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Topic: Grain boundary

	Grain Growth & Grain Size Reduction
		Grain growth is driven by neighbouring grains that possess different energy levels due to the curvature of energetic grain boundaries and/or different amounts of accumulated strain energy.
		Grain growth driven by curvature of boundaries would continue indefinitely if it were not for the presence of impurities, dust and bubbles which pin grain boundary migration (Alley et al.
		Grain size reduction occurs in a shear zone developed in coarse ice deformed at -2°C. A compression (applied to the upper surface) and simple shear are applied simultaneously with the shear strain confined to a ~15mm wide zone, bounded by undeformed region.
	web.earthsci.unimelb.edu.au /wilson/ice1/graingrowth.html (578 words)

	Grain Boundary Migration
		The motion of grain boundaries is the dominant process of microstructural evolution during recrystallization and grain growth, which are liable to occur during heat treatment of a material, except if grain boundary motion is supressed by special measures.
		The grain boundary migration is an anisotropic physical process – non-linearly depending on misorientation and inclination of neighbouring grains – changing microstructure of polycrystalline materials due to change of its grain size and texture.
		Migration of the intersections of the grain boundary segments with the free surfaces and migration of the triple junctions – for the quadricrystal named 'normal-H' configuration and other 'H' configutrations – was observed.
	home.zcu.cz /~krocj/GB-migration.html (657 words)

	Dynamics of Grain Boundaries in 2D Colloids (Site not responding. Last check: 2007-10-14)
		Grain boundaries are the longest known crystal defects and the development of grain structures plays a critical role in the properties of many kinds of materials such as ceramics, metals, and semiconductors [1].
		While the equilibrium structures of grain boundaries have been known very well to atomic resolution through electron microscopy [2] and soap bubble model studies [3], the dynamics process of grain boundary migration driven by external forces or thermal fluctuation is not well established.
		The detail process of grain boundary migration is in general rather complex, because the mobility of a grain boundary depends not only on the relative orientation of the two grains, but also on the direction of the boundary.
	microgravity.grc.nasa.gov /fcarchive/fluids/papers/Wei/Dynamics_of_Grain.htm (491 words)

	Principal Metals
		Grain sizes are reported in terms of grains per unit area or volume, average diameter, or as a grain-size number derived form area measurements.
		Grain size is reported in terms of number of grains per unit area or volume, average diameter, or as a number derived from area measurements.
		An intermediate stage of overheating in which sulfide inclusions are redistributed to the austenitic grain boundaries by partial solution at the overheating temperature and reprecipitation during subsequent cooling.
	www.principalmetals.com /glossary/gdoc.htm (1093 words)

	Investigation of Grain Boundaries in Colloidal Crystals
		Grain boundaries are also important for diffusion phenomena as they provide pathways for diffusions into or within a material that are orders of magnitude faster than through crystalline regions.
		The direct observation of grain boundary structure is limited by the lack of resolution of experimental techniques such as high resolution transmission electron microscopy.
		At the bottom layer the bigger part of the grain boundary is intact and thus the particle density is significantly reduced.
	www.deas.harvard.edu /weitzlab/researchpage.html (766 words)

	The National Board of Boiler and Pressure Vessel Inspectors-Classic Series-Grain Boundaries (Site not responding. Last check: 2007-10-14)
		The juncture between adjacent grains is called a "grain boundary." The grain boundary is a transition region in which some atoms are not exactly aligned with either grain.
		Grain boundaries are usually considered to be two dimensional, but are actually a finite thickness, perhaps 2-10 atomic distances.
		With a grain boundary perhaps 2-10 atomic dimensions thick, the grains are clearly seen to be regions of long-range atomic order, and the grain boundaries, regions of short-range atomic disorder.
	www.nationalboard.org /NationalBoard/Articles/Classics/classic20.aspx (816 words)

