Grain Boundary Structural Transformations Induced by Solute Segregation

1984 ◽  
Vol 41 ◽  
Author(s):  
K. Sickafus ◽  
S. L. Sass
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Structural Changes ◽  
Temper Embrittlement ◽  
Analytical Techniques ◽  
Major Change ◽  
Solute Segregation ◽  
Boundary Structure ◽  
Low Alloy Steels ◽  
Fracture Surfaces

AbstractThe problem of solute segregation came to prominence with relation to studies of the temper embrittlement of low alloy steels. McLean and Northcott1(1948) first suggested that segregation of various elements to the grain boundaries was primarily responsible for the intergranular fracture observed in steels susceptible to this embrittlement. Direct evidence for segregation came much later with the development of surface sensitive analytical techniques, especially Auger electron spectroscopy (AES). Using AES, it was determined that impurity elements such as P, Sb and Sn, as well as alloying elements such as Ni and Cr, were highly concentrated at the fracture surfaces in embrittled steels2. It is not clear, however, why solute segregation changes the mechanical strength of the grain boundaries in these materials. Based on recent calculations, Messmer and Briant3 proposed that certain solute species at a grain boundary change the chemical bonding at the interface. However, other more dramatic structural rearrangements may be possible upon segregation. Such structural changes were first suggested by the observation of facetted fracture surfaces in tellurium-doped iron alloys4. In the study presented here, it is shown that low concentrations of solute can cause changes in grain boundary structure. In particular, small concentrations of Au solute were found to cause a major change in the dislocation structure of low angle [001] Fe twist boundaries. Preliminary observations on the str ucture of a Fe-0.18 at.% Au* twist boundary were presented elsewhere5. Additional results will be presented here on the effect of changes in solute concentration and misorientation angle, θ, on this structural transformation. It is believed that these observations are evidence for the occurrence of a two-dimensional phase transformation in the grain boundary, similar to that predicted by Hart6

Cavitation control in steels of high residual element content

1980 ◽  
Vol 295 (1413) ◽  
pp. 305-305 ◽  
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Prior Austenite ◽  
Low Alloy Steels ◽  
Boundary Zone ◽  
Austenite Grain ◽  
Alloy Steels ◽  
Austenite Grain Boundary ◽  
Prior Austenite Grain ◽  
Transverse Boundary

The cavitational mode of failure of prior austenite grain boundaries in bainitic creep-resisting low alloy steels is now well established as a principal factor in the high incidence of cracking problems which has developed on modern power plant in recent years. The microstructural features dominating the cavitation process at the reheat temperature in a ½CMV bainitic steel of high classical residual level have been determined. The prior austenite grain boundaries become zones of comparative weakness ca . 1 pm thick at 700 °C and are incapable of sustaining significant shear loads. Deformation is therefore initiated by a relaxation of load, through a process of prior austenite grain boundary zone shear, from inclined to transverse boundaries such that a concentration of normal stress develops across the latter. The overall deformation is thereafter determined by cavitation of the transverse boundary zones, the necessary inclined boundary displacements being accommodated by further grain boundary zone shear. Transverse boundary cavitation is shown to be an essentially time-independent process of localized ductile microvoid coalescence resulting from the plastic deformation of the boundary zone.

Structural and Mechanical Properties of Nanophase Ni: A Molecular-Dynamics Study of the Influence of Grain-Boundary Structure on Elastic and Plastic Behavior

1997 ◽  
Vol 492 ◽  
Author(s):  
H. Van Swygenhoven ◽  
M. Spaczér ◽  
A. Caro
Keyword(s):  
Molecular Dynamics ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Diffusion Mechanism ◽  
Distribution Functions ◽  
Boundary Structure ◽  
Plastic Behavior ◽  
Self Diffusion ◽  
Common Neighbour ◽  
Grain Boundary Structure

ABSTRACTMolecular dynamics computer simulations of high load plastic deformation at temperatures up to 500K of Ni nanophase samples with mean grain size of 5 nm are reported. Two types of samples are considered: a polycrystal nucleated from different seeds, each having random location and random orientation, representing a sample with mainly high angle grain boundaries, and polycrystals with seeds located at the same places as before, but with a limited missorientation representing samples with mainly low angle grain boundaries. The structure of the grain boundaries is studied by means of pair distribution functions, coordination number, atom energetics, and common neighbour analysis. Plastic behaviour is interpreted in terms of grain-boundary viscosity, controlled by a self diffusion mechanism at the disordered interface activated by thermal energy and stress.

