Peter Staron

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

Spinodal decomposition of cubic Ti1-xAlxN : Comparison between experiments and modeling

Abstract Annealing of cubic (c) Ti1−xAlxN, possessing NaCl structure, leads to decomposition into the stable constituents c-TiN and hexagonal (h) AlN (ZnS wurtzite structure) via the formation of metastable c-TiN rich and metastable c-AlN rich phases. In this paper, we describe the influence of sizes of the newly formed particles and strain energy due to their different lattice parameter and elastic constants with respect to the remaining matrix on decomposition processes and energetics. Good agreement between the enthalpy output obtained from differential scanning calorimetry and values derived from ab-initio and continuum mechanical based calculations for the decomposition and transformation processes occurring is obtained. Based on the comparison between experiments including X-ray diffraction and small-angle neutron scattering of annealed samples and modeling we can conclude that spinodal decomposition is present in c-Ti1−xAlxN coatings with x = 0.50 and 0.66, whereas the alloy with x = 0.25 is outside the spinodal.

Combining complementary techniques to study precipitates in steels

Abstract Understanding the precipitation reactions is of vital importance for the development of advanced steels. A comprehensive characterization of all phases, however, is still demanding in thes...

Critical consideration of precipitate analysis of Fe-1 at.% Cu using atom probe and small-angle neutron scattering.

An Fe-1 at.% Cu model alloy was examined by atom probe (3DAP) and small-angle neutron scattering (SANS) to verify the accordance of the gained results. The Fe-Cu alloy was heat-treated for various times at 500°C, forming Cu-rich precipitates within the Fe matrix. The chemical compositions of the precipitates and matrix found by 3DAP were used to calculate the magnetic scattering contrast. Additionally, a magnetic moment of the precipitates that contain a significant amount of Fe was taken into account for the calculation of magnetic scattering contrast. This in turn is used for the evaluation of the magnetic scattering curves gained by SANS. Both the 3DAP data as well as the scattering curves were analyzed with regard to radius, number density, and volume fraction of the precipitates as a function of aging time. The results yielded by both techniques are in good agreement and correspond to the development of the hardness of the alloy. Minor differences can be related to the cluster search algorithm used for the analysis of the 3DAP data as well as Fe overestimation based on different field phases.

Residual Stresses in Laser Beam Welded Butt Joints of the Airframe Aluminium Alloy AA6056

Residual stresses in CO2 laser beam welded AA6056 Al-sheets of 3.2 and 6.0 mm thicknesses were studied using neutron and high-energy X-ray diffraction. The influence of the temper T4 and T6 before welding, the effect of sheet thickness in T6 temper, and the effectiveness of post-weld heat treatments T6 and T78 for the reduction of residual stresses in the sheets welded initially in the T4 temper were examined. It was found that tensile longitudinal stresses were significantly higher when welded in T6 than in T4. With the increase in the sheet thickness from 3.2 to 6.0 mm, the residual stress profile was affected more than the stress level when welded in T6. For 3.2 mm sheet, the post-weld heat treatments T6 and T78 did not lead to a significant reduction in residual stresses when welded in T4.

Influence of the Welding Sequence on Residual Stresses in Laser Welded T-Joints of an Airframe Aluminium Alloy

The effect of different welding sequences between a 4.5 mm thick AA 6156 T6 base plate and a 2 mm thick AA 6013 T6 clip – resembling a skin-clip joint of an airframe – using a 3.3 kW Nd:YAG laser is investigated. Under cyclic loading the breakdown of such T-joints happens at one end of the clip, which is due to local residual stress concentrations. Recent measurements indicated that tensile stresses could be lower at the run-in than at the run-out locations. For a deeper investigation of this effect sheets with different welding sequences were produced. One welding sequence was made with two starting points in the centre, and a second with starting points at the clip ends. Temperature measurements were made using thermocouples to verify the heat conditions for a finite element simulation of the welding process, which is used for predictions of the residual stress distribution. Actual values of the residual stress fields were determined by neutron diffraction. The influences of the welding sequence on the measured temperatures and the residual stresses are discussed.

