Peter Hähner

European Commission | ec · Joint Research Centre (JRC)

Nanoindentation of ion-irradiated materials has attracted much interest as a tool envisaged to derive the dose dependence of bulk-equivalent hardness from small samples. A major challenge arises from the steep damage gradient in the thin ion-irradiated layer and its unavoidable interplay with the indentation size effect. The present study relies on...

The M4F project brings together the fusion and fission materials communities working on the prediction of radiation damage production and evolution and its effects on the mechanical behaviour of irradiated ferritic/martensitic (F/M) steels. It is a multidisciplinary project in which several different experimental and computational materials science...

This work reports results from quasi-static nanoindentation measurements of iron, in the un-strained state and subjected to 15% tensile pre-straining at room temperature, 125 °C and 300 °C, in order to extract room temperature hardness and elastic modulus as a function of indentation depth. The material is found to exhibit increased disposition for...

This work compares different measurement and analysis protocols of spherical nanoindentation tests performed at different temperatures on a ferritic/martensitic P91 grade steel, in order to derive meaningful indentation stress−strain curves (ISSC) and estimate material parameters such as indentation modulus, yield strength, work hardening exponent...

While force–displacement curves are often preferred in Small Punch (SP) tests due to the ease of the experimental set-up, they encompass significant uncertainties arising from frame compliance. In this work, a methodology is presented to predict yield stresses from the force vs. deflection curves. The present method relies on determining different...

During their service in a nuclear power plant, structural materials are subject to high temperature, mechanical stress, corrosive coolant environments, and neutron irradiation. The combination of radiation, corrosion and thermo-mechanical loading represents a unique environment that materials must endure: radiation can significantly alter the mater...

The paper presents a statistical study of nanoindentation results obtained in seven European laboratories which have joined a round robin exercise to assess methods for the evaluation of indentation size effects. The study focuses on the characterization of ferritic/martensitic steels T91 and Eurofer97, envisaged as structural materials for nuclear...

The Small Punch (SP) test serves the screening of mechanical material properties and their degradation in a virtually non-invasive way. It requires robust frameworks for the derivation of mechanical properties and microstructure-mechanical property correlation. The tensile yield stress sigma_y is commonly associated with an elastic-plastic transiti...

A new standard is currently being developed under the auspices of ECISS/TC 101 WG1 for the small punch testing technique for the estimation of both tensile and creep properties. Annex G of the new standard is covering the assessment and evaluation of small punch creep (SPC) data. The main challenge for estimating uniaxial creep properties from SPC...

The paper presents a comparative study of different nanoindentation methods as applied to the ferritic/martensitic steels T91 and Eurofer97, here investigated in the non-irradiated reference state, but envisaged as structural materials for nuclear fission and fusion applications, respectively. Depth-controlled single cycle measurements at various i...

A unified experimental-computational study on ductile fracture initiation and propagation during small punch testing is presented. Tests are carried out at room temperature with unnotched disks of different thicknesses where large-scale yielding prevails. For thinner specimens fracture occurs with severe necking under membrane tension, whereas for...

Tensile and Charpy tests were carried out to investigate the effect of phase separation on the mechanical properties of MA956 oxide dispersion strengthened high chromium steel. The ferritic matrix of the investigated material separates into Fe-rich α and Cr-rich α’ phases during thermal ageing at 475°C. The yield stress and tensile strength increas...

The integrity assessment of the Reactor Pressure Vessel (RPV) is essential for the safe and Long Term Operation (LTO) of a Nuclear Power Plant (NPP). Hardening and embrittlement of RPV caused by neutron irradiation and thermal ageing are main reasons for mechanical properties degradation during the operation of an NPP. The thermal ageing-induced de...

We present a systematic numerical study on temperature dependent fracture mode change in small punch tests. Following Needleman-Tvergaard [Needleman and Tvergaard, Int. J. Frac., 101, 73, (2000)], we model the material as thermo-inelastic, where the ductile fracture mode, by void nucleation, growth and coalescence is accounted for by Gurson’s porou...

Ultrasonic techniques are an established means for carrying out fatigue tests at very highnumbers of cycles. These techniques are based on the formation of a standing ultrasonic wave inthe specimen and usually use frequencies around 20 kHz. Although such systems allow testing to avery high number of cycles in a relatively short time, the use of a s...

