ATOMIC RESOLUTION STUDIES OF SOLUTE-ATOM SEGREGATION AT GRAIN BOUNDARIES : EXPERIMENTS AND MONTE CARLO SIMULATIONS

1990 ◽  
Vol 51 (C1) ◽  
pp. C1-47-C1-57 ◽  
Author(s):  
D. N. SEIDMAN ◽  
J. G. HU ◽  
S.-M. KUO ◽  
B. W. KRAKAUER ◽  
Y. OH ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Grain Boundaries ◽  
Solute Atom ◽  
Atomic Resolution

Monte Carlo Simulations of Solute-Atom Segregation at [001] Symmetrical Twist Boundaries in the Ni-Pi System

1992 ◽  
Vol 278 ◽  
Author(s):  
D. Udler ◽  
D. N. Seidman
Keyword(s):  
Phase Diagram ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Solute Atom ◽  
Atom Concentration ◽  
Embedded Atom ◽  
Pt Alloy ◽  
Solute Atoms ◽  
Rich Side ◽  
Twist Boundaries

AbstractAtomistic Monte Carlo simulations utilizing many-body embedded atom method (EAM) potentials have been carried out for a series of symmetrical [001] twist boundaries in Pt-3 at.% Ni and Ni-3 at.% Pt alloy bicrystals at 850 K throughout the misorientation range 0° to 45°. The results demonstrate enhancement of the solute-atom concentration at twist boundaries for both alloys; the interfacial Gibbsian excess is a factor of two greater on the Ni-rich side of the phase diagram. The spatial distributions of solute atoms in the vicinity of the interfaces are found to be markedly different on the two sides of the Ni-Pt phase diagram. For low-angle boundaries on the Pt-rich side solute atoms tend to segregate in hourglass-like regions along the cores of the primary grain boundary screw dislocations, while in the case of Ni-3 at.% Pt they occupy bipyramidal regions centered on the cells of the dislocation grid. The former behavior explains the oscillatory solute-atom concentration profiles nomnal to the plane of an intetface.

Atomistic Monte Carlo Simulations of Homogeneous and Heterogeneous Precipitation on Grain Boundaries of NbC in Steels

2005 ◽  
Vol 237-240 ◽  
pp. 721-726 ◽  
Author(s):  
Céline Hin ◽  
Frédéric Soisson ◽  
Philippe Maugis
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Grain Boundaries ◽  
Vacancy Concentration ◽  
Recrystallization Process ◽  
Thermal Treatments ◽  
Heterogeneous Precipitation ◽  
Defect Source ◽  
Equilibrium Segregation ◽  
Diffusion Properties

The precipitation of niobium carbides in industrial steels is commonly used to control the recrystallization process or the amount of interstitial atoms in solid solution. It is then important to understand the precipitation kinetics and especially the competition between homogeneous and heterogeneous precipitation, since both of them have been observed experimentally, depending on the alloy composition, microstructure and thermal treatments. We propose Monte Carlo simulations of NbC precipitation in α-iron, based on a simple atomic description of the main parameters which control the kinetic pathway : - realistic diffusion properties, with a rapid diffusion of C atoms by interstitial jumps and a slower diffusion of Fe and Nb atoms by vacancy jumps - a simple model of grain boundaries which reproduces the equilibrium segregation properties of Nb and C - a point defect source which drives the vacancy concentration towards its equilibrium value. Depending on the precipitation conditions, MC simulations predict different kinetic behaviours, including homogeneous and heterogeneous NbC precipitation, early segregation of C atoms and its importance as a first stage for NbC precipitation, wetting phenomena on grain boundaries and transient precipitation of metastable carbides.

Solute-atom segregation is high-angle (002) twist boundaries in dilute Au–Pt alloys

1995 ◽  
Vol 10 (8) ◽  
pp. 1933-1941 ◽  
Author(s):  
D. Udler ◽  
D.N. Seidman
Keyword(s):  
Phase Diagram ◽  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Solute Atom ◽  
Perfect Crystal ◽  
High Angle ◽  
Structural Units ◽  
Crystal Type ◽  
Rich Side ◽  
Twist Boundaries

Solute-atom segregation is studied by Monte Carlo simulations for three high-angle symmetrical (002) twist boundaries in Au-1 at. % Pt and Pt-1 at. % Au alloys at T = 850 K. It complements our previous study, that focused mainly on low-angle boundaries in the same alloys. Solute enhancement occurs on the Pt-rich side of the phase diagram, while on the Au-rich side net depletion in solute is observed. Following the trend observed for low-angle boundaries, Au as a solute prefers the structural units of the perfect crystal type, while Pt as a solute is depleted at those sites. The solutc concentration at structural units depends on the planar fraction of those units in the boundary.

Low-voltage EDS of magnesium ferrite Dendrites in a FEG-SEM

1996 ◽  
Vol 54 ◽  
pp. 478-479
Author(s):  
Matthew T. Johnson ◽  
Ian M. Anderson ◽  
Jim Bentley ◽  
C. Barry Carter
Keyword(s):  
Monte Carlo ◽  
Quantitative Analysis ◽  
Monte Carlo Simulations ◽  
Cross Section ◽  
Spatial Resolution ◽  
Low Voltage ◽  
Magnesium Ferrite ◽  
X Ray ◽  
Interaction Volume ◽  
Ferrite Spinel

Energy-dispersive X-ray spectrometry (EDS) performed at low (≤ 5 kV) accelerating voltages in the SEM has the potential for providing quantitative microanalytical information with a spatial resolution of ∼100 nm. In the present work, EDS analyses were performed on magnesium ferrite spinel [(MgxFe1−x)Fe2O4] dendrites embedded in a MgO matrix, as shown in Fig. 1. spatial resolution of X-ray microanalysis at conventional accelerating voltages is insufficient for the quantitative analysis of these dendrites, which have widths of the order of a few hundred nanometers, without deconvolution of contributions from the MgO matrix. However, Monte Carlo simulations indicate that the interaction volume for MgFe2O4 is ∼150 nm at 3 kV accelerating voltage and therefore sufficient to analyze the dendrites without matrix contributions.Single-crystal {001}-oriented MgO was reacted with hematite (Fe2O3) powder for 6 h at 1450°C in air and furnace cooled. The specimen was then cleaved to expose a clean cross-section suitable for microanalysis.

Sign in / Sign up

Export Citation Format

Share Document