Introduction. Copper alloyed steel is considered to be a possible alternative to expensive bronze in the manufacture of large-sized parts of heavy-duty sliding friction units. The operating conditions of these units assume the presence of large specific loads. Thus, the materials for its production should have a high complex of strength and tribological properties. Quenched iron-carbon steels have the greatest strength, however, nowadays, the issue of the effect of copper on the structure and properties of medium-carbon steels after quenching remains open. The purpose of the work: to study the structure, strength and tribotechnical properties of cast medium-carbon steel, alloyed with copper (0...9 wt. %), after quenching from 800, 900, 1000 and 1150 degrees C and low tempering at 200 degrees C. The methods of investigation. Structural studies were performed using optical metallography, scanning electron microscopy and X-ray phase analysis. The mechanical properties of alloys after casting and quenching with low tempering were studied, the hardness of the Rockwell materials was evaluated, and the wear resistance test was carried out on fixed and non-rigidly fixed abrasive particles. Results and discussion. With the increase of copper content in the steel the size of the ferritic grains decreases and the dispersion of perlite increases. The nanosized inclusions of the copper e-phase formed in the ferrite matrix were studied by transmission electron microscopy. Heating up to 800 degrees C doesn't provide an opportunity for complete quenching of steels alloyed with copper. In addition to martensite, the microvolumes of ferrite and perlite are present in the structure of alloys. Quenching from 900 degrees C leads to the formation of a completely martensitic structure. A further increase in the quenching temperature doesn't lead to a qualitative change in the structural composition. Inclusions of the copper phase predominantly have a shape close to spherical. However, after quenching from 1150 degrees C in an alloy with 9% copper, the e-Cu inclusions precipitates as a thin films along the former boundaries of austenitic grains. The TEM investigations showed that heating for quenching leads to dissolution of copper nanosized inclusions. At the fast cooling stage, copper in the form of inclusions is not released. Alloying with copper up to 6 wt. % provides the growth of tribotechnical characteristics of medium-carbon steels. It was found that samples quenched from 900 degrees C have the highest complex of mechanical properties.

A nondestructive hybrid method combines two or more testing methods. Hybrid methods acquire several measuring quantities with different physical information content of the tested materials and different sensitivities against disturbing influences. After calibration procedures this allows a quantitative determination of material properties like residual stresses, hardness, hardening depth, yield strength, etc. This section will give an insight into combinations of micromagnetic, eddy current and ultrasonic methods, and it presents examples of applying such nondestructive hybrid methods.

Materials Characterization Using Nondestructive Evaluation (NDE) Methods discusses NDT methods and how they are highly desirable for both long-term monitoring and short-term assessment of materials, providing crucial early warning that the fatigue life of a material has elapsed, thus helping to prevent service failures. Materials Characterization Using Nondestructive Evaluation (NDE) Methods gives an overview of established and new NDT techniques for the characterization of materials, with a focus on materials used in the automotive, aerospace, power plants, and infrastructure construction industries. Each chapter focuses on a different NDT technique and indicates the potential of the method by selected examples of applications. Methods covered include scanning and transmission electron microscopy, X-ray microtomography and diffraction, ultrasonic, electromagnetic, microwave, and hybrid techniques. The authors review both the determination of microstructure properties, including phase content and grain size, and the determination of mechanical properties, such as hardness, toughness, yield strength, texture, and residual stress.Gives an overview of established and new NDT techniques, including scanning and transmission electron microscopy, X-ray microtomography and diffraction, ultrasonic, electromagnetic, microwave, and hybrid techniquesReviews the determination of microstructural and mechanical propertiesFocuses on materials used in the automotive, aerospace, power plants, and infrastructure construction industriesServes as a highly desirable resource for both long-term monitoring and short-term assessment of materials

Nanoscale coherent precipitates and the corresponding micro residual stresses play a dominant role in the strengthening process of materials. At present, there exists no experimental method for measuring micro residual stresses of IIIrd kind non-destructively. In the frame of the present work, it will be shown that micro-magnetic measurement techniques based on the tensile loading dependent maximum Barkhausen noise amplitude can be used for the analysis of micro residual stresses (MRS) of IIIrd kind (coherency residual stresses). For this purpose, Fe-Cu-alloys with well-defined contents of Cu-precipitates were produced and investigated. (C) 2014 Published by Elsevier Ltd.

