ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04636.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe different kinds of crystalline interfaces can be classified by means of the O‐lattice method. Two groups of parameters have to be known for the description of an interface. The first group concerns the structures and the relative orientation of the adjoining crystals and the second group deals with the position and orientation of the interface. The O‐lattice method allows one to deal with the two groups of parameters independently. This method gives a description of the interface in terms of dislocations, and hence of the possible relaxation in the boundary. Different kinds of interface will be discussed and illustrated by electron microgra

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04637.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe observation of grain boundaries using the optical microscope, the electron microscope and the field‐ion microscope has considerably aided our understanding of grain boundary structure. The study of etch pits in the optical microscope has proved that low angle boundaries are composed of dislocations.A large number of grain boundary observations have been made by transmission electron microscopy. Here, various classes of boundary structural features have been characterized in grain boundaries; they can be classified into three categories: (1) features which are essentially independent of the true structure of the boundary (thickness fringes, moiré fringes); (2) accidental features which result from a perturbation of the boundary by phenomena originating in the adjacent grains (dislocations, ledges); (3) features of the true structure of the grain boundary (features of the equilibrium structure‐features of the perturbed structure). It must be appreciated that certain features of the structure are not resolved because of their poor contrast in the electron microscope image.The field‐ion microscope has been used for a relatively short time in studies of grain boundaries. Nevertheless it has yielded very interesting results. Unfortunately, at the present time, it seems that the positions of the atoms may not be determined sufficiently accurately in this instrument to allow a precise determination of the structure. Only in a limited number of cases has it been possible to account for the observed features on the basis of theoretical consider

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04638.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe theory of interfaces between crystals of different structure and/or composition is briefly reviewed. The review is limited to planar semi‐coherent interfaces with an abrupt transition from one crystal to the other. Equilibrium, obeyingminimum(free) energyrequirements, is introduced as a governing principle. Thus the energy dependence on misfit, strain, atomic bonding, crystal thickness and other parameters is needed for minimization.The following approaches to this problem are dealt with briefly. Thecoincidence latticeandball‐and‐wiremodels, introduced to describe systems with isotropic and covalent bonding respectively, simply correlate low energy with good matching across the interface. Thevariationalapproach uses pairwise interface forces and adjusts the positions of atoms adjoining the interface to minimize the energy. TheVolterraapproach introduces dislocations explicitly for misfit accommodation and to facilitate energy considerations. TheFrank‐van der Merwemodel recognizes the lattice periodicity by employing an interfacial periodic interaction potential. In this model the resolution of the interface into a sequence of misfit dislocations is a natural consequence of the analysis. It is believed that the latter model has the widest predictive power, while the variational method has greatest potential for accuracy.Possibly the most prominent prediction is the joint accommodation of misfit by overall strain and misfit dislocations. However, the equilibrium theory failed to predict the correct dependence of the contributions of dislocations and strain to misfit accommodation on increasing film thickness. This is now accounted for in terms of the imperfection and difficulty of acquiring misfit dislocations.Some of the consequences of the interface structure of small epitaxial islands are briefly me

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04639.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYA review is presented of experimental observations reported on the structure of interphase boundaries since 1968. Nearly all observed boundaries are of the partially or fully coherent type, and hence the principal structural features examined were misfit dislocations and ledges. Observations were drawn from studies of precipitation, spinodal decomposition, oriented overgrowths and eutectics. Interphase boundary structures were found to be little affected in the main by the type of reaction through which they were developed and were consistent with Van der Merwe theory and a theory of precipitate morphology. Observations of these structures have been considerably facilitated by the efforts of Weatherly and co‐workers to define the visibility and the optimum TEM viewing conditions of misfit dislocations and ledges. Important new observations on misfit dislocations made since 1968 include: misfit dislocation spacing in the Cr(Mo)/NiAl eutectic in good agreement with theoretical expectation because misfit dislocations are also glide dislocations and the interface plane is also the glide plane; misfit dislocations on θ′ Al‐Cu and η Al‐Au plates with a Burgers vector (a/2) stable only at an interphase boundary; reduction of the interfacial energy of partially coherent boundaries on the same precipitates by dislocation interactions and rearrangements; reduction of interfacial energy of interfaces developed during spinodal decomposition through rotation of the interface itself from {100} to {110}; and misfit dislocation boundaries between f.c.c. (Cu‐rich) and b.c.c. (Cr) crystals made possible with the assistance of ‘structural ledges’. Growth ledges have now been observed in a number of alloy systems which have undergone precipitation from solid solution or eutectic solidification; they appear to be confirmed as a customary feature of migrating partially or fully coherent interphase boundaries. Much new experimental information has been obtained on the sources (exceedingly diverse), heights (usually appreciably higher than monatomic), spacings (irregular) and migration kinetics (diffusion‐controlled if their edges are disordered) of ledges. New observations continue to confirm the complexity of the processes through which misfit dislocations are acquired. The Ashby‐Johnson and the Brown‐Woolhouse theories of misfit dislocation nucleation or acquisition by spherical precipitates are in encouraging agre

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04640.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe observation of different types of order present in grain boundaries is discussed. It is shown that, while the majority of boundaries in a cubic random polycrystalline aggregate may possess order characteristics of a ‘plane matching’ or CAD situation, very few boundaries will possess order characteristic of a CSL. Frequent observations of CSL or CAD order in the electron microscope indicate a non random polycrystalline aggreg

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04641.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThis paper describes how a transmission electron microscope may be used to study rigid body displacements between coincidence related grains. Computer calculations have predicted that such displacements reduce grain boundary internal energy in metals by relieving atomic over‐crowding. Displacements are revealed as fringe patterns by a Bloch wave interference mechanism resembling that which gives rise to stacking fault fringes. The sensitivity of the technique in detecting very small displacements and its potential applications are discusse

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04642.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThe orientation relationships which lead to three‐ and two‐dimensional coincidence site lattices in hexagonal lattices are defined. Electron microscopy results on magnesium grain boundaries show dislocation structures which are discussed in terms of theories of coincidence and near coincide

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04643.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYThis paper discusses methods of analysing grain boundary structure in a commercial alloy system using transmission electron microscopy of thin foils. The results illustrate how the fine scale structure of grain boundaries may be analysed by employing weak beam imaging techniques and grain boundary diffraction effects.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04644.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

SUMMARYBicrystals with [011] symmetrical tilt boundaries rotated 36° have been examined by transmission electron microscopy. The boundary which was near a (41) plane showed networks of structural grain boundary dislocations. Possible vectors were derived from Bollmanns coincident site lattice theory for the nearest C.S.L., i.e. Σ9. The networks have been examined in a number of reflections and are considered to be composed of dislocations withb2(i.e. 1/9 [12]) andb3(1/6 [121] or 1/18 [127]) vectors. Fourb3vectors can change from one to the other by interactions with other structural dislocations. Evidence of iron additions reducing the mobility of dislocations is presented, and evidence of lattice dislocation dissociations are discussed. The mobility of dislocations in this Σ9 C.S.L. boundary is compared with a Σ27 coincidence latt

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1974.tb04645.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY