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

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 sin2ψ 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 cos2φ 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

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

A novel approach for nondestructive depth resolved analysis of residual stress and grain interaction in the near surface zone applied to an austenitic stainless steel sample subjected to mechanical polishing

The choice of the grain interaction model is a critical element of residual stress analysis using diffraction methods. For the near surface region of a mechanically polished austenitic steel, it is shown that the application of the widely used Eshelby Kröner model does not lead to a satisfactory agreement with experimental observations. Therefore, a new grain interaction model called tunable free surface is proposed, allowing for the determination of the in depth evolution of the elastic interaction between grains. It has a strong physical justification and is adjusted to experimental data using three complementary verification methods. It is shown that a significant relaxation of the intergranular stresses perpendicular to the sample surface occurs in the subsurface layer having a thickness comparable with the average size of the grain. Using the new type of X ray Stress Factors, the in depth evolution up to the depth of 45 amp; 956;m of residual stresses and of the strain free lattice parameter is determine