32 research outputs found

    Application of multireïŹ‚ection grazing incidence method for stress measurements in polished Al–Mg alloy and CrN coating

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    Multi-reïŹ‚ection grazing incidence geometry, referred to as MGIXD, characterized by a small and constant incidence angle, was applied to measure low surface stresses in very thin layers of Al–Mg alloy and CrN coating. These two materials were selected in order to deal with the low and high levels of residual stress, respectively. The inïŹ‚uence of different mechanical treatments on residual stresses was studied for Al–Mg samples. It was found that both rolling and mechanical polishing inïŹ‚uence the distribution and amplitude of residual stress in surface layers. In the case of CrN coating, a very high compressive stress was generated during the deposition process. The stress distributions determined by the MGIXD method is in good agreement with the classic sin2 technique results for all studied samples. In performing stress measurements for a powder sample, it was found that the application of the Göbel mirror in the incident beam strongly reduces statistical and misalignment errors. Additionally, the root mean square values of the third order lattice strain within diffracting grains were determined

    Evolution of microstructure and residual stress during annealing of austenitic and ferritic steels

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    International audienceIn this work the recovery and recrystallization processes occurring in ferritic and austenitic steels were studied. To determine the evolution of residual stresses during material annealing the nonlinear sin 2 ψ diffraction method was used and an important relaxation of the macrostresses as well as the microstresses was found in the cold rolled samples subjected to heat treatment. Such relaxation occurs at the beginning of recovery, when any changes of microstructure cannot be detected using other experimental techniques. Stress evolution in the annealed steel samples was correlated with the progress of recovery process, which significantly depends on the value of stacking fault energy

    Scattering vector (h 2 k 2 l 2 ) Scattering vector (h 1 k 1 l 1 ) α α 2Ξ 2 t New developments of multireflection grazing incidence diffraction

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    Abstract. The multireflection grazing incident X-ray diffraction (MGIXD) is used to determine a stress gradient in thin surface layers (about 1-20 ”m for metals). In this work two theoretical developments of this method are presented. The first procedure enables determination of c/a parameter in hexagonal polycrystalline materials exhibiting residual stresses. In the second method, the influence of stacking faults on the experimental data is considered. The results of both procedures were verified using X-rays diffraction. Introduction Multireflection grazing incidence X-ray diffraction (MGIXD) is a non-destructive method which allows performing an analysis of the heterogeneous stress field for different volumes below the surface of the sample. The penetration depth of X-ray radiation is well defined and does not change during experiment in a wide 2Ξ range for a given incidence angle

    Evolution of microstructure and residual stress during annealing of austenitic and ferritic steels

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    In this work the recovery and recrystallization processes occurring in ferritic and austenitic steels were studied. To determine the evolution of residual stresses during material annealing the nonlinear sin 2 ψ diffraction method was used and an important relaxation of the macrostresses as well as the microstresses was found in the cold rolled samples subjected to heat treatment. Such relaxation occurs at the beginning of recovery, when any changes of microstructure cannot be detected using other experimental techniques. Stress evolution in the annealed steel samples was correlated with the progress of recovery process, which significantly depends on the value of stacking fault energy

    Stress measurements by multi-reflection grazing-incidence X-ray diffraction method (MGIXD) using different radiation wavelengths and different incident angles

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    The presented study introduces the development of the multi-reflection grazing-incidence X-ray diffraction method (MGIXD) for residual stress determination. The proposed new methodology is aimed at obtaining more reliable experimental data and increasing the depth of non-destructive stress determination below the sample surface. To verify proposed method measurements were performed on a classical X-ray diffractometer (Cu Kα radiation) and using synchrotron radiation (three different wavelengths: λ = 1.2527 Å, λ = 1.5419 Å and λ = 1.7512 Å). The Al2017 alloy subjected to three different surface treatments was investigated in this study. The obtained results showed that the proposed development of MGIXD method, in which not only different incident angles but also different wavelengths of X-ray are used, can be successfully applied for residual stress determination, especially when stress gradients are present in the sample

    Application of multireïŹ‚ection grazing incidence method for stress measurements in polished Al–Mg alloy and CrN coating

    Get PDF
    Multi-reïŹ‚ection grazing incidence geometry, referred to as MGIXD, characterized by a small and constant incidence angle, was applied to measure low surface stresses in very thin layers of Al–Mg alloy and CrN coating. These two materials were selected in order to deal with the low and high levels of residual stress, respectively. The inïŹ‚uence of different mechanical treatments on residual stresses was studied for Al–Mg samples. It was found that both rolling and mechanical polishing inïŹ‚uence the distribution and amplitude of residual stress in surface layers. In the case of CrN coating, a very high compressive stress was generated during the deposition process. The stress distributions determined by the MGIXD method is in good agreement with the classic sin2 technique results for all studied samples. In performing stress measurements for a powder sample, it was found that the application of the Göbel mirror in the incident beam strongly reduces statistical and misalignment errors. Additionally, the root mean square values of the third order lattice strain within diffracting grains were determined

