The smallest macroscale tensile test - a model to describe constrained flow at the microscale

This work addresses the strain response and plastic flow behavior of grain boundary or interface containing materials during small scale mechanical testing. We introduce a set of geometric criteria allowing us to constrain a sample to obtain macroscopic-like flow behavior on a microscale test, as shown in Figure 1. Furthermore, the featured parameter, the blocked volume ratio, provided a new description of plasticity of microscale tensile samples in a constrained volume due to external interfaces such as coating and grain boundaries. The proposed description was experimentally validated with different Ni-based materials and different constraints (grain boundary and coating interfaces). The developed theory would open new research avenues in establishing the connection between microscale response to bulk properties as follows: Please click Additional Files below to see the full abstract

Alpha ' formation kinetics and radiation induced segregation in neutron irradiated 14YWT nanostructured ferritic alloys

Nanostructured ferritic alloys are considered as candidates for structural components in advanced nuclear reactors due to a high density of nano-oxides (NOs) and ultrafne grain sizes. However, bimodal grain size distribution results in inhomogeneous NO distribution, or vice versa. Here, we report that density of NOs in small grains (2µm) before and after irradiation. After 6dpa neutron irradiation at 385–430°C, α′ precipitation has been observed in these alloys; however, their size and number densities vary considerably in small and large grains. In this study, we have investigated the precipitation kinetics of α′ particles based on the sink density, using both transmission electron microscopy and kinetic Monte Carlo simulations. It has been found that in the presence of a low sink density, α′ particles form and grow faster due to the existence of a larger defect density in the matrix. On the other hand, while α′ particles form far away from the sink interface when the sink size is small, Cr starts to segregate at the sink interface with the increase in the sink size. Additionally, grain boundary characteristics are found to determine the radiation-induced segregation of Cr

Stable, Ductile and Strong Ultrafine HT-9 Steels via Large Strain Machining

Beyond the current commercial materials, refining the grain size is among the proposed strategies to manufacture resilient materials for industrial applications demanding high resistance to severe environments. Here, large strain machining (LSM) was used to manufacture nanostructured HT-9 steel with enhanced thermal stability, mechanical properties, and ductility. Nanocrystalline HT-9 steels with different aspect rations are achieved. In-situ transmission electron microscopy annealing experiments demonstrated that the nanocrystalline grains have excellent thermal stability up to 700 & DEG;C with no additional elemental segregation on the grain boundaries other than the initial carbides, attributing the thermal stability of the LSM materials to the low dislocation densities and strains in the final microstructure. Nano-indentation and micro-tensile testing performed on the LSM material pre- and post-annealing demonstrated the possibility of tuning the material's strength and ductility. The results expound on the possibility of manufacturing controlled nanocrystalline materials via a scalable and cost-effective method, albeit with additional fundamental understanding of the resultant morphology dependence on the LSM conditions

Report on the Gaithersburg NanoNuclear Workshop and Strategic Planning Recommendations

Not applicable. This report not written by INL personnel--Is only being screened through STIMS by Jon Carmack of INL, Battelle. No Abstract or brief Summary/Introduction was included

Correlation of in-situ transmission electron microscopy and microchemistry analysis of radiation-induced precipitation and segregation in ion irradiated advanced ferritic/martensitic steels

This article presents a novel method combining ion irradiation, in-situ transmission electron microscopy (TEM), and microchemistry analysis before/after irradiation, which allows to examine same microstructural areas throughout ion irradiation. A 12 wt% Cr Ferritic/Martensitic steel (HT9) was irradiated in the TEM to 1.17 x 10(20) ions.m(-2) at 440 degrees C using 1 MeV Kr2+ ions, and the in-situ characterization focused on radiation-induced precipitation and segregation. Results of in-situ experiments were compared with those obtained from ex-situ experiments, to showcase how this method helps to better understand precipitation kinetics in the irradiated material examined ex-situ, for which only snapshots are available at limited doses. Published by Elsevier Ltd on behalf of Acta Materialia Inc

Report on the Gaithersburg NanoNuclear Workshop and Strategic Planning Recommendations

Not applicable. This report not written by INL personnel--Is only being screened through STIMS by Jon Carmack of INL, Battelle. No Abstract or brief Summary/Introduction was included