Papers by Keyword: Micro Strain

Abstract: The objective of this study is to evaluate the effect of hydrogen on the micro-and macro-strain of austenitic stainless steel using X-ray diffraction. When hydrogen is trapped in lattice sites, it can affect both the micro-and macro-strain. The micro-strain was evaluated through fitting profiles to measured X-ray diffraction profile using a fundamental parameter method. The macro-strain, i.e., the residual stress, was evaluated by a 2D method using a two-dimensional PSPC. The experimental samples were charged with hydrogen by a cathodic charging method. The results revealed that the induced residual stress was equi-biaxial and compressive, and that the micro-strain increased. Both of these varied rapidly with increasing hydrogen charging time. Saturation occurred at a compressive stress of around 130 MPa. On reaching saturation, the hydrogen charging was terminated and desorption of hydrogen began at room temperature. Then, the strains decreased and the compressive stress reverted, ultimately, to a tensile stress of 180 MPa. Martensitic transformation occurred due to hydrogen charging and this had a significant effect on the X-ray diffraction profile.

Abstract: Under the terrible environment in the aero-engine, the blade, made of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy, is prone to result in fatigue failure. So improving the titanium alloy performance is becoming very significant. In this paper, the microstructure and microhardness of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy with and without laser shock peening (LSP) were examined and compared by XRD, TEM and microhardness test. The XRD tests pointed out that LSP generated the microstrains and grains refinement in the material surface. The TEM results indicated that great high density dislocations were generated and evolved into the dislocation wall, small-angle boundary and large-angle boundary. The nanocrystallites were formed and became more and more uniform after 4GW/cm2. The grains nanocrystallization in the surface layer helps to improve the material performance. The microhardness test result showed that LSP could increase the hardness by 20 percent or so. And the affected depth is about 700μm.

Abstract: Nano - crystalline Al-Mg-Mn was synthesized by ball milling technique. Microstructure of these alloys has been studied from X-ray line broadening. The crystallite size of nano - crystalline Al-Mg-Mn system decreases by increasing the Mg content, While the micro-strain, median diameter,, and geometrical standard deviations,  increases by increasing the Mg content. Micro-hardness of our system has been investigated by Vickers hardness test. The hardness increases by increasing the Mg content.

Abstract: Neutron and synchrotron strain or stress evaluations are reliable when the probe volume is completely immersed in the studied material. However, acquisitions carried out close to interfaces are much more difficult to analyze. Under these conditions, it is indeed very difficult to characterize precisely the volume analyzed by the radiation and finally to define the measured depth. To solve this problem, a complete Monte Carlo simulation of neutron spectrometers and synchrotron experiments has been developed. This method allows defining precisely the size and shape of the probe used. It permits then predicting the evolution of the diffracted intensity versus the position of this volume in the matter. The calculations finally let to define the real analyzed depth, accounting for the local conditions of diffraction and absorption in the material. The method is illustrated by neutron and synchrotron experiments carried out to characterize stress fields existing close to interfaces. The simulations also permit predicting the shape of diffraction profiles that would be observed on perfect specimens. Such information can then be used to correct the instrumental broadening existing in real experiments. This allows a fine Fourier analysis of the diffraction peaks recorded for several orders of reflection and finally permits defining the mean size of the crystallites and the root mean squares of the strains of second and third kind. Such information is useful to characterize and analyze the mechanical behavior of materials.