Laue microdiffraction on polycrystalline samples above 1500 K achieved with the QMAX-µLaue furnace

X-ray Laue microdiffraction aims to characterize microstructural and mechanical fields in polycrystalline specimens at the sub-micrometre scale with a strain resolution of ∼10-4. Here, a new and unique Laue microdiffraction setup and alignment procedure is presented, allowing measurements at temperatures as high as 1500 K, with the objective to extend the technique for the study of crystalline phase transitions and associated strain-field evolution that occur at high temperatures. A method is provided to measure the real temperature encountered by the specimen, which can be critical for precise phase-transition studies, as well as a strategy to calibrate the setup geometry to account for the sample and furnace dilation using a standard α-alumina single crystal. A first application to phase transitions in a polycrystalline specimen of pure zirconia is provided as an illustrative example.

Stepwise Alloying in Liquid-like Solid Solutions to Achieve Crystallographic Distortion for Regulating Thermoelectric Transport Behavior

With the surge of energy consumption, environmental-protection Cu2-xSe thermoelectric materials are increasingly attracting attention. In this work, multilayered structures are constructed in Cu2-xSe solid solutions by alloying (SnSe)0.75(AgBiSe2)0.25, which strongly scatters full-wavelength phonons by carefully regulating the crystallographic distortion. By using the stepwise alloying strategies, crystallographic distortion and the resultant strain fields presented in microstructure were strengthened markedly, which enhanced the phonon scattering. Meanwhile, by adjusting the coalloying content of Ag, Bi, and Sn elements, the carrier and phonon transports were well decoupled in p-type Cu2-xSe, and the thermoelectric performance was significantly enhanced. By optimized power factor as well as depressed heat transport originating from the moderate coalloying, the maximum zT of 1.23 at 750 K was achieved in Cu1.9Se - 1 wt % (SnSe)0.75(AgBiSe2)0.25. This study indicated that the stepwise alloying strategy was a suitable method for optimizing zT of Cu2-xSe.

Direct Observation of Quadrupolar Strain Fields forming a Shear Band in Metallic Glasses

For decades, scanning/transmission electron microscopy (S/TEM) techniques have been employed to analyze shear bands in metallic glasses and understand their formation in order to improve the mechanical properties of metallic glasses. However, due to a lack of direct information in reciprocal space, conventional S/TEM cannot characterize the local strain and atomic structure of amorphous materials, which are key to describe the deformation of glasses. For this work, 4-dimensional-STEM (4D-STEM) is applied to map and directly correlate the local strain and the atomic structure at the nanometer scale in deformed metallic glasses. Residual strain fields are observed with quadrupolar symmetry concentrated at dilated Eshelby inclusions. The strain fields percolate in a vortex-like manner building up the shear band. This provides a new understanding of the formation of shear bands in metallic glass.

Determination of Displacement Fields at the Sub-Nanometric Scale

Macroscopic behavior of materials depends on interactions of atoms and molecules at nanometer/sub-nanometer scale. Experimental mechanics (EM) can be used for assessing relationships between the macro world and the atomic realm. Theoretical models developed at nanometric and sub-nanometric scales may be verified using EM techniques with the final goal of deriving comprehensive but manageable models. Recently, the authors have carried out studies on EM determination of displacements and their derivatives at the macro and microscopic scales. Here, these techniques were applied to the analysis of high-resolution transmission electron microscopy patterns of a crystalline array containing dislocations. Utilizing atomic positions as carriers of information and comparing undeformed and deformed configurations of observed area, displacements and their derivatives, as well as stresses, have been obtained in the Eulerian description of deformed crystal. Two approaches are introduced. The first establishes an analogy between the basic crystalline structure and a 120° strain gage rosette. The other relies on the fact that, if displacement information along three directions is available, it is possible to reconstruct the displacement field; all necessary equations are provided in the paper. Remarkably, the validity of the Cauchy-Born conjecture is proven to be correct within the range of observed deformations.