Crystal Grain Boundaries Research Articles

A model for stress-induced migration of tilt grain boundaries in crystals of NaCl structure

We present a qualitative model for stress-induced migration of tilt grain boundaries which we have observed during creep of sodium chloride. The elementary mechanism of the model consist in the propagation of the ledge associated to an extrinsic grain boundary dislocation. The model appears as an extension of the mechanism for growth of deformation twins and is compatible with but more general than Read's and Shockley's model for migration of low angle boundaries.

六方結晶における粒界模型 氷結晶の粒界の性質を中心として

Relationships between the rotation angle θ and the reciprocal density of coincident sites Σ in the coincidence site lattice (CSL) model for the ideal hexagonal crystal in which the axial ratio c/a=√8/3 were calculated for three rotation axes of low indices: [0001], [1210] and [1010] . For determining the Burgers vectors of grain boundary dislocations, the displacement shift complete (DSC) lattices were also calculated for the above cases. Results of the calculations in the range of Σ<50 were tabulated in Tables 2-4 besides the generating equations in Table 1. The structure and behavior of grain boundaries in ice crystals, especially those found experimentally by the present authors with artificially grown ice bicrystals of <1010 >/34°were well explained by the model presented above.

General theory of grain boundaries in crystal

Abstract Presented is a microscopic derivation of the theory of grain boundaries in crystal. Fundamental properties of the grain boundaries are also discussed.

High-resolution TEM of grain boundaries in silicon

In contrast to grain boundaries in metals, little is known about the structure and the properties of grain boundaries in covalent crystals, especially in semiconductors. The reason for this lack of knowledge is that grain-boundary-free crystals of, e.g., silicon, are easy to grow; commercially used silicon crystals are free of dislocations and thus nearly perfect. It was not until after the use of polycrystalline silicon had been proposed for the large scale production of cheap solar cells that grain-boundary properties in silicon gained considerable interest. In particular their electronic properties and their influence on device performance is important in this case. Moreover, “grain boundary devices”, i.e., devices with a grain boundary as the active element and with rather interesting properties, are conceivable - provided the relationship between the grain boundary structure and their electronic behaviour can be understood (cf. /l/). In addition, the study of grain boundaries in silicon, with an electronic structure and a binding configuration very different from metals, may provide a valuable tool to test competing grain boundary models (see, e.g., /2,3/) and may lead to a deeper insight into the crystal parameters governing the grain boundary properties.

Measurement of the Displacement Across a Coincidence Grain Boundary

Many high-angle grain boundaries in cubic crystals are thought to be either coincidence boundaries (1) or coincidence boundaries to which grain boundary dislocations have been added (1,2). Calculations of the arrangement of atoms inside coincidence boundaries suggest that the coincidence lattice will usually not be continuous across a coincidence boundary (3). There will usually be a rigid displacement of the lattice on one side of the boundary relative to that on the other. This displacement gives rise to a stacking fault in the coincidence lattice.Recently, Pond (4) and Smith (5) have measured the lattice displacement at coincidence boundaries in aluminum. We have developed (6) an alternative to the measuring technique used by them, and have used it to find two of the three components of the displacement at {112} lateral twin boundaries in gold. This paper describes our method and presents a brief account of the results we have obtained.

Coincidence-site lattices and complete pattern-shift in cubic crystals

Two interpenetrating point lattices contain under certain conditions a common sublattice, i.e. a 'coincidence-site lattice' (CSL). The present study is restricted to cubic lattices [primitive cubic (p.c.), f.c.c. and b.c.c.]. It is shown that it is necessary for the existence of a CSL that the two lattices are related by a rotation R represented by a rational matrix in the cubic coordinate system of one of the lattices. It is further shown that the common denominator N in R is equal to the ratio Σ of the unit volume of the CSL referred to the unit volume of the crystal lattice. The 'complete pattern-shift lattice' (DSCL) is defined as the coarsest lattice which, in CSL orientation, contains both crystal lattices as sublattices. Further it is proved that the volume of the DSCL unit referred to the crystal unit is 1/Σ and that for the p.c. structure the CSL and the DSCL are reciprocal lattices. For both f.c.c. and b.c.c. the CSL and the DSCL have to be face-centred or body-centred respectively. Methods are described for all three cases to determine explicitly the CSL, the DSCL and the planar density of coincidence sites. A table is given for R, the CSL's and the DSCL's up to Σ = 49. This study is of importance for the investigation of grain boundaries in cubic crystals.