The sensitivity of thermo-electric power (TEP) measurement to detect the undesired α–α′ phase separation occurring in Cr-rich oxide dispersion strengthened steels was investigated. TEP values were found to increase with time of exposure to 475 °C—the maximum temperature of the miscibility gap in Fe–Cr alloys. Exposure to 650 °C did not induce any c...

A 14Cr ODS steel was characterized at elevated temperatures with regard to its behavior in small punch and uniaxial creep tests and in low cycle fatigue tests. A comparison of small punch and uniaxial creep tests at 650 °C revealed a strong anisotropy of the material when strained parallel and perpendicular to the extrusion direction with rupture t...

The influence of hydrogen on the high cycle fatigue (HCF) behaviour of Inconel 718 has been studied at room temperature in asymmetric push-pull mode using an ultrasonic HCF test rig. Fatigue tests have been carried out in gaseous hydrogen (GH2) and in Ar at a pressure of 30 MPa. Oscillating stresses with amplitudes (σaσa) up to 450 MPa and mean str...

Local creep properties of a P91 weldment consisting of distinct zones, namely base metal, weld metal, as well as the fine-grained and the coarse-grained parts of the heat-affected zone were examined by Small Punch creep tests. Deflection vs. time graphs showed the zones' different creep resistances with that of the Heat Affected Zone-Fine Grained b...

Small punch (SP) fracture testing with subsequent SEM fractographic analysis was applied to an A 508 Class 3 reactor pressure vessel (RPV) steel, used originally in the NESC-I spinning cylinder experiment, in order to determine the SP ductile–brittle transition temperature of both the base material and the sub-clad heat affected zone. In addition t...

The increasing lifetime of many engineering components leads to a growing demand for accelerated testing methods. Fatigue failure of components submitted to cyclic loading at stress levels below the endurance limit occurs even beyond 107 cycles which has been the traditional limit for fatigue testing in most laboratories. Test programs covering thi...

Small Punch fracture tests were carried out in order to determine low temperature mechanical behaviour of a P91 steel weldment: weld metal, base metal, Heat Affected Zone-Fine Grained and Heat Affected Zone-Coarse Grained. The Heat Affected Zone-Fine Grained showed superior tensile properties in terms of displacement at fracture (ductility) and str...

In the present paper the small-angle neutron scattering (SANS) technique was used to investigate the phase separation in two oxide dispersion strengthened (ODS) ferritic steels, PM2000 and MA956, during isothermal ageing at 475 °C. The ferritic matrix of the investigated materials separates into Fe-rich α and Cr-rich α′ phases during ageing at this...

In order to assess the validity of post-irradiation annealing as a method to predict results of high temperature irradiation a new analysis of experimental data has been performed revealing the combined influence of annealing temperature and impurities content on residual embrittlement after annealing. For 2CrMoV (WWER-440 reactor pressure vessel)...

Recent high temperature reactor (HTR) concepts for nuclear co-generation foresee hot gas temperatures up to 850°C. While suitable materials for the high temperature exposed components well-known from conventional technologies are taken into consideration, extended material qualification tests must still be performed for reactor design and licensing...

The small punch testing technique was used to assess both creep and fracture properties of the MA956 oxide dispersion strengthened ferritic steel. The anisotropy in mechanical properties was addressed, as well as the alloy’s susceptibility to thermal embrittlement. Strong anisotropy was found in the material’s creep resistance at 725°C for longer r...

A comparative positron annihilation lifetime study has been performed on various commercial ferritic and ferritic/martensitic oxide dispersion strengthened (ODS) steels. Both as-extruded and recrystallized materials were investigated. In the materials with recrystallized coarse-grained microstructures, only the positron trapping at small vacancy cl...

Haynes 282 alloy is a newly developed nickel-base superalloy, with properties focussed on high creep strength, thermal stability, good weld-ability and fabricability, which might qualify it as a substitute for established materials like Hastelloy-X or Rene-41 e.g. in aerospace applications. However, so far no information on the sensitivity for hydr...

In the current research, the effect of heat treatment on the morphology of the dispersoids and their phase composition were investigated in three Cr-rich ferritic oxide dispersion strengthened (ODS) steels: PM2000, MA956, and ODM751. The steels were aged at 475 °C for times ranging from 100 to 1,000 h. The microstructure was characterized using tra...

