scholarly journals Mixed diffusion-controlled growth of pearlite in binary steel

2010 ◽  
Vol 467 (2126) ◽  
pp. 508-521 ◽  
Author(s):  
A. S. Pandit ◽  
H. K. D. H. Bhadeshia
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Growth Rate ◽  
Volume Diffusion ◽  
Controlled Growth ◽  
Mechanical Equilibrium ◽  
Interfacial Diffusion ◽  
Diffusion Controlled ◽  
Simplified Method ◽  
Transformation Front

A kinetic theory for the diffusion-controlled growth of pearlite is presented, which accounts simultaneously for diffusion through the austenite and via the transformation front. The simplified method abandons the need for mechanical equilibrium at the phase junctions and yet is able to explain experimental data on the growth rate of pearlite. Furthermore, unlike previous analyses, the deduced value for the activation energy for the interfacial diffusion of carbon is found to be realistic when compared with corresponding data for volume diffusion.

scholarly journals Diffusion-controlled growth of pearlite in ternary steels

2011 ◽  
Vol 467 (2134) ◽  
pp. 2948-2961 ◽  
Author(s):  
A. S. Pandit ◽  
H. K. D. H. Bhadeshia
Keyword(s):  
Experimental Data ◽  
Local Equilibrium ◽  
Chemical Compositions ◽  
Controlled Growth ◽  
Interfacial Diffusion ◽  
Diffusion Parameters ◽  
Diffusion Controlled ◽  
Substitutional Solute ◽  
Transformation Front ◽  
Rate Controlling Step

A theory for the diffusion-controlled growth of pearlite in steels containing manganese is presented and assessed in the light of experimental data. Given the overwhelmingly rapid diffusivity that a substitutional solute has within the transformation front, the growth rate is found to be dominated by diffusion parallel to the interface with austenite as the rate controlling step. The relevant interfacial diffusion parameters have been derived by fitting experimental data to kinetic theory. All reported measurements of pearlite growth where the full set of necessary parameters have been listed, are shown to be inconsistent with mechanisms that do not involve the partitioning of substitutional solutes. The method adopted here, which is based on the local equilibrium at the transformation interface with the long-range partitioning of substitutional solutes by migration within the interface, has been shown to reasonably explain experimental data over a range of temperatures and chemical compositions.

The Effects of Doping and Temperature on the Fermi Level and its Relationship to the Recrystallization Growth Velocity in Ion-Implanted Silicon

1988 ◽  
Vol 100 ◽  
Author(s):  
L. E. Mosley ◽  
M. A. Paesler ◽  
P. D. Richard
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Growth Rate ◽  
Fermi Level ◽  
Growth Velocity ◽  
Growth Process ◽  
Arrhenius Plot ◽  
Velocity Versus ◽  
Band Bending ◽  
P Type

ABSTRACTIt has been observed that doping produces an enhancement in the recrystallization growth rate of silicon made amorphous by ionimplantation. This enhancement has been attributed to a shift of the Fermi level with doping. Evidence supporting this is based on the compensating effect of implantation of n- and p-type dopants together. We have previously proposed a model of the recrystallization growth process based on the diffusion of dangling bonds. We suggested that the rate enhancement is due to band bending at the amorphous-crystalline interface produced by doping. We have calculated the change in activation energy for the recrystallization growth velocity for a number of doping concentrations as a function of temperature. The major contribution to the apparent lowering of the activation energy with doping in an Arrhenius plot of the growth velocity versus I/kT is due to the temperature dependence of the Fermi level. Experimental data are compared with the calculated results. In addition differences in the measured growth rates in thermal and laser annealed samples are discussed, with primary emphasis on the lack of a change in the activation energy with doping in the laser annealed case.

