摘要:

In a recent letter from Dai, convergent-beam electron diffraction is used to determine the modulus of the Burgers vector of dislocations in icosahedral AlCuFe. In the analysis the phason strain component is neglected. We argue that this is an inadmissible simplification. We further show that a correct interpretation of the experimental data presented yields the result that the phason part of the dislocation strain field is larger than the phonon part, which contradicts the conclusions drawn by Dai.

ISSN:0950-0839    

DOI:10.1080/09500839308242902

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The recent comment paper by Wollgarten and Urban in 1993 criticizing an early paper of Dai in 1992 is considered. It is concluded that, not only the result from the early paper (|b∥| = 0·307±0·03 nm) is correct, but also the simplificationg∥·b∥≊nis reliable when estimating the modulus |b∥| of the Burgers vector of quasicrystalline dislocations in real space byusingg∥·b∥=nin convergent-beam electron diffraction, although the Burgers vector ᵬ of dislocations in the Al–Cu–Fe icosahedral phase should be better characterized in six-dimensional space: ᵬ = ⟨0 – 110 – 11⟩.

ISSN:0950-0839    

DOI:10.1080/09500839308242903

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The crack growth behaviour at 1400°C of polycrystalline Si3N4has been investigated by use of dynamic- and static-fatigue tests on Vickers- and Knoop-indented bending bars, and the crack growth law determined as an exponential curve ofvagainstK1with exponentn= 20·7. No threshold behaviour was found for initial stress intensity factors greater than 1·75 MPa m1/2. The material investigated was a model Si4N4sintered without external addition of densification aids. The crack growth law found for this material may constitute a reference equation for polycrystalline Si4N4with an oxide grain boundary since it was obtained on a high-purity system and under experimental conditions for which the hypothesis of linear elastic behaviour was strictly satisfied.

ISSN:0950-0839    

DOI:10.1080/09500839308242904

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Samples of Ti–50 at.% Al–2 at.% Nb–2 at.% Mn, which have been ice–water quenched from the α-phase region, have been shown to transform via a massive transformation to the γ-phase. Examination of the massively transformed region shows that the γ-phase contains regions which show contrast which is very similar to that shown by antiphase boundaries. Part of these boundaries give rise to diffraction maxima, and it appears that a discrete phase may be present in these parts of the boundaries. The significance of these observations is discussed in terms of the factors which can give rise to the observed behaviour.

ISSN:0950-0839    

DOI:10.1080/09500839308242905

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The character of long-range stresses of disordered finite dislocation walls is studied. It is shown that near such walls a rather thick region exists where the fluctuations of the stress predominate over its mean value given by the classical expression for disclination dipoles.

ISSN:0950-0839    

DOI:10.1080/09500839308242906

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Two different decay laws for fluctuations of the long-range stress field induced by disordered planar dislocation ensembles have been reported in the literature: σ ∝x−3/2and σ ∝x−1/2. The limits of these laws are established and corresponding physical processes are discussed.

ISSN:0950-0839    

DOI:10.1080/09500839308242907

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The equilibrium atomic structure of the (101) and (301) twin boundaries in rutile (TiO2) has been computed using an ionic shell model and compared with high resolution electron microscopy images of the same boundaries using image simulation. The lowest-energy (101) twin boundary structure is characterized by an in-plane translation of 1/2⟨111⟩ which conserves the mirror symmetry of the metal sublattice but which imposes a displacement on the oxygen sublattice. The lowest-energy (301) twin-boundary structure involves no in-plane translation and is characterized by mirror symmetry of both the metal and the oxygen sublattices. The computed mirror symmetry of the metal sublattice for both twin boundaries is in agreement with the electron microscopy observations. A small distortion present in the simulated images is discussed in terms of the interatomic potential used in the calculations.

ISSN:0950-0839    

DOI:10.1080/09500839308242908

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Self-diffusion of54Mn in Al72Pd20Mn8icosahedral quasicrystals has been investigated over the temperature range from 723 to 1022 K. Concentration depth profiles of the radioisotope54Mn in the Al–Pd–Mn quasicrystals and crystals have been measured by an ion-beam sputter-sectioning technique. The temperature dependence of the self-diffusivity of Mn in Al72Pd20Mn8icosahedral quasicrystals is expressed as

ISSN:0950-0839    

DOI:10.1080/09500839308242909

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new six-dimensional Burgers vector of dislocations in Al–Cu–Fe and Al–Pd–Mn icosahedral quasicrystals has been determined to be 1/2⟨11 – 200 – 2⟩ by means of defocused convergent-beam electron diffraction. The component of the Burgers vector in the physical space is parallel to a twofold axis with a magnitude of 0·18nm, which is about an eleventh of that in the complementary space.

ISSN:0950-0839    

DOI:10.1080/09500839308242910

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor