Misorientation Of Blocks Research Articles

СПЕЦИФИКА ПРИМЕНЕНИЯ РЕНТГЕНОВСКИХ МЕТОДОВ «КАЧАНИЯ» И ЛАУЭ ПРИ ОЦЕНКЕ КАЧЕСТВА СТРУКТУРЫ ОТЛИВОК НИКЕЛЕВЫХ ЖАРОПРОЧНЫХ СПЛАВОВ

Systematically analyzes and justifies the characteristics of equipment operating in monochromatic radiation by the «swing» method and in polychromatic radiation by the Laue method in relation to the specifics of controlled samples in the technology of single-crystal casting from nickel heat-resistant alloys. The main application of the «swing» method is the mass control of seed blanks, seedings, growth cones of samples and blades. The main application of the Laue method is local measurements of block misorientation in the casting of the turbine blade, determination of the crystallographic orientation misorientation in controlled areas on the blade. An optimized configuration is proposed for a compact modification of a diffractometer operating in monochromatic radiation for mass control of the structure in production.

Matching X-ray beam and detector properties to protein crystals of different perfection.

An analysis is given of the effect of different beam and detector parameters on the sharpness of recorded diffraction features for macromolecular crystals of different quality. The crystal quality parameters include crystal strain, crystal or mosaic block size and mosaic block misorientation. Calculations are given for instrument parameters such as angular resolution of the detector, beam divergence and wavelength bandpass to be matched to the intrinsic diffraction properties from these crystals with the aim of obtaining the best possible data out of each crystal. Examples are given using typical crystal imperfections obtained from the literature for both room-temperature and cryo-cooled crystals. Possible implications for the choice of X-ray source, beamline design, detector specifications, instrument set-up and data processing are discussed, together with the limitations of the approach.

High-quality ZnO/GaN/α-Al2O3 heteroepitaxial structures grown by CVD

The first results on the preparation of (0001)ZnO/(0001)GaN/(0001) α-Al2O3 heteroepitaxial structures by CVD in a low-pressure flow-type reactor are reported. Study of the surface morphology and X-ray diffraction patterns showed high structural perfection of the zinc oxide layer, with a block misorientation in the basal plane not exceeding 21′. The photoluminescence spectra of samples exhibited dominating emission in the exciton region.

An experimental assessment of X-ray diffraction theory in high purity aluminium crystals

An experimental test of Zachariasen's X-ray diffraction formula was carried out for high purity aluminium crystals with a wide range of mosaic block sizes and mosaic block misorientations. These crystals were produced by cold rolling to different strains three samples (crystals 1, 2 and 3) cut from a large single crystal grown by the Bridgman method. The (100), (200) and (220) X-ray integrated intensities were measured for each crystal, and the block sizes and block misorientations were obtained using transmission electron microscopy techniques (the mean linear intercept method for the block size and Kikuchi line techniques for the block misorientation). With the exception of crystal 2 in the undeformed condition, for a given state the three crystals showed a common diffraction efficiency, the value of which increased with increasing deformation. The different diffraction efficiency of crystal 2 with respect to crystals 1 and 3 in the undeformed condition is rationalized in terms of a segragation of impurities at the bottom of the large single crystal. Comparison between the integrated intensities determined experimentally and the intensities calculated by substituting the measured block size and block misorientation parameters into Zachariasen's formula showed good agreement between the two sets of values. In view of this, it was concluded that Zachariasen's formula is closely consistent with the diffraction efficiency of the crystals under study; the behaviour of the crystals is characteristic of Zachariasen's type II crystals, i.e. the extinction is primarily controlled by the mosaic block size rather than by the mosaic block misorientation.

X-ray diffraction in crystals of intermediate perfection. I. Calculation of the integral diffracted power for flat and curved crystals in symmetrical Bragg geometry

A method for the treatment of x-ray extinction and absorption is developed for thick flat crystals in symmetrical Bragg geometry and for curved crystals in symmetrical Bragg geometry where the diffraction region may be approximated as a thin crystal in Laue geometry. This method permits the calculation of diffracting power vs wavelength. The crystals may have the full range of properties between the ideally imperfect and perfect cases. The parameters describing the mosaic blocks (mosaic block size and mosaic block misorientation) are related to the dislocation arrangement for crystals of Zachariasen's type I (where extinction is primarily controlled by the mosaic block misorientation). It is indicated that for crystals of type II (where extinction is primarily controlled by the mosaic block size) the mosaic blocks are usually due to defects other than dislocations.

X-ray diffraction in crystals of intermediate perfection. II. A treatment of LiF in symmetrical Bragg geometry

In part I of this series we presented a method for the calculation of the integral diffracting power applicable to flat and curved crystals in symmetrical Bragg geometry. In the present paper we report a test of the above method. The integral reflection coefficient vs wavelength has been measured and calculated for an unusually perfect crystal of LiF and for a crystal of LiF rendered relatively imperfect by ``flexing''. Agreement was good. The mean mosaic block size and misorientation used in the calculation were deduced by using dislocation etch pitting. It is concluded that LiF is of Zachariasen's type I (i.e., extinction is primarily controlled by the mosaic block misorientation).

Block structure of fragments of martensite crystals from structural steels

1. The maximum misorientation of blocks in fragments of martensite crystals from quenched steel is approximately the same in all directions. For steel 40Kh5MVFS after ordinary quenching it is about 3°; as the result of LTTMT it increases to 4–5°. This is particularly notable when the size of the fragments decreases at the same time. 2. The size of blocks in fragments of martensite crystals from quenched steels apparently characterizes the periodicity in the arrangement of defects and dispersed carbide precipitates.

The study of the misorientation of mosaic blocks in the surface deformed Fe-Si single crystal by X-ray measurement

The misorientation of blocks in the surface layer of an Fe-Si single crystal deformed by engraving with a sapphire needle or by rolling of a steel ball is followed by the method of the measurement of rocking curves. The rocking curves are followed in dependence on the direction in the surface plane and on the load when deformed. Further on the influence of the penetration of radiation on the rocking curve is studied, if the misorientation of blocks changes with the growing depth under the surface and an equation for the distribution of orientations on the basis of the measured rocking curves is derived. The distribution of orientations in two directions on the surface plane and at several depths under the surface was calculated for one case of the engraved specimen.