Computer Modelling of Structural Transformations of Nanopores in Fcc Metals

2019 ◽  
Keyword(s):  
Computer Modelling ◽  
Structural Transformations ◽  
Fcc Metals

scholarly journals Mathematical modelling of formation process for multi-layer 3D structure produced by additive method using arc heat sources

2019 ◽  
Vol 91 (7) ◽  
pp. 45-54
Author(s):  
Walery A. Kostin ◽  
Georgy M. Grigorenko ◽  
Viktor A. Shapovalov ◽  
Alexandr N. Pikulin
Keyword(s):  
Computer Modelling ◽  
Layer Structure ◽  
3D Structure ◽  
Structural Transformations ◽  
Temperature Fields ◽  
Effect Of Temperature ◽  
Maximum Temperature ◽  
Physical Parameters ◽  
Heat Sources ◽  
Kinetics Of

The results of modelling of temperature fields, kinetics of deposition of layers of dissimilar metals and nature of structural transformations in formation of multi-layer structure of 17G1S and 30KhGS steels are presented. Computer modelling was performed using COMSOL Multiphysics software package. The work takes into account effect of temperature on thermal and physical parameters of steels. To increase productivity of additive process the work has studied simultaneous effect of 3 arcs on process of deposit formation, kinetics of structural transformations and diffusion processes of alloying elements redistribution. The calculations show that preheating of the substrate by arc in the beginning of the process before application of deposited material is necessary in order to decrease a stress level between additive deposit and substrate to 50 MPa. It is shown that the time of passing between neighbor arc heat sources shall be kept in 5- 30 s range. It is determined that low power of arc (1 kW) mainly provokes formation of ferrite-bainite structure in the deposit, portion of bainite in which makes 71 %, ferrite 28% and martensite ~ 1%. Application of larger power arc (5 kW) forms in the deposit bainite-martensite structure, portion of bainite in which makes ~  50%, portion of martensite rises up to 40% and that of ferrite to 10%. Increase of arc power results in rise of maximum temperature of liquid pool to 1750-1850 °C, growth of cooling rate to 15 – 25 °C/s , and, as a consequence, increase of martensite portion in the structure of deposited layers. 

Structural Transformation of a Germanium Σ=13 (510) [001] Tilt Grain Boundary under the Electron Beam

1990 ◽  
Vol 48 (1) ◽  
pp. 52-53 ◽  
Author(s):  
Jean-Luc Rouvière ◽  
Alain Bourret
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Structural Transformation ◽  
Mirror Symmetry ◽  
High Resolution Electron Microscopy ◽  
Structural Transformations ◽  
Covalent Bonds ◽  
Resolution Electron ◽  
Tilt Grain Boundary

The possible structural transformations during the sample preparations and the sample observations are important issues in electron microscopy. Several publications of High Resolution Electron Microscopy (HREM) have reported that structural transformations and evaporation of the thin parts of a specimen could happen in the microscope. Diffusion and preferential etchings could also occur during the sample preparation.Here we report a structural transformation of a germanium Σ=13 (510) [001] tilt grain boundary that occurred in a medium-voltage electron microscopy (JEOL 400KV).Among the different (001) tilt grain boundaries whose atomic structures were entirely determined by High Resolution Electron Microscopy (Σ = 5(310), Σ = 13 (320), Σ = 13 (510), Σ = 65 (1130), Σ = 25 (710) and Σ = 41 (910), the Σ = 13 (510) interface is the most interesting. It exhibits two kinds of structures. One of them, the M-structure, has tetracoordinated covalent bonds and is periodic (fig. 1). The other, the U-structure, is also tetracoordinated but is not strictly periodic (fig. 2). It is composed of a periodically repeated constant part that separates variable cores where some atoms can have several stable positions. The M-structure has a mirror glide symmetry. At Scherzer defocus, its HREM images have characteristic groups of three big white dots that are distributed on alternatively facing right and left arcs (fig. 1). The (001) projection of the U-structure has an apparent mirror symmetry, the portions of good coincidence zones (“perfect crystal structure”) regularly separate the variable cores regions (fig. 2).

INTERACTION BETWEEN LATTICE DISLOCATIONS AND GRAIN BOUNDARIES IN FCC METALS AND ORDERED COMPOUNDS

1990 ◽  
Vol 51 (C1) ◽  
pp. C1-311-C1-316 ◽  
Author(s):  
B. J. PESTMAN ◽  
J. Th. M. DE HOSSON ◽  
V. VITEK ◽  
F. W. SCHAPINK
Keyword(s):  
Grain Boundaries ◽  
Fcc Metals

Analysis and CAD modelling of a new geometric spiroid hob

2015 ◽  
Vol 6 (2) ◽  
pp. 89-93
Author(s):  
S. Bodzás ◽  
I. Dudás
Keyword(s):  
Computer Modelling ◽  
Cad Model ◽  
Axial Section ◽  
Cad Modelling ◽  
Definition Of

The objectives of this publication are the analysis of surfaces and edges of a new geometric spiroid hob with arched profile in axial section and the definition of their equations for computer modelling. On the basis of this we will work out the CAD model of hob for our further geometric calculations.

Modelling Lunar Extremes

2018 ◽  
Vol 3 (2) ◽  
pp. 207-216 ◽  
Author(s):  
David Fisher ◽  
Lionel Sims
Keyword(s):  
High Precision ◽  
Celestial Mechanics ◽  
Computer Modelling ◽  
Landscape Context ◽  
The Sun ◽  
The Moon

Claims first made over half a century ago that certain prehistoric monuments utilised high-precision alignments on the horizon risings and settings of the Sun and the Moon have recently resurfaced. While archaeoastronomy early on retreated from these claims, as a way to preserve the discipline in an academic boundary dispute, it did so without a rigorous examination of Thom’s concept of a “lunar standstill”. Gough’s uncritical resurrection of Thom’s usage of the term provides a long-overdue opportunity for the discipline to correct this slippage. Gough (2013), in keeping with Thom (1971), claims that certain standing stones and short stone rows point to distant horizon features which allow high-precision alignments on the risings and settings of the Sun and the Moon dating from about 1700 BC. To assist archaeoastronomy in breaking out of its interpretive rut and from “going round in circles” (Ruggles 2011), this paper evaluates the validity of this claim. Through computer modelling, the celestial mechanics of horizon alignments are here explored in their landscape context with a view to testing the very possibility of high-precision alignments to the lunar extremes. It is found that, due to the motion of the Moon on the horizon, only low-precision alignments are feasible, which would seem to indicate that the properties of lunar standstills could not have included high-precision markers for prehistoric megalith builders.

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