Radomir Kuzel

ε-Ti2N phase growth control in titanium nitride films

Etude detaillee de la formation de la phase Ti 2 N−e et determination de criteres permettant de prevoir la creation de couches a phase Ti 2 N−e

Laser-stimulated growth of the εTi2N phase in TiN films during d.c. reactive magnetron sputter deposition

Abstract The paper deals with the influence of laser irradiation of growing TiN films on their phase composition. The TiN films were prepared by d.c. reactivity magnetron sputtering under concurrent irradiation by a continuous argon ion laser beam (4 W) continuous wave) with a diameter of 6 mm. Films were characterized by X-ray diffraction analysis. It has been demonstrated that the laser irradiation of the growing film can stimulate the growth of eTi 2 N phase.

Characterization of severe matrix distortions during phase separation from the redistribution of diffracted intensities

Severe matrix deformation has been examined at an early stage of age-hardening in a polycrystalline Brush 25 alloy containing Cu–11.50 at % Be–0.23 at % Co aged at 200°C. Simplified anisotropic elastic models for the atomic displacement field about coherent disc-shaped precipitates provide quantitative estimates of the atomic displacement field in the surrounding matrix. This requires a separation of diffracted intensity into Bragg peaks, static diffuse scattering, and quasilines. The latter originates from the severely distorted zone about the precipitates. Elastic models include single discs, and [1 0 1] stair-step pairs. Ageing at 200°C introduces larger changes in the diffraction profiles than at 315°C. This is observed mainly as large variations in quasiline intensities, as well as in their relative peak positions. Comparisons are made at about one-half the maximum hardness. These variations result from the response of the coherent anisotropic copper matrix to large tetragonal Bain strains in disc-shaped precipitates, and a strong preference for the largest deformations to be perpendicular to the free surface. Quasiline shifts are used along with Vegards Law to extend the metastable Guinier-Preston (GP)-zone boundary to 200°C. This boundary extension is smooth and continuous with published data, and thereby relates the metastable GP boundary to a highly distorted matrix about disc-shaped precipitates. Disc diameters range from 4.8–6.4 nm with a thickness of 0.29 nm after 16–64 h at 200°C. The [1 0 1] stair-step pair model best fits the experimental results.

Influence of Al2O3 Nanoparticles on the Thermal Stability of Ultra-Fine Grained Copper Prepared by High Pressure Torsion

Ultra-fine grained (UFG) Cu (grain size 80 nm) containing 0.5wt.% Al2O3 nanoparticles (size 20 nm) was prepared by high pressure torsion (HPT). Positron lifetime spectroscopy was employed to characterize the microstructure of this material, especially with respect to types and concentration of lattice defects. The evolution of microstructure with increasing temperature was studied by positron lifetime spectroscopy and X-ray diffraction measurements. The thermal stability of the Cu + 0.5 wt.% Al2O3 nanocomposite was compared with that of pure UFG Cu prepared by the same technique. The processes taking place during thermal recovery of the initial nanoscale structure in both studied materials are described.

Temperature evolution of microstructure of deformed submicrocrystalline Cu–Zr samples

The addition of zirconium to copper improves the microstructural stability from the region of only slightly above 100 °C to about 400 oC. This also decreases with the number of ECAP passes. With annealing temperature the diffraction profiles became of anomalous shape with a sharp peak and long tails. Simple 2D diffraction patterns indicated the presence of multimodal microstructure leading to wide and narrow components of diffraction profiles. Therefore, bimodal microstructure model was applied for the evaluation and whole measured diffraction patterns were fitted by our own software MSTRUCT [1] as a sum of two Cu phases with different microstructures. This software combines different procedures and algorithms known from the software created by M. Leoni and P. Scardi or by G. Ribárik with some features of MAUD by L. Lutterotti. It appeared that two factors had main influence on the diffraction profiles and, consequently, could be reliably determined from the experiment – microstrain (and/or dislocation density) in the deformed component and the ratio of deformed and recovered fractions.

Structural studies of M-type ferrites used as template layers for the growth of oriented Y-type ferrites through chemical solution deposition method

Thin films of trigonal Ba2Zn2Fe12O22 (Y-type) ferrite were prepared by the chemical solution deposition using SrTiO3(111) substrates covered with hexagonal magnetoplumbite (M-Type) seed layers. Seven M phases with different chemical composition, magnetic character and lattice misfit (-0.8 % to -7.0 %) values were investigated in their use as template and buffer layers. The films were studied by X-ray diffraction, atomic force microscopy and electron back-scatter diffraction. X-ray diffraction analysis in parallel beam setup with Eulerian cradle was concentrated on the precise determination of lattice parameters, studies of preferred orientation by symmetric and asymmetric scans (w and j) and studies of possible stresses for all the layers by measurement of reflections at different inclinations j and y. For this, correct reference values of lattice parameters are required in particular for non-cubic phases. For most of the phases tested, the values are either completely missing in PDF4+ database or often a number of values can be found there for a single phase. Therefore some data analysis of PDF4+ with respect to the statistics and/or also to the stoichiometry was performed. For all the seed layers strong out-of-plane (000l) orientation of Mand Y-films was observed but with somewhat different degree. The in-plane orientation depended on misfit between the M-interlayer and substrate and also M-interlayer and the top Y-film. The optimum growth was reached using SrTiO3(111)/(BaSr)(GaAl)12O19, SrTiO3(111)/Ba(FeAl)12O19, and SrTiO3(111)/SrGa12O19 substrate/seed layer architectures. In general, the best results were achieved when the misfit values between the seed layer and substrate, and between the seed layer and top Y-layer are approximately equal and when the surface of seed layers are formed by hexagons. Then single domain perfect hexagon-on-hexagon orientation was observed for M-film. For Y-layer also the in-plane orientation (001)Y // (111)STO // and [100]Y // STO was observed but six maxima detected in j -scans instead of three confirmed in-plane obverse/reverse twinning. The results demonstrated the possibilities of the intelligent material design (namely anisotropy manipulation) for this important class of magnetic materials by proper design of key constituents: lattice misfits and surface topography of seeding structures.