	Grain boundaries
		In the core of the grain boundary, the average coordination number of atoms is reduced and the average bond length is changed compared to the single crystal structure [figure 1].
		The grain boundary structures in the forsterites developed already at 400 °C or lower and did not change by annealing with ~ 90% of the melting temperature at 1650 °C. Grain boundaries do not have necessarily the composition of the crystal in which they are embedded in.
		The composition of the Manebach twin grain boundary in a KAlSi3O8 feldspar synthetic bicrystal is K½H½AlSi3O8 [figure 7] (Heinemann, Wirth and Dresen 2002).
	www.gfz-potsdam.de /pb3/pb32/projects/grains.html (559 words)

	Grain boundary - Wikipedia, the free encyclopedia
		Grain boundaries disrupt the motion of dislocations through a material; reducing crystallite size is therefore a common way to improve strength, as described by the Hall-Petch relationship.
		Since grain boundaries are defects in the crystal structure they tend to decrease the electrical and thermal conductivity of the material.
		Generally speaking a low-angle boundary is composed of an array of dislocations and its properties and structure are a function of the misoriention.
	en.wikipedia.org /wiki/Grain_boundary (1447 words)

	Metals and Alloys Group: Grain Boundary Atomic Structure (Site not responding. Last check: 2007-10-14)
		Two views of the calculated Sigma 5 (310)/[001] symmetric tilt grain boundary structure in Tantalum: (a) the mirror symmetry as viewed down the [001] axis and (b) the relative shift along the [001] axis of the two grains.
		Grain boundaries are ubiquitous in polycrystalline metals of practical interest.
		The calculated positions of the atoms at the grain boundary are quite sensitive to an accurate representation of the angular forces between atoms.
	www-phys.llnl.gov /Research/Metals_Alloys/Research/Grains (361 words)

	GRAIN BOUNDARY CURVATURE DISTRIBUTION OF DYNAMICALLY RECRYSTALLIZED QUARTZ AGGREGATES IN A MYLONITE (Site not responding. Last check: 2007-10-14)
		Serrated grain boundaries are often observed in polycrystals deformed by dislocation creep.
		The serration of grain boundaries is controlled by the misorientations and spacing of subgrain boundaries developed in the grain.
		We demonstrate that serrated grain boundaries have a common direction dependence of the curvature distribution and this morphological feature can be used for the determination of direction of grain boundary migration.
	gsa.confex.com /gsa/2002AM/finalprogram/abstract_42091.htm (328 words)

	ELECTROMIGRATION PROPERTIES OF MULTIGRAIN ALUMINUM THIN FILM CONDUCTORS AS INFLUENCED BY GRAIN BOUNDARY STRUCTURE
		The crystallographic texture and grain boundary character distributions of the films were measured by orientation imaging in the SEM [16].
		represents the grain boundary width, d is the average grain size, j is current density, p is the metal resistivity, and z is the effective charge.
		The value for the annealed lines is close to that of twin grain boundaries in pure aluminum [18,19], and that for the as-deposited lines is near the value cited for the energy of a random grain boundary [20].
	www.mme.wsu.edu /~field/6kVjmr.2000.htm (2567 words)

	Lamellar Diblock Copolymer Grain Boundary Morphology. 3. Helicoid Section Twist Boundary Energy
		Grain boundary energies were calculated for the helicoid section morphology both as a function of diblock chain characteristics and as a function of grain boundary twist angle.
		The basic approach to grain boundary energy calculation is to formulate a general expression for local free energy density as a function both of chain characteristics and of the local curvature of the interface.
		The helicoid section grain boundary energies were compared to energies of a competing twist boundary morphology, the Scherk surface, which was analyzed in the preceding paper of this series.
	pubs.acs.org /cgi-bin/abstract.cgi/mamobx/1997/30/i13/abs/ma9603037.html (340 words)

	Grain Coarsening Simulation
		Grain boundaries are defects associated with an excess energy per unit area.
		Large grains tend to grow at the expense of smaller ones, leading to an increase in the mean size and a net reduction in the total amount of grain boundary per unit volume of material.
		In this method, the boundary is treated as a continuous transition between adjacent grains across a thin layer of finite thickness.
	www.msm.cam.ac.uk /phase-trans/abstracts/grain.movies.html (336 words)

