title: Characterisation of interfacial segregation to Cu-enriched precipitates in two thermally aged reactor pressure vessel steel welds.
abstract: To understand the contribution of long term thermal ageing to Reactor Pressure Vessel (RPV) embrittlement two high Cu steel welds with different Ni contents were thermally aged for times up to 100,000 h at 330 °C and 365 °C. Microstructural characterisation using Atom Probe Tomography was performed. Thermal ageing produced a high number density of nano-scale Cu-enriched precipitates. The precipitate-matrix interfaces were enriched in Ni, Mn and Si. The characterisation of these interfaces using a double cluster search approach is the subject of this work. The interface region around thermally-induced precipitates was found to be wider in steels with higher bulk Ni contents and where precipitates had larger core radii. The effect of ageing temperature on interface width was small when comparing precipitates of equal core radius. The narrower interface width in the lower Ni steels is reflected in the composition of the interface, which has a lower Ni content than in the higher Ni material. The reduction in interfacial energy due to the segregation of Ni, Mn and Si has been calculated and shows enhanced reductions in interfacial energy with increasing precipitate size, but no obvious effect of temperature.
authors.affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK; National Nuclear Laboratory, B168, Harwell Business Centre, Didcot, Oxon OX11 0QT, UK. Electronic address: paul.styman@materials.ox.ac.uk.
authors.forename: P D
authors.initials: PD
authors.lastname: Styman
authors.affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK; National Nuclear Laboratory, B168, Harwell Business Centre, Didcot, Oxon OX11 0QT, UK.
authors.forename: J M
authors.initials: JM
authors.lastname: Hyde
authors.affiliation: Rolls-Royce, PO Box 2000, Raynesway, Derby DE21 7XX, UK.
authors.forename: K
authors.initials: K
authors.lastname: Wilford
authors.affiliation: Rolls-Royce, PO Box 2000, Raynesway, Derby DE21 7XX, UK.
authors.forename: D
authors.initials: D
authors.lastname: Parfitt
authors.affiliation: Rolls-Royce, PO Box 2000, Raynesway, Derby DE21 7XX, UK.
authors.forename: N
authors.initials: N
authors.lastname: Riddle
authors.affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.
authors.forename: G D W
authors.initials: GD
authors.lastname: Smith
keywords: Atom Probe Tomography; Cu clustering; Interface segregation; RPV steels; Thermal ageing