    Multireflection grazing-incidence X-ray diffraction: A new approach to experimental data analysis

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    The multireflection grazing-incidence X-ray diffraction method is used to test surface stresses at depths of several micrometres in the case of metal samples. This work presents new ways of analysing experimental data obtained by this method for Ni samples exhibiting significant elastic anisotropy of crystals. Three different methods of determining biaxial stresses and lattice parameter were compared. In the first approach, the calculations were performed using the linear least-squares method, and then two simplified procedures based on simple linear regression (weighted and non-weighted) were applied. It was found that all the tested methods give similar results, i.e. almost equal values of the determined stresses and lattice parameters and the uncertainties of their determination. The advantage of analyses based on simple linear regression is their simplicity and straightforward interpretation, enabling easy verification of the influence of the crystallographic texture and the presence of shear stresses, as well as graphical determination of the stress-free lattice parameter

    A multireflection and multiwavelength residual stress determination method using energy dispersive diffraction

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    The main focus of the presented work was the investigation of structure and residual stress gradients in the near-surface region of materials studied by X-ray diffraction. The multireflection method was used to measure depth-dependent stress variation in near-surface layers of a Ti sample (grade 2) subjected to different mechanical treatments. First, the multireflection grazing incidence diffraction method was applied on a classical diffractometer with Cu Kα radiation. The applicability of the method was then extended by using a white synchrotron beam during an energy dispersive (ED) diffraction experiment. An advantage of this method was the possibility of using not only more than one reflection but also different wavelengths of radiation. This approach was successfully applied to analysis of data obtained in the ED experiment. There was good agreement between the measurements performed using synchrotron radiation and those with Cu Kα radiation on the classical diffractometer. A great advantage of high-energy synchrotron radiation was the possibility to measure stresses as well as the a0 parameter and c0/α0 ratio for much larger depths in comparison with laboratory X-rays. © 2018 International Union of Crystallography

    Etude par diffraction des propriétés mécaniques et des contraintes résiduelles résultant de la transformation de matériaux polycristallins

