摘要:

The specimen temperature rise during the ion milling of transmission electron microscopy (TEM) specimens of II-VI semiconductors has been measured systematically. The rise was found to increase with increasing ion energy, beam current and angle between the beam and the specimen surface. The growth of dislocation loops in CdTe and ZnTe during Ar+-ion beam thinning is considered to be due to thermally enhanced diffusion. A model involving competition between loop expansion and ion-beam etching is proposed, which leads to the possibility of preparing TEM specimens of CdTe and ZnTe free from visible radiation defects.

ISSN:0950-0839    

DOI:10.1080/09500839308242269

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A three-cylinder model for the fibre-push-out test has been developed to evaluate the interfacial properties of ceramic matrix composites. The effects of constraints due to the neighbourhood fibres, the transverse isotropic property of the fibre and the Poisson expansion of the fibre are considered in this analysis.

ISSN:0950-0839    

DOI:10.1080/09500839308242270

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The existence of transformation-induced γ antiphase boundaries (APBs) is discussed in TiAl-based alloys in which two phases, γ and α2, are in equilibrium at low temperatures. While such APBs are frequently observed in the metastable γ-phase after the massive transformation α → γ, they are rarely observed within the γ lamellae of the so-called lamellar structure. In both cases (massively transformed structure and lamellar structure), however, other possible transformation-induced defects, such as twin and pseudo-twin boundaries as well as order-related domain boundaries, are found in abundance in the γ-phase (ordered tetragonal L10). The possibility of coupling of APBs with the other boundaries is examined in order to explain the above-mentioned experimentally observed difference regarding the γ APBs.

ISSN:0950-0839    

DOI:10.1080/09500839308242271

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Dislocations with Burgers vectors b given by b = [100] have been observed as products of a reaction occurring between dislocations with b=½⟨112] gliding on inclined {111} planes in lamellar Ti-50at.% Al. This reaction may be described as ½[112](111)+1/2[112](111) = [100] and is the most energetically favourable of all possible reactions in the TiAl system. The reaction product is presumably sessile. The origin of these defects may be associated with the thickening on thinning of laths of Ti3Al during initial processing and/or subsequent heat treatment of the material.

ISSN:0950-0839    

DOI:10.1080/09500839308242272

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

All the experimental methods for the measurement of structure factors are reviewed with emphasis on determining the electron charge-density distributions of intermetallic alloys, in particular γ-TiAl. The techniques discussed include X-ray diffraction, X-ray pendellösung methods, γ-ray diffraction and high-energy electron diffraction (intersecting Kikuchi line, critical voltage and convergent-beam rocking-curve procedures). All these methods (except for electron diffraction) require high-quality single crystals which seem impossible to prepare for equiatomic γ-TiAl. However, the critical-voltage electron diffraction measurements presented in this work indicate that the 001, 110, 111, 200, 002, 220 and 202 structure factor amplitudes of stoichiometric γ-TiAl can be determined with sufficient accuracy for a charge-density study provided that great care is taken.

ISSN:0950-0839    

DOI:10.1080/09500839308242273

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The enhanced X-ray production by channelled electrons is used to investigate the planarity of the periodically stacked (00001) planes in decagonal Al62Cu20Co15Si3. The results strongly suggest that the planes are not perfectly flat as assumed in previous models but that a fraction of the Al atoms and probably all Si atoms are displaced out of the planes.

ISSN:0950-0839    

DOI:10.1080/09500839308242274

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor