Query: 14YWT

title: In situ observation of nano oxide and defect evolution in 14YWT alloys
abstract: Nanostructured ferritic alloys (NFAs) are considered as candidates for structural components in advanced nuclear reactors due to their excellent radiation resistance as a result of a high density of nano oxides (NOs) in the microstructure. Therefore, gaining an understanding on the stability of NOs under irradiation is crucial. In this study, we have investigated the evolution of defects and NOs in 14YWT NFAs under in situ Kr ion irradiation at room temperature (RT) and 450 degC up to 10 dpa. It has been found that irradiations at 450 degC do not create any changes in the NOs, similar to the bulk irradiations. On the other hand, elemental mapping indicates that NOs dissolve mostly after 10 dpa irradiations at RT. Thus, while defects are both annihilated and pinned by NOs at low doses (before the dissolution of NOs) glissile loops start to escape to the foil surface at high doses (after the dissolution of NOs) justifying the significantly low fraction of loops compared to the literature values. High resolution transmission electron microscopy analysis has shown that the NOs are mostly coherent Y2Ti2O7 particles with pyrochlore crystal structure after both RT and 450 degC irradiations, similar to those observed before irradiation.

title: Microstructural and micro mechanical analysis of 14YWT nanostructured Ferritic alloy after varying thermo mechanical processing paths into tubing
abstract: Microstructural analyses and micro pillar compression were conducted on 14YWT nanostructured ferritic alloy (NFA) to compare different processing pathways: hydrostatic extrusion and Pilger processing with varying annealing temperatures into thin walled tubing, and after hot extrusion and cross rolling into a plate. Hydrostatic extrusion at 815 degC resulted in the smallest grain sizes and highest yield strength of 1.20 GPa. Pilger processing with annealing at 800 degC had fine grained regions and bands of coarse grains, leading to a large variation in yield strength of 0.9 1.40 GPa. Higher annealing temperatures of 1200 degC after pilger processing significantly increased the grain size and lowered the yield strength to 1.01 GPa. These tubes showed a stronger <111> crystallographic texture in the normal direction and elongated grains in the extrusion direction. Characterization of the nano oxides using TEM reveals more numerous, smaller oxides present in tubing processed at lower temperatures. This work shows NFA tubing after hydrostatic extrusion and pilger processing can lead to fine grained microstructures and texturing leading to higher yield strengths at lower annealing temperatures (e.g. 800 degC)

title: 14YWT TEM images for LAUR

title: Shear Punch Testing of Neutron Irradiated HT 9 and 14YWT
abstract: Shear punch mechanical testing was performed on neutron irradiated HT 9 and 14YWT alloys, comparing the traditional ferritic/martensitic steel with the advanced oxide dispersion strengthened nanostructured ferritic alloy. The samples were irradiated at various temperatures between 380degC and 520degC. In HT 9, on increasing the irradiation temperature, the 1% offset shear stress and maximum shear stress decreased. The advanced 14YWT alloy was less sensitive to irradiation temperature with respect to irradiation hardening. However, it still exhibited irradiation hardening at each temperature.

title: Characterization of polyhedral nano oxides and helium bubbles in an annealed nanostructured ferritic alloy
abstract: Nanostructured ferritic alloys (NFAs) contain an ultra high density of 2 4 nm fcc pyrochlore Y2Ti2O7 nano oxides (NOs) embedded in a bcc Fe 14Cr ferritic matrix. Characterization of helium interactions with NOs and associated Fe Y2Ti2O7 interfaces is important to the development of structural materials for nuclear fusion and fission applications. A benchmark 14YWT NFA was first annealed to coarsen the NOs, then insoluble helium was implanted at 700 degC to produce a high number density of bubbles. High resolution scanning transmission electron microscopy characterization shows two dominant Fe Y2Ti2O7 crystallographic orientation relationships (cube on edge and cube on cube) The smallest NOs 2 nm) are associated with the smaller bubbles 1.5 nm) while some of the largest NOs 6 nm) have larger, and sometimes multiple, bubbles. NO corner {111} facets are the preferred sites for He bubble nucleation. A refined sequence of events for He trapping and bubble formation is presented. These observations offer new insight on He management in NFAs, and provide a foundation for detailed modeling studies.

title: Nanoscale analysis of ion irradiated ODS 14YWT ferritic alloy
abstract: In this work, the nanoscale microstructure of an advanced oxide dispersion strengthened (ODS) 14YWT ferritic alloy (SM13 heat) with nominal composition Fe 14Cr 3W 0.4Ti 0.3Y2O3 (wt. has been characterized by atom probe tomography (APT) before and after ion irradiation with 70 MeV Fe9+ ions at 450 degC to a total dose of 21 dpa. A detailed solute cluster analysis of APT data reveals that, in the manufacturing process, larger nanoparticles form in or close to the grain boundaries respective to those inside grains. The evolution of the nanoparticles after irradiation seems to be related to their location, as a higher increase in the number density and in the Y:Ti ratio is observed for the nanoparticles in or close to grain boundaries. APT analysis also shows Cr, W and C segregation to grain boundaries enhanced by the irradiation. A previous study of this same alloy before and after irradiation reports that the mechanical properties do not seem to be affected, but the microstructure was not investigated to confirm. The present work confirms little microstructural evolution after irradiation in this 14YWT alloy, indicating tolerance at the given irradiation conditions.