Disruption of Dislocation Cores at Grain Boundary in Nb-Doped SrTiO3 Bicrystals

2007 ◽  
Vol 558-559 ◽  
pp. 869-872
Author(s):  
S.Y. Choi ◽  
J.P. Buban ◽  
Naoya Shibata ◽  
Takahisa Yamamoto ◽  
Yuichi Ikuhara
Keyword(s):  
Grain Boundary ◽  
Tilt Angle ◽  
Structural Changes ◽  
Boundary Region ◽  
Boundary Structure ◽  
Regular Array ◽  
Density Of Dislocations ◽  
Discrete Dislocation ◽  
Grain Boundary Structure ◽  
Oriented Region

Bicrystals of Nb-doped SrTiO3, having tilt angles of 4o~18 o with respect to [001], were prepared by joining two single crystals at 1873 K and then investigated to identify the effect of tilt angle on the grain boundary structure. The boundaries consisted of a regular array of dislocations but the positioning of cores along the boundary was found to be changed from a line to a zigzag as a tilt angle was increased up to 10o. The 14° - tilted boundary exhibited two kinds of boundary region exist at the same grain boundary; (1) the discrete cores region as observed in 4° ~ 10° - tilted boundaries and (2) the randomly oriented region as found in the 18° boundary. Thus it was observed that the structure of low-angle tilt boundary changed from the discrete dislocation structure to the randomly oriented structure as a tilt angle increases. These structural changes at the grain boundaries are considered to be related to a minimization of strain due to the high density of dislocations.

Systematic Study of Grain Boundary Structure and Chemical Analysis of [100] and [111] Tilt Grain Boundaries in Yttria-Stabilized Zirconia

2004 ◽  
Vol 10 (S02) ◽  
pp. 304-305 ◽  
Author(s):  
James P Buban ◽  
Katsuyuki Matsunaga ◽  
Takahisa Yamamoto ◽  
Yuichi Ikuhara
Keyword(s):  
Chemical Analysis ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Systematic Study ◽  
Yttria Stabilized Zirconia ◽  
Boundary Structure ◽  
Stabilized Zirconia ◽  
Grain Boundary Structure

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

GRAIN BOUNDARIES: PHASE TRANSITIONS AND CRITICAL PHENOMENA

1991 ◽  
Vol 05 (19) ◽  
pp. 2989-3028 ◽  
Author(s):  
E.I. RABKIN ◽  
L.S. SHVINDLERMAN ◽  
B.B. STRAUMAL
Keyword(s):  
Phase Transitions ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Critical Phenomena ◽  
External Surface ◽  
Theoretical Models ◽  
Boundary Structure ◽  
Boundary Phase ◽  
Recent Experimental Data ◽  
Grain Boundary Structure

Recent theories of grain boundary structure have been reviewed briefly. The possibility of existence of the same variety of phase transitions on grain boundaries as that on the crystal external surface has been demonstrated. Recent experimental data and theoretical models concerning grain boundary phase transitions are critically analysed. Grain boundary phase transitions connected with the formation of thin disordered layers on the boundary (prewetting, premelting) are particularly distinguished. Results of recent indirect experiments, which may be treated in terms of prewetting and premelting, have been reviewed. Experimentally observed critical phenomena in the vicinity of the prewetting transition on the tin-germanium interphase boundary have been discussed in terms of the critical exponents theory. Some ideas regarding directions of further research are presented.

Observations and implications of grain boundary dislocation networks in high-angle YBa2Cu3O7−δ grain boundaries

1990 ◽  
Vol 5 (5) ◽  
pp. 919-928 ◽  
Author(s):  
S. E. Babcock ◽  
D. C. Larbalestier
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Weak Link ◽  
Coincidence Site Lattice ◽  
Boundary Structure ◽  
High Angle ◽  
Grain Boundary Structure ◽  
Transmission Electron ◽  
Means Of Transmission ◽  
Regular Networks

Regular networks of localized grain boundary dislocations (GBDs) have been imaged by means of transmission electron microscopy in three different types of high-angle grain boundaries in YBa2Cu3O7-δ, implying that these boundaries possess ordered structures upon which a significant periodic strain field is superimposed. The occurrence of these GBD networks is shown to be consistent with the GBD/Structural Unit and Coincidence Site Lattice (CSL)/Near CSL descriptions for grain boundary structure. Thus, these dislocations appear to be intrinsic features of the boundary structure. The spacing of the observed GBDs ranged from ∼10 nm to ∼100 nm. These GBDs make the grain boundaries heterogeneous on a scale that approaches the coherence length and may contribute to their weak-link character by producing the “superconducting micro-bridge” microstructure which has been suggested on the basis of detailed electromagnetic measurements on similar samples.

