Valentin Pauly

experiment to a single set of irradiation parameters (e.g., dose, fluence, injection rate, temperature etc.). Despite being capable of achieving damage rates up to three orders of magnitude higher than neutron irradiation, its overall sample throughput remains low due to the need to conduct separate irradiations for each unique parameter set. To address these limitations, a novel capability has been developed at the Michigan Ion Beam Laboratory (MIBL), enabling for the creation of two-dimensional lateral ion implantation gradients using recently installed motorized-controlled ion beam shutters. This advancement can generate a wide scope of the two dimensional (H+, He2+) implantation parameter space within a single sample. Integration of this new capability enables dual- and triple-ion beam experiments to be performed with full user control over not only the ion implantation depth profile, but also over the lateral imposed concentration gradients, thus providing researchers with a high-throughput means for material testing under various irradiation conditions. Furthermore, the recent installation of a microbeam in the ion-beam analysis (IBA) target station now allows for probing these concentration gradients in irradiated alloys with unprecedently high spatial resolutions. These developments promise to significantly improve ion irradiation capabilities, offering researchers a robust and high-throughput method to efficiently investigate candidate alloys for both advanced fission and fusion reactor applications, in both a time- and cost-effective manner. This paper demonstrates all the above through showcasing detailed implantation profiling and swelling characterization conducted over the lateral gradients imposed on single crystal Si and the fusion candidate alloy F82H-IEA.

Ferritic/martensitic steels T91 and HT9 were irradiated with neutrons (BOR-60 reactor) and dual ions (9 MeV Fe3+ and 3.42 MeV energy degraded He2+) from 369 to 520 °C and damage levels of 16.6 to 72 dpa to quantify the possibility of using ion irradiation to simulate neutron irradiation in terms of microstructures and mechanical properties. Nanoindentation testing was performed to obtain the bulk equivalent hardness of the dual-ion irradiated samples. For the neutron irradiated samples, both nanoindentation and Vickers hardness testing were conducted. Transmission Electron Microscopy (TEM) characterizations of the cavities, dislocation loops and precipitates were conducted to account for the strengthening contribution of each microstructure element. The good agreement between the microstructure-predicted (dispersed barrier hardening) and measured strength of the irradiated specimens demonstrated the accuracy of the strengthening model and the nanoindentation tests. The comparison of mechanical property and microstructure changes in ion and neutron irradiated structural materials indicated that ion irradiation replicated many neutron irradiation features. However, a single 70 °C temperature shift is insufficient to match all complex microstructures of neutron vs. ion irradiation over the irradiation temperature range of 369–520 °C.

We explore the effects of thermo-chemical aluminization on wear resistance of candidate alloys Incoloy 800HT and Inconel 617 for high-temperature gas-cooled reactor (HTGR) components. Aluminized samples were conditioned for 22 days in a once-through helium loop to simulate oxidizing conditions of HTGRs. The tribological performance of unconditioned and conditioned samples was tested using pin-on-disk tribometer in an air environment at 750 °C for 800HT and 900 °C for 617. Aluminized 800HT exhibited superior wear resistance compared to that of the as-received 800HT due to harder Fe-Al intermetallic compounds that formed at the surface of the alloy. Aluminized 617 exhibited wear resistance superior to that of the as-received 617 at higher loads but inferior resistance at lower loads. Conditioned 800HT as well as aluminized and then conditioned 800HT exhibited negligible wear when the protective oxide remained intact during tribotesting. When the oxide wore through, aluminized and then conditioned 800HT exhibited superior wear resistance compared to that of conditioned 800HT due to the increased hardness of intermetallic zones. Aluminized and then conditioned 617 exhibited inferior wear resistance compared to that of conditioned 617 due to significant ceramic wear of the aluminum oxide. Connections between surface hardness, chemical composition, initial friction coefficients, and wear resistance are established.