Heterophase dislocations — An approach towards interpreting high temperature grain boundary behavior

When the conditions of full thermodynamic equilibrium are added to the conventional linear elastic theory of dislocations a hybrid concept of “heterophase” dislocations arises. As developed here, heterophase dislocation theory provides a self-consistent method for calculating the core configuration, energy, and stress-strain field which minimize the thermodynamic potential of a dislocated crystal. Simple grain boundaries in crystals near the melting point are treated as constrained arrays of heterophase misfit dislocations with a liquid-like core phase similar to, but not identical with the properties of ordinary liquid phase. Measurements of the properties and behavior of {011̄} tilt boundaries in bismuth crystals near the melting point show that the new theory accounts accurately for the energetic dependence on tilt misorientation in the range 0° to 6°, and then deviates from the observed dependence. The new theory also permits prediction of a structural transition in grain boundaries which is extremely sensitive to the density of misfit dislocations. This transition, predicted to occur in bismuth at a tilt misorientation of 15° was also confirmed by hot-stage electron microscopy.

Absorption Kinetics of Nitrogen+Tantalum System

The dependence of the absorption rate on temperature is studied for a single-crystal tantalum wire, and is compared with those for polycrystal wires and ribbons. Two processes of absorption of nitrogen in tantalum are found. In the first process absorption occurs at boundaries of crystal grains and is observed for polycrystal ribbons with surface of the (311) planes; the activation energy of absorption is 1.9 eV/2-atoms. The second process is observed for crystallized or sufficiently flashed wires. In this process atoms chemisorbed on the surface are directly absorbed into the bulk at their absorption sites; the activation energy of absorption is 4.0 eV/2-atoms, which is larger than that of diffusion of nitrogen in tantalum.

銅およびニッケルの電析機作の考察

Observations and discussions were made for the mechanisms of electrodepositions of copper from sulfate and cyanide baths and of nickel from sulfamate and sulfate baths.The behavior of initial crystal nucleation and crystal growth was observed under an electron microscope.Main considerations obtained were as follows:(1) The electrodeposits of Cu and Ni were nearly identical in crystal forms, because the both metal had the same crystal lattices (face centered cubic lattices).(2) Different types of electrodeposited crystals were observed between simple salt and complex salt baths.(3) Initial crystal nuclei had semi-spherical form with diameter of less than 3000A. The machanism of nucleation was supposed to consist of the followig three stages; that is, the presence of a huge ionic mass in the electrolytic bath, its continuons discharge, and instantaneous deposition of the corresponding metal.(4) The nucleation seemed to be concentrated around the scratches on the substrate caused by grinding and in the neighborhood of grain boundaries of crystals.

Low-angle grain boundaries in natural barite single crystals

Natural barite (BaSO4) crystals have been cleaved along (110) and (001) cleavages and etched in H2SO4 and KOH. Rows of equally spaced pits are observed on both the cleavage faces. By etching matched cleavage faces correspondence has been established for intersecting grain boundaries. Correspondence has also been established on the two sides of a thin flake 1000 μm thick. For all the intersecting grain boundaries observed, the condition na=nb+nc is satisfied, na, nb and nc being the numbers of dislocations per micrometre in the three branches.