Diffusion-controlled growth

1989 ◽  
Vol 423 (1864) ◽  
pp. 123-132 ◽  
Keyword(s):  
Growth Rate ◽  
Cone Angle ◽  
High Growth ◽  
High Growth Rate ◽  
Two Dimensions ◽  
Flow Diagram ◽  
Equivalent Model ◽  
Controlled Growth ◽  
Diffusion Controlled ◽  
Tip Radius

The conditions of diffusion-controlled growth are outlined and the observed importance of anisotropy is discussed through a tentative flow diagram. A crucial role is played by the forwardmost tips, which lead to growth. The nature of the singularity in their growth rate determines the overall fractal dimension. This has been estimated in two dimensions from effective cone-angle models, which work well for the most extreme anisotropic growth and can be augmented into a self-consistent approximation for the isotropic fractal case. The way in which the tip growth rate singularity is limited by finite tip radius is also a key ingredient. For diffusion-limited solidification where it is set by competition with surface tension, this significantly changes the form of the equivalent model with a fixed (e. g. lattice spacing) imposed tip scale. The full distribution of growth rates everywhere provides a much richer problem. We show new data and examine the consistency of how sites can evolve from the regions of high growth rate where they are born, into well-screened regions devoid of further growth.

A TEM investigation of a hyper-eutectic lead-tin alloy

1988 ◽  
Vol 46 ◽  
pp. 562-563
Author(s):  
John A. Sutliff
Keyword(s):  
Volume Diffusion ◽  
Eutectic Mixture ◽  
Precipitation Reaction ◽  
Directionally Solidified ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Diffusion Controlled ◽  
Discontinuous Precipitation Reaction ◽  
Controlled Precipitation

Near-eutectic Pb-Sn alloys are important solders used by the electronics industry. In these solders, the eutectic mixture, which solidifies last, is the important microstructural consituent. The orientation relation (OR) between the eutectic phases has previously been determined for directionally solidified (DS) eutectic alloys using x-ray diffraction or electron chanelling techniques. In the present investigation the microstructure of a conventionally cast, hyper-eutectic Pb-Sn alloy was examined by transmission electron microscopy (TEM) and the OR between the eutectic phases was determined by electron diffraction. Precipitates of Sn in Pb were also observed and the OR determined. The same OR was found in both the eutectic and precipitation reacted materials. While the precipitation of Sn in Pb was previously shown to occur by a discontinuous precipitation reaction,3 the present work confirms a recent finding that volume diffusion controlled precipitation can also occur.Samples that are representative of the solder's cast microstructure are difficult to prepare for TEM because the alloy is multiphase and the phases are soft.

Effect of ionizing radiation on the kinetics of hydrogenation on the Ni-MgO mixed catalyst

1982 ◽  
Vol 47 (7) ◽  
pp. 1780-1786 ◽  
Author(s):  
Rostislav Kudláček ◽  
Jan Lokoč
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Liquid Phase ◽  
Ionizing Radiation ◽  
Oxide Catalyst ◽  
Absorbed Dose ◽  
Hydrogenation Rate ◽  
Solution Composition ◽  
Mixed Catalyst ◽  
Kinetics Of

The effect of gamma pre-irradiation of the mixed nickel-magnesium oxide catalyst on the kinetics of hydrogenation of maleic acid in the liquid phase has been studied. The changes of the hydrogenation rate are compared with the changes of the adsorbed amount of the acid and with the changes of the solution composition, activation energy, and absorbed dose of the ionizing radiation. From this comparison and from the interpretation of the experimental data it can be deduced that two types of centers can be distinguished on the surface of the catalyst under study, namely the sorption centres for the acid and hydrogen and the reaction centres.

Diffusion model for deposition of epitaxial GaAs layers prepared by the MOCVD method

1991 ◽  
Vol 56 (10) ◽  
pp. 2020-2029
Author(s):  
Jindřich Leitner ◽  
Petr Voňka ◽  
Josef Stejskal ◽  
Přemysl Klíma ◽  
Rudolf Hladina
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Kinetic Model ◽  
Gas Phase ◽  
Substrate Surface ◽  
Deposition Process ◽  
Hydrogen Atmosphere ◽  
Epitaxial Gaas ◽  
Kinetics Of ◽  
Good Agreement

The authors proposed and treated quantitatively a kinetic model for deposition of epitaxial GaAs layers prepared by reaction of trimethylgallium with arsine in hydrogen atmosphere. The transport of gallium to the surface of the substrate is considered as the controlling process. The influence of the rate of chemical reactions in the gas phase and on the substrate surface on the kinetics of the deposition process is neglected. The calculated dependence of the growth rate of the layers on the conditions of the deposition is in a good agreement with experimental data in the temperature range from 600 to 800°C.

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