Incoloy 800HT and Inconel 617 have been selected as candidate structural alloys for the high-temperature gas-cooled reactor (HTGR) concept. Helium, the primary coolant, contains impurities (e.g., H2O and CH4) that can induce corrosion reactions at high temperatures, which in turn can affect the tribological behavior of components in sliding contact such as valves and control-rod drive systems. This paper presents results from the study of the tribological behavior of both alloys before and after conditioning them in either an impure-helium oxidizing environment or in an air environment. Both alloys were conditioned for 22 days at elevated temperatures in a once-through helium loop with 4 ppmv H2O and tested subsequently at elevated temperatures with a pin-on-disk tribometer in an air environment - 650 °C and 750 °C for 800HT; 850 °C and 900 °C for 617 – with various applied loads - 1 N, 2 N and 5 N. SEM-EDS analysis revealed that conditioning the samples in an oxidizing environment leads to the formation of a mixed Fe/Cr-oxide on alloy 800HT and a Cr-oxide on alloy 617, both increasing the wear resistance compared to that of as-received samples. Alloy 617 exhibited lower steady-state friction coefficients compared to those of alloy 800HT. There was a significant decrease in the scatter of the steady-state friction coefficient of the conditioned samples compared to that of the unconditioned samples. The steady-state friction coefficient for alloy 800HT and 617 were found to be 0.53 ± 0.07 and 0.25 ± 0.04, respectively. The wear resistance of alloy 800HT is approximately one order of magnitude lower than that of alloy 617 in all cases that exhibited measurable wear. After sample conditioning, the wear volumes measured at low loads were undistinguishable from the unworn background, a result attributed to the formation of a compacted glaze layer under high temperatures and high contact stresses.

An international collaboration was established as a Coordinated Research Project (CRP) under the IAEA and entitled Accelerator Simulation and Theoretical Modelling of Radiation Effects-II (SMoRE-II). It was created to determine, by way of a Round Robin process, the degree to which ion irradiations produced the same irradiated microstructure when conducted in different labs on the same alloy and provided with the same irradiation protocol. The Round Robin consisted of 13 participating organizations from 9 IAEA member states with ion irradiations conducted at all CRP partner sites on samples of a single alloy (T91) from a single billet with the same thermal-mechanical history, and with a specific protocol for conducting the irradiations. Of the 14 parameters specified for the ion irradiations, only 1 of 12 facilities was able to follow the protocol exactly. Major differences included vacuum pressure, temperature measurement and control, beam mode (raster-scanning vs. steady beam), and dosimetry. The microstructure features characterized were the sizes and number densities of cavities, dislocation loops, precipitates, and the radiation induced segregation. While loop size and number density appeared to correlate with carbon content, no such correlation was identified for cavities. The divergence from the irradiation protocol undoubtedly affected the irradiated microstructure with carbon contamination occurring in most cases. The cavity, dislocation loop and precipitate microstructures all fell within the range of that in the literature. Additionally, a T91 sample that was irradiated to 47 dpa at 376°C in the BOR-60 reactor was selected for comparison of the microstructure to those in the Round Robin study.

Dual-ion irradiations using 5.0 MeV defocused Fe2+ ions and co-injected energy degraded 2.00 to 2.85 MeV He2+ ions were conducted on a Fe9CrMo ferritic-martensitic steel T91 to 17 dpa at a damage rate range of 5 × 10−5 dpa/s to 3 × 10−3 dpa/s at 445°C, followed by characterization of the microstructure using conventional and scanning transmission electron microscopy. Radiation induced Ni/Si clusters and radiation induced segregation were quantified using energy dispersive X-ray spectroscopy at each condition and were compared with the same material irradiated in the BOR-60 reactor and in the as-received condition. No significant Cr segregation was found at lath boundaries after dual-ion irradiation, while Ni and Si enrichments both decreased with increasing damage rate leading to a sharp decrease in the density of Ni/Si clusters with damage rate. Increased point defect recombination at higher ion damage rates likely reduced the Ni/Si cluster density compared with BOR-60. Although the overall vacancy concentration and diffusion are enhanced by the irradiation damage rate, the lack of time for thermal diffusion and ballistic displacements of solutes are significant limiting factors for Ni/Si cluster formation. This work demonstrates the effect of irradiation damage rate on elemental segregation and clustering when using ion irradiation to simulate reactor irradiation.

Incoloy™ 800HT and Inconel™ 617 are primary candidate structural materials for high-temperature gas-cooled reactors (HTGRs). Impurities (e.g., H2O, CH4) in the coolant induce corrosion reactions that affect tribological behavior. We investigate the high-temperature tribological performance of the alloys under surface conditions including: conditioned in H2O-containing helium at elevated temperatures, hardened via the carbon-diffusion Kolsterising® treatment, and conditioned after hardening. Initial friction coefficients and volume removed serve as metrics for wear performance. We find that wear mechanisms including scuffing, glaze-oxide formation, and oxide-layer wear and break-through are governed by surface hardness, chemistry, and applied load. The formation of a glaze-oxide layer is achieved with an oxide of sufficient mechanical integrity if the oxide-substrate interface is strong and the load is low.