The influence of small impurity contents on the diffusion controlled stabilization of Cu–Zn–Al martensitic single crystals

2005 ◽  
Vol 52 (7) ◽  
pp. 541-545 ◽  
Author(s):  
J.L. Pelegrina ◽  
M.A. Arribere ◽  
M. Ahlers
Keyword(s):  
Single Crystals ◽  
Diffusion Controlled

Pressure Effect on the Kinetics of Reaction Between Solid NaCl and ZrCl4 or HfCl4 Vapors

1971 ◽  
Vol 49 (17) ◽  
pp. 2885-2890 ◽  
Author(s):  
P. Pint ◽  
S. N. Flengas
Keyword(s):  
Sodium Chloride ◽  
Single Crystals ◽  
Constant Temperature ◽  
Pressure Effect ◽  
Heterogeneous Reaction ◽  
Zirconium Tetrachloride ◽  
Hafnium Tetrachloride ◽  
Diffusion Controlled ◽  
Kinetics Of Reaction ◽  
Kinetics Of

The kinetics of reaction between single crystals of sodium chloride and zirconium tetrachloride and hafnium tetrachloride vapors, to form sodium hexachlorozirconate and sodium hexachlorohafnate, respectively, have been investigated as a function of the tetrachloride pressures at a constant temperature of 485 °C. The rate of formation of Na2ZrCl6 is kinetically more favorable. The heterogeneous reaction is diffusion controlled, with the rate of diffusion depending on the availability of Cl− vacancies.

scholarly journals Thermodynamic and Kinetic Characteristics of Variations in Shapes of Ridges Formed on {100} Lithium Fluoride Surfaces

1991 ◽  
Vol 238 ◽  
Author(s):  
J. W. Bullard ◽  
A. M. Glaeser ◽  
Alan W. Searcy
Keyword(s):  
Theoretical Model ◽  
Melting Point ◽  
Single Crystals ◽  
Surface Diffusion ◽  
Lithium Fluoride ◽  
Kinetic Characteristics ◽  
Surface Sites ◽  
Diffusion Controlled ◽  
Shape Changes

ABSTRACTChannels with widths in the range from 5 μm to 25 μm were formed in {100} surfaces of LiF single crystals by a photolithographic technique. Specimens annealed at or above 0.90 Tm, where Tm is the melting point, and then quenched showed die channels and the ridges between them develop rounded profiles. Evolution of these profiles was evaluated for the various channel widths and for interchannel ridge spacings of 5 to 100 μm in terms of: a) an accepted theoretical model for a surface diffusion controlled process, and b) a model which assumes that shape changes depend only on the relative energies of attachment of atoms in surface sites with various surface curvatures. Either model is consistent with the experimental observations to within the reproducibility in measurements.

The deformation of single crystals of copper and copper-zinc alloys containing alumina particles - II. Microstructure and dislocation-particle interactions

1970 ◽  
Vol 318 (1532) ◽  
pp. 73-92 ◽  
Keyword(s):  
Single Crystals ◽  
Friction Stress ◽  
Cross Slip ◽  
Zinc Alloys ◽  
Slip Mechanism ◽  
Diffusion Controlled ◽  
Alumina Particles ◽  
Copper Zinc ◽  
Zn Alloys ◽  
Brass Alloys

Electron microscope studies of deformed single crystals of Cu and Cu + Zn alloys of various compositions containing small alumina particles show that the dislocation structures generated and associated with the particles consist generally of prismatic loops, Orowan loops as well as prismatic loops in some brass alloys, and groups of dipoles. The formation of predominantly interstitial prismatic loops is explained in terms of a cross-slip mechanism controlled by the interstitial misfit strains around the particles. The transition from prismatic loop to prismatic plus Orowan loop structures in the brass alloys for Zn contents greater than ca . 20 wt % is considered to be due to the dependence of the activation energy for cross-slip on the stacking fault energy and to the solution hardening friction stress. In the Cu + 20% Zn alloys, measurements of the height of the loops and their numbers show that some dislocations by-pass the particles without forming loops. The mechanism of cross-slip leading to the formation of prismatic loops or ‘by-passing’ is discussed in some detail. The number of prismatic loops generated decreases with temperature. This fact is explained in terms of pipe or interface diffusion controlled climb of dislocations at the particles.

