Walter Reimers

Determining grain resolved stresses in polycrystalline materials using three‐dimensional X‐ray diffraction

An algorithm is presented for characterization of the grain resolved (type II) stress states in a polycrystalline sample based on monochromatic X-ray diffraction data. The algorithm is a robust 12-parameter-per-grain fit of the centre-of-mass grain positions, orientations and stress tensors including error estimation and outlier rejection. The algorithm is validated by simulations and by two experiments on interstitial free steel. In the first experiment, using only a far-field detector and a rotation range of 2 × 110°, 96 grains in one layer were monitored during elastic loading and unloading. Very consistent results were obtained, with mean resolutions for each grain of approximately 10 µm in position, 0.05° in orientation, and 8, 20 and 13 × 10−5 in the axial, normal and shear components of the strain, respectively. The corresponding mean deviations in stress are 30, 50 and 15 MPa in the axial, normal and shear components, respectively, though some grains may have larger errors. In the second experiment, where a near-field detector was added, ∼2000 grains were characterized with a positional accuracy of 3 µm.

Neutrons and Synchrotron Radiation in Engineering Materials Science

PART I: GENERAL MICROSTRUCTURE AND PROPERTIES OF ENGINEERING MATERIALS INTERNAL STRESSES IN ENGINEERING MATERIALS TEXTURE AND TEXTURE ANALYSIS IN ENGINEERING MATERIALS PHYSICAL PROPERTIES OF PHOTONS AND NEUTRONS RADIATION SOURCES GENERATION AND PROPERTIES OF NEUTRONS PRODUCTION AND PROPERTIES OF SYNCHROTRON RADIATION PART II: METHODS INTRODUCTION TO DIFFRACTION METHODS FOR INTERNAL STRESS ANALYSES STRESS ANALYSIS BY ANGLE-DISPENSIVE NEUTRON DIFFRACTION STRESS ANALYSIS BY ENERGY-DISPERSIVE NEUTRON DIFFRACTION RESIDUAL STRESS ANALYSIS BY MONOCHROMATIC HIGH-ENERGY X-RAYS RESIDUAL STRESS ANALYSIS BY WHITE HIGH ENERGY X-RAYS REFLECTION MODE TRANSMISSION MODE DIFFRACTION IMAGING FOR MICROSTRUCTURE ANALYSIS BASICS OF SMALL-ANGLE SCATTERING METHODS SMALL-ANGLE NEUTRON SCATTERING DECOMPOSITION KINETICS IN COPPER-COBALT ALLOY SYSTEMS: APPLICATIONS OF SMALL-ANGLE X-RAY SCATTERING New Developments in Neutron Tomography NEUTRON AND SYNCHROTRON -RADIATION-BASED IMAGING FOR APPLICATIONS IN MATERIALS SCIENCE - FROM MACRO- TO NANOTOMOGRAPHY mu-TOMOGRAPHY OF ENGINEERING MATERIALS DIFFRACTION ENHANCED IMAGING PART III: NEW AND EMERGING METHODS 3D X-RAY DIFFRACTION MICROSCOPE 3D MICRON-RESOLUTION LAUE DIFFRACTION QUANTITATIVE ANALYSIS OF THREE-DIMENSIONAL PLASTICS STRAIN FIELD USING MARKERS AND X-RAY ABSORPTION TOMOGRAPHY COMBINED DIFFRACTION AND TOMOGRAPHY PART IV: INDUSTRIAL APPLICATIONS DIFFRACTION-BASED RESIDUAL STRESS ANALYSIS APPLIED TO PROBLEMS IN THE AIRCRAFT INDUSTRY OPTIMIZATION OF RESIDUAL STRESSES IN CRANKHAFTS

Evaluation of Residual Stresses in the Bulk of Materials by High Energy Synchrotron Diffraction

High energy synchrotron diffraction is introduced as a new method for residual stress analysis in the bulk of materials. It is shown that energy dispersive measurements are sufficiently precise so that strains as small 10−4 can be determined reliably. Due to the high intensity and the high parallelism of the high energy synchrotron radiation the sample gauge volume can be reduced to approximately 50 μm×1 mm×1 mm compared to gauge volume of one mm3 up to several mm3 achievable by neutron diffraction. The benefits of the high penetration depth and the small gauge volume are demonstrated by the results of stress studies performed on a fiber reinforced ceramic, a functional gradient material and a metal-ceramic compound. Furthermore, it is shown that in case of a cold extruded metal specimen the energy dispersive measurement technique yields simultaneous information about texture and residual stresses and thus allows a detailed investigation of elastic and plastic deformation gradients.

A self-consistent method for X-ray diffraction analysis of multiaxial residual-stress fields in the near-surface region of polycrystalline materials. II. Examples

The application of the formalism for residual-stress gradient evaluation based on the measuring principle of the scattering-vector method, which has been derived in the first paper of this series [Genzel (1999). J. Appl. Cryst. 32, 770–778], is demonstrated by practical examples. Depending on the statistical scattering of the experimental data, either biaxial or even triaxial residual-stress states may be analysed; the latter case yields self-consistently the depth profiles of the in-plane stresses, σ11(τ) and σ22(τ), the normal stress component, σ33(τ), as well as the strain-free lattice spacing, d0(hkl). The results obtained by this new evaluation procedure are compared with those obtained by X-ray stress-gradient analysis performed on the basis of the sin2ψ method.

