Diffraction Stress Measurements Research Articles

Residual stress measurement with focused acoustic waves and direct comparison with X-ray diffraction stress measurements

The technique of measuring small changes in acoustic wave velocity due to external or internal stress has been used for quantitative determination of residual stress in materials during the last decade. Application of similar methodology with focused acoustic waves leads to residual stress measurement with spatial resolution of a few millimeters to a few microns. The high spatial resolution residual stress measurement required development of new methodologies in both the design of acoustic lenses and the instrumentation for acoustic wave velocity determination. This paper presents two new methodologies developed for the measurement of residual stress with spatial resolution of a few millimeters. The design of new type of acoustic lens for achieving higher spatial resolution in residual stress measurement is introduced. Development of instrumentation for high precision local surface wave velocity measurement will be presented. Residual stresses measured around a crack tip in a sample of Ti–6A1–4V using a focused beam will be compared with X-ray diffraction measurements performed on the same region of the sample. Results of residual stress measurements along a direction perpendicular to the electron beam weld in a sample of Ti–6A1–4V, determined using focused acoustic waves and X-ray diffraction technique, are also presented. The spatial resolution and penetration depth of X-rays and focused acoustic beams with reference to residual stress measurements are discussed.

Investigation of the latent heat associated with the solidification of an Al–TiB2 composite

Abstract Differential scanning calorimetry was used to measure the latent heat evolved or absorbed during solidification or melting of a composite made from commercial-purity aluminium reinforced with TiB2 particulate. The measured latent heat was up to 10% less than that expected assuming a rule of mixtures. The analysis of the particles revealed that up to 20 at.% of Ti is substituted by Al in the boride. The concomitant increase in volume fraction of particulate (Al3Ti) and the associated reduction in Al accounted for the latent heat discrepancy. It was previously suggested that strain energy could explain the discrepancy; however, X-ray and neutron diffraction stress measurements showed that this is unlikely.

Origin and implications of the observed rhombohedral phase in nominally tetragonal Pb(Zr0.35Ti0.65)O3 thin films

The structural and electrical properties of Pb(Zr0.35Ti0.65)O3 (PZT) thin films ranging in thickness from 700 to 4000 Å have been investigated. These (001)/(100)-textured films were grown by metalorganic chemical vapor deposition on (111)-textured Ir bottom electrodes. It was observed that, in the as-deposited state, the thinnest PZT films are rhombohedral even though bulk PZT of this composition should be tetragonal. Thicker films have a layered structure with tetragonal PZT at the surface and rhombohedral PZT at the bottom electrode interface. In this article we investigate the origin of this structure and its effect of the ferroelectric and dielectric properties of PZT capacitors. It has been suggested that thin films stresses can affect the phase stability regions of single domain PZT. This possibility has been investigated by piezoresponse microscopy and thin film stress measurements. In the as-deposited state the majority of PZT grains contain a single ferroelastic domain, whereas after a high temperature anneal, a large fraction of the grains contain several ferroelastic domains. Wafer curvature measurements in combination with x-ray diffraction stress measurements in the Ir bottom electrode showed that the as-deposited PZT films are, within experimental error, stress free at room temperature. Landau–Ginbzurg–Devonshire formalism was used to explain the origin of the rhombohedral phase as a result of substrate constraint on single domain PZT grains. Annealing was found to affect the relative volume fractions of the rhombohedral and tetragonal phases and the electrical properties of PZT films. Intermediate temperature anneals increased the volume fraction of the rhombohedral phase and the coercive field extracted from the polarization-electric field hysteresis loops. After a high temperature anneal (650 °C) the majority of the grains transformed into a polydomain state, decreasing the volume fraction of the rhombohedral phase and the coercive field. If the high temperature anneal was performed after deposition of the top electrode, the coercive field became independent of the PZT thickness.

