摘要:

Amorphous powders of the Al-Ni-Mm system and nanocrystalline powders of the Al-Ni-Mm-Zr system (Mm ≡ misch metal) were produced by a high-pressure gas atomization technique. Following degassing, the powders were extruded with a reduction ratio of 10:1. Tensile tests were performed for as-extruded alloys. High values of tensile strength and elastic modulus were obtained in both alloy systems. The maximum tensile strength reached was as high as 1000 MPa for an Al-14·9Ni-3·3Mm–5·1Zr alloy (where the composition is in weight per cent). The structure of the Al-Ni-Mm-Zr alloys is a finely mixed structure consisting of fine intermetallic compounds of Al3Ni, Al11Mm3and Al3Zr homogeneously embedded in an ultra-fine-grained aluminium matrix. The structure of the Al-Ni-Mm-Zr alloys is finer than that of Al-Ni-Mm alloys because of the additional effect of zirconium. A Hall-Petch relationship was investigated for the Al-Ni-Mm and Al-Ni-Mm-Zr alloys. Both the grain size refinement of the aluminium matrix and the dispersion strengthening of intermetallic compounds are interpreted as contributing to the achievement of the ultra-high tensile strength.

ISSN:0950-0839    

DOI:10.1080/09500839308240933

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This letter reports in detail on the temperature dependence of the time-resolved infrared-stimulated luminescence and long-time luminescence decay at low carrier densities. We find a peculiarity of the recombination process at temperaturesT< 30 K. It is shown that the observed quenching of the luminescence flux cannot be caused by Auger processes. The effect is interpreted as an enhanced non-radiative recombination via defect states owing to potential fluctuations caused by carrier clusters.

ISSN:0950-0839    

DOI:10.1080/09500839308240934

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In this letter we propose a new dephasing mechanism for the infrared absorption of a molecule adsorbed on a crystal surface. Explicit application to CO adsorbed at the on-top site of Pt(111) shows that this new dephasing process has a dominant role in defining the temperature dependence of the absorption linewidth compared with experiment. Application to CO on Ni(100) is also discussed.

ISSN:0950-0839    

DOI:10.1080/09500839308240935

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Dislocations produced in Ge by high-temperature indentation have been studied using high-resolution transmission electron microscopy. An interesting defect has been observed which consists of a 1/6⟨411⟩ partial dislcation separated by an intrinsic stacking fault from a 1/6⟨121⟩ 30° partial. The unusual 1/6⟨411⟩ partial dislocation forms by the reaction of a perfect 1/6⟨110⟩ 60° and 1/6⟨211⟩ 90° partial dislocation belonging to different glide planes.

ISSN:0950-0839    

DOI:10.1080/09500839308240936

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This letter shows that the displacive phase transformation from the h.c.p. α-phase to the hexagonal co-phase can be triggered in titanium targets in an unusual way during swift heavy ion irradiations. This unexpected result is a consequence of the high level of energy deposition in electronic excitation. A model based on the Coulomb explosion mechanism can account for such a phase transformation.

ISSN:0950-0839    

DOI:10.1080/09500839308240937

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

High-angle annular dark-field scanning-transmission electron microscopic imaging of inclined dislocation segments revealed a number of characteristic contrast effects that have been shown to depend on the specific position of the dislocation in the foil. The dislocation contrast is initially very dark at the entrant foil surface due to stress relaxation-induced scattering of the incident electrons. Below the entrant surface of the foil, the dislocation exhibits oscillatory contrast which disappears for large incident beam divergence angles. Ultimately, the dislocation contrast remains bright beyond a certain depth in the crystal towards the exit foil surface. A qualitative Bloch-wave scattering description has been formulated to describe consistently the observed contrast features.

ISSN:0950-0839    

DOI:10.1080/09500839308240938

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The effects of aluminium on the electro-optical properties of high quality sputtered hydrogenated amorphous germanium are reported. Two distinct effects are found: at low concentrations, the aluminium atoms act as active p-type dopants making the Fermi level shift towards mid-gap compensating the intrinsically n-type material. At higher concentrations, a hydrogenated germanium-aluminium alloy is formed. The optical gap shrinks and transport is probably dominated by holes.

ISSN:0950-0839    

DOI:10.1080/09500839308240939

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The dislocation microstructure associated with the loss of coherency of CdTe(001), as grown on GaAs(001), is characterized using high-resolution trans-mission electron microscopy. The examination of cross-sectional specimens allowed characteristic local variations in the relative orientation of the overgrowth and the substrate to be quantified and related to associated local changes in the form and distribution of the interface dislocation array. In the interface array, the relative proportion of 60° dislocations and Lomer-Cottrell locks proved to be related to the local misorientation between the CdTe and GaAs. The extent to which this is indicative of the mode of stress relief during the loss of coherency is discussed. Interestingly, it was also found that such variations in the relative proportions of the different types of dislocation proved to be associated with microtwin formation. The significance of this with regard to the strain relief mechanism is also noted.

ISSN:0950-0839    

DOI:10.1080/09500839308240940

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Three new orthorhombic approximants, C1, C2and C3, have been found in the Al70Co15Ni10Tb5decagonal quasicrystal, which was prepared by a method of quenching from the melt under a high static pressure. The lattice parameters of these orthorhombic phases are as follows: C1,a= 2.28nm,b= 1.60nm andc= 5.46nm (B type); C2a= 6.1 nm,b= 0.4 nm andc= 8.4 nm (P type); C3,a= 6.1 nm,b= 0.4 nm andc= 8.4nm (Btype). The strong diffraction spots in the electron diffraction patterns of these phases show the same intensity modulation as those of the decagonal quasicrystal, implying a close relationship between them.

ISSN:0950-0839    

DOI:10.1080/09500839308240941

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A dynamical convergence criterion for the real-space multislice method for simulating high-resolution electron microscopy images has been derived. This criterion imposes a practical limitation in determining dynamically the number of terms of the propagation operatorP(R)expanded in the subsequent dynamical diffraction calculations concerned with the phase grating selected, the wavefunction and its variation during propagating after choosing the sampling interval Δ and the slice thickness σ. It has been found that, as long as the dynamic criterion is satisfied, much better agreement with the results using a fast Fourier transform multislice method can be obtained.

ISSN:0950-0839    

DOI:10.1080/09500839308240942

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor