Subsurface Microstructure Induced by Sliding Wear in a Copper Single Crystal

A sliding wear test was conducted in a copper single crystal having (001) surface. Microstructures induced by the sliding wear were investigated by means of the electron channelling contrast (ECC) imaging and electron backscattered diffraction (EBSD) analysis. The microstructures below the worn surface consisted of the stack of dislocation cell structure, layered structure and equiaxed fine-grained structure. At the dislocation cell structure, there was no significant change in crystallographic orientation. On the other hand, the crystal at the layered structure rotated continuously around the axis which was perpendicular to sliding wear direction. In the fine-grained structure, preferential orientations no longer existed. The authors attempted to explain grain boundary formation in terms of a rotation angle gradient which is proportional to density of geometrically-necessary dislocations.

Systematical Characterization of Material Response to Microscale Laser Shock Peening

The response of materials after microscale laser shock peening (μLSP) was experimentally characterized and compared with the theoretical prediction from FEM analysis in microlength level. Since μLSP is predominantly a mechanical process instead of a thermal process, the characterization focuses on mechanical properties and associated microstructures. An X-ray microdiffraction technique was applied on the postpeened single crystal aluminum of (001) and (110) orientations, and an X-ray profile was analyzed by subprofiling and Fourier analysis method. Spatially resolved residual stress and strain deviation was quantified and explained in terms of the heterogeneous dislocation cell structure. In-plane crystal lattice rotation induced by μLSP were measured by electron backscatter diffraction (EBSD) and compared with the FEM simulation. Average mosaic size was evaluated from X-ray profile Fourier analysis and compared with the result from EBSD. Surface strength increase and dislocation cell structure formation were studied. The systematical characterization helps develop more realistic simulation models and obtain better understanding in microlength level.

X-ray determination of dislocation density and arrangement in plastically deformed copper

Using the kinematical theory of X-ray scattering by crystals with dislocations as developed by Krivoglazet al.and Wilkens, the dislocation content of compressed copper single and polycrystals was investigated by means of profile analysis of selected diffraction peaks. Measurements of radial intensity distributionsI(2θ) were performed with a double-crystal spectrometer in the case of the single crystals and with conventional polycrystal diffractometers in the case of the polycrystals. Additionally, the misorientations Θ occurring within the dislocation cell structure because of the accumulation of excess dislocations of one sign were investigated by means of rocking curves of the single-crystal reflections and by evaluation of electron backscattering patterns (EBSPs). Within a wide deformation range, the mean total dislocation density ρdcan be related well to the flow stressviathe Taylor relationship. Assuming a random distribution of the misorientations Θ between adjacent dislocation cells, the evaluation of the rocking curves gives mean values 〈|Θ|〉 much smaller than those determined by EBSP analysis. For this reason, a model of a dislocation cell structure with restrictedly correlated misorientations, which leads to better agreement of the X-ray and the EBSP data, is proposed.