New methods for diffraction stress measurement: a critical evaluation of new and existing methods

New methods of diffraction stress analysis of polycrystalline materials, consisting of cubic elastically anisotropic crystallites, are proposed and compared with existing methods. Whereas for the existing methods knowledge of the diffraction elastic constants is presupposed, three new methods are presented that require only knowledge of the (macroscopic) mechanical elastic constants. The stress values obtained with these new methods on the basis of the mechanical elastic constants are more reliable than those obtained with the methods on the basis of the diffraction elastic constants. New and existing methods are illustrated by means of measurements of X-ray diffraction from a magnetron-sputtered TiN layer.

Unerwartete Ergebnisse von Barkhausenrauschmessungen an einem Rollenwälzlager nach Trockenlauf

Locally increased amplitudes of Barkhausen Noise are usually due to changes of residual stresses versus tension and/or reduction of mechanical hardness. This rule was found not to be valid for a 5 to 10 μm thick surface layer with microstructural changes similar to friction martensite which was detected in a roller bearing of a helicopter intermediate gear, after running without lubrication for about 20 minutes. Besides of Barkhausen Noise Measurements and conventional Non Destructive Testing, X-Ray Diffraction Analysis and Stress Measurements, Scanning Electron Microscopy, ESCA and metallographic investigations were carried out. It is assumed that rearrangements of dislocations and interstitial atoms in connection with transformation of retained austenite have lead to an increase of the mobility of Bloch Walls and so caused the observed high noise amplitudes.

Mapping two-dimensional state of strain using synchroton X-ray diffraction

Department of Materials Scienceand Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, UK(Received February 16, 1998)(Accepted in revised form September 14, 1998)IntroductionComposite strain mapping is a procedure which is naturally addressed by techniques utilising diffrac-tion. Measurements in both the matrix and reinforcement cannot be made using conventional methods,such as strain gauging or hole drilling. Diffraction techniques most commonly used for strain mea-surements include neutron diffraction, conventional (laboratory) X-ray, and synchrotron X-ray diffrac-tion. Compared to laboratory X-ray, synchrotron radiation offers dramatic improvements in beamintensity and penetration depths. Where conventional diffraction stress measurements rely on interro-gating only a thin surface layer (,50mm) of such material as aluminium, synchrotron X-ray possessessufficient flux to allow collection of diffraction patterns from sampling volumes over 20mm thick.Important additional benefits of using such high flux beams are the improved spatial resolution, and thepossibility of using extremely short collection times. These two experimental parameters are interre-lated, and both influence the quality of data in a complex way. Additionally, acceptable data qualityvaries depending on the interpretation procedures and the requirements of accuracy and consistency. Asa consequence, suitable values of the test parameters, such as sampling volume and collection time,must be determined experimentally, using carefully selected test systems, possessing suitable geometryand subjected to controlled loading. The main content of the present paper is the description of such anexperiment.In this study, measurements were made on the ID11, BL2 materials science beamline (1) at theEuropean Synchrotron Radiation Facility at Grenoble, a diffractometer allowing controlled translationof the sample in three linear directions. The technique involved direct collection of diffracted patternsin digital form using a high resolution CCD camera. Due to the novel nature of this application, thecapabilities and limitations of the present configuration for engineering strain measurement had not yetbeen fully explored in a systematic way. The aim of the present experiment was to test the capabilitiesof both the hardware and software for making accurate and reliable strain measurements in thetransmission geometry, to investigate their limitations, and to determine the routes for further devel-opment.

A model for stress in thin layers induced by misfitting particles: An origin for growth stress

The stress caused by misfitting particles in thin layers adherent to substrates is modelled. The model assumes an elastically isotropic matrix with holes in which the misfitting particles are introduced. The stress field generated in the matrix consists of a hydrostatic stress resulting directly from the misfitting particles and a biaxial state of stress resulting from the condition that the layer should remain attached to its substrate. The model and its implications for diffraction stress measurements are illustrated using magnetron sputtered TiN layers.

Corrections to Equations for Estimating the Counting-Statistical Errors in Diffraction Stress Measurements

Two corrections are made to the equations for estimating the counting statistical errors in diffraction stress measurements. It is shown that the previous equations provide a conservative estimate of the counting-statistical component of the random errors in stress measurements. The results from the corrected equations are compared to a Monte Carlo model and to replicated measurements. A procedure to handle other sources of random error is also suggested.

