wolfgang hoffelner - Academia.edu (original) (raw)

Papers by wolfgang hoffelner

Ferritic oxide dispersion strengthened steels with different microstructure were in-beam creep te... more Ferritic oxide dispersion strengthened steels with different microstructure were in-beam creep tested in a temperature range from 300 °C to 500 °C. Irradiation was by He-ions. Elongation was determined as a function of stress and irradiation damage rate. Damage was investigated by transmission electron microscopy. A thorough analysis of the loops developing during irradiation creep did not show any dependence of orientation or size on the direction of the applied stress. At 400 °C radiation induced segregation was found (most probably an iron aluminide) which had no effect on irradiation creep. No pronounced influence of microstructure or dispersoid size on the irradiation creep behavior was detected. Irradiation creep compliance of PM2000 with dispersoids of about 30 nm diameter were found to differ little from material with dispersoids of only 2–3 nm diameter. This is in contrast to thermal creep where dislocation–obstacle interactions are extremely important. An assessment of the technical relevance of irradiation creep in advanced nuclear systems is presented.

This scientific assessment serves as the basis for a materials research roadmap for the nuclear f... more This scientific assessment serves as the basis for a materials research roadmap for the nuclear fission technology, itself an integral element of an overall "Materials Roadmap Enabling Low Carbon Technologies", a Commission Staff Working Document published in December 2011. The Materials Roadmap aims at contributing to strategic decisions on materials research funding at European and Member State levels and is aligned with the priorities of the Strategic Energy Technology Plan (SET-Plan). It is intended to serve as a guide for developing specific research and development activities in the field of materials for energy applications over the next 10 years. This report provides an in-depth analysis of the state-of-the-art and future challenges for energy technologyrelated materials and the needs for research activities to support the development of nuclear fission technology both for the 2020 and the 2050 market horizons. It has been produced by independent and renowned Europ...

This technical report uses the same nomenclature as the ASME Boiler and Pressure Vessel Code. The... more This technical report uses the same nomenclature as the ASME Boiler and Pressure Vessel Code. The organization of ASME Code Section III is summarized below. ASME Code Section III consists of Divisions. Divisions are broken down into Subsections. Subsections may be divided into Subparts, or more generally into Articles, subarticles, paragraphs, and, where necessary, subparagraphs and subsubparagraphs. Articles are designated by the applicable letters indicated above for the Subsections and Subparts where applicable, followed by Arabic numbers, such as NB-1000. Where possible, Articles dealing with the same topics are given the same number in each Subsection, except NCA. Details of the analysis supporting the need for further review are given in Section 4 Table HBB-I-14.12.

Nuclear Engineering and Technology, 2009

Despite the worldwide developments towards advanced fission reactors there is a worldwide demand ... more Despite the worldwide developments towards advanced fission reactors there is a worldwide demand for conventional light water reactors. Key elements of such reactors are the cladding pipes which contain the nuclear fuel (UO2) tablets and which are in direct contact with the coolant i.e. water. As cladding materials zirconium alloys are used because of their good neutronic and corrosion properties. The family of these alloys containing small amounts of elements like Sn, Fe, Ni, Cr is called Zircaloy. Claddings are typically 10 mm in diameter with a wall thickness of 0.6 to 0.9 mm up to several meters long. In order to improve the efficiency of nuclear fuel-thereby reducing high level waste-higher fuel burnups are required. One limiting factor is the interaction of the cladding with the products of the radiolysis of water: oxygen and hydrogen. Hydrogen forms needle like hydrides which reduce the toughness of the material considerably. Oxygen forms oxide layers consuming the metallic cross-section of the cladding. Many attempts were made to improve the oxidation behaviour of Zircaloy by changing the alloy chemistry but there is still potential for improvement. Additional damage can occur due to fretting between the cladding and fixtures which can lead to premature failure.

Superalloys 1984 (Fifth International Symposium), 1984

Fatigue crack growth rates of a variety of high temperature alloys (nickel-base, iron-base) were ... more Fatigue crack growth rates of a variety of high temperature alloys (nickel-base, iron-base) were investigated at various temperatures in air and in vacuum. Growth rates at intermediate cyclic stress intensity ranges and also in the threshold regime were studied. At room temperature the materials show a rather similar crack growth behaviour in the Paris regime. Differences in the threshold regime can be explained by microstructural and closure effects. Even in vacuum the temperature dependence of the Paris regime cannot be explained only by the temperature dependence of Young's modulus. Oxidation predominantly influences the crack growth rates at elevated temperatures. Under these conditions crack growth in the threshold regime is governed by mechanisms similar to those at room temperature but additionally by oxidation induced mechanisms (crack branching, oxide induced closure) occur.

The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.

