Grain Boundary Segregation and Core/Shell Structured Nanofeatures in Oxide-Dispersion Strengthened Fe-Cr Alloys

Since the oxygen-rich nanofeatures (NFs) in oxide-dispersion-strengthened (ODS) ferritic steels is a key factor for improving their whole mechanical properties [1-3], atom-probe tomography (APT) and transmission electron microscopy (TEM) have been widely employed to identify the oxygen-rich NFs in the materials The current work presents three challenges to deeply understand the chemical origin of the nano-sized precipitates containing Y, O, and Ti. First, the segregation of alloying elements at grain boundaries is observed. Secondly, we compare the concentrations of nano-sized precipitates with a size of ~3 nm to those of 10-nm precipitates. Finally, the existence of NF structure with the Y-rich cores and Ti-and Cr-enriched shells is confirmed as previously reported by APT. The nominal composition of the materials studied here is 14Cr, 3.0W, 0.4Ti in wt.%. Analyses were performed using a LEAP-4000HR microscope in voltage-pulsing mode at 200 kHz pulse repetition rate, 0.005 atom/pulse detection rate, 20% pulse fraction and 70 K.