Xunxiang Hu

A phase-cut method for multi-species kinetics: Sample application to nanoscale defect cluster evolution in alpha iron following helium ion implantation

Many kinetic processes in materials involve clustering of multiple species. Tracking concentrations of all compositions throughout the multi-species phase, space can readily become formidable when significant cluster growth occurs. Here, using nanoscale defect cluster evolution in alpha iron following helium ion implantation as an example, we demonstrate a phase-cut method that can effectively reduce this widely encountered problem. The method cuts out unnecessary compositions in the phase space and hence is much more efficient than a full-phase-space calculation. Yet, it retains the same precision in predicted experimental observables. The cutting of phase space does not require an accurate nucleation and growth path to be known a priori. The method may be applicable to other multi-species kinetic phenomena that are driven by irradiation and/or thermal annealing.

Modeling of irradiation hardening of iron after low-dose and low-temperature neutron irradiation

Irradiation hardening is a prominent low-temperature degradation phenomena in materials, and is characterized both by an irradiation-induced increase in yield strength along with the loss of ductility. In this paper, a reaction?diffusion cluster dynamics model is used to predict the distribution of vacancy and interstitial clusters in iron following low-temperature (<373?K) and low-dose (<0.1?dpa) neutron irradiation. The predicted microstructure evolutions of high-purity iron samples are compared to published experimental data (positron annihilation spectroscopy and transmission electron microscopy) and show good agreement for neutron irradiation in this regime. The defect cluster distributions are then coupled to a dispersed barrier hardening model that assumes a strength factor, ?, which varies with cluster type and size to compute the yield strength increase; the results of which agree reasonably well with tensile tests performed in previous studies. The modeling results presented here compare quite well to the experimental observations in the low-dose regime, and provide insight into the underlying microstructure?property relationships and the need for spatially dependent modeling to accurately predict the saturation behavior of yield strength changes observed experimentally at higher dose levels.

First Annual Progress Report on Radiation Tolerance of Controlled Fusion Welds in High Temperature Oxidation Resistant FeCrAl Alloys

The present report summarizes and discusses the first year efforts towards developing a modern, nuclear grade FeCrAl alloy designed to have enhanced radiation tolerance and weldability under the Department of Energy (DOE) Nuclear Energy Enabling Technologies (NEET) program. Significant efforts have been made within the first year of this project including the fabrication of seven candidate FeCrAl alloys with well controlled chemistry and microstructure, the microstructural characterization of these alloys using standardized and advanced techniques, mechanical properties testing and evaluation of base alloys, the completion of welding trials and production of weldments for subsequent testing, the design of novel tensile specimen geometry to increase the number of samples that can be irradiated in a single capsule and also shorten the time of their assessment after irradiation, the development of testing procedures for controlled hydrogen ingress studies, and a detailed mechanical and microstructural assessment of weldments prior to irradiation or hydrogen charging. These efforts and research results have shown promise for the FeCrAl alloy class as a new nuclear grade alloy class.

Combining Transmission Kikuchi Diffraction and Scanning Transmission Electron Microscopy for Irradiated Materials Studies

Transmission Kikuchi diffraction (tKD) has exploded into the characterization field over the last few years [1], and we have found it to be extraordinarily useful to examine neutron-, ionand plasmairradiated materials here at ORNLs Low Activation Materials Development and Analysis (LAMDA) laboratory [2, 3]. Advanced nanostructured materials, intended to provide improved radiation tolerance, and materials that develop nanostructures under irradiation, benefit from high-resolution characterization to understand their mechanical, thermal, or other properties. We examined many irradiated materials using tKD, and have combined tKD with scanning/transmission electron microscopy (S/TEM), primarily X-ray mapping and multivariate statistical analysis (MVSA). We used a JEOL J6500F SEM with EDAX Hikari I EBSD system for non-radioactive materials, and an FEI Versa3D FIB-SEM with Oxford Nordlys EBSD system for both radioactive and non-radioactive materials, and an FEI Talos F200X ChemiSTEM system for S/TEM and X-ray mapping [4,5].

Preliminary Results on FeCrAl Alloys in the As-received and Welded State Designed to Have Enhanced Weldability and Radiation Tolerance

The present report summarizes and discusses the recent results on developing a modern, nuclear grade FeCrAl alloy designed to have enhanced radiation tolerance and weldability. The alloys used for these investigations are modern FeCrAl alloys based on a Fe-13Cr-5Al-2Mo-0.2Si-0.05Y alloy (in wt.%, designated C35M). Development efforts have focused on assessing the influence of chemistry and microstructure on the fabricability and performance of these newly developed alloys. Specific focus was made to assess the weldability, thermal stability, and radiation tolerance.

Technology Implimentation Plan - ATF FeCrAl Cladding for LWR Application

Technology implimentation plan for FeCrAl development under the FCRD Advanced Fuel program. The document describes the activities required to get FeCrAl clad ready for LTR testing