Smart Tungsten-based Alloys for a First Wall of DEMO

During an accident with loss-of-coolant and air ingress in DEMO, the temperature of tungsten first wall cladding may exceed 1000 °C and remain for months leading to tungsten oxidation. The radioactive tungsten oxide can be mobilized to the environment at rates of 10–150 kg per hour. Smart tungsten-based alloys are under development to address this issue. Alloys are aimed to function as pure tungsten during regular plasma operation of DEMO. During an accident, alloying elements will create a protective layer, suppressing release of W oxide. Bulk smart alloys were developed by using mechanical alloying and field-assisted sintering technology. The mechanical alloying process was optimized leading to an increased powder production by at least 40 %. Smart alloys and tungsten were tested under a variety of DEMO-relevant plasma conditions. Both materials demonstrated similar sputtering resistance to deuterium plasma. Under accident conditions, alloys feature a 40-fold reduction of W release compared to that of pure tungsten.</p

Atom probe tomography of interfaces in ceramic films and oxide scales

Atomic-scale characterization of interfaces in ceramic materials is needed in order to fully understand their electronic, ionic, mechanical, magnetic, and optical properties. The latest development of laser-assisted atom probe tomography ( APT), as well as new specimen preparation methods, have opened the realm of ceramics for structural and chemical characterization with high sensitivity and nearly atomic spatial resolution. This article reviews recent APT investigations of interfaces in thin nitride films and thermally grown oxides: TiAlN layers and oxide scales on alumina- and chromia-formers and Zr alloys. The selected examples highlight the role of interfaces in the decomposition of films and in transport processes

Effect of Nb Addition on Oxidation Mechanisms of High Cr Ferritic Steel in Ar-H2-H2O

High chromium ferritic steels are being used as construction materials for interconnects in solid oxide electrolysis cells (SOEC). Addition of niobium in the range of a few tenths of a percent is suitable for increasing the high-temperature creep strength of this type of ferritic steel. In the present work, the high-temperature isothermal oxidation behavior of a niobium containing ferritic steel at 800 °C was investigated in Ar–4%H2–4%H2O gas simulating the service environment in an SOEC (cathode side) and compared with that of a Nb-free counterpart alloy. Gravimetric data were correlated with the results from microstructural analyses using, among others, scanning and transmission electron microscopy as well as glow discharge optical emission spectroscopy. Atom probe tomography was used for obtaining atomic-scale insight into the segregation processes in external oxides and their interfaces. The oxidation rate was substantially higher for the Nb-containing than for the Nb-free alloy. Both alloys formed double-layered oxide scales consisting of inner chromia and outer MnCr2O4 spinel. Additionally, a thin layer of rutile-type Nb(Ti,Cr)O2 oxide of 200–300 nm thickness was observed at the scale–alloy interface in the Nb-containing steel. Nb addition to the alloy led to its segregation at chromia grain boundaries which affected the diffusion of Cr and other solute species such as Ti, Mn and Si

Atom probe tomography of interfaces in ceramic films and oxide scales

Atomic-scale characterization of interfaces in ceramic materials is needed in order to fully understand their electronic, ionic, mechanical, magnetic, and optical properties. The latest development of laser-assisted atom probe tomography ( APT), as well as new specimen preparation methods, have opened the realm of ceramics for structural and chemical characterization with high sensitivity and nearly atomic spatial resolution. This article reviews recent APT investigations of interfaces in thin nitride films and thermally grown oxides: TiAlN layers and oxide scales on alumina- and chromia-formers and Zr alloys. The selected examples highlight the role of interfaces in the decomposition of films and in transport processes