculations were carried out using the thermodynamic software MatCalc to analyze the stable phases and the solidification process, respectively. Precipitation calculations during solution annealing and subsequent ageing at 700°C and 750°C up to 10.000h ageing time were performed to predict the phase fraction and precipitates radius. SEM and TEM investigations of aged specimens revealed three different precipitates: M23C6, γ' and MX. MatCalc also predicted these precipitates. The calculated phase fraction and mean radius show good agreement with experimental data. © (2014) Trans Tech Publications, Switzerland.

Kerschbaumer K.G.,Institute for Materials Science and Welding | Vallant R.,Institute for Materials Science and Welding | Enzinger N.,Institute for Materials Science and Welding | Sommitsch C.,Institute for Materials Science and Welding
Materiali in Tehnologije | Year: 2013

Increasing the energy efficiency of household refrigeration appliances as a result of legal requirements is more and more important (2010/30/EUEG2010 Directive). This means that the equipment with the energy efficiency lower than D can no longer find its place in the European trading. In this investigation aluminium alloys (AW5083-O, AW6181-T4) and a magnesium alloy (AZ31) were selected via a material selection. They are compared to the currently used deep-drawing steels (DD11, DD13) with respect to the corrosion and strength properties of similar overlap-welded joints. To verify the corrosion properties the neutral salt spray test (NSS) and the fruit acid spray test were performed with an overall test duration of 480 h. The type of corrosion, its influence on the corrosion rate and the strength of the welded joints were evaluated. Magnesium shows a very high corrosion and therefore cannot be used uncoated, like deep-drawing steel. The aluminium alloys show only slight selective corrosion phenomena and are, from the welding and corrosion point of view, an attractive alternative to steel. Due to a higher thermal conductivity of aluminium, in comparison with steel, a higher energy efficiency of the cooling compressor is expected.

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