MRS Proceedings, 1997

ABSTRACTPlasma processes become more and more attractive for the treatment of radioactive low/med... more ABSTRACTPlasma processes become more and more attractive for the treatment of radioactive low/medium level waste. Plants with throughput rates ranging from 20 kilograms to several hundred kilograms per hour are under construction or under evaluation in different countries. One major installation is under construction at the ZWILAG-site in Wurenlingen (Switzerland). ZWILAG (Zwischenlager Wurenlingen AG) is a company being responsible for treatment and intermediate storage of all radioactive wastes occurring in Switzerland. Thermal destruction (pyrolysis) of organic material and melting of the inorganic residuals and inorganic feed stock can be done simultaneously in a plasma heated vessel. The following output materials are obtained: Metal, glassy slag, off-gas. Depending on feed stock and storage requirements these outputs can have different properties. The distribution of the activity is of particular importance. Isotopes like cobalt-60 (as a metal) partition almost quantitatively ...

Fourth International Topical Meeting on High Temperature Reactor Technology, Volume 2, 2008

Advanced nuclear plants are designed for long-term operation in quite demanding environments. Lim... more Advanced nuclear plants are designed for long-term operation in quite demanding environments. Limited operation experience with the materials used in such plants necessitate a reliable assessment of damage and residual life of components. Non-destructive condition monitoring of damage is difficult, if not impossible for many materials. Periodic investigation of small samples taken from well defined locations in the plant could provide an attractive tool for damage assessments. This paper will discuss possibilities of using very small samples taken from plant locations for complementary condition monitoring. Techniques such as micro/nano-indentation, micropillar compression, micro bending, small punch and thin strip testing can be used for the determination of local mechanical properties. Advanced preparation techniques such as focused ion beam (FIB) allow the preparation of samples from these small volumes for micro-structural analyses with transmission electron microscope (TEM) and...

Physical Review Letters, 2011

Relaxation processes of dislocation systems are studied by two-dimensional dynamical simulations.... more Relaxation processes of dislocation systems are studied by two-dimensional dynamical simulations. In order to capture generic features, three physically different scenarios were studied and power-law decays found for various physical quantities. Our main finding is that all these are the consequence of the underlying scaling property of the dislocation velocity distribution. Scaling is found to break down at some cutoff time increasing with system size. The absence of intrinsic relaxation time indicates that criticality is ubiquitous in all states studied. These features are reminiscent of glassy systems and can be attributed to the inherent quenched disorder in the position of the slip planes.

Physical Review Letters, 2007

Synergistic synchrotron x-ray absorption experiments using imaging magnetic microspectroscopy, x-... more Synergistic synchrotron x-ray absorption experiments using imaging magnetic microspectroscopy, x-ray magnetic circular dichroism, and ab initio calculations on FeCr alloys reveal that the Cr content strongly influences the ferromagnetic microstructure and the Fe magnetic moments. The Cr local structure resolved by extended x-ray absorption fine structure (EXAFS) is also found to be affected by the alloy's composition. Both EXAFS and ab initio calculations show a change in the Cr local atomic structure above 10 at.% Cr content from the distance contraction of the first two coordination shells around the Cr absorbing atom. These results indicate the strong dependence of magnetic and structural properties of these alloys on Cr concentration.

Physical Review B, 2007

A simulation of dislocation patterning in a two-dimensional multislip configuration is carried ou... more A simulation of dislocation patterning in a two-dimensional multislip configuration is carried out by means of coarse graining in the presence of plastic strain. In order to study the influence of climb on the dislocation cell pattern formation, fatigue simulations with and without climb mobility are performed and compared. The main result is that, in the presence of climb, cellular structures with well-defined characteristic length emerge, in contrast to the self-similar dislocation patterns developing under similar deformation conditions in the absence of climb. Despite the simplicity of our model, the fractal dimension of the self-similar dislocation patterns emerging without climb confirms the previous results for fcc crystals deformed in a multislip configuration. The cell structures emerging when climb is not negligible ͑in our simulations a climb mobility 1000 times smaller than the glide mobility was considered͒ resemble the dislocation patterns seen in thermal recovery or melt-grown experiments.

Modelling and Simulation in Materials Science and Engineering, 2011

Simulation of subgrain growth during recovery is carried out using two-dimensional discrete dislo... more Simulation of subgrain growth during recovery is carried out using two-dimensional discrete dislocation dynamics on a hexagonal crystal lattice having three symmetric slip planes. To account for elevated temperature (i) dislocation climb was allowed and (ii) a Langevin type thermal noise was added to the force acting on the dislocations. During the simulation, a random ensemble of dislocations develop into subgrains and power-law type growth kinetics are observed. The growth exponent is found to be independent of the climb mobility, but dependent on the temperature introduced by the thermal noise. The in-depth statistical analysis of the subgrain structure shows that the coarsening is abnormal, i.e. larger cells grow faster than the small ones, while the average misorientation between the adjacent subgrains remains nearly constant. During the coarsening Holt's relation is found not to be fulfilled, such that the average subgrain size is not proportional to the average dislocation spacing. These findings are consistent with recent high precision experiments on recovery.

