Creep cavity growth under interaction between lattice diffusion and grain-boundary diffusion

1998 ◽  
Vol 29 (10) ◽  
pp. 2533-2542 ◽  
Author(s):  
Tadahiro Shibutani ◽  
Takayuki Kitamura ◽  
Ryuichi Ohtani
Keyword(s):  
Grain Boundary ◽  
Boundary Diffusion ◽  
Cavity Growth ◽  
Lattice Diffusion ◽  
Grain Boundary Diffusion ◽  
Creep Cavity

Diffusion and solubility of holmium ions in barium titanate ceramics

2004 ◽  
Vol 19 (12) ◽  
pp. 3512-3520 ◽  
Author(s):  
Junichi Itoh ◽  
Hajime Haneda ◽  
Shunichi Hishita ◽  
Isao Sakaguchi ◽  
Naoki Ohashi ◽  
...  
Keyword(s):  
Barium Titanate ◽  
Grain Boundary ◽  
Diffusion Coefficients ◽  
Boundary Diffusion ◽  
Diffusion Mechanism ◽  
Annealed Sample ◽  
Lattice Diffusion ◽  
Grain Boundary Diffusion ◽  
A Site ◽  
Titanate Ceramics

Ho ion solubility and diffusivity were evaluated in barium titanate ceramics in which Ho ions were implanted with an accelerating voltage of 500 keV. The depth profile of the ions was composed of three regions in the post-annealed sample: the first was the precipitation region, the second was a region created by lattice diffusion of Ho ions, and the third was a region created by grain-boundary diffusion. The Ho lattice diffusion characteristics were similar to those of Ni ion diffusion in barium titanate ceramics, and we concluded that the diffusion mechanism was the same as that responsible for Ni ions. The Ho ions diffused through the B-site (Ti-site) and were then exchanged with A-site ions. This mechanism suggests that a small number of Ho ions dissolved in the B-site. Preferential grain-boundary diffusion was also observed. The grain-boundary diffusion coefficients were four to five orders of magnitude larger than the volume diffusion coefficients. The solubility of Ho ions was estimated to be a few thousand parts per million in barium titanate ceramics.

Mechanistic Two Stage Fission Gas Release Model

2002 ◽  
Author(s):  
Yong-Soo Kim ◽  
Chan-Bok Lee
Keyword(s):  
Grain Boundary ◽  
Diffusion Coefficients ◽  
Boundary Diffusion ◽  
Diffusion Processes ◽  
Lattice Diffusion ◽  
Grain Boundary Diffusion ◽  
Factor Α ◽  
Two Stages ◽  
Grain Surface ◽  
Release Model

In this study, a mechanistic two stages model is developed which analytically simulates the two-step diffusion processes, grain lattice diffusion and grain boundary diffusion, coupled with the bubbles trap/resolution. Mathematical manipulation reveals that the release at high burn-up depend on the ratio of the diffusivities in the both processes, i.e., α ≅ Dveff/Dgbeff where Dveff and Dgbeff are effective volume and grain boundary diffusion coefficients, respectively. Thus, the ratio α is incorporated in the time-dependent third kind boundary condition at the equivalent grain surface. This model brings forth analytical solutions of the fractional release which are identical to that of either ANS5.4 or modified ANS5.4 model when α goes to the infinity. It turns out that this model describes the release behavior well in the high burn-up fuel and puts out a comparable prediction to the solution of FRAPCON-3 model under the same condition. It is also demonstrated that the new factor α not only ease the computational treatment for the high burn-up fuel performance evaluation, but also enables us to possibly separate the burn-up enhancement from the diffusion coefficients and to easily simulate the bubble-related phenomena in the grain boundary.

A Mathematical Formulation for Interfacial Diffusion, Incorporating Deviation from the Classical Random Walk Theory

2007 ◽  
Vol 266 ◽  
pp. 63-71
Author(s):  
N.S. Raghavan ◽  
A.H. King
Keyword(s):  
Random Walk ◽  
Grain Boundary ◽  
Boundary Diffusion ◽  
Mathematical Formulation ◽  
Lattice Diffusion ◽  
Grain Boundary Diffusion ◽  
Interfacial Diffusion ◽  
Structural Differences ◽  
Diffusion Phenomena ◽  
Random Walk Theory

Fisher’s model for grain boundary diffusion considers the lattice and the grain boundary on the same basis by presuming the validity of Fick’s second law for both cases, despite the significant structural differences between them. Recent studies [1-3] have, however, shown that grain boundary diffusion is profoundly different from lattice diffusion. We propose an alternative mathematical formulation that incorporates these structural differences and consequently models grain boundary diffusion phenomena more accurately than Fisher’s model. This is achieved by considering possible deviations from the classical random walk for solute atoms diffusing through grain boundaries. This formalism can also be applied to surface diffusion and triple junction diffusion.

Effect of Elastic Accommodation on Diffusion-Controlled Cavity Growth in Metals

2000 ◽  
Vol 122 (3) ◽  
pp. 294-299
Author(s):  
R. Mohan ◽  
J. Zhang ◽  
F. W. Brust
Keyword(s):  
Grain Boundary ◽  
Growth Rates ◽  
Void Growth ◽  
Boundary Diffusion ◽  
Virtual Work ◽  
Cell Model ◽  
Cavity Growth ◽  
Grain Boundary Diffusion ◽  
Transient Time ◽  
Diffusion Controlled

The effect of elastic accommodation on the grain boundary diffusion-controlled void growth was analyzed using an axisymmetric unit cell model. An incremental form of the virtual work principle was used to formulate the boundary value problem involving grain boundary diffusion. The model accounts for material elasticity and void interaction effects. Analyses are performed for initially spherical voids spaced periodically along the grain boundary. The results of the analyses on void growth rates agree well with the Hull-Rimmer model after the initial transient time. During the elastic transient, void growth rates can be several orders of magnitude higher than the steady state growth rate. Though the elastic transient time may occupy a small portion of the total rupture time, in metallic components experiencing cyclic loading conditions with short hold times, elasticity effects may be important. [S0094-4289(00)00903-8]

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