Clustering of coincident site lattice boundaries in polycrystals

1988 ◽  
Vol 46 ◽  
pp. 630-631
Author(s):  
Valerie fendle ◽  
Brian Ralph
Keyword(s):  
Electron Microscope ◽  
Grain Boundary ◽  
Thermomechanical Processing ◽  
Austenitic Stainless Steels ◽  
Coincident Site Lattice ◽  
Thin Foil ◽  
Texture Measurement ◽  
Bulk Specimen ◽  
Site Lattice ◽  
Special Boundaries

The distribution of coincident site lattice (CSL) and other geometrically special boundaries have been analysed in the form of “grain misorientation texture” (GMT) plots for several systems (pure nickel, a number of austenitic stainless steels and a complex superalloy, 1-5). Several heat treatment conditions have been investigated for each system. Principally, electron back scattering (EBS) in a scanning electron microscope has been used to collect the “microtexture” (i.e. grain specific) data which combines the considerable advantages of bulk specimen texture analysis, grain environment specification with semi-automatic operation. These data are currently being supplemented with thin foil transmission electron microscope (TEM) analyses which permit more detailed investigation of the grain boundary parameters (especially grain boundary planes).Conventional texture measurement shave akey role in assessing the overall changes which occur during thermomechanical processing. However, the very detailed orientation measurements give only a statistical picture and this means that neither the geometry of individual boundaries (the GMT) nor ary tendency for clustering of particular texture types or boundary types may be detected.

Fracture Strengths of Individual Grain Boundaries in Ni3Ai Using a Miniaturized Disk Bend Test

1991 ◽  
Vol 238 ◽  
Author(s):  
Douglas E. Meyers ◽  
Alan J. Ardell
Keyword(s):  
Plastic Deformation ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Grain Growth ◽  
Coincident Site Lattice ◽  
Bend Test ◽  
High Angle ◽  
Load Drop ◽  
Site Lattice ◽  
Special Boundaries

ABSTRACTThe results of our initial efforts at measuring the fracture strengths of grain boundaries In Ni3Al using a miniaturized disk-bend test are presented. The samples tested were 3 mm in diameter and between 150 and 300 μm thick. An Ingot of directlonally-solidlfled, boron-free Ni3Al containing 24% Al was annealed between 1300 and 1350 °C to induce grain growth, producing many grain boundaries In excess of 1.5 mm in length. Specimens were cut from these In such a way that one long grain boundary was located near a diameter of the specimen. The relative orientations of the grains on either side of the boundary were determined from electron channeling patterns. Low-angle boundaries are so strong they do not fracture; Instead the samples deform In a completely ductile manner. High-angle boundaries always fracture, but only after considerable plastic deformation of the two grains flanking them. Fracture is Indicated by a load drop in the load vs. displacement curves. A method involving extrapolation of the elastic portion of these curves to the displacement at fracture is used to estimate the fracture stresses. This procedure yields consistent values of the fracture strengths of high-angle boundaries. The measured stresses are large (∼2 to 3 GPa), but considerably smaller than those required for the fracture of special boundaries, as predicted by computer simulations. No correlation was found between the fracture stresses or loads and the geometry of the high-angle boundaries, many of which are close to, but deviate from, coincident site lattice orientations.

A Grain Boundary Engineering Approach to Promote Special Boundaries in a Pb-base Alloy

2002 ◽  
Vol 730 ◽  
Author(s):  
D.S. Lee ◽  
H.S. Ryoo ◽  
S.K. Hwang
Keyword(s):  
Grain Boundary ◽  
Thermomechanical Processing ◽  
Base Alloy ◽  
Coincidence Site Lattice ◽  
Grain Boundary Engineering ◽  
Site Lattice ◽  
Special Boundaries ◽  
Engineering Approach ◽  
Electrochemical Evaluation ◽  
Battery Application

AbstractA grain boundary engineering approach was employed to improve the microstructure of a commercial Pb-base alloy for better performance in automobile battery application. Through a combination of cold working, recrystallization and subsequent thermomechanical-processing, it was possible to increase the fraction of the low ∑ coincidence site lattice boundaries up to 91% in addition to the substantial grain refinement. A preliminary electrochemical evaluation indicated a better corrosion resistance in the experimental material laden with the special boundaries. The high frequency of the coincidence site lattice boundaries in the specimens was interpreted in terms of the '∑3 regeneration' model proposed in previous works.

A projection-based reformulation of the coincident site lattice Σ for arbitrary bicrystals at finite temperature

2017 ◽  
Vol 73 (2) ◽  
pp. 87-92 ◽  
Author(s):  
B. Runnels
Keyword(s):  
Grain Boundary ◽  
Closed Form ◽  
Finite Temperature ◽  
Coincident Site Lattice ◽  
Inner Product ◽  
Site Lattice ◽  
Numerical Result ◽  
Regularization Parameters ◽  
Continuous Fields

The coincident site lattice and, specifically, the `Σ value' of a grain boundary are a ubiquitous metric for experimental classification of grain boundaries. However, the mathematical nature of Σ – a pathological function taking values of either an integer or infinity – has been relatively unexplored. This work presents a framework for interpreting Σ as the inverse of a projection defined using the standardL2inner product over continuous fields that represent lattices. `Pre-mollifiers' are used to introduce thermal regularization in the context of the inner product, and a closed-form analytic result is derived. For all nonzero values of the regularization parameters, the formulation is mathematically smooth and differentiable, providing a tool for computationally determining experimental deviation from measured low-Σ boundaries at finite temperatures. It is verified that accurate Σ values are recovered for sufficiently low Σ boundaries, and that the numerical result either converges towards an integer value or diverges to infinity.