Residual stresses in forged IN718 turbine discs

Abstract Residual stresses play an important role in the production of forged components like turbine discs. Variations in the processing parameters can lead to different residual stress states, which complicate subsequent processing steps, e.g. turning to the final shape. Therefore, a deeper understanding of the residual stress evolution during thermo-mechanical processing and the resulting distortions during machining is essential in order to optimize the manufacturing process with respect to cost efficiency and quality of the product. Consequently, the development of residual stresses in a forged turbine disc made of nickel-based superalloy IN718 was simulated using a finite element (FE) model. The experimental verification of the model was done by independently performed neutron strain scanning. For the studied forged and subsequently water-quenched disc the obtained residual stresses agree well with the stresses predicted by the used FE.

Analysis of Residual Stress in Laser Welded Aerospace Aluminium T-joints by Neutron Diffraction and Finite Element Modelling

The residual stress distribution in three laser welded T-joint configurations of aerospace aluminium alloys were measured using neutron diffraction and FE-simulation was conducted to compare with the experimental results. A 2 mm thick AA 6013 T6 sheet (as clip) was welded to a 4.5 mm thick and 400 mm wide AA 6156 T4 base plate (as skin of the airframe). In two samples, the thickness of the plate was reduced in some areas after welding to produce so-called “pockets” with the purpose of the weight reduction to resemble the fabrication practise in aircraft industry. The effect of pocketing process, which produced two different geometries around the clip weld on the residual stress evolution was analysed. In the plain sample (without pockets), residual stresses were predicted using the SYSWELD finite element software. The strain measurements on the base plate were performed at three locations; namely, the middle of the weld length (mid-clip), welding start (run-in) and end (run-out) locations. In all welded plates, slightly higher longitudinal tensile residual stresses were detected at the midclip locations, whereas transverse residual stresses were similar for all locations. In the run-out location, higher longitudinal tensile residual stresses were present than in the run-in location, which was the case in our previous results on other samples. The first results of the SYSWELD FE-simulation of the plain sample were compared with experimental results. The comparison has shown particularly good agreement for the transverse stresses. Although the simulation yields higher longitudinal tensile stresses than the experimental results, the stress distributions were very similar.

On the evolution of secondary hardening carbides in a high-speed steel characterised by APFIM and SANS

Abstract Secondary hardening carbides in high-speed steels are very important microstructural constituents, responsible for the excellent properties of this type of steel. Therefore, detailed knowledge about their precipitation behaviour with respect to type, size and chemical composition is of paramount interest. Atom probe field ion microscopy and small-angle neutron scattering have emerged to be important techniques for the characterisation of nanometre-sized precipitates, such as secondary hardening carbides. In this paper, the precipitation behaviour of the high-speed steel HS6-5-2 with the nominal composition (in wt.%) Fe-0.9C-4.1Cr-6.4W-5Mo-1.8V was investigated. Differently tempered specimens were analysed to determine size, volume fraction and chemical composition of the secondary hardening carbides using a three-dimensional tomographic atom probe and small-angle neutron scattering. The results obtained from both techniques were compared with emphasis on the chemical composition of the precipitates.

Depth-Resolved Residual Stress Analysis with High-Energy Synchrotron X-Rays Using a Conical Slit Cell

A conical slit cell for depth-resolved diffraction of high-energy X-rays was used for residual stress analysis at the high-energy materials science synchrotron beamline HEMS at PETRA III. With a conical slit width of 20 µm and beam cross-sections of 50 µm, a spatial resolution in beam direction of 0.8 mm was achieved. The setup was used for residual stress analysis in a drawn steel wire with 8.3 mm diameter. The residual stress results were in very good agreement with results of a FE simulation.