Metallurgical and Materials Transactions A, 2009

Titanium aluminides are well-accepted elevated temperature materials. In conventional application... more Titanium aluminides are well-accepted elevated temperature materials. In conventional applications, their poor oxidation resistance limits the maximum operating temperature. Advanced reactors operate in nonoxidizing environments. This could enlarge the applicability of these materials to higher temperatures. The behavior of a cast gamma-alpha-2 TiAl was investigated under thermal and irradiation conditions. Irradiation creep was studied in beam using helium implantation. Dog-bone samples of dimensions 10 9 2 9 0.2 mm 3 were investigated in a temperature range of 300°C to 500°C under irradiation, and significant creep strains were detected. At temperatures above 500°C, thermal creep becomes the predominant mechanism. Thermal creep was investigated at temperatures up to 900°C without irradiation with samples of the same geometry. The results are compared with other materials considered for advanced fission applications. These are a ferritic oxide-dispersion-strengthened material (PM2000) and the nickel-base superalloy IN617. A better thermal creep behavior than IN617 was found in the entire temperature range. Up to 900°C, the expected 10 4 hour stress rupture properties exceeded even those of the ODS alloy. The irradiation creep performance of the titanium aluminide was comparable with the ODS steels. For IN617, no irradiation creep experiments were performed due to the expected low irradiation resistance (swelling, helium embrittlement) of nickel-base alloys.

Metallurgical Transactions A, 1988

The crack growth behavior of several high temperature nickel-base alloys, under cyclic and static... more The crack growth behavior of several high temperature nickel-base alloys, under cyclic and static loading, is studied and reviewed. In the oxide dispersion strengthened (ODS) MA 6000 and MA 754 alloys, the high temperature crack propagation exhibited orientation dependence under cyclic as well as under static loading. The creep crack growth (CCG) behavior of cast nickel-base IN-738 and IN-939* superalloys at 850 °C could be characterized by the stress intensity factor, Kt. In the case of the alloy IN-901 at 500 °C and 600 °C, Kt was found to be the relevant parameter to characterize the creep crack growth behavior. The energy rate line integral, C*, may be the appropriate loading parameter to describe the creep crack growth behavior of the nickel-iron base IN-800H alloy at 800 °C. The creep crack growth data of 1Cr-Mo-V steel, with bainitic microstructure, at 550 °C could be correlated better by C* than by K 1 .

Metallurgical Transactions A, 1982

The high cycle fatigue (HCF) properties of two cast nickel base-superalloys, IN 738 LC and IN 939... more The high cycle fatigue (HCF) properties of two cast nickel base-superalloys, IN 738 LC and IN 939, were investigated using both fracture mechanics samples and smooth specimens. The crack propagation behavior was studied in terms of linear fracture mechanics at RT and at 850 ~ In addition to the influence of temperature, the influences of frequency, mean stress, and environment (vacuum, air, sulfidizing atmosphere) were studied. At 850 ~ the fatigue thresholds were found to be higher in air than in vacuum. This could be explained by crack branching. The high scatter of fatigue crack propagation rates could be related also to this phenomenon. The S/N curves at 850 ~ can be predicted treating crack growth from casting pores as the predominant failure mechanism. At RT the same method is not as successful. The reason for this may be that crack growth laws measured on long, branched cracks are not applicable to short, unbranched cracks. At RT, no significant influence of frequency on S/N-curves and fatigue crack growth rates was observed for frequencies up to 20 kHz.

Journal of ASTM International, 2005

Metal-oxide interfaces of three different materials irradiated in a pressurized water reactor hav... more Metal-oxide interfaces of three different materials irradiated in a pressurized water reactor have been analyzed by TEM and AEM. Standard Zircaloy-4, low-tin Zircaloy-4, and Zr-2.5%Nb were used for this study. The microstructure of the material on the two sides of the metal-oxide interface, the geometry of the interface, the distribution of different alloying elements, and the oxygen profile have been examined in each material. Results of the examinations showed that the three materials had different microstructure and oxygen distribution on the two sides of the metal-oxide interface. In particular, the following parameters were noticed: a) the geometry of the interface seems to be of a different nature in the case of Zr-2.5%Nb alloy. Unlike the Zircaloy-4 alloys, which show an undulated interface, this material has a "jigsaw" type interface. This point is discussed, and its role on the oxidation is considered. b) Hydrides are observed and analyzed in the vicinity of the interface in the case of low-tin Zircaloy-4, and it is shown that they can have an influence on the occurrence of cracks in this material. c) The origins of stress are discussed, and it is shown that it can have different sources. The crystal structure of the oxides is mainly monoclinic. A tetragonal oxide is observed at some regions, in particular in the standard Zircaloy-4.

Journal of Nuclear Materials, 2011

In Ni-base superalloys with low Al and/or Ti content the precipitation and subsequent coarsening ... more In Ni-base superalloys with low Al and/or Ti content the precipitation and subsequent coarsening of γ particles at intermediate temperatures contribute to the degradation of the mechanical properties of the alloy. In the present paper the coarsening process is modelled and the change of the critical resolved shear stress of the alloy due to coarsening of the γ particles is calculated by means of statistical analysis of the depinning of a single gliding edge dislocation. It is found that the contribution of γ hardening to the critical resolved shear stress at 973 K reduces to more than half of its original value in less than one year.

Journal of Nuclear Materials, 2009