The Microstructure of Shock-Synthesized Diamond

1967 ◽  
Vol 25 ◽  
pp. 324-325
Author(s):  
Lucien F. Trueb
Keyword(s):  
Single Crystals ◽  
Preferred Orientation ◽  
High Magnification ◽  
Texture Pattern ◽  
Shock Process ◽  
New Type ◽  
Diffraction Diagram

A new type of synthetic industrial diamond formed by an explosive shock process has been recently developed by the Du Pont Company. This material consists of a mixture of two basically different forms, as shown in Figure 1: relatively flat and compact aggregates of acicular crystallites, and single crystals in the form of irregular polyhedra with straight edges.Figure 2 is a high magnification micrograph typical for the fibrous aggregates; it shows that they are composed of bundles of crystallites 0.05-0.3 μ long and 0.02 μ. wide. The selected area diffraction diagram (insert in Figure 2) consists of a weak polycrystalline ring pattern and a strong texture pattern with arc reflections. The latter results from crystals having preferred orientation, which shows that in a given particle most fibrils have a similar orientation.

A New Defect in Polyethylene Single Crystals

1973 ◽  
Vol 31 ◽  
pp. 70-71
Author(s):  
E. L. Thomas ◽  
S. L. Sass
Keyword(s):  
Single Crystals ◽  
Screw Dislocation ◽  
Small Distance ◽  
Dipole Model ◽  
Dislocation Dipole ◽  
Chain Folding ◽  
Black And White ◽  
Polymer Crystal ◽  
Different Types

In polyethylene single crystals pairs of black and white lines spaced 700-3,000Å apart, parallel to the [100] and [010] directions, have been identified as microsector boundaries. A microsector is formed when the plane of chain folding changes over a small distance within a polymer crystal. In order for the different types of folds to accommodate at the boundary between the 2 fold domains, a staggering along the chain direction and a rotation of the chains in the plane of the boundary occurs. The black-white contrast from a microsector boundary can be explained in terms of these chain rotations. We demonstrate that microsectors can terminate within the crystal and interpret the observed terminal strain contrast in terms of a screw dislocation dipole model.

Preferential Sputtering of Ni3Al Single Crystals Studied Using Atom-Probe Field-Ion Microscopy and XPS

1981 ◽  
Vol 39 ◽  
pp. 16-17
Author(s):  
M.P. Thomas ◽  
A.R. Waugh ◽  
M.J. Southon ◽  
Brian Ralph
Keyword(s):  
Single Crystals ◽  
Photoelectron Spectroscopy ◽  
Surface Composition ◽  
Depth Profiling ◽  
Analytical Techniques ◽  
Atom Probe ◽  
Probe Field ◽  
Preferential Sputtering ◽  
Argon Ion Bombardment ◽  
Argon Ion

It is well known that ion-induced sputtering from numerous multicomponent targets results in marked changes in surface composition (1). Preferential removal of one component results in surface enrichment in the less easily removed species. In this investigation, a time-of-flight atom-probe field-ion microscope A.P. together with X-ray photoelectron spectroscopy XPS have been used to monitor alterations in surface composition of Ni3Al single crystals under argon ion bombardment. The A.P. has been chosen for this investigation because of its ability using field evaporation to depth profile through a sputtered surface without the need for further ion sputtering. Incident ion energy and ion dose have been selected to reflect conditions widely used in surface analytical techniques for cleaning and depth-profiling of samples, typically 3keV and 1018 - 1020 ion m-2.

Dislocation structures around SiO2 Particles in aged Cu-Cr-SiO2

1978 ◽  
Vol 36 (1) ◽  
pp. 594-595
Author(s):  
N.J. Long ◽  
M.H. Loretto ◽  
C.H. Lloyd
Keyword(s):  
Flow Stress ◽  
Single Crystals ◽  
Room Temperature ◽  
Thin Foil ◽  
Age Hardening ◽  
Dispersion Strengthening ◽  
Accurate Picture ◽  
The Matrix ◽  
Very High ◽  
Good Agreement

IntroductionThere have been several t.e.m. studies (1,2,3,4) of the dislocation arrangements in the matrix and around the particles in dispersion strengthened single crystals deformed in single slip. Good agreement has been obtained in general between the observed structures and the various theories for the flow stress and work hardening of this class of alloy. There has been though some difficulty in obtaining an accurate picture of these arrangements in the case when the obstacles are large (of the order of several 1000's Å). This is due to both the physical loss of dislocations from the thin foil in its preparation and to rearrangement of the structure on unloading and standing at room temperature under the influence of the very high localised stresses in the vicinity of the particles (2,3).This contribution presents part of a study of the Cu-Cr-SiO2 system where age hardening from the Cu-Cr and dispersion strengthening from Cu-Sio2 is combined.

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.

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