Mechanism of Surface Dissolution in Dense Hydroxyapatite

2007 ◽  
Vol 121-123 ◽  
pp. 1241-1244 ◽  
Author(s):  
Dong Seok Seo ◽  
Hwan Kim ◽  
Jong Kook Lee
Keyword(s):  
Mechanical Properties ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Xrd Analysis ◽  
Boundary Structure ◽  
Molar Ratio ◽  
Dissolution Mechanism ◽  
Grain Boundary Structure ◽  
High Resolution Tem ◽  
Moisture Protection

In this study, it was demonstrated how second phases with small amount, which are hardly detected by XRD analysis, affect grain boundary dissolution and related mechanical properties of HA. All HA disks sintered at 1200 oC for 2 h in air with under moisture protection were phase pure and had Ca/P molar ratio of 1.67. Following certain period of exposure to the distilled water, the surface dissolution initiated at grain boundaries and particle loosening, subsequently resulting in decrease in mechanical properties of HA. In order to understand the dissolution mechanism, grain boundary structure of HA was identified by transmission electron microscopy (TEM) and high resolution TEM observation. From the analysis, it was found that the non-stoichiometric phase as α-tricalcium phosphate (TCP) transformed from β-TCP was existed at grain boundaries and caused surface dissolution of HA. From the XRD analysis, it was found that (211) and (112) planes of hydroxyapatite were susceptible to dissolution, whereas (300) plane was relatively stable.

A Highly Reliable Al Line with Controlled Texture and Grain Boundaries

1995 ◽  
Vol 391 ◽  
Author(s):  
M. Hasunuma ◽  
H. Toyoda ◽  
T. Kawanoue ◽  
S. Ito ◽  
H. Kaneko ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Single Crystal ◽  
Grain Boundaries ◽  
Empirical Relation ◽  
Boundary Structure ◽  
Homogeneous Microstructure ◽  
Grain Boundary Structure ◽  
Dislocation Arrays ◽  
Order Of Magnitude ◽  
Individual Grains

AbstractIn order to clarify the relationship between Al line reliability and film microstructure, especially grain boundary structure and crystal texture, we have tested three kinds of highly textured Al lines, namely, single-crystal Al line, quasi-single-crystal Al line and hypertextured Al line, and two kinds of conventional Al lines deposited on TiN/Ti and on SiO2. Consequently, the empirical relation between the electromigration (EM) lifetime of Al line † and the (111) full width at half maximum (FWHM) value ω is described by † ∝ ω-2 [1]. This improvement of Al line reliability results from as following reasons; firstly, homogeneous microstructure and high activation energy of 1.28eV for the single-crystal Al line (ω=0.18°); secondly, sub-grain boundaries which consisted of dislocation arrays found in the quasi-single-crystal Al line (ω=0.26°) has turned out to be no more effective mass transport paths because dislocation lines are perpendicular to the direction of electron wind. Although there exist plural grain boundary diffusion paths in the newly developed hypertextured Al line (ω=0.5°) formed by using an amorphous Ta-Al underlayer {1], the vacancy flux along the line has been suppressed to the same order of magnitude of single crystal line. It has been clarified that the decrease of FWHM value has promoted the formation of sub-grain boundaries and low-angle boundaries with detailed orientation analysis of individual grains in the hypertextured film. The longer EM lifetime for the hypertextured Al line is considered to be due to the small grain boundary diffusivities for these stable grain boundaries, and this diffusivity reduction resulted in the suppression of void/hillock pair in the Al lines. These results have confirmed that controlling texture and/or grain boundary itself is a promising approach to develop reliable Al lines which withstand higher current densities required in future ULSIs.

An Intergranular Fracturing Technique for Grain Boundary Segregation Studies of Austenitic Stainless Steel

CORROSION ◽  
1977 ◽  
Vol 33 (8) ◽  
pp. 304-306 ◽  
Author(s):  
J. Y. PARK ◽  
S. DANYLUK
Keyword(s):  
Stainless Steel ◽  
Grain Boundary ◽  
Boundary Segregation ◽  
Austenitic Stainless Steels ◽  
Analytical Techniques ◽  
304 Stainless Steel ◽  
Auger Electron Spectroscopy Analysis ◽  
Fracture Surfaces ◽  
Type 304 ◽  
Type 304 Stainless Steel

Abstract A creep-deformation, heat treatment impact-fracture technique that can be used to produce grain boundary surfaces is described. The technique is especially useful for exposing grain boundaries of austenitic stainless steels and can also be used with surface-sensitive analytical techniques. Intergranular fracture surfaces of Type 304 stainless steel have been produced using this technique. Auger electron spectroscopy analysis was performed on these fracture surfaces.

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