TY  - JOUR
AU  - Garcia-Fresnillo, L.
AU  - Chyrkin, Anton
AU  - Boehme, C.
AU  - Barnikel, J.
AU  - Schmitz, F.
AU  - Quadakkers, Willem J.
TI  - Oxidation Behaviour and Microstructural Stability of Alloy 625 During Long-Term Exposure in Steam
JO  - Journal of materials science
VL  - 49
IS  - 17
SN  - 0022-2461
CY  - Dordrecht [u.a.]
PB  - Springer Science + Business Media B.V
M1  - FZJ-2014-06678
SP  - 6127-6142
PY  - 2014
AB  - Nickel-based alloys are being considered as construction materials for various components in high-efficiency steam turbines with envisaged operating temperatures around 700 °C. In the present study, the steam oxidation behaviour of the nickel-based alloy 625 in the temperature range of 700–800 °C was investigated whereby exposures up to 10000 h were carried out. Gravimetric data in combination with results from a variety of post exposure analysis techniques showed in all cases the formation of protective oxide scales mainly consisting of chromia with minor amounts of outer Cr/Mn spinel and internal silica. The phases found in the bulk alloy after long-term exposure were mainly needle-shaped δ-Ni3(Nb,Mo) phase, μ-phase and Si-rich η-M6C carbide. Microstructural features and phase formation were found to be related to minor variations in the alloy composition, especially iron and silicon content. The oxidation-induced chromium depletion caused a number of microstructural changes in the subsurface depletion layer. Most important was an enrichment of the intermetallic δ-phase at the scale–alloy interface. DICTRA modelling revealed this effect to be caused by uphill diffusion as a result of a negative niobium activity gradient in the subscale chromium depletion zone. Although the available kinetic and thermodynamic data allowed qualitative explanation of the δ-phase enrichment, the databases do not correctly describe the high molybdenum solubility in the δ-phase.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000337507100035
DO  - DOI:10.1007/s10853-014-8344-7
UR  - https://juser.fz-juelich.de/record/173267
ER  -