Size-dependent characteristics of ultra-fine oxygen-enriched nanoparticles in austenitic steels

Abstract

Here, a coordinated investigation of the elemental composition and morphology of ultra-fine-scale nanoparticles as a function of size within a variety of austenitic oxide dispersion-strengthened (ODS) steel is reported. Atom probe tomography was utilized to evaluate the elemental composition of these nanoparticles. Meanwhile, the crystal structures and orientation relationships were determined by high-resolution transmission electron microscopy. The nanoparticles with sufficient size (>4 nm) to maintain a Y 2 Ti 2−x O 7−2x stoichiometry were found to have a pyrochlore structure, whereas smaller Y x Ti y O z nanoparticles lacked a well-defined structure. The size-dependent characteristics of the nanoparticles in austenitic ODS steels differ from those in ferritic/martensitic ODS steels.

Temperature dependent strengthening contributions in austenitic and ferritic ODS steels

“…To analyze particle strengthening, information about the composition and structure of ODS particles is necessary. Although there is still some controversy on the crystal structure of the nanoclusters in both, ferritic as well as austenitic ODS steels, the existence of cubic Y2Ti2O7 is reported in most cases for oxide particles with about 4 nm in size [27,35,36,85]. Predominantly, a (semi-)coherent cube-oncube orientation relation between particles and matrix is found, from which it can be assumed that dislocations cannot penetrate the nanoclusters without destroying the crystal structure of the clusters.…”

“…Furthermore, larger particles (> 10 nm) are reported to be incoherent [35], while APT analysis of the smallest nanoclusters (< 2 nm) revealed a non-stoichiometric composition and a lack of a well-defined crystal structure [35,86]. Hence, it can be expected that dislocations could possibly cut only the smallest particles, but a majority of oxide particles has to be overcome by the Orowan mechanism.…”

“…Additionally, processing of austenitic ODS steels by MA revealed to be challenging, as a consequence of either the formation or the presence of the very ductile FCC phase. Hence, the powder tends to stick to the container walls and milling balls and often so-called process-control agents like alcohols are used to increase powder yield [26,27,35,36].…”

Effect of Laser Shock Peening on the Microstructures and Properties of Oxide‐Dispersion‐Strengthened Austenitic Steels

“…The void swelling resistance of austenitic steels could be increased by the dispersion of oxide nanoparticles inside the matrix . The particle/matrix interfaces in ODS austenitic steels can act as nanoscale sinks for point defects, thus inhibiting void formation and increasing the void swelling resistance . In addition, oxide nanoparticles retard the motion of dislocations and reduce grain coarsening, thus increasing the mechanical strength and creep resistance of austenitic steels.…”

Temperature effect of elastic anisotropy and internal strain development in advanced nanostructured alloys: An in-situ synchrotron X-ray investigation

“…In order to further enhance the material properties of NFAs, it is important to understand the mechanical behavior and material response when both external load and elevated temperature are applied. Different chemical compositions and different thermal-mechanical treatments can cause variations in the nanocluster size and grain size for different NFAs, leading to various responses to external tensile loadings [26][27] [28]. In this study, we adopted a high-energy synchrotron X-ray diffraction technique to investigate the microstructural development of three types of NFAs during in-situ uniaxial tensile tests at the temperature from room temperature (RT) to 600ºC.…”