The basic-safety-principle concerning components in German nuclear power plants (NPP) requires a high material quality in terms of characteristic toughness values. For this purpose, at present, notched-bar impact tests are carried out for example for the determination of the brittle fracture transition temperature. Compact tension tests are performed to determine mechanical and technological characteristics such as the fracture toughness, crack initiation, the crack growth. Because of the scattering in the data, the quantification of the failure behavior in the transition zone of the toughness is only possible with restrictions. Therefore considerably high safety margins are asked for in the design to avoid failure behavior. So far, the crack growth can only be determined in standardized bending tests and requires partial load relief cycles observing the development of the crack opening displacement by a clip-gauge. The time of the crack initiation can be determined with additional time-consuming microscopic analyses of the crack surface after the bending test. The additional instrumentation of the mentioned tests with NDT should provide further information about the failure process and a more precise and reliable determination of the failure probability. In order to document the principle feasibility, three point bending tests and drop impact tests were carried out using SE(B) samples with several nondestructive sensors applied. These sensors are Electromagnetic Acoustic Transducers (EMATs) to record the ultrasonic time of flight (TOF) of an ultrasonic wave travelling around the crack, and Giant Magnetoresistance (GMR) sensors to measure magnetic flux leakage (MFL) signals emanating from the crack. It was shown that both TOF and the MFL provide information about the crack growth during the bending test. In particular, the TOF was shown to increase with the crack length, thus allowing the determination of the crack length without the partial load relief cycles that were needed before. During the drop impact tests, the high-speed acquisition of MFL signals resolved details of the crack formation process.

With an increasing number of power plants operated in excess of their original design service life an early recognition of critical material degradation in components will gain importance. Many years of reactor safety research allowed for the identification and development of electromagnetic NDE methods which detect precursors of imminent damage with high sensitivity, at elevated temperatures and in a radiation environment. Regarding low-alloy heat-resistant steel grade WB 36 (1.6368, 15NiCuMoNb5), effects of thermal and thermo-mechanical aging on mechanical-technological properties and several micromagnetic parameters have been thoroughly studied. In particular knowledge regarding the process of copper precipitation and its acceleration under thermo-mechanical load has been enhanced. Whilst the Cu-rich WB 36 steel is an excellent model material to study and understand aging effects related to neutron radiation without the challenge of handling radioactive specimens in a hot cell, actually neutron-irradiated reactor pressure vessel materials were investigated as well. The neutron fluence experienced and the resulting shift of the ductile-brittle transition temperature were determined electromagnetically, and it was shown that weld and base material can be distinguished from the cladded side of the RPV wall. Low-cycle fatigue of the austenitic stainless steel AISI 347 (1.4550, X6CrNiNb18-10) has been characterized with electromagnetic acoustic transducers (EMATs) at temperatures of up to 300 degrees C. Time-of-flight and amplitude of the transmitted ultrasound signal were evaluated against the number of load cycles applied and observed as an indication of the imminent material failure significantly earlier than monitoring stresses or strains.

Electromagnetic non-destructive testing ( NDT) systems have been used in steel strip production lines for a long time. Indirect electromagnetic determination of approximate yield and ultimate strength values can be considered state of the art. However, the excellent mechanical properties of advanced high strength steel ( AHSS) are particularly sensitive to process variations. Characteristics and homogeneity of texture, grain size and secondary phase content are crucial during forming and welding of steel strips. Ultrasonic methods can be applied in order to indirectly characterize these properties. Deviations which have not been detected in the rolling mill are known to cause flaws or expensive and time-consuming downtimes of the press. The crash performance of the automotive structure is affected by these properties as well. Current in-line NDT systems determine only a subset of the required parameters and do not assess their homogeneity across the strip width. This raises the demand for NDT solutions which assess a larger set of material characteristics in multiple locations at high strip speeds. This paper describes a probe design which allows ultrasonic time-off-light measurements as well asMicromagnetic Multi-Parameter Microstructure and Stress Analysis (3MA) using a common, minimal set of components. The implementation of a simplified yet advantageous incremental permeability and eddy current impedance analysis based on this probe type is discussed, and first results are presented.