Microstructure and mechanical properties of the extruded Mg-alloys AZ31, AZ61, AZ80

Abstract In order to obtain optimum lightweight constructions in the automobile and aircraft industry, it is important to consider the use of extruded magnesium sections. A lot of the recent research has dealt with the extrusion of AZ31. These extrudates often miss the requirements of the automobile or aircraft industry for mechanical properties. A possible solution might be an increase in the aluminum content. Therefore, this paper deals with the extrusion of AZ31, AZ61 and AZ80 and the effect of the aluminum on the extrusion process as well as on microstructure and the mechanical properties of the extrudates. Whereas the aluminum content does not have a significant influence on the texture of the extrudates, the grain size and structure and, thereby, the mechanical properties can be improved by adding more aluminum to the Mg wrought alloys.

Some new aspects in X-ray stress analysis of thin layers

Abstract Due to their influence on the mechanical properties, residual stresses in thin hard coatings and their non-destructive analysis by X-ray diffraction have become an important topic in materials science. Because it is possible today to achieve defined internal stress gradients with respect to the layer thickness by appropriate variation of the deposition parameters, the applied diffraction methods have to meet the demand for a depth-resolved stress evaluation. By the example of thin PVD coatings of Ti1−xCrxN with a marked 〈111〉 fibre texture, the paper compares several methods in X-ray stress analysis (XSA) concerning their suitability for the detection of stress gradients in thin layers. The best results are obtained by means of the scattering vector method, where the lattice spacing depth profiles, d ϕ ψ ( h k l , τ ) , are measured after stepwise rotation of the sample around the scattering vector g ϕ ψ near the intensity poles of the texture.

Analysis of the Deformation Behavior of Magnesium-Rare Earth Alloys Mg-2 pct Mn-1 pct Rare Earth and Mg-5 pct Y-4 pct Rare Earth by In Situ Energy-Dispersive X-ray Synchrotron Diffraction and Elasto-Plastic Self-Consistent Modeling

The deformation behavior of the Mg-RE alloys ME21 and WE54 was investigated. Although both alloys contain rare earth elements, which alter and weaken the texture, the flow curves of the alloys deviate significantly, especially in uniaxial compression test. Apart from the higher strength of the WE54 alloy, the compression flow curve does not exhibit the typical sigmoidal shape, which is associated with tension twinning. However, optical microscopy, X-ray texture measurements, and EBSD analysis reveal the activity of tension twinning. The combination of in situ energy-dispersive X-ray synchrotron diffraction and EPSC modeling was used to analyze these differences. The investigation reveals that twin propagation is decelerated in the WE54 alloy, which requires a change of the twinning scheme from the ‘finite initial fraction’ to the ‘continuity’ assumption. Furthermore, an enhanced activity of the 〈c+a〉 pyramidal slip system was observed in case of the WE54 alloy.

Analysis of tool wear and residual stress of CVD diamond coated cemented carbide tools in the machining of aluminium silicon alloys

Aluminium alloys have found increasing applications in the automotive and aeronautical industries in recent years. Due to their extraordinary properties however, the machining of these alloys still poses difficulties, and requires the optimized combination of cutting tool material and geometry. The potential of CVD diamond coated carbide tools has been demonstrated in recent years, however tool wear and short tool life remain as issues to be resolved. Key to increasing the tool life of CVD diamond coated tools is the further development of the coating process to optimize the coating adhesion. An understanding of the substrate and coating residual stress profiles must be gained in order to achieve this. Compressive residual stresses in cutting tools can lead to a higher crack resistance, but also to early coating delamination and tool failure. To analyze the influence of residual stresses on the coating quality and tool life, the residual stress profiles of tungsten carbide substrates and CVD diamond coatings were measured using X-ray and synchrotron radiation. The influence of the tungsten carbide substrate type and the CVD diamond coating process on the residual stress profiles was thus determined. In order to analyze the performance of the coated tools and the influence of the residual stresses on the tool lifetime, machining tests were performed with two aluminium silicon alloys. The tool wear, tool lifetime and workpiece quality were examined. Finally, many of the commonly used wear tests used to analyze the wear resistance of tool coatings cannot be implemented for CVD diamond coatings due to their high hardness. An impact test was therefore constructed to allow the determination of the wear resistance of CVD diamond tools.

In situ strain measurement in the chip formation zone during orthogonal cutting

The strain and stress state in the chip formation zone determines the chip formation. However, it is difficult to obtain experimental data about the strain/stress fields during machining. For this reason, present chip formation models highly simplify the chip formation process. In order to extend the knowledge regarding the chip formation mechanisms, an experimental method for the in situ measurement of the elastic deformations within the chip formation zone during the cutting process has been developed. Using these deformations, the stress state can subsequently be calculated. The method is based on X-ray diffraction using high-energy synchrotron X-radiation during machining the workpiece in an orthogonal cutting process under quasistatic experimental conditions. The diffraction patterns are captured with a 2D detector. A comparison of the experimentally determined stresses at different measuring positions within the chip formation zone with results from a FEM cutting simulation shows a good qualitative and partially also quantitative consistency. Possibilities for the further performance increase of the method are identified so that the method can be used for the verification and extension of existing chip formation models in future.

Microstructure and mechanical properties of differently extruded AZ31 magnesium alloy

Abstract Profiles of the magnesium alloy AZ31 were produced by conventional indirect extrusion and by indirect extrusion into counterpressure with variations of the billet temperature TB from 200 °C up to 350 °C. Microstructural examination by optical microscopy showed that for extrusion trials carried out with billet temperatures TB ≤ 250 °C fine dynamically recrystallized grains are found while elongated grains of the former cast structure remain. Above TB ≥ 300 °C most grains show higher dynamic recrystallization kinetics and additional static recrystallization and increase to grain sizes of d = 30 – 50 μm. At TB ≤ 250 °C the typical extrusion fiber texture is found, at TB ≥ 300 °C a double fiber texture is formed due to static recrystallization. The results of the quasistatic mechanical tests are due to these differences in the microstructure.