Correlation between subgrains and coherently scattering domains

Crystallite size determined by X-ray line profile analysis is often smaller than the grain or subgrain size obtained by transmission electron microscopy, especially when the material has been produced by plastic deformation. It is shown that besides differences in orientation between grains or subgrains, dipolar dislocation walls without differences in orientation also break down coherency of X-rays scattering. This means that the coherently scattering domain size provided by X-ray line profile analysis provides subgrain or cell size bounded by dislocation boundaries or dipolar walls

SOME STRUCTURAL ASPECTS OF MAGNETIC PROPERTY EVOLUTION IN FINEMET-TYPE SENSOR MATERIAL DURING AMORPHOUS-NANOCRYSTALLINE TRANSFORMATIONS

Devitrification of glassy Fe73.5Si13.5B9Nb3Cu1 alloy used as potential sensor material was followed by magnetic measurements and X-ray diffraction, and transmission electron microscopy. It was found, that the permeability, and the coercive field of the alloy changed well below the crystallisation onset, showing a remarkable increase, which was attributed to the structural relaxation and a heterogen nucleation of iron rich phase on Cu clusters. On the basis of lattice parameter measurements the iron rich clusters were depleted from Si atoms during the nucleation process and the Si atoms built in them only during annealing at higher temperatures as 500 \circC and 540 \circC forming a DO3 structure. From the structural study of samples annealed near to the optimal transformation stage it was concluded, that size distribution of the bcc-Fe(Si) nanocrystallites (not exclusive factor) was only one of the most important factors to achieve the optimal soft magnetic properties, but at the same time, their volume fraction, as well as the degree of ordering in DO3 structure did also contribute to the property optimization. The average grain size produced by laser pulse heat treatment was nearly the same, as that obtained during the traditional heat treatments

The Contact Angle Between Ag-Based Melts and Graphite Substrate and the Texture Evolution During the Subsequent Solidification

Ag based alloys are widely used in the modern brazing technologies for the substitution of tin-lead based alloys. In the present work the wetting ability between graphite substrate and diluted Ag-M (M: Cd, In, Sn, Sb) has been studied using the sessile drop method. The contact angle between the liquids and solid substrate was measured at 1200˚C. Subsequently the micro structure of the solidified drops was investigated applying X-ray diffraction (XRD) and transmission electron microscopic (TEM) measurements. A texture formation was found in the substrate/drop interface region. Comparing the values of the contact angles measured on the Ag- M samples with the degree of the texture determined by XRD it was found, that the contact angle is smaller the degree of texture higher

Csúszási rendszerek, Burgers vektor és rétegződési hibák meghatározás köbös, ortorhombos és hexagonális rendszerekben a röntgen vonalprofil analízis módszere alapján = Active slip-systems, Burgers vectors and twinning in hexagonal, cubic and ortorhombic systems determined by X-ray line profile analysis

