Effect of Ti and Cr on dispersion, structure and composition of oxide nano-particles in model ODS alloys

Abstract

a b s t r a c tThree model ODS alloys (Fe-0.3Y 2 O 3 , Fe-0.2Ti-0.3Y 2 O 3 and Fe-14Cr-0.2Ti-0.3Y 2 O 3 ) were prepared by ball milling and then hot extrusion to study the effect of Ti and Cr on the size, distribution, crystal structure and composition of the nano-oxide particles. All alloys were characterized by high resolution transmission electron microscopy (HRTEM), atom probe tomography (APT) and synchrotron-X-ray diffraction (S-XRD) to determine the distribution, structure and composition of the oxide nanoparticles samples. The median particle sizes were 9.6 nm, 7.7 nm and 3.7 nm for the Fe-Y 2 O 3 , Fe-Ti-Y 2 O 3 and Fe-Cr-Ti-Y 2 O 3 alloys, respectively, so the presence of Ti resulted in a significant reduction in oxide particle diameter and the addition of Cr gave a further reduction in size. In the Fe-0.3Y 2 O 3 alloy, the particles are found to be bcc Y 2 O 3 , whereas in the other two alloys (Fe-Ti-0.3Y 2 O 3 and Fe-Cr-Ti-Y 2 O 3 ), the oxide particles were found to be structurally consistent with both orthorhombic Y 2 TiO 5 and fcc Y 2 Ti 2 O 7 . Detailed APT studies showed Cr shells around oxide particles of all sizes in the Fe-Cr-Ti-Y 2 O 3 alloy, that a range of cluster compositions are present and that the particle chemistry varies with cluster size. We show that the addition of Cr has a strong effect on both the size and stoichiometry of the particles.

Glancing angle XRD analysis of particle stability under self-ion irradiation in oxide dispersion strengthened alloys

“…They have a composition of Fe-14Cr-0.03C-0.2Ti-0.3Y 2 (all wt%), and were prepared by mechanical alloying and hot extrusion. The initial microstructure of these alloys has been previously reported [29]. 12 mm diameter, 0.5 mm thick disks were cut from extruded bars and mechanically polished to a mirror finish prior to ion irradiation by Fe ions as detailed in Table 1.…”

Relaxation path of nanoparticles in an oxygen-enriched ferritic oxide-dispersion-strengthened alloy

“…In a material similar to ours, London et al [28] found up to 85% of Y 2 TiO 5 orthorhombic particles. Their bulk metal to oxygen ratio ((Ti + Y) / O) experimentally measured is 0.29.…”

“…More broadly, If we which to make comparisons with the literature, it should always be done with the measured concentrations and not nominal compositions. Indeed, the metal to oxygen ratio of the reference [28,20] calculated from the nominal composition are respectively 1.83 and 2.38. An important oxygen pollution during the manufacture is supposed in these materials.…”

Structural Evolution of Nano-sized Oxide Particles Formed in Mechanically Alloyed Fe-10Cr-5Y2O3 Powders

“…The samples for in-situ TEM analysis were prepared using the Focused Ion Beam (FIB) method. HRTEM, Selected Area Diffraction (SAD) patterns and Fast Fourier Transformation (FFT) images were evaluated to identify the crystal structure of nano-sized oxide particles and their crystallographic orientation relationship with the matrix [13,14]. Figure 1 shows the SEM and EPMA images of the mechanically alloyed Fe-10Cr-5Y 2 O 3 powders.…”