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X-Ray Topography of the Subsurface Crystal Layers in the Skew Asymmetric Reflection Geometry

Świątek Z., Fodchuk I.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 4

1931--1938

EN

The technique of X ray topography with the asymmetric reflection geometry of X-ray diffraction presented in this paper as useful tool for structural characterization of materials, particularly, epitaxial thin films and semiconductor multi-layered crystal systems used for the optoelectronic devices. New possibilities of this technique for a layer-by-layer visualization of structural changes in the subsurface crystal layers are demonstrated for semiconductors after various types of surface treatment, such as chemical etching, laser irradiation and ion implantation.

2

Dendritic Structure Analysis of CMSX-4 Cored Turbine Blades Roots

Krawczyk J.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 2B

1129--1134

EN

The microstructure of as-cast cored turbine blades roots, made of the single-crystal CMSX-4 nickel-based superalloy was investigated. Analysed blades were obtained by directional solidification technique in the industrial ALD Bridgman induction furnace. The investigations of the microstructure of blades roots were performed using SEM and X-ray techniques including diffraction topography with the use of Auleytner method. Characteristic shapes of dendrites with various arrangement were observed on the SEM images taken from the cross-sections, made transversely to the main blades axis. The differences in quality of the structure in particular areas of blades roots were revealed. Based on the results, the influence of cooling bores on blades root structure was analysed and the changes in the distribution and geometry of cooling bores were proposed.

3

Dislocation - Assisted Initiation of Energetic Materials

Armstrong R. W.

Central European Journal of Energetic Materials

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2005

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Vol. 2, nr 3

21-37

EN

The role of dislocations in assisting initiation of (explosive) chemical decomposition of energetic materials has connection with the known influences for crystals and polycrystals of dislocations facilitating permanent deformations and phase transformations. X-ray topographic observation of relatively few dislocations in solution-grown crystals relates to the influence of large Burgers (displacement) vectors that are characteristic of molecular crystal bonding. Both model evaluations of the load dependence of cracking at hardness indentations and the derived hardness stress-strain behaviors show that dislocation movement is difficult whether in the indentation strain fields or at the tips of indentation-induced cracks. Thus, energetic crystals are elastically compliant, plastically hard, and relatively brittle [1]. Nevertheless, cracking is shown to be facilitated by the shear stress driven, normally limited, dislocation flow that, on molecular dynamics and dislocation pile-up model bases, is shown to be especially prone to producing localized hot spot heating for explosive initiations. Such model consideration is in agreement with greater dropweight heights being required to initiate smaller crystals. The crystal size effect carries over to more difficult combustion occurring for compaction of smaller crystals. The total results relate to dual advantages of greater strength and reduced mechanical sensitivity accruing for the development of nanocrystal formulations. In consequence, also, several levels of dislocation-assisted modeling are described for initiation mechanisms under shock wave loading conditions.