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    Methodology of stress measurements with multireflection grazing incidence method (MGIXD)was investigated and developed. The parallel beam geometry was applied. The incident beam in classicaldiffractometers was collimated by Göbel mirror and the tests of parallel configuration were performed for Alpowder. Results confirmed that both statistical error and the misalignment error can be reduced when theGöbel mirror is used. Physical factors were taken into account in XSA (X-ray stress analysis): Lorentzpolarizationand absorption factor (LPA) and also refraction correction (RC). Results showed that theinfluence of LPA correction is minor in XSA but the RC can significantly influence analysis. In the thesisthe issue of RC was considered and compared with approaches presented in the literature. In the thesistwo theoretical developments of the MGIXD method were presented: the procedure of c/a parameterdetermination and the influence of stacking faults on the results was taken into account. It was shown thatboth developments significantly improves the quality of experimental data analysis. In the present work theproblem of X-ray stress factors (XSF) used for the interpretation of XSA results was studied. Differenttheoretical grain elasto-plastic interaction models were considered and applied in XSA. Verification of theXSF was during tensile test for austenitic stainless steel and for the isotropic sample. Anisotropy of XSFwas also observed in: ground Ni alloy, polished austenitic stainless steel and CrN coating. The resultsshows that Reuss and free surface grain interaction models are in the best agreement with theexperimental results. Finally the MGIXD method was verified using synchrotron radiation and 3 differentwavelengths. The methodology was developed to treat data not only for different incident angles but alsousing simultaneously different wavelengths. Stresses vs. z – ‘real depth’ was calculated using the inverseLaplace transform applied to polynomial function. Wiliamson-Hall analysis was applied for collected data.Next multireflection method was applied for the energy dispersion diffraction measurements in which whitebeam containing radiation having different wavelengths was used (λ (Çș): 0.3–0.18/ E (keV): 40-68). Thestress analysis was performed using three different methods: standard sin2ψ method, Universal plotmethod and by using multireflection analysis. In the range of penetration depth to 0-15 ÎŒm theconvergence of the results obtained from different methods was gained. Moreover the synchrotron dataperfectly agree with the results obtained on laboratory diffractometer (Cu Kα radiation) close to the surface.For depth larger than 14 ÎŒm the experimental points exhibit significant spread and do not agree with theresults of standard methodMĂ©thodologie de mesures de contraintes avec la mĂ©thode multireflection pĂąturage d'incidence(MGIXD) a Ă©tĂ© Ă©tudiĂ© et dĂ©veloppĂ©. La gĂ©omĂ©trie du faisceau parallĂšle a Ă©tĂ© appliquĂ©e pour mensurationsde stress. Le faisceau incident dans diffractomĂštres classiques a Ă©tĂ© collimatĂ© par le miroir Göbel et lesessais de configuration en parallĂšle ont Ă©tĂ© effectuĂ©es pour Al poudre. Les rĂ©sultats confirmĂ© que le erreurstatistique et l'erreur d'alignement peuvent ĂȘtre rĂ©duits lorsque le miroir Göbel est utilisĂ©. Facteursphysiques ont Ă©tĂ© prises en compte dans la CSX (analyse aux rayons X du stress): Lorentz - polarisationet facteur d'absorption (LPA) et aussi correction de la rĂ©fraction (RC). Les rĂ©sultats montrent quel'influence de LPA est mineur dans CSX, mais la RC peut influencer de maniĂšre significative l'analyse.Dans la thĂšse de la question de RC a Ă©tĂ© examinĂ© et comparĂ© avec les approches prĂ©sentĂ©es dans lalittĂ©rature. Dans la thĂšse de deux dĂ©veloppements thĂ©oriques de la mĂ©thode MGIXD ont Ă©tĂ© prĂ©sentĂ©s: laprocĂ©dure de dĂ©termination de paramĂštre c/a et l'influence des dĂ©fauts d'empilement sur les rĂ©sultats. Il aĂ©tĂ© montrĂ© que les deux dĂ©veloppements amĂ©liore de maniĂšre significative la qualitĂ© de l'analyse desdonnĂ©es expĂ©rimentales. Dans le prĂ©sent travail le problĂšme de la X -ray facteurs de stress (XSF) utilisĂ©spour l'interprĂ©tation des rĂ©sultats CSX a Ă©tĂ© Ă©tudiĂ©e. DiffĂ©rents modĂšles thĂ©oriques de grains Ă©lastoplastiqueinteraction ont Ă©tĂ© envisagĂ©es et appliquĂ©es dans la CSX. VĂ©rification de la XSF durant l'essaide traction pour l'Ă©chantillon Ă©lastique anisotrope (en acier inoxydable austĂ©nitique) et pour l'Ă©chantillonisotrope (Ti - note2). Anisotropie de XSF a Ă©galement Ă©tĂ© observĂ©e dans: rectifiĂ© alliage Ni, acierinoxydable austĂ©nitique poli et revĂȘtement CrN. Les rĂ©sultats montre que Reuss et modĂšle de la surfacelibre sont en meilleur accord avec les rĂ©sultats expĂ©rimentaux. Enfin, la mĂ©thode MGIXD a Ă©tĂ© vĂ©rifiĂ©e enutilisant le rayonnement synchrotron et 3 longueurs d'onde diffĂ©rentes. La mĂ©thodologie a Ă©tĂ© dĂ©veloppĂ©epour traiter les donnĂ©es non seulement pour les diffĂ©rents angles d'incidence, mais aussi en utilisantdiffĂ©rentes longueurs d'onde simultanĂ©ment. Contraintes en fonction de «vraie profondeur» a Ă©tĂ© calculĂ©een utilisant la transformĂ©e de Laplace inverse. Analyse Wiliamson-Hall a Ă©tĂ© appliquĂ©e pour les donnĂ©es.MĂ©thode MGIXD a Ă©tĂ© appliquĂ© pour les mesures de diffraction de dispersion d'Ă©nergie dans lequel lefaisceau blanc a Ă©tĂ© utilisĂ©: 0,3 Ă  0,18 Å. L' analyse des contraintes a Ă©tĂ© effectuĂ©e en utilisant troismĂ©thodes diffĂ©rentes : la mĂ©thode de sin2ψ norme, la mĂ©thode de terrain universelle et en utilisantmultireflection analyse . Dans la gamme de profondeur de pĂ©nĂ©tration Ă  0-15 um de la convergence desrĂ©sultats obtenus Ă  partir de diffĂ©rentes mĂ©thodes a Ă©tĂ© acquise . En outre, les donnĂ©es de synchrotronparfaitement en accord avec les rĂ©sultats obtenus en laboratoire sur diffractomĂštre (rayonnement Cu Ka) Ă proximitĂ© de la surface . Pour profondeur supĂ©rieure Ă  14 um points expĂ©rimentaux prĂ©sentent desvariations importantes et ne sont pas d'accord avec les rĂ©sultats de la mĂ©thode standard.Mots clĂ©s : contraintes rĂ©siduelles, diffraction des rayons X, mĂ©thode de l’incidence rasante, miroir Göbe
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