In view of the possible application of SiC‐based ceramic laminates as critical components of hydrogen generation plants based on sulfur‐iodine or hybrid‐sulfur thermochemical cycles, the effect of corrosion on this kind of ceramics has been investigated. For this purpose, the material was exposed for 1000 h at 850°C to the corrosive action of a gas...

HycycleS was a cooperation of nine European partners and further non-European partners and aimed at the qualification and enhancement of materials and components for key steps of solar and nuclear powered thermochemical cycles for hydrogen generation from water. The focus of HycycleS was the decomposition of sulphuric acid which is the central step...

In the present article, a positron annihilation lifetime technique was used for the study of VVER-440/230 weld materials, manufactured in the frame of the international PRIMAVERA project on microstructural investigation of the irradiated WWER-440 reactor pressure vessel steel. The present results complement our previous report of positron angular c...

Non destructive characterization of oxide dispersion strengthened steels

The small punch (SP) testing technique can be used to assess fracture properties from a very small volume of material. However, the correlation of fracture parameters obtained from SP testing with those produced using standard methods is non-trivial, not only due to the size effect, but also due to the absence of a notch in most existing types of S...

Presently, one of the most interesting approaches to the generation of H2 is based on sulphur-based cycles, that however require structural components able to work in a corrosive environment at high temperature. Silicon carbide (SiC) is one of the most promising materials for this application, and to increase its limited toughness multilayered stru...

A comparison between pearlitic 2CrMoV steel (WWER-440) and 9% Cr based ferritic–martensitic steels (EUROFER 97 and LA12TaLC) is presented as regards irradiation induced ductile–brittle transition temperature shifts. For neutron doses of 1.5–2dpa and irradiation temperatures around 300°C the transition temperature shifts for WWER-440 steel and EUROF...

Positron annihilation spectroscopy is shown to be an efficient method for determining the size of nanoobjects (vacancies and their clusters), the free volumes of pores, cavities, voids, and their concentrations and chemical compositions at the annihilation sites of porous systems and certain defective materials, including metals. The results of exp...

In the present work, fatigue crack growth in two nickel-base mono-materials and one bi-material has been investigated at 450 and 550 °C. The electric potential drop technique was found to better estimate the crack length during cycling as compared to the compliance method. This finding is supported by microscopic observations of the fracture surfac...

The 5th International Symposium on Supercritical Water-Cooled Reactors (ISSCWR-5), Vancouver, British Columbia, Canada, March 13-16, 2011

Steels used in the nuclear industry have been experimentally studied by positron annihilation spectroscopy. Analysis of the experimental results and their comparison with the existing data make it possible to reveal vacancy defects, in particular, those caused by neutron radiation, and to determine their size.

Journal of Nuclear Materials - article in press The presented paper summarizes the results of general corrosion and stress corrosion cracking (SCC) susceptibility tests in supercritical water (SCW), studied for austenitic stainless steel 316L, with the aim to identify maximum SCW temperature usability and specific failure mechanisms prevailing duri...

An experimental set-up has been developed to perform slow strain rate tensile (SSRT) tests on tubular 304L stainless steel (SS) specimens in supercritical water (SCW) environment (550 °C, 250 bar). The supercritical water is circulated inside an internally pressurized tubular specimen mounted into a universal mechanical test rig and heated by a sin...

Various oxide dispersion strengthened (ODS) steels (PM2000, MA956, ODM751 and ODS Eurofer) have been investigated using positron annihilation lifetime spectroscopy. Preliminary characterization of the vacancy type defects and the yttria nanoparticles are reported in this paper. The interpretation of the experimental data considers also the results...

The European FP7 project HycycleS is a European R&D Project on the development of thermo-chemical hydrogen production processes. It concentrates on providing detailed solutions for the design of specific key components for sulfur based thermochemical cycles. The key components necessary for the high temperature part of those processes, the thermal...

The web-enabled materials properties database MatDB of the European Commission Joint Research Centre (EC-JRC) is a database application for the storage, retrieval and evaluation of experimentally measured materials data coming from European R&D projects. Data exchange and interoperability are important database issues to reduce costs of expensive m...