Evolution of Microstructure in Pure Nickel during Processing for Grain Boundary Engineering

2013 ◽  
Vol 753 ◽  
pp. 97-100 ◽  
Author(s):  
Brian Lin ◽  
Gregory S. Rohrer ◽  
Anthony D. Rollett ◽  
Yuan Jin ◽  
Nathalie Bozzolo ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Thermomechanical Processing ◽  
Electron Backscatter Diffraction ◽  
Experimental Studies ◽  
Recrystallization Process ◽  
Grain Boundary Engineering ◽  
Triple Junctions ◽  
Special Boundaries ◽  
Before And After ◽  
Over Time

Grain boundary engineered (GBE) materials have improved properties that are associated with the high fraction special Σ3n boundaries in the microstructure, where n = 1,2,3. Previous experimental studies with high purity nickel before and after thermomechanical processing have shown that the fraction of Σ3 boundaries increased by at least factor of two [1]. Electron backscatter diffraction (EBSD) is used to characterize the evolution of these special boundaries throughout the recrystallization process of a 25% cold rolled sample annealed at 490°C. The fractions of the Σ3 boundaries and coherent twins have been measured over time revealing a steadily increasing behavior over the entire microstructure. However partitioning to only include recrystallized regions reveals a different behavior in the Σ3 boundaries as fractions, which increase rapidly at first and then stagnate over time. Additional triple junction characterization was performed to monitor the evolution of triple junctions containing special boundaries.

Grain Boundary Engineered Lead Alloys

1996 ◽  
Vol 458 ◽  
Author(s):  
E. M. Lehockey ◽  
G. Palumbo ◽  
A. Brennenstuhl ◽  
P. Lin
Keyword(s):  
Grain Boundary ◽  
Intergranular Corrosion ◽  
Electrochemical Corrosion ◽  
Coincident Site Lattice ◽  
Grain Boundary Sliding ◽  
Boundary Structure ◽  
Clear Correlation ◽  
Special Boundaries ◽  
Grain Boundary Structure ◽  
Fold Reduction

ABSTRACTThe present work reports oii the effect of grain boundary structure on intergranular corrosion and creep by grain boundary diffusion in polycrystalline lead (Pb). “Special” boundaries characterized by low-Σ misorientations in the Coincident Site Lattice (CSL) model have been shown to exhibit resistance to grain boundary sliding and corrosion. PbCa and PbCaSn alloys having “special” grain boundary frequencies greater than 50% showed a 30 fold reduction in steady-state creep compared with corresponding as-received alloys containing 10% to 28% of low-Σ CSL boundaries in the microstructure of comparable grain size. At the same time, increasing the frequency of “special” boundaries enhanced alloy ductility with no compromize in tensile strength. Results from electrochemical corrosion tests on polarizied Pb alloys immersed in H2SO4 (S.G.=1.28) at 70°C indicate a clear correlation between the frequency of “special” boundaries and the prolifíeration of intergranular corrosion resulting in bulk weight loss from grain-dropping. Collectively, these results advocate adopting a “gram boundary design” approach in developing advanced lead-acid battery electrodes.

Role of Coincident Site Lattice Boundaries in Creep and Stress Corrosion Cracking

2004 ◽  
Vol 819 ◽  
Author(s):  
G.S. Was ◽  
B. Alexandreanu ◽  
Peter Andresen ◽  
Mukul Kumar
Keyword(s):  
Grain Boundary ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
High Purity ◽  
Coincident Site Lattice ◽  
Corrosion Cracking ◽  
304 Stainless Steel ◽  
Boundary Structure ◽  
Site Lattice

AbstractInterfaces control many properties in engineering materials, several of which are critical to the integrity of the engineering structure. In single phase, solid solution, austenitic alloys, grain boundaries are often the weak link, displaying susceptibility to creep, corrosion and stress corrosion cracking. As such, grain boundary structure control affords the opportunity to improve the overall performance of alloys in a variety of applications. The role of coincident site lattice boundary (CSLB) enhancement and grain boundary connectivity is examined for how it affects the response of an alloy to stress and the environment. Specifically, the effect of grain boundary character on creep, grain boundary sliding, intergranular stress corrosion cracking, and irradiation assisted stress corrosion cracking in austenitic nickel-base (high purity Ni-Cr-Fe and alloy 600) and iron-base (high purity Fe-Cr-Ni and 304 stainless steel) alloys and for ferritic- martensitic alloy T91 is discussed.

scholarly journals Determination of grain boundary geometry using TEM

1992 ◽  
Vol 7 (7) ◽  
pp. 1707-1717 ◽  
Author(s):  
H. Jang ◽  
D. Farkas ◽  
J.T.M. De Hosson
Keyword(s):  
Electron Microscope ◽  
Grain Boundary ◽  
Transmission Electron Microscope ◽  
Boundary Plane ◽  
Statistical Distribution ◽  
Special Boundaries ◽  
Grain Boundary Plane ◽  
Transmission Electron ◽  
Boundary Geometry

An experimental method to obtain the grain boundary geometry using the transmission electron microscope is presented. The method allows Σ determination including grain boundary plane orientation. In order to determine the specialness of the grain boundary, three different criteria for maximum allowable deviations from exact CSL misorientations were examined. We tested these three criteria from a statistical distribution of grain boundary types in terms of Σ. We compared grain boundary distributions from other studies in Ni3Al and found discrepancies among them. It seems that the discrepancy came from the different criteria for special boundaries in Σ determination and different experimental procedures they used. The statistical distribution of grain boundary plane orientations showed that low Σ boundaries (Σ < 11) were oriented to the plane of high density of coincident sites.

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