Tim Gräning

Oak Ridge National Laboratory | ORNL · Materials Science and Technology Division

Citation: Robin, I.K.; Gräning, T.; Yang, Y.; Haider, S.B.; Lass, E.A.; Katoh, Y.; Zinkle, S.J. Evaluation of Tungsten-Steel Solid-State Bonding: Options and the Role of CALPHAD to Screen Diffusion Bonding Interlayers. Abstract: Critical aspects of innovative design in engineering disciplines like infrastructure, transportation , and medical applic...

Plasma-facing components (PFCs) are among the most critical gaps for fusion energy to establish technical and economic feasibility. Tungsten as a first wall/blanket material in PFCs requires to be integrating with reduced activation ferritic martensitic (RAFM) steels as a structural component. Currently, major drawbacks are the requirement of brazi...

Accident-tolerant fuel concepts have been developed recently in diverse research programs. Recent research has shown clear advantages of Cr-coated Zr cladding over bare cladding tubes regarding oxidation behavior under the design basis loss-of-coolant accident condition. However, limited data are available about the hydriding behavior of the Cr coa...

Accident tolerant fuel claddings seek to improve safety margins during loss-of-coolant accident (LOCA) scenarios by reducing cladding steam oxidation rates, hydrogen production, delaying or mitigating cladding burst, and reducing cladding deformation. After rapid and extensive progress in recent years, Cr coated Zr-based alloys, ferritic FeCrAl, an...

Cr-coated Zr-alloys are a near-term cladding concept to improve reactor safety during accident scenarios. Burst and steam oxidation behavior of bare and Cr-coated Zirlo claddings were examined under simulated loss-of-coolant accident conditions. The 4.4 µm coating had no substantial effect on ballooning or opening geometry but did increase burst te...

Reduced activation ferritic (RAF) martensitic steels are promising candidates for the first wall of fusion reactors. However, current manufacturing capabilities call for these components to be made by welding wrought plates. This limits design freedom and necessitates the use of post-weld heat treatments (PWHT) in accordance with the boiler and pre...

Austenitic oxide dispersion strengthened steels were developed to serve as a structural material in power plants. Mechanical alloying is used with the aim to homogeneously distribute rare earth elements like yttrium inside a steel matrix to form strengthening nano-scaled particles. Due to the ductile nature of a face centered cubic austenite matrix...

To develop advanced nuclear fuel claddings, two oxide dispersion strengthened (ODS) alloys were designed, manufactured, and evaluated. First, 12%Cr alloy, is an ODS-version of ferritic steel, and second, 10%Cr-6%Al alloy, is a high-strength version of accident tolerant iron-chrome-aluminum alloy. Their properties and performance were compared with...

Ten Eurofer97 steel variants, produced by non-standard fabrication-processing routes and modified alloying chemistries, were studied by neutron irradiations in the high flux isotope reactor. The irradiations were performed to ITER-TBM relevant conditions of ∼255–350 °C, 2.94–3.24 dpa. We quantified the irradiation-induced degradation of the steels...

Presently available data on neutron irradiation damage raise doubts on the feasibility of using EUROFER97 steel for a water-cooled starter blanket in a DEMO reactor, since the ductile-to-brittle transition temperature (DBTT) increases significantly for irradiation temperatures below 350°C. The additional DBTT shift caused by H and He transmutation...

In this study, we performed fracture toughness characterization of ten neutron-irradiated Eurofer97 variants using precracked miniature multi-notch bend bar (M4CVN) specimens based on the Master Curve method in the ASTM E1921 standard. The neutron irradiation was performed in the flux trap position of the High Flux Isotope Reactor (HFIR) of the Oak...

To develop advanced reduced-activation ferritic-martensitic (RAFM) steels for fusion reactor structural applications, both carbonitride- and carbide-strengthened castable nanostructured alloys (CNAs) were explored for higher densities of MX (M = Ti/Ta/V/etc. and X = C/N) nanoprecipitates. Systematic comparisons between the two types of CNAs indicat...