Since 1976 the 3MA–methodology (Micromagnetic, Multiparameter, Microstructure and Stress Analysis) was developed in the German Nuclear Safety Research Program. The basis is in micromagnetic NDT techniques as the measurement of magnetic Barkhausen noise, of the magnetic incremental permeability, of the eddy current impedance, the harmonic analysis of the magnetic tangential field strength, and the measurement of the dynamic or also called incremental magnetostriction. 3MA can only be applied at ferromagnetic materials and was used to characterise ageing phenomena in pressure vessel and pipeline steels as thermal ageing and neutron degradation as well as material states when thermal ageing and low–cycle fatigue were superimposed. In the case of austenitic stainless steels when exposed to mechanical static or cyclic loads - the material reacts localised with phase transformation to bcc α' martensite - 3MA techniques can be applied. In all other cases UT is utilised and - for instance a time–of–flight–measurement - can characterise cyclic deformation.

The influence of carbon content in the form of globular cementite precipitates in unalloyed steels was macroscopically characterized by means of magnetic hysteresis loop and Barkhausen noise techniques. The choice of the frequency of the applied field has a strong influence on the Barkhausen noise profiles. At sufficiently high frequency (0.5Hz) there are two peaks, one at lower field, the amplitude of which corresponds to the amount of ferrite and one at higher field, the amplitude of which corresponds to the amount of the cementite phase, respectively. Magnetic force microscopy and electron backscattered diffraction techniques were used to determine the magnetic and crystallographic microstructures of the steels. Cementite has its own domain structure and stray fields which influence the magnetization process of the steel by its own magnetic contribution. When an external magnetic field is applied, the magnetization process in ferrite occurs mainly at lower fields through the 180° and 90° domain walls. A higher field is required for the observation of 180° domain wall movements in cementite.

Starting in 1976, the 3MA-methodology (Micromagnetic, Multiparameter, Microstructure and Stress Analysis) was developed. 3MA has its basis in micromagnetic NDT techniques which are the measurement of magnetic Barkhausen noise, of the magnetic incremental permeability, of the eddy current impedance, the harmonic analysis of the magnetic tangential field strength, and the measurement of the dynamic or also called incremental magnetostriction. All of these techniques ask for a local magnetization in a hysteresis loop and therefore 3MA can only be applied at ferromagnetic materials. 3MA was used to characterize ageing phenomena in pressure vessel and pipeline steels as thermal ageing and neutron degradation as well as material states when thermal ageing and low cycle fatigue were superimposed. In the case of austenitic stainless steels when exposed to mechanical static or cyclic loads – the material reacts localized with phase transformation to bcc α’ martensite - 3MA techniques can be applied. In all other cases UT is utilized and - for instance a time-of-flight-measurement – can characterize cyclic deformation. When the mechanical loading is performed at elevated temperatures (300°C) EMAT are applied.