Assessing the Validity of Diffraction Stress Data with the Goodness-Of-Fit Statistic

According to the standard model, strain in polycrystalline materials transforms like a tensor when measured with diffraction in different directions. This model predicts linear variation of d-spacing with sin2ѱ if the stresses σ13 and σ23 are absent or predicts ѱ-splitting if they are present. In diffraction stress measurements, d vs. sin2ѱ plots often exhibit behavior that cannot be predicted from this model. When such discrepancies are observed, stresses calculated from the data will not always be valid. Current practice is to determine the validity of data by visually inspecting d vs. sin2ѱ plots and subjectively assessing the goodness-of-fit. This paper proposes the χ2 statistic as a tool for quantitatively determining goodness-of-fit, and it presents experimental results from the application of the statistic.

Use of position-dependent stress-free standards for diffraction stress measurements

Residual stress measurements using neutron diffraction are inherently triaxial in nature due to the low adsorption, and thus high penetration, of neutrons in samples of interest. This means that stress-free reference standards are required to convert measured changes in peak position to strain and stress tensors. Althogh a number of empirical and analytical approaches have been utilized to obtain accurate stress-free reference cell parameters, they all presume the presence of a single reference value for the material being measured. However, important cases can arise for which the local stress-free cell parameter varies from point to point. One such case, a circumferentially welded cylinder, is presented here. A method of point-to-point correction is employed, involving the sectioning of a companion piece into small cubes corresponding to the positions of stress measurement. The variations in peak position and peak breadth are presented. It is shown that accurate stress tensors can be obtained and that use of a constant value of stress-free reference cell parameter from the unaffected base metal leads to errors of up to 700 MPa in some stress tensor components. Effects on the principal stresses are also presented.

Mesure par diffraction des rayons X des microdéformations dans des films minces texturés d'Au

Microdistorsion analysis in Au 150 nm thin films is presented in this study. Applying the method of the «integral width», known and employed in bulk materials, we have shown its feasibility and its interest in the case of thin films. Furthermore, in relation with X-Ray diffraction stress measurement, we found important effects of the deposition conditions on the films microstructure

XRD Pattern Fitting as a Tool to Control Plating Parameters in Zinc Nickel Electroplates

AbstractRietveld X-ray powder diffraction (XRD) and uniaxial stress measurement procedures are being evaluated as a means of correlating the crystalline structure properties of zinc-nickel electroplate with observed plating properties. The study is being performed on a suite of six samples of varying composition (6 to 20%Ni) electrodeposited on mild steel. Rietveld refinement of the XRD data (Rietveld, 1969) has been performed on a specially prepared ingot (9%Ni:91%Zn) to determine the structural parameters and relative abundances for the γ(Ni4Zn22), δ(Ni3Zn22) and η(Zn) phases which could possibly be present in the electroplate. Relative phase abundances were verified by Atomic Absorption Spectrometry (AAS) and electron probe microanalysis (EPMA) image mapping techniques.The structural parameters for the ingot zinc-nickel phases were subsequently used as initial parameters in Rietveld calculations for the six electroplate samples. Structure refinement of the electroplate XRD data was hampered by extremely high preferred orientation and the corresponding lack of quality diffraction peaks. However, Rietveld refinements produced accurate cell dimensions (which correlate linearly with nickel composition), a means of quantifying the degree of preferred orientation, and crystalline phase verification. For residual stress determination, d-sin2ψ plots were produced for each electroplate sample. The plots were found to be linear for Ni < 12%, allowing calculation of residual stress, and distinctly curved for Ni > 12%.