	Grain Boundaries and Electronic Materials
		Once this is better understood, materials and their grain boundary characteristics can be designed with improved electronic performance and, in some cases, smart capabilities to give more reliable electronic devices and systems with improved functionality and speed.
		The movement of current through materials with significant grain boundary scattering is largely determined by the size of the angles between the grains.
		This means that special attention must be paid to the grain boundary orientation of the metallic substrate being used and the buffer layers on which the superconducting coating is grown.
	www.azom.com /details.asp?ArticleID=628 (2391 words)

	THE MEASUREMENT OF GRAIN BOUNDARY GEOMETRY (Site not responding. Last check: 2007-10-14)
		There are many books on grain boundary fracture, grain boundary migration and diffusion, grain boundary kinetics and grain boundary structure both in metallic and ceramic materials.
		The introduction chapter deals with the significance and the structure of grain boundaries as well as the development of techniques for measurement and analysis of grain boundary geometry.
		General boundaries are investigated in Chapter 2 and periodic geometries are the subject of Chapter 3.
	www.cap.ca /news/books/Grain-Randle-Uguz.html (451 words)

	Crystallite - Wikipedia, the free encyclopedia
		Grain boundaries disrupt the motion of dislocations through a material; reducing crystallite size is therefore a common way to improve strength, often without any sacrifice in toughness.
		In nanocrystalline solids, grain boundaries become a significant volume fraction of the material, with profound effects on such properties as diffusion and plasticity.
		This is because grain boundaries are amorphous, and serve as nucleation points for the liquid phase.
	en.wikipedia.org /wiki/Crystallite (629 words)

	Physics Today November 2001
		The atomic-scale structure of a grain boundary fabricated with the bicrystal technology is shown in figure 1b.
		The current-carrying properties of all the grain boundaries in the cuprate superconductors are qualitatively similar.
		The grain boundary is generally believed to have an even lower carrier concentration, which could enable an electric field to modify the Josephson current across a grain boundary embedded in a superconducting drain&-source channel, much as a gate voltage modifies the current through a semiconductor FET.
	www.aip.org /pt/vol-54/iss-11/p48.html (3689 words)

	Grain Structure and Boundary (Site not responding. Last check: 2007-10-14)
		The grain structure refers to the arrangement of the grains in a metal, with a grain having a particular crystal structure.
		The grain boundary is a region of misfit between the grains and is usually one to three atom diameters wide.
		Grain structure is the arrangement of grains in a metal, with a grain having a particular crystal structure.
	www.tpub.com /doematerialsci/materialscience5.htm (508 words)

	Grain boundary structure and solute segregation in titanium-doped sapphire bicrystals
		Understanding the evolution and implications of grain boundary chemistry is a vital component in the greater effort to engineer ceramics with controlled microstructures.
		This study examines solute segregation to engineered grain boundaries in titanium-doped sapphire (Al2O3) bicrystals, and explores relationships between grain boundary structure and chemistry at the nanometer scale using spectroscopic and imaging techniques in the transmission electron microscope (TEM).
		Evidence suggests that grain boundary faceting occurs in low-angle twist boundaries to accommodate nonequilibrium solute segregation related to slow specimen cooling rates, while faceting of tilt grain boundaries often occurs to expose special planes of the coincidence site lattice (CSL).
	repositories.cdlib.org /lbnl/LBNL-50644 (302 words)

	OIM Analysis - Grain Boundary Density (Site not responding. Last check: 2007-10-14)
		One challenge in OIM is interpreting grain boundaries and grains.
		The Boundary Density chart shows the line length of boundaries divided by the area as a function of misorientation.
		Below is another example of using the Grain Boundary Density chart, derived from a series of samples of partially recrystallized low carbon steel.
	www.edax.com /products/TSL/OIM/OIM-Analysis/Maps/boundary_density.html (284 words)