The European FP7 project HycycleS focuses on providing detailed solutions for the design of specific key components for sulphur-based thermochemical cycles for hydrogen production. The key components necessary for the high temperature part of those processes, the thermal decomposition of H2SO4, are a compact heat exchanger for SO3 decomposition for...

The European FP7 project HycycleS is a European R&D Project on the development of thermo-chemical hydrogen production processes. It concentrates on providing detailed solutions for the design of specific key components for sulfur based thermochemical cycles. The key components necessary for the high temperature part of those processes, the thermal...

In the present article, a positron annihilation spectroscopy investigation of VVER-440/230 weld materials is discussed. Important characteristics of metals such as Fermi energy, concentration of electrons in the conduction band, size and concentration of defects were experimentally determined for three model materials with higher level of copper (0...

Many materials like silicon, tungsten or ferritic steels show a transition between high temperature ductile fracture with stable crack grow and high deformation energy absorption and low temperature brittle fracture in an unstable and low deformation mode, the ductile-brittle-transition. Especially in steels, the temperature transition is accompani...

The HFR Petten is a key research reactor in Europe and in the course of the last decades several dedicated irradiation facilities have been developed and successfully operated. For example, as regards materials irradiation, in the frame of the European Network AMES (Ageing Materials and Evaluation Studies), the irradiation behaviour of reactor pres...

Thermo-mechanical fatigue (TMF) testing plays an increasingly important role in the design, the reliability assessment and the lifecycle management of safety critical components used, for instance, for power generation, in the process industry and in aeronautical and automotive applications, with a view to increasing the fuel efficiency, safety and...

A major international inter-comparison exercise on strain-controlled thermo-mechanical fatigue (TMF) has been undertaken to validate a new European Code of Practice for TMF Testing and to provide underpinning information for an ISO Standard. This paper focuses on (a) distribution of samples of Nimonic 90, (b) the establishment of a protocol for tes...

The mechanical performance in terms of tensile properties of a nickel-base superalloy bi-material was investigated, to study the tensile strength of the joint. The results of strain measurement and control by means of usual clip-on extensometry, which gives the overall strain, cannot reveal the local deformation. To have more detail about the local...

Thermo-mechanical fatigue (TMF) data are needed for dimensioning of safety-critical parts, e.g. in power generation and in transportation by air, rail and road, and for designing of components, which operate at higher levels of efficiency and safety for longer periods of time. However, the current lack of a validated international standard for TMF...

The phenomenon of the Portevin-LeChatelier effect is described on the basis of a constitutive model of dynamic strain ageing, which was implemented in three-dimensional finite element analysis. The simulation of the deformation behaviour of Al–Cu alloys is performed, using the constitutive parameters as required by the model. The simulations confir...

The development of Portevin-LeChâtelier (PLC) deformation bands and their propagation are studied by laser scanning extensometry during room temperature deformation of a polycrystalline Al-3wt.%Mg alloy. Tensile tests with imposed constant strain-rates are compared with imposed constant stress-rates. The jerkily propagating PLC type B bands as obse...

Applying laser scanning extensometry the development and propagation of Portevin-LeChâtelier (PLC) deformation bands is recorded by measuring local strains in up to 22 neighboring 2 mm sections along the specimen length. The quantities characterizing deformation band shape and propagation, i.e. width and concentrated strain in the band, propagation...

Plastic deformation of solid solutions at elevated temperatures is often accompanied by plastic instabilities due to dynamic strain aging (DSA) and dislocation interaction. The repeated breakaway of dislocations from and their recapture by (clouds of) solute atoms lead to stress serrations and localized strain (deformation bands) in strain controll...

The mechanical performance of gas turbine material systems consisting of a Ni-base superalloy substrate with three different MCrAlY overlay coatings with various Al contents was assessed, close to service temperature spectrum, by means of stepwise tensile tests. Furthermore, acoustic emission (AE) activity was monitored during the tensile testing....

A new model is presented for a physically-consistent description of plastic material instabilities referred to as Portevin–Le Chatelier (PLC) effect, namely the oscillatory plastic flow that may be observed in metallic alloys subjected to load-or displacement-controlled plastic deformation in a certain range of strain, strain rate and temperature....