Stress analysis and failure possibility assessment of multilayer physically vapour deposited coatings

A mathematical model for stress analysis and failure possibility assessment of multilayer coatings produced by ion-assisted physical vapour deposition (PVD) is proposed. Stresses in coating layers are divided into thermal, intrinsic and operational stresses. Calculations of thermal stresses and intrinsic stresses caused by interstitials are performed for TiN and titanium layers on stainless steel substrates. Coating failures as a result of a single layer failure, interface crack propagation and peeling above an area with imperfect adhesion are discussed. The model enables the determination of optimal thicknesses and deposition conditions of layers. X-ray diffraction stress measurements make it possible to estimate the model errors, which are found to be 15%–20%. As an example, calculations for PVD coatings with TiN and titanium layers are carried out. It is concluded that it is useful to interpose the ceramic and metal layers to reduce interface shear forces.

Enhanced Gate Oxide Reliability through Fluorine Incorporation and the Influence of Polysilicon Process Variations

ABSTRACTThere has been some uncertainty as to the impact of fluorine (F) on SiO2 quality and reliability. Several laboratories have shown greatly enhanced quality and reliability with fluorinated oxides, while others have been unable to repeat the results. In addition, the laboratories which have shown enhanced reliability with the fluorinated oxides have differed in their interpretation of the mechanism by which the enhancement occurs. X-ray diffraction stress measurements, partial time dependent dielectric breakdown (TDDB) measurements, SIMS depth profiling, transmission electron microscopy, standard high/low frequency C-V measurements, and hot-carrier aging of variously processed MOSFETs have been used to investigate a variety of fluorinated films. We believe that the apparent lack of consistency of the effects of fluorine on MOSFET reliability between laboratories may be explained by slight variations in the gate polysilicon processing which result in variations in polysilicon morphology. The polysilicon morphology determines both mechanical stress and F diffusion which ultimately impacts interface state density and thus hot carrier reliability.

Growth Characteristics of Co-Cr Thin Films for Magnetic Recording

AbstractThe growth characteristics of magnetron sputtered Co-22%Cr thin films on amorphous glass or carbon substrates have been investigated utilizing transmission electron microscopy,. X-ray diffraction, electrical resisivity and in-plane stress measurements. Results indicate that the initial deposit is “amorphous”, but that isolated islands of small crystallites form before the film reaches 5nm film thickness. By 10nm, well oriented grains with hcp c axis perpendicular to the film plane develop, and by 50nm, a twinned columnar microstructure is evident. As this occurs, the in-plane film stress becomes constant. Also, we have observed a distinct subgrain structure in the thinner films (10–50 nm), and this is reflected in the electrical resistivity. This cannot be accounted for by an “evolutionary selection” growth scenario, but must be related to the low surface mobility of adatoms at these low substrate deposition temperatures.

A Comparison of X-Ray Diffraction Residual Stress Measurement Methods on Machined Surfaces

The two-angle and Sin2ψ methods of x-ray diffraction, residual stress measurement have been shown to yield anomalous results When applied to samples which have been plastically deformed uniaxially in tension or by rolling. These anomalous stresses, which are not true mechanical macrostresses, have been shown to arise from a nonlinear dependence,of d, the interplanar spacing employed for stress measurement, upon Sin2 ψ. A new method of x-ray diffraction stress measurement has been developed by Marion and Cohen which aLlows the separation of the Linear and nonlinear components of the dependence of d upon Sin2 ψ.The two-angle and the Marion-Cohen x-ray diffraction methods are applied to the measurement of residual stresses in the machined and shot peened surfaces of steel and aluminum samples. The results indicate that machining deformation results in a nearly linear dependence of d upon Sin2ψ , and onLy a slight deformation texture. The two x-ray methods yield stress values in ground, turned, and shot peened steel and aluminum samples which agree within the estimated experimental error. Previous results are sighted showing agreement between the two-angle method and a mechanical stress measurement technique. The results indicate that, at least in steels, the multiaxial plastic deformation produced by machining does not significantly effect the accuracy of the two-angle x-ray diffraction stress mea surement method.

X-ray diffraction stress measurements in thin films : T. J. Louzon and T. H. Spencer. Solid State Techn. July 1975, p. 25

X-ray diffraction stress measurements in thin films : T. J. Louzon and T. H. Spencer. Solid State Techn. July 1975, p. 25