Obviously it is a fact: The nuclear energy technology worldwide was and still is an important driver for the development of NDT/NDE. This is true in Germany too. Concerning the most relevant task of NDT - detection, classification, and sizing of material irregularities (inhomogeneity, defects) the development of NDT technologies and methodologies like UT and imaging with phased array transducers or defect reconstruction algorithms like SAFT (synthetic aperture focusing technique) or ET of steam generator heat exchanger tubes with eddy current probes and multi-frequency approaches primarily were in the focus of R&D. However, in Germany there was also a strong demand to develop NDT for characterizing the materials of the nuclear components in their properties. The basic idea was to have NDT technology available for inservice inspection of primary circuit components which can characterize the microstructure as well as load-induced and residual stresses. The characterizing should be performed in terms of mechanical properties as hardness, strength like yield and tensile strength but also toughness properties like Charpy energy and fracture appearance transition temperature. Beginning in 1976 the 3MA Methodology (Micromagnetic, Multiparameter, Microstructure and Stress Analysis) was developed. 3MA has its basis in micromagnetic NDT techniques which are the measurement of magnetic Barkhausen noise, of the magnetic incremental permeability, of the eddy current impedance, the harmonic analysis of the magnetic tangential field strength, and the measurement of the dynamic or also called incremental magnetostriction. All of these techniques ask for a local magnetization in a hysteresis loop of the material under inspection and therefore 3MA can only be applied at ferromagnetic materials. The techniques collect information which is generated by interaction of Bloch walls with microstructural parameters (lattice defects as vacancies, dissolved atoms, dislocations, precipitations, grain and phase boundaries as well as stress fields). The magnetization processes utilized are reversible and irreversible. Therefore the information collected is divers and redundant which helps to enhance the statistical significance for prediction and tu suppress disturbance influences. 3MA was applied to characterize aging phenomena in pressure vessel and pipeline steels as thermal ageing and neutron degradation as well as material states when thermal ageing and low cycle fatigue were superimposed. In the case of characterizing material states of austenitic stainless steels it strongly depends on the chemical composition whether the material - for instance when exposed to mechanical static or cyclic loads - reacts localized with phase transformation to bcc α' martensite or not. The phase-transformed microstructure is ferromagnetic and therefore 3MA techniques can be applied. In all other cases UT is applied and - for instance a time-of-flight-measurement - is the tool to characterize cyclic deformation. When the mechanical loading is at elevated temperatures (300°C) EMAT are applied. Monitoring of mechanical-technological destructive tests by NDT technology can significantly enhance the information content. Fatigue as well as fracture mechanical tests were on-line monitored.

Early detection of damage in cyclically loaded austenitic steel was performed with electromagnetic acoustic transducer measurements in total strain controlled low cycle fatigue tests at ambient and elevated temperature. The application of physically based measurement data, e.g. time of flight from electromagnetically activated ultrasonic signals in austenitic fatigue specimens and total strain, enables measurements of a new hysteresis relationship. This hysteresis gives, in analogy to the stress-strain hysteresis, information about the actual state of fatigue of the austenitic steel and shows significant changes in shape before specimen failure.

Test methods based on microwaves are well suited to characterize mainly electrically non-conducting materials and to detect and image defects in non-destructive and in many cases in contactless way. While in the past the often complicated and expensive microwave equipment prevented the widespread application of microwave methods this situation is now changing due to the increasing availability of low-cost high integrated microwave components. Microwave testing has found an important application in the field of security, e. g. to detect and image dangerous objects hidden under clothes. The principles of this technique can be applied in the domain of joining (e. g. welding of plastics or gluing plastic to plastic) for contactless detection of defects under cover layers.

Micro-residual stresses (MRS) of the IInd and IIIrd orders play an important role in the fracture mechanical analysis of thermally-cycled materials and thus in lifetime analysis of such affected components. In multi-phase materials there can exist two kinds of MRS: thermally-induced MRS of the IInd order and coherent MRS of the IIIrd order. The first appear when individual material phases exhibit different thermal expansion coefficients and the second occur when the lattice parameter of the second phase particles which are embedded coherently in the matrix and the lattice parameter of the matrix are different. The main emphasis of the presented research work is the development of a micro-magnetic non-destructive technique for quantitative characterization of MRS of the IInd and IIIrd orders in iron-based materials. Forthat goal Fe-Cu-(Ni-Mn) samples were manufactured and characterized by means of a non-destructive procedure based on the tensile load dependence of the maximum Barkhausen noise amplitude.

