Phosphorus Interface Segregation Measurement: Cross comparison between XPS, WDS, TEM-EDS, and APT
Interface segregation denotes the gathering of solute atoms as fractional monolayers at the material interfaces (grain boundaries, surfaces, interphase boundaries). Phosphorus intergranular segregation is known to influence the fracture properties of steels. It can happen due to the fabrication process of the material or the operation condition of the final component. This phenomenon is critical in the assessment of nuclear pressure vessel life time, as vessel steels are susceptible to grain boundary embrittlement due to phosphorus. Although many studies of this phenomenon were conducted over the last decades, there is still a need of reliable and comparable quantification methods for grain boundary segregation.
The analysis of intergranular segregation is most commonly done by Auger electron spectroscopy (AES) which has some limitations, such as obtaining intergranular fracture of the specimen in ultra-high vacuum chamber to avoid surface contamination. Other characterization techniques such as X-ray photoelectron spectroscopy (XPS), wavelength dispersive X-ray spectroscopy (WDS), energy dispersive X-ray spectroscopy (EDS) on transmission electron microscope (TEM), and atom probe tomography (APT) can also be adapted for intergranular segregation quantification.
This study aims to develop a reliable TEM-EDS methodology to quantify phosphorus intergranular segregation without being influenced by the beam-specimen interaction volume. The results are cross-compared with the different possible intergranular segregation quantification techniques: XPS, WDS, and APT. To achieve this goal, a Fe-P-Fe sandwich specimen with a known phosphorus concentration at the interface was fabricated. Analysis of each technique was performed at the same location of the sample. Attention is paid to the way of expressing the results of the different techniques (XPS, WDS and TEM-EDS) so that they can be compared with one another. The quantification results highly accord with one another. The experiment of APT is ongoing for the moment.