An in situ powder neutron diffraction study of nano-precipitate formation during processing of oxide-dispersion-strengthened ferritic steels (original) (raw)
Microstructural characterization of oxide dispersion strengthened ferritic steel powder
Journal of Nuclear Materials, 2013
Oxide dispersion strengthened ferritic steel powder was prepared by mechanical alloying of pre-alloyed ferritic steel powder together with nano Y 2 O 3 in a dual drive planetary ball mill. A detailed investigation was carried out using X-ray diffraction, field emission electron microscopy and transmission electron microscopy. Microstructural parameters such as, crystallite size, lattice strain, deformation stress and dislocation character were evaluated using different Williamson-Hall models; uniform deformation model, uniform stress deformation model and modified Williamson-Hall model and the results obtained were compared and discussed. Uniform stress deformation model and modified Williamson-Hall model were observed to give better estimation of crystallite size as they consider strain anisotropy. With mil ling, dislocation character was observed to be changing, from near edge to mixed type. Lattice parameters of the milled powders were also estimated. Uniform milling with convoluted particle shape and homogeneous distribution of Y 2 O 3 throughout the matrix was observed by using electron microscopy.
Structure of oxide nanoparticles in Fe–16Cr MA/ODS ferritic steel
Materials Letters, 2010
Oxide nanoparticles in Fe-16Cr ODS ferritic steel fabricated by mechanical alloying (MA) method have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. A partial crystallization of oxide nanoparticles was frequently observed in as-fabricated ODS steel. The crystal structure of crystalline oxide particles is identified to be mainly Y 4 Al 2 O 9 (YAM) with a monoclinic structure. Large nanoparticles with a diameter larger than 20 nm tend to be incoherent and have a nearly spherical shape, whereas small nanoparticles with a diameter smaller than 10 nm tend to be coherent or semi-coherent and have faceted boundaries. The oxide nanoparticles become fully crystallized after prolonged annealing at 900 °C. These results lead us to propose a three-stage formation mechanism of oxide nanoparticles in MA/ODS steels.
Journal of Nuclear Materials, 2009
By introducing a dispersion of nanosized yttrium oxides particles into a steel matrix, the upper temperature limit in mechanical creep strength can be enhanced in temperature by 100 K at least. Production routes for the production of a new class of oxides dispersion strengthened (ODS) steels are investigated within this work. Preliminary results obtained when doping pure iron matrix phase with two types of yttrium oxides (Y 2 O 3 ) nanoparticles (commercial as well as laboratory fabricated nanopowder) are presented. The twofold purpose of this work is firstly to obtain a comparative analysis between the commercial and the laboratory fabricated Y 2 O 3 nanopowder used to produce the doped iron, and secondly to demonstrate the feasibility of new production route by observing the nanostructure of the first test batches with pure iron. Observations are carried out with transmission electron microscopy (TEM) to determine the size distribution of the particles in the powder, while glow discharge optical emission spectroscopy (GDOES) and high resolution-scanning electron microscopy (HR-SEM) are used to analyze the chemical composition and the homogeneity of the produced doped iron. It is demonstrated, that even with small size particles nanopowder fabricated in the laboratory, the distribution is fairly homogeneous compared to the one obtained with a relatively large particles commercial nanopowder, confirming the feasibility of the new production route.
Quantification of oxide particle composition in model oxide dispersion strengthened steel alloys
Ultramicroscopy, 2015
Oxide dispersion strengthened ferritic steels (ODS) are being considered for structural components of future designs of fission and fusion reactors because of their impressive high-temperature mechanical properties and resistance to radiation damage, both of which arise from the nanoscale oxide particles they contain. Because of the critical importance of these nanoscale phases, significant research activity has been dedicated to analysing their precise size, shape and composition (Odette et al., Annu. Rev. Mater. Res. 38 (2008) 471-503 [1]; Miller et al., Mater. Sci. Technol. 29(10) (2013) 1174-1178 [2]). As part of a project to develop new fuel cladding alloys in India, model ODS alloys have been produced with the compositions, Fe-0.3Y2O3, Fe-0.2Ti-0.3Y2O3 and Fe-14Cr-0.2Ti-0.3Y2O3. The oxide particles in these three model alloys have been studied by APT in their as-received state and following ion irradiation (as a proxy for neutron irradiation) at various temperatures. In order ...
In situ neutron diffraction during tensile deformation of a ferrite-cementite steel
Acta Materialia, 2003
A fully pearlitic steel (specimen P1) was subjected to cold-drawing (P2) followed by aging at 423 K (P3) or 673 K (P4). Some drawn samples were annealed to make cementite particles spherical (P5). By using neutron diffraction, high compressive residual stress component parallel to the drawing direction was detected in the ferrite matrix of specimen P2, whereas this stress level was partly relaxed in P3 and mostly in P4. In situ neutron diffraction experiments performed during tensile tests have revealed different work hardening behaviors in these specimens. Based on the data provided by a profile analysis of diffraction spectra, i.e. microstrain related to dislocation density and block size, strength and work-hardening of these specimens are discussed. In particular, it is documented that the treatment of the specimen P4 which is equivalent to commercially Zn-plated steel wires produces the largest internal stress by tensile deformation leading to a good balance of strength and uniform elongation.
Real-time observations of the oxidation of mild steel at high temperature by neutron diffraction
Metallurgical and Materials Transactions B, 1996
The in situ characterization of the phase composition of iron oxides, ''scale,'' that form on low carbon steel during oxidation at elevated temperatures was carried out using the neutron diffraction technique. Growths in the intensities of diffraction peaks from the crystal planes of the various oxides (Fe x O, Fe 3 O 4 , and Fe 2 O 3 ) were monitored on-line. The volume fractions of the oxides in the scale were calculated on the basis of ideal structure factors and measured relative intensities of diffraction peaks. These were selected from a small region of the diffraction pattern. Calculated volume fractions of these oxides in the scale layer were in agreement with the area fractions obtained from scanning electron microscopy (SEM) analysis of the scale.
Second Phase Precipitation in Ultrafine-grained Ferrite Steel
Grain size refinement is one of the most efficient strengthening mechanisms applied to modern High-Strength Low-Alloy steels (HSLA) because yield strength and toughness are both improved. This paper discusses the distribution of carbides by using transmission electron microscopy (TEM) in a low-carbon steel with ultrafine grained (UFG) ferrite. Fine cementite particles were formed during water quenching due to the auto-tempering of highly distorted martensite. Other fine particles observed under the same condition were nucleated due to the presence of carbide formers such as niobium, titanium and vanadium. TEM analysis showed that cementite particles underwent Ostwald ripening during warm rolling but they were still able to inhibit ferrite grain growth, which was maintained 1µm size approximately.