In several magnetic Non-Destructive Testing (NDT) methods, the local measurement of the magnetic field inside the material is required. Moreover, looking at difficult part geometries, magnetic field sensors have to be small enough in order to reach the measuring position. The most-used magnetic field sensors are coils, Hall-effect sensors, flux gates and magnetoresistive sensors. However, regarding the industrial application, those sensors are often packaged and cannot be placed close enough to the measuring position. As part of an ongoing research project funded by the German Ministry of Economics and Technology (BMWi), a new kind of magnetic field sensor was developed and used in order to measure the strength of remanent magnetic field spots. This so-called 'Point Probe' is based upon a needle-shaped ferromagnetic core having a primary coil as a magnetic field source and a secondary coil as an inductive pick-up. This contribution describes the details of the sensor design and its operating principle. The sensitivity of the measured signals for local magnetic fields is described. Finally, a method for nondestructive hardness estimation of materials by using the Point Probe is presented. The results show a high correlation between hardness and a new coercivity-dependent testing parameter.

Micromagnetic materials characterization requires sensors which essentially consist of two critical elements: an electromagnet which introduces a well-defined magnetic field to the material, and a sensor system which detects the material's response to the applied magnetic field. The devices developed at Fraunhofer IZFP obtain a multiparametric “magnetic fingerprint” with these sensors by means of several methods. The magnetic fingerprints of calibration samples are used as input for pattern recognition or regression analysis, thus allowing the prediction of mechanical-technological material characteristics (hardness, yield strength, etc.) or residual stress. This approach is called micromagnetic multiparameter microstructure and stress analysis (3MA). The long-term stability and reproducibility of the sensor and device characteristics are crucial for the reliability of the measured results. Therefore, the measuring hardware should follow a minimalistic approach. In this paper, we propose a way of simplifying the measuring hardware by multiple use of sensor elements, reducing the analog signal processing chain and transferring most signal processing tasks to the PC.

Using nuclear power for energy generation, pressure vessel walls are exposed to neutron fluences of different levels depending on the distance to the core. Hence materials undergo a change of microstructure in terms of embrittlement, to be measured as toughness reduction and shift of the Ductile-to-Brittle Transition Temperature (DBTT) to higher temperatures. Normally plant safety concerning this change in microstructure is ensured by destructive testing of surveillance samples. These are standard tensile and Charpy specimens which consist of exactly the same material as the pressure vessel and its weldments, being exposed to accelerated irradiation rates within special irradiation channels allowing a pronounced ageing. During revision downtime of the plant these samples are tested destructively in standard tensile tests at 423 K and 548 K respectively or by measuring the impact energy as a function of temperature in Charpy tests to determine the shift of DBTT. It is demonstrated that electromagnetic parameters allow characterizing the changes in the microstructure generated through neutron irradiation. After a defined calibration process a quantitative characterization of the embrittlement especially in terms of DBTT is possible. This has been demonstrated for reactor pressure vessel steels according to western design as well as to eastern specifications. As testing methods 3MA (Micromagnetic, Multiparameter, Microstructure and stress Analysis) and dynamic magnetostriction using EMATs (ElectroMagnetic Acoustic Transducers) have been applied.

Ferromagnetic materials are essential for data recording devices. For inductive or magnetoresistive (MR) sensors softmagnetic thin layer systems are used. Optimal performance of these layers requires homogeneous magnetic properties, especially a pronounced uniaxial magnetic anisotropy. Furthermore, microstructural imperfections and residual stresses influence the magnetic structure in the layer system. Barkhausen Noise Microscopy enables the characterization of such thin layers. By cycling the magnetic hysteresis of ferromagnetic material electrical voltages (the Barkhausen noise) are induced in an inductive sensor. Miniaturization of the sensor and the scanning probe technique provides resolution down to few micrometers. Two materials were examined in terms of their structure, thickness, residual stresses and heat treatment condition: Sendust, used in inductive sensors and nanocrystalline NiFe, used in MR-sensors. In quality correlations to Barkhausen noise parameters were found. For representative sample a quantification of residual stress distribution could be established employing X-ray stress analysis.