In this study, we performed fracture toughness testing of ten Eurofer97 steel variants using precracked miniature multi-notch bend bar (M4CVN) specimens based on the Master Curve method in the ASTM E1921 standard. Additional Vickers microhardness and room temperature tensile testing complemented the fracture toughness testing. Compared with standar...

Austenitic oxide dispersion strengthened (ODS) steel rods containing a carbon-rich process control agent were annealed at 700, 900 and 1100 °C for up to 1500 h. The addition of a process control agent was necessary during the mechanical alloying process to achieve a reproducible production process. In this study, the impact of the added carbon-rich...

Under the framework of EUROfusion, we performed comprehensive mechanical and microstructure characterization of ten Eurofer97 steel variants with varying compositions and heat treatment conditions. We characterized the pre-irradiation fracture toughness of the materials along with their Vickers hardness, tensile properties, and microstructure. Comp...

The adhesion of austenitic oxide dispersion strengthened (ODS) steel during mechanical alloying and a decreased powder production yield can be overcome by the addition of a process control agent: stearic acid. Here, the influence of stearic acid and the introduction of carbon in an extruded and annealed austenitic ODS steel was investigated. In par...

Transmission electron microscopy (TEM) was applied to study the microstructure and composition of a novel austenitic oxide dispersion strengthened (ODS) steel (16 wt.% Cr, 14 wt.% Ni, 1 wt.% W). Special attention was paid to characterize the dispersed nano-oxide particles. It was found, that these embedded particles have a size distribution ranging...

In this work, a high-temperature low-cycle fatigue (LCF) behavior of a newly developed austenitic oxide dispersion strengthened (ODS) steel is investigated. The LCF tests were performed in air at 650 °C under three different strain amplitudes (0.4, 0.5, and 0.7%) with a nominal strain rate of 10-3 s-1. The measured cyclic stress response showed fou...

Austenitic oxide dispersion strengthened (ODS) steels are one of the candidates as a structural material for high-temperature applications in future power plants. To guarantee the necessary high production yield, the production process was improved in terms of reproducibility and scalability, by adding a process control agent (PCA) during the milli...

The thesis shows the production, characterization and optimization of austenitic ODS steels. A conventional mechanical alloying approach was utilized and optimized to achieve a higher production yield. The microstructure of more than 16 different alloys has been investigated in form of powder, extruded rods and hot-rolled sheets. A production proce...

This article is to summarize and examine processing parameters of novel developed austenitic oxide dispersed strengthened (ODS) steels. Comparing hot-rolled and extruded conditions after the same degree of deformation after and before annealing, are just some examples to give insights into the complex processing of austenitic ODS steels. One of the...

The focus of this study is to investigate the low-cycle fatigue (LCF) behavior of two newly developed austenitic 17Cr13Ni-W ODS steels. The LCF tests were performed at 650 °C with strain amplitudes ranging from 0.4 to 0.9 %. The cyclic stress response and the cyclic strain-life resistance were analyzed in detail and compared with two non-ODS austen...

The local structure and lattice dynamics in cubic Y2O3 were studied at the Y K-edge by X-ray absorption spectroscopy in the temperature range from 300 to 1273 K. The temperature dependence of the extended X-ray absorption fine structure was successfully interpreted using classical molecular dynamics and a novel reverse Monte Carlo method, coupled w...

Oxide dispersion strengthened (ODS) steels are promising materials for fusion power reactors, concentrated solar power plants, jet engines, chemical reactors as well as for hydrogen production from thermolysis of water. In this study we used X-ray absorption spectroscopy at the Fe and Cr K-edges as a tool to get insight into the local structure of...

The aim of this paper is to present the mechanical properties of tungsten laminate pipes made of tungsten foil and to discuss their use in innovative high temperature energy conversion systems. Tungsten is the metal with the highest melting point of all metals and would therefore be an excellent fit for high temperature applications. But tungsten h...