	Tight-Binding Simulations of Diamond Grain Boundaries (Site not responding. Last check: 2007-10-14)
		The atomic structure of grain boundaries in diamond structures affects the strength of industrial diamonds and diamond films, as well as the electronic properties of semiconductors.
		We have examined a number of symmetric tilt grain boundary structures in diamond, using a transferable tight-binding carbon potential.
		The low angle {199}[011] grain boundary structure is shown at left, using a simulation cell of 1600 atoms.
	www.public.iastate.edu /~cmpthy/accomp96/grain.html (283 words)

	Seminar Series (Site not responding. Last check: 2007-10-14)
		Combined molecular-dynamics and mesoscopic simulations are used to elucidate the mechanism of grain growth and deformation in nanocrystalline materials.
		The growth process is characterized by two regimes: if the average grain size is smaller than Rc, grain growth is grain-rotation dominated; by contrast, growth is dominated by grain-boundary migration for grain sizes greater than Rc.
		The stress distribution along the grain-boundaries in a polycrystalline solid under externally applied stress is determined and the mechanism of how topological inhomogenieties (distributions in grain size and shape) introduces stress concentrations into a microstructure beyond those already present in perfectly homogeneous microstructure (equiaxed hexagonal grains) is investigated.
	www.unl.edu /emhome/seminars/2003-04/DMoldovan.html (249 words)

	Amazon.com: Grain Boundaries: Their Microstructure and Chemistry: Books: P. E. J. Flewitt,R. K. Wild (Site not responding. Last check: 2007-10-14)
		Over recent years the understanding of grain boundaries, interphase boundaries and free surfaces has advanced greatly, leading to a clear recognition that these discontinuities make a significant contribution to the physical and mechanical properties of materials from multiphase metals and alloys to electronic materials.
		Grain Boundaries -Their Microstructure and Chemistry discusses the interrelationship between microstructure and chemistry of the grain boundary, with particular emphasis on the influence of the environment (air, liquid and liquid metal) and composition (bulk and impurity).
		Grain Boundaries - Their Microstructure and Chemistry is an indispensable text for design and safety engineers in many industries, including power and aerospace, as well as for materials scientists and engineers in academia and research institutes.
	www.amazon.com /Grain-Boundaries-Their-Microstructure-Chemistry/dp/0471979511 (707 words)

	The Hindu : Metallurgy: Role of grain boundaries highlighted
		The team suggests that imperfections preferentially form on twin grain boundaries-areas where the atoms of one crystal grain lie in mirror image position to the atoms of a neighbouring crystal grain.
		The team analyzed samples with grain sizes ranging from 3 to 60 micrometers and found that strain hardening from plastic deformation was completely independent of grain size.
		Their refined interpretation of both grain size and the role of twin grain boundaries could have important implications for materials science.
	www.hinduonnet.com /thehindu/2001/08/09/stories/08090002.htm (1066 words)

	Grain Boundaries, Point Defects, & Heterogeneous Interfaces
		Impurity and point defect segregation to ionic grain boundaries and surfaces is known to influence the physical properties of ceramic materials.
		grain boundary model structures are examined and the most energetically favorable models are determined.
		Segregation energies at the grain boundaries after Y3+ doping are also determined and a preferred doping site with the lowest segregation energy is identified.
	www.mse.ufl.edu /~ssinn/sub03c_grainboundary.html (408 words)

	Grain Boundary Phosphorous Segregation and Its Influence on the Ductile Brittle Transition Temperature in Reactor ...
		The AES measurements revealed that the peak height ratio (PHR) of P/Fe at the grain boundaries of the high-P steel were 0.066, 0.141, and 0.120 in the specimens aged at 400 degrees C for 3000 h, 450 degrees C for 3000 h, and 500 degrees C for 1000 h, respectively.
		The grain boundary fracture ratio (GBFR) increased with increasing the PHR of P/Fe.
		Grain boundary fracture mode was located at the area close to the V-notch root.
	www.astm.org /JOURNALS/JAI/PAGES/347.htm (542 words)

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