title: Tensile deformation and fracture properties of a 14YWT nanostructured ferritic alloy
abstract: A new larger heat of a 14YWT nanostructured ferritic alloy (NFA) FCRD NFA 1, was synthesized by ball milling FeO and argon atomized Fe 14Cr 3W 0.4Ti 0.2Y (wt. powders, followed by hot extrusion, annealing and cross rolling to produce an 10 mmthick plate. NFA 1 contains a bimodal size distribution of pancake shaped, mostly very fine scale, grains. The as processed plate also contains a large population of microcracks running parallel to its broad surfaces. The small grains and large concentration of Y Ti O nano oxides (NOs) result in high strength up to 800degC. The uniform and total elongations range from 1 to 8% and 10 to 24% respectively. The strength decreases more rapidly above 400degC and the deformation transitions to largely viscoplastic creep by 600degC. While the local fracture mechanism is generally ductile dimple microvoid nucleation, growth and coalescence, perhaps the most notable feature of tensile deformation behavior of NFA 1 is the occurrence of periodic delamination, manifested as fissures on the fracture surfaces.

title: On delamination toughening of a 14YWT nanostructured ferritic alloy
abstract: The FCRD NFA 1 is a high strength, irradiation tolerant nanostructured ferritic alloy (NFA) produced by ball milling argon atomized Fe 14Cr 3W 0.35Ti 0.25Y (wt. and FeO powders, followed by hot extrusion at 850oC, and subsequent annealing and crossrolling at 1000oC. The microstructure of the resulting 10 mm thick NFA 1 plate is dominated by ultrafine sub micron pancake shaped grains, and a large population of microcracks lying on planes parallel to the plate faces. Pre cracked fracture toughness tests in four different orientations (L T, T L, L S and T S) show stable crack growth by ductile tearing, with peak load KJc from 88 to 154 MPam at ambient temperature. Stable crack tearing persists down to 175degC and is accompanied by extensive delamination due to the propagation of the microcracks. Depending on the specimen orientation, this unusual toughening mechanism is either due to reduction of crack tip stresses in thin ligaments formed by the delaminations (L T and T L) or 90deg deflection of cracks initially running normal to the delaminations (L S and T S) thereby

title: Investigation of high temperature oxidation behavior of silicon added 14Cr nanostructured ferritic alloys synthesized via mechanical alloying and spark plasma sintering
abstract: In the present study, the effect of Si addition on the microstructure and subsequently, on the oxidation behavior of nanostructured oxide dispersion strengthened (ODS, 14YWT) ferritic steel was investigated. Two types of nanostructured ODS ferritic steel powders viz. Fe 14Cr 2W 0.3Ti 0.3Y2O3 (Si free) and Fe 14Cr 2W 0.3Ti 1Si 0.3Y2O3 (Si containing) were mechanically alloyed up to 50 h and consolidated via spark plasma sintering. The Si containing sintered ODS steel contained single phase ferritic microstructure with finer grains and nanoparticles of Y2Ti2O7, SiO2, and Cr2TiO4; whereas, the Si free one contained different phases such as ferrite, austenite, and martensite with nanoparticles of Cr2O3 and Y2Ti2O7. After performing oxidation at 850oC for 100 h, the weight gain in the Si containing sample (1.5 mg/cm2) was 18 times lower than that of the Si free sample (27.5 mg/cm2) Analyzing the surface and cross section of the oxide layers via SEM EDS, XRD, Rietveld refinement of XRD patterns and Raman spectroscopy, it was revealed that Si free ODS steel consisted of outer Fe2O3 and inner FeCr2O4 layers which were porous and possessed whisker like morphology. However, the oxidized Si containing ODS steel possessed thin, dense, adherent and strong protective outer layer of (Fe, Cr)2O3 and the inner layer consisted mixture of Cr2O3 and Fe2SiO4 oxides. Synergistic effect of the single crystal structure matrix and Si addition in the Si containing ODS steel played a crucial role in forming a thin, dense and protective oxide layers during the oxidation process, resulting in improved oxidation resistance.

title: Processing and Characterization of Pilgered 14YWT Tubing
abstract: The Nuclear Technology Research Development program of the Office of Nuclear Energy has implemented a program to develop an advanced reactor cladding fabrication capability by using the extrusion and pilgering processes. Oxide dispersion strengthened (ODS) steels are a promising class of advanced materials, but processes need to be developed to produce tubing for these advanced alloys. The Pacific Northwest National Laboratory (PNNL) has converted its rolling mill into a lab scale pilger mill, which required designing pilger tooling and rolls that contained multiple pilgering grooves and designing a servo driven feed mechanism. Upon assembling and checking out the system, pilgering runs on stainless steel, MA956, and 14YWT iron (Fe) based alloys were completed. Once the feed rates and rotation rates were established, the reduction schedules were determined. This report will focus on the processing and characterization of pilgered 14YWT thin wall tubing that was processed from an extruded thickwall tube using the PNNL laboratory pilger rolling mill. Characterization included optical metallography of the pilgered tube and microhardness of the processed material. The 14YWT characterization is being done in cooperation with researchers at Los Alamos National Laboratory (LANL) with LANL performing mechanical property testing of pilgered 14YWT and 14YWT tubes produced by hydrostatic extrusion at Case Western Reserve University (CWRU) Processing and Characterization of Pilgered 14YWT Tubing August 15, 2019 v Acronyms and Abbreviations 14YWT steel cladding material that has been used in liquid metal reactors CWRU Case Western Reserve University OD outer diameter ODS Oxide Dispersion Strengthened PNNL Pacific Northwest National Laboratory ROA reduction of area Processing and Characterization of Pilgered 14YWT Tubing vi August 15, 2019