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

Multi-reflection 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 influence of different mechanical treatments on residual stresses was studied for Al–Mg samples. It was found that both rolling and mechanical polishing influence 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

Stress evolution in plastically deformed austenitic and ferritic steels determined using angle- and energy-dispersive diffraction

In the presented research, the intergranular elastic interaction and the second-order plastic incompatibility stress in textured ferritic and austenitic steels were investigated by means of diffraction. The lattice strains were measured inside the samples by the multiple reflection method using high energy X-rays diffraction during uniaxial in situ tensile tests. Comparing experiment with various models of intergranular interaction, it was found that the Eshelby-Kr\"oner model correctly approximates the X-ray stress factors (XSFs) for different reflections hkl and scattering vector orientations. The verified XSFs were used to investigate the evolution of the first and second-order stresses in both austenitic and ferritic steels. It was shown that considering only the elastic anisotropy, the non-linearity of $\sin^2{\psi}$ plots cannot be explained by crystallographic texture. Therefore, a more advanced method based on elastic-plastic self-consistent modeling (EPSC) is required for the analysis. Using such methodology the non-linearities of $\cos^2{\phi}$ plots were explained, and the evolutions of the first and second-order stresses were determined. It was found that plastic deformation of about 1- 2% can completely exchange the state of second-order plastic incompatibility stresses

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

Multi-reflection 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 influence of different mechanical treatments on residual stresses was studied for Al–Mg samples. It was found that both rolling and mechanical polishing influence 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

Grain and phase stress criteria for behaviour and cleavage in duplex and bainitic steels

Stress analyses by X-ray diffraction are performed on a cast duplex (32% ferrite) stainless steel elbow and a bainitic (95% ferrite) pressure vessel steel. During an in situ tensile test, micrographic observations are made (visible glides and microcracks) and related to the stress state determined in the individual ferritic grains (aged duplex) and the ferritic phase (bainite loaded at low temperatures). Several material parameters have been identified at different scales, as for example, the critical resolved shear stress of 245 MPa for the aged ferritic grain (duplex) or 275 MPa for bainite (–60 ◦C), a crystallographic cleavage propagation criterion of 465 MPa (stress normal to {100} planes), and a fracture stress of approximately 700 MPa in the ferritic phase. Even though the two steels are different in many respects, the macroscopic fracture strains and stresses are well predicted by the polycrystalline model developed for bainite, whatever the temperatures tested (considering 7% of the grains reaching the local criterion)

Gradient of Residual Stress and Lattice Parameter in Mechanically Polished Tungsten Measured Using Classical X rays and Synchrotron Radiation

In this work, the stress gradient in mechanically polished tungsten sample was studied using X ray diffraction methods. To determine in depth stress evolution in the very shallow subsurface region up to 10 amp; 956;m , special methods based on reflection geometry were applied. The subsurface stresses depth up to 1 amp; 956;m were measured using the multiple reflection grazing incidence X ray diffraction method with classical characteristic X rays, while the deeper volumes depth up to 10 amp; 956;m were investigated using energy dispersive diffraction with white high energy synchrotron beam. Both complementary methods allowed for determining in depth stress profile and the evolution of stress free lattice parameter. It was confirmed that the crystals of tungsten are elastically isotropic, which simplifies the stress analysis and makes tungsten a suitable material for testing stress measurement methods. Furthermore, it was found that an important compressive stress of about amp; 8722; 1000 MPa was generated on the surface of the mechanically polished sample, and this stress decreases to zero value at the depth of about 9 amp; 956;m. On the other hand, the strain free lattice parameter does not change significantly in the examined subsurface regio

Multireflection grazing incidence diffraction used for stress measurementsin surface layers

The geometry based on the multireflection grazing incidence X-ray diffraction can be applied to measure residual stresses. Using this method, it is possible to perform a non-destructive analysis of the heterogeneous stresses for different and well defined volumes below the surface of the sample (range of several μm). As the result, the average values of stresses weighted by absorption of X-ray radiation are measured. In this work the stress profiles as a function of penetration depth were determined for mechanically polished Al sample. Measurements and verification of the method were performed using classical X-ray diffractometer and synchrotron radiation with different wavelengths

Elastoplastic deformation of Al/SiC_p metal–matrix composite studied by self-consistent modelling and neutron diffraction

Neutron diffraction was used to measure the lattice strains in Al/SiCp metal–matrix composite under an external load applied while the sample was in situ in the neutron beam. The evolution of the internal stresses and of the critical-resolved shear stress during bending were predicted by elastoplastic models. Calculations based on these models were verified by comparison with the results of the diffraction experiment. It was found that the self-consistent model correctly predicts the distribution of stresses between the two phases of the Al/SiCp composite. Finally, the parameters characterising elastoplastic deformation of the Al–matrix were determined

Residual stresses induced by cross-rolling

Deformation in rolling induces in general a strong crystallographic texture, hence an important material anisotropy. This is a reason why the cross-rolling is sometimes applied in order to symmetrize the crystallographic texture. Such an operation modifies also residual stresses. The goal of this study was to characterize residual stress and texture changes during simple and cross-rolling in polycrystalline copper and ferritic steel. The obtained results show that important modification of the first order residual stresses occurs during cross-rolling, while the level of the second order ones is approximately constant. Experimental results were analysed using an elastoplastic deformation model

Quantitative estimation of incompatibility stresses and elastic energy stored in ferritic steel

Plastic incompatibility second-order stresses were determined for different orientations of a polycrystalline grain, using X-ray diffraction data and results of the self-consistent elasto-plastic model. The stresses in cold rolled ferritic steel were determined both in as-received and under tensile loaded conditions. It has been shown that the Reuss model and the self-consistent model applied to near surface volume provide the best approaches to determine diffraction elastic constants. For the first time, the elastic energy in an anisotropic material (arising from plastic incompatibilities between grains having various lattice orientations) has been determined. The second-order incompatibility stresses and stored elastic energy are presented in Euler space