Properties of centrifugal castings of the Kh16N36MBTYuR alloy

1. An excess phase of the (Ni, Fe)3TiAl type is precipitated in the grain boundaries of the primary crystals of centrifugal castings of the Kh16N36MBTYuR alloy; it is responsible for cracking of the cold worked alloy. 2. Homogenization of the alloy at 1200°C for 3–5 h leads to solution of the excess phase in the austenite, equalization of the mechanical properties through the section of the casting, and removal of the anisotropy. 3. Precipitation-hardening of the alloy by aging under our experimental conditions does not depend on preliminary homogenizing. 4. Cold working substantially increases the effect of precipitation-hardening on the cast alloy. 5. Increasing the austenitizing temperature, which produces a more homogeneous solid solution, reduces the effect of precipitation-hardening of the cold worked alloy.

Quench-hardening gradients near vacancy sinks in crystals of zone refined lead

Microhardness studies were carried out using a very light load on quenched single crystals and bicrystals of zone-refined lead. The results indicate that the microhardness test is a suitable probe technique for revealing local changes in defect concentration near free surfaces and grain boundaries in pure metal crystals.

Relation between Microstructure and Emissions of Steels

Emission spectrochemical analysis of steels is considerably affected by their metallurgical conditions. As a guide for elimination of this harmful effect in the quantovac analysis, a study is made concerning the relation between microstructure and emission of steels.The obtained results are the following:(1) The investigation of discharge craters showed that considerable preferential discharges occur on boundaries of crystal grains, inclusions and joined metals.Hence carbon spectrum line intensity varies by heat treatment of samples.The spectrum intensity of the internal standard line also varies to some extent by preferential discharges.(2) Relation between erosion rate and chemical composition of carbon steel, alloy steel and stainless steel is expressed by respective linear equations which show that C, Mn, Ni promote the erosion and Si, Cr, Mo diminish it.

Mechanisms of Virus Infection.Wilson Smith

Previous articleNext article No AccessNew Biological BooksMechanisms of Virus Infection. Wilson Smith John HollandJohn Holland Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Quarterly Review of Biology Volume 39, Number 3Sep., 1964 Published in association with Stony Brook University Article DOIhttps://doi.org/10.1086/404308 Citations: 1Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Masatoshi TOSAKA High Resolution TEM of Grain Boundaries in Polymer Crystals, Journal of The Adhesion Society of Japan 49, no.1010 (Jan 2013): 381–388.https://doi.org/10.11618/adhesion.49.381

Dislocation Theory of the Formation of Small-Angle Boundaries

The elastic interaction energy of some simple arrays of edge dislocations is calculated as a function of position of one member of the array on its glide plane. The resulting energy relations are interpreted as binding potentials for the capture of a dislocation by the array. This mechanism is assumed to be operative in the formation of small-angle grain boundaries in crystals.

ENERGIES OF GRAIN BOUNDARIES IN SILVER CHLORIDE CRYSTALS

The relative energies of grain boundaries in silver chloride crystals have been measured. The measurements were made on tricrystals grown by simultaneously drawing three single crystals vertically from a melt. Tricrystals of three different isoaxial orientations, [Formula: see text], [Formula: see text], and [Formula: see text], were studied. The relative grain boundary energies were measured as a function of the orientation differences between two grains forming a boundary in crystals of each of the orientations given above. From these measurements the following conclusions are drawn: the grain boundary energies of silver chloride follow the equation of Read and Shockley; for small orientation differences, that is, differences less than 10°, the boundary energy is a function of the axial orientation of the grains forming the boundary; for large orientation differences, that is, differences greater than 10°, the boundary energy is not a function of the axial orientation, except when cusps occur; the maximum energy of a boundary made of crystals each with a [Formula: see text] axial orientation equals the maximum energy of a boundary between crystals of [Formula: see text] axial orientations.

Surface tension at the boundaries of crystal grains in metals

Recueil des Travaux Chimiques des Pays-BasVolume 42, Issue 9 p. 822-825 Articles Surface tension at the boundaries of crystal grains in metals Cecil H. Desch, Cecil H. Desch Sheffield, Department of Applied ScienceSearch for more papers by this author Cecil H. Desch, Cecil H. Desch Sheffield, Department of Applied ScienceSearch for more papers by this author First published: 1923 https://doi.org/10.1002/recl.19230420920Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume42, Issue91923Pages 822-825 RelatedInformation