Polikristályos Ti mintában, krisztallitonként kiértékelve a szinkrotronos diffrakciós vonalprofilokat, meghatároztuk az egyes krisztallitokban a legvalószínűbb csúszási rendszereket. Krisztallitonként meghatároztuk a legvalószínűbb diszlokációkat az MgGeO3 poszt-perovszkitban. A mintát gyémánt cellában 90 GPa nyomással melegítés közben vittük a poszt-perovszkit fázisba. A Co-Ti és Co-Zr ötvözeteken méréseket végeztünk a Chicago-i APS szinkrtorton mellett az 1-ID szinkrotron nyalábbal. Ezzel áttörést sikerült elérni az itt fejlesztett egykristály-diffrakció polikristályos-aggregátumon módszerben. Az Co-Ti és Co-Zr ötvözet rendszerek eredményeinek mind a végső kiértékelése mind a publikálása túlmutatnak a jelen OTKA projekt keretein és jelenleg még folyamatban vannak. Új módszert dolgoztunk ki erőteljesen textúrált mintákban a különböző textúra komponensek mikroszerkezetének kísérletes meghatározására. Erőteljesen textúrált Cu-Nb nanokristályos multirétegekben meghatároztuk a diszlokáció és ikerhatár sűrűséget a rétegvastagság és a hengerlés függvényében. Nanokristályos Cu vékonyrétegben meghatároztuk a diszlokáció sűrűségeket és a nanoikerhatár távolságokat a porlasztott és a hengerelt állapotokban. Meghatároztuk különböző textúrájú Ni vékonyrétegek diszlokáció és ikerhatár sűrűségét a különböző textúra komponensekben. Meghatároztuk egy extrudált Mg ötvözetben a diszlokáció sűrűségeket a különböző textúra komponensekben. Az OTKA szám feltüntetésével 27 cikket publikáltunk. | We determined the most likely slip systems in the individual grains of polycrystalline Ti and MgGeO3 post-perovskite from line profiles measured in polycrystalline aggregates at the ESRF synchrotron in Grenoble. The post-perovskite phase was attained in a diamond-anvil-cell during heating. We did synchrotron measurements on the Co-Ti and Co-Zr alloys at the 1-ID beamline at the APS in Chicago. With the evaluation of these data we could achieve a breakthrough in the processing of the complex and several tens of gigabit data of such experiments. We developed a novel method to evaluate the substructure in the different texture components of strongly textured materials. This we applied to extruded Mg, to Ni thin films and several different types of multilayers of Cu-Nb and thin films with nanotwins. We worked out the procedure for the determination of twinning on the pyramidal and prismatic planes in hexagonal materials from X-ray line broadening. We published 27 research papers with indicating the OTKA-71594 number

A simple model for the vibrational modes in honeycomb lattices

The classical lattice dynamics of honeycomb lattices is studied in the harmonic approximation. Interactions between nearest neighbors are represented by springs connecting them. A short and necessary introduction of the lattice structure is presented. The dynamical matrix of the vibrational modes is then derived, and its eigenvalue problem is solved analytically. The solution may provide deeper insight into the nature of the vibrational modes. Numerical results for the vibrational frequencies are presented. To show that how effective our method used for the case of honeycomb lattice is, we also apply it to triangular and square lattice structures. A few suggested problems are listed in the concluding section.Comment: 9 pages, 12 figures, submitted to American Journal of Physic

Dislocations in Grain Boundary Regions: The Origin of Heterogeneous Microstrains in Nanocrystalline Materials

Nanocrystalline materials reveal excellent mechanical properties but the mechanism by which they deform is still debated. X-ray line broadening indicates the presence of large heterogeneous strains even when the average grain size is smaller than 10 nm. Although the primary sources of heterogeneous strains are dislocations, their direct observation in nanocrystalline materials is challenging. In order to identify the source of heterogeneous strains in nanocrystalline materials, we prepared Pd-10 pct Au specimens by inert gas condensation and applied high-pressure torsion (HPT) up to γ ≅ 21. High-resolution transmission electron microscopy (HRTEM) and molecular dynamic (MD) simulations are used to investigate the dislocation structure in the grain interiors and in the grain boundary (GB) regions in the as-prepared and HPT-deformed specimens. Our results show that most of the GBs contain lattice dislocations with high densities. The average dislocation densities determined by HRTEM and MD simulation are in good correlation with the values provided by X-ray line profile analysis. Strain distribution determined by MD simulation is shown to follow the Krivoglaz–Wilkens strain function of dislocations. Experiments, MD simulations, and theoretical analysis all prove that the sources of strain broadening in X-ray diffraction of nanocrystalline materials are lattice dislocations in the GB region. The results are discussed in terms of misfit dislocations emanating in the GB regions reducing elastic strain compatibility. The results provide fundamental new insight for understanding the role of GBs in plastic deformation in both nanograin and coarse grain materials of any grain size