Simulation of Microstructural Evolution during Superplastic Deformation

1999 ◽  
Vol 601 ◽  
Author(s):  
B.-N. Kim ◽  
K. Hiraga
Keyword(s):  
Aspect Ratio ◽  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Tensile Deformation ◽  
Grain Boundary Diffusion ◽  
Initial Value ◽  
The Matrix ◽  
Dynamic Growth ◽  
Equiaxed Grains

AbstractSuperplastic tensile deformation is simulated in 2 dimensions by incorporating grain boundary diffusion and concurrent grain growth derived from static and dynamic growth mechanisms. The following relationship is found between microstructural changes and deformation behavior for constant stress conditions. Grain boundary diffusion produces an increase in the aspect ratio of the matrix grains during deformation and the increased aspect ratio causes a change in creep rate parameters: the stress exponent is decreased from the initial value of 1.0 for equiaxed grains and the grain size exponent is increased from the initial value of 3.0. Accelerated grain growth is also found by the present simulation.

Diffusion Mechanisms in Nanocrystalline and Nanolaminated Au-Cu

2007 ◽  
Vol 266 ◽  
pp. 13-28 ◽  
Author(s):  
Alan F. Jankowski
Keyword(s):  
Low Temperature ◽  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Bulk Diffusion ◽  
Grain Boundary Diffusion ◽  
Dominant Mechanism ◽  
Temperature Range ◽  
Diffusion Mechanisms ◽  
Kinetics Of

Thermal anneal treatments are used to identify the temperature range of the two dominant diffusion mechanisms – bulk and grain boundary. To assess the transition between mechanisms, the low temperature range for bulk diffusion is established utilizing the decay of static concentration waves in composition-modulated nanolaminates. These multilayered structures are synthesized using vapor deposition methods as thermal evaporation and magnetron sputtering. However, at low temperature the kinetics of grain-boundary diffusion are much faster than bulk diffusion. The synthesis of Au-Cu alloys (0-20 wt.% Cu) with grain sizes as small as 5 nm is accomplished using pulsed electro-deposition. Since the nanocrystalline grain structure is thermally unstable, these structures are ideal for measuring the kinetics of grain boundary diffusion as measured by coarsening of grain size with low temperature anneal treatments. A transition in the dominant mechanism for grain growth from grain boundary to bulk diffusion is found with an increase in temperature. The activation energy for bulk diffusion is found to be 1.8 eV·atom-1 whereas that for grain growth at low temperatures is only 0.2 eV·atom-1. The temperature for transitioning from the dominant mechanism of grain boundary to bulk diffusion is found to be 57% of the alloy melt temperature and is dependent on composition.

Iron Redistribution in Aluminum Thin Films

1993 ◽  
Vol 309 ◽  
Author(s):  
David L. Barr ◽  
G.J. Gualtieri ◽  
C.B. Case ◽  
M.A. Marcus ◽  
W.L. Brown
Keyword(s):  
Thin Films ◽  
Grain Boundary ◽  
Grain Growth ◽  
Deposition Temperature ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Subsequent Annealing ◽  
Precipitate Formation ◽  
Substrate Interface ◽  
Depth Distributions

AbstractStrongly non uniform Fe depth distributions have been observed in AI(0.13 at% Fe) thin films deposited at temperatures of 350ºC and above. The concentration of Fe is uniform in depth at a deposition temperature of 300ºC but is increasingly enhanced toward the substrate interface at 450ºC. Subsequent annealing produces only a slight redistribution of Fe. The Fe is primarily present as precipitates smaller than 100 nm. A model of grain boundary diffusion of Fe and precipitate formation and grain growth is proposed to explain the observed behavior.

Effects of grain growth on grain-boundary diffusion creep by molecular-dynamics simulation

2004 ◽  
Vol 52 (7) ◽  
pp. 1971-1987 ◽  
Author(s):  
A.J. Haslam ◽  
V. Yamakov ◽  
D. Moldovan ◽  
D. Wolf ◽  
S.R. Phillpot ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion ◽  
Dynamics Simulation ◽  
Diffusion Creep

Investigation of grain boundary diffusion and grain growth of lithium zinc ferrites with low activation energy

2018 ◽  
Vol 101 (11) ◽  
pp. 5037-5045 ◽  
Author(s):  
Fang Xu ◽  
Huaiwu Zhang ◽  
Fei Xie ◽  
Yulong Liao ◽  
Yuanxun Li ◽  
...  
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Grain Boundary Diffusion

scholarly journals Fabrication and Characterizations of YSZ Electrolyte Films for SOFC

2010 ◽  
Vol 434-435 ◽  
pp. 705-709 ◽  
Author(s):  
Min Fang Han ◽  
Zhi Bin Yang ◽  
Ze Liu ◽  
Hui Rong Le
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Diffusion ◽  
Boundary Migration ◽  
Single Step ◽  
Grain Boundary Diffusion ◽  
Raw Material ◽  
Grain Boundary Migration ◽  
Sintering Process ◽  
Ysz Electrolyte

Yttria stabilized zirconia (YSZ) has been widely used as electrolyte in solid oxide fuel cell (SOFC). The effect of fabrication process on the properties of YSZ electrolyte thick film is discussed in the paper. With YSZ nano-powders of about 20-60nm as raw material, YSZ green adobe was fabricated by tape calendering process. Three-step sintering process was performed firstly holding at 1000°C for 2h, then raising to 1300~1400°C, then decreasing to 1200~1300°C within 30 minutes, and finally calcining at 1200~1300°C for 5~20 hrs. Dense YSZs with relative density of 96-99% are obtained; the grain size of YSZ was reduced to 0.5-3µm. During the process of grain growth, there are both grain boundary diffusion and grain boundary migration. The feasibility of densification without grain growth relies on the suppression of grain boundary migration while keeping grain boundary diffusion active at a temperature as low as 1200~1300°C. Whereas the electric conductivities of the YSZs are even higher than that obtained in conventional single step sintering process. The process is applied to the anode-supported SOFCs co-fired at 1250~1300°C, and the cathode-supported SOFCs co-fired at 1200~1250°C.

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