Powder diffraction in Bragg-Brentano geometry with straight linear detectors

A common way of speeding up powder diffraction measurements is the use of one- or two-dimensional detectors. This usually goes hand in hand with worse resolution and asymmetric peak profiles. In this work the influence of a straight linear detector on the resolution function in the Bragg-Brentano focusing geometry is discussed. Because of the straight nature of most modern detectors geometrical defocusing occurs, which heavily influences the line shape of diffraction lines at low angles. An easy approach to limit the resolution-degrading effects is presented. The presented algorithm selects an adaptive range of channels of the linear detector at low angles, resulting in increased resolution. At higher angles the whole linear detector is used and the data collection remains fast. Using this algorithm a well behaved resolution function is obtained in the full angular range, whereas using the full linear detector the resolution function varies within one pattern, which hinders line-shape and Rietveld analysis.

Defect in Ultra-Fine Grained Mg-Based Alloys Deformed by High-Pressure Torsion

Applications of Mg-based alloys at elevated temperatures are limited by the low melting point of Mg. This difficulty can be overcome by an addition of rare earth elements. A number of novel promising Mg-based hardenable alloys with high creep resistance at elevated temperatures have been developed, e.g. Mg-Gd, Mg-Mn-Sc etc. Despite the favorable strength and thermal stability, a disadvantage of these alloys consists in a low ductility, which is not sufficient for industrial applications. Grain refinement is known as a way how to improve ductility. It has been demonstrated that an extreme grain size reduction can be achieved by methods based on severe plastic deformation (SPD). In the present work we used high pressure torsion (HPT), which is the most efficient in grain size reduction among the SPD-based techniques, for preparation of selected Mg-based alloys with ultra fine grained (UFG) structure. Microstructure investigations and defect studies of HPT deformed UFG Mg-based alloys are presented in this paper. The extraordinary properties of UFG materials are closely related with defects (grain boundaries, dislocations) introduced by HPT. Positron lifetime (PL) spectroscopy [1] is a well-established non-destructive technique with high sensitivity to open volume defects. It enables identification of the defect types present in the material studied and determination of defect densities. Thus, PL spectroscopy represents an ideal tool for defect studies of UFG materials. In the present work PL spectroscopy was combined with X-ray diffraction (XRD), microhardness measurements, and direct observations of microstructure by TEM.

Textured PbTiO3, Pb(Ca)TiO3-Al2O3 Composite Films Prepared by Chemical Solution Deposition Method

Chemical solution deposition method (CSD) method was used to prepare PbTiO3 (PT), Pb1− xCaxTiO3 (PCT), PbTiO3-Al2O3 (PT-AL) and Pb1 − xCaxTiO3-Al2O3 (PCT-AL) thin films on amorphous (soda-lime glass, SiO2 glass) substrates. The films were examined by XRD methods to describe the phase composition, cell parameters, type and degree of texture. In dependence on the molar ratio of Ti:Al, the different extent of crystallographic ordering was observed ranging from randomly oriented to strongly textured crystallites of PT. (100)〈uvw〉 preferred orientation growth of PT grains was identified.

Simplified elastic models for disk-shaped precipitates

A procedure is presented to calculate the elastic displacement fields found in the early stages of coherent precipitation in age hardenable alloys. The procedure is designed for a subsequent calculation of X-ray diffraction profiles. Displacement fields from precipitates of finite size having local order may be examined with reduced computer times. Point sources consisting of a doublet combined with a spherical field are distributed over the plane of a disk shaped precipitate. The relative strength of this combination is adjustable; however, the total strength is scaled to be in agreement with lattice parameter data. An empirical correction for elastic anisotropy, is guided by Green’s function calculations. Examples are given for calculating fields from single disks and stair step pairs. These calculations may be carried out with reduced computer time. This is made possible by reducing a large number of uniformly distributed point sources to an optimum number having weighted strengths and special locations throughout the plane of a disk. In order to assess directional effects and more readily relate the displacements to diffraction data, projected displacements are used. The tetragonality of the interplanar d-spacings is examined within zones of severe deformation located in the immediate vicinity of the precipitate.