摘要:

AbstractThe aerospace industry is currently making extensive use of both structural adhesives and composite materials in aircraft and space vehicle construction. Within the past decade, there has been a growing requirement for adhesives and composites capable of withstanding temperatures in excess of 150°C for both short- and long-term applications. Although polymers offering such capabilities have been commercially available for many years, in numerous cases adverse processing characteristics have severely restricted their acceptance. As a result, substantial efforts have been made to develop high temperature resistant polymers having considerably improved processing characteristics. In this paper, a critical assessment is given of the use of high-temperature polymers in both adhesive and composite applications with particular emphasis on some of the newer, more easily processed types which are, or will probably be, commercially acceptable.MST/659

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.589

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractMethods for the in situ measurement of foil thickness in the transmission electron microscope (TEM) are reviewed for the non-specialist. The techniques described range from those based upon the analysis of crystallographic features contained in the specimen, as may be carried out with the most basic TEM configuration, to those which involve measurements of electron energy loss spectra or X-ray emission characteristics and require the addition of sophisticated analytical equipment to the electron microscope. Some methods are seen to give the foil thickness directly, while others must be regarded as being relative since they require calibration using reference foils of known thickness and composition. Factors such as the range of applicability, ease of use, and accuracy of the techniques are discussed as well as the possibility of misinterpreting the data.MST/665

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.600

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe widely used shear-lag theory for the stresses and displacements in a short fibre composite is discussed and compared with more exact theories in the literature. A simple modification of shear-lag theory, using stress functions, is proposed that allows prediction of radial stresses in the fibre, while being easy to use for calculations. Predictions from the present theory are compared with those from the shear-lag theory and with some of the more exact theories. At low fibre concentrations, the present theory underestimates the radial stress at the fibre ends while predicting shear stresses comparable with those from shear lag. At high fibre concentrations both radial and shear stresses are overestimated.MST/635

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.609

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractAlkaline earth sulphide phosphors (CaS, SrS, and BaS) doped with rare earth ion (Sm and Ce) impurities were prepared by carbon reduction of pure sulphates of Ca, Sr, and Ba in a N2atmosphere and using NaCl as flux. The thermally stimulated luminescence of these phosphors was studied by excitation with ultraviolet-,γ-, and X-rays. Intense glow maxima in the temperature range from 60 to 85°C were exhibited by most of the phosphors under the three methods of excitation. Some results on thermally stimulated conductivity and photoluminescence relevant in this context are also reported. Considering all these results, the trapping centres responsible for the energy storage in this system of phosphors were identified as Sm and Ce and their complexes involving native defects.MST/405

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.616

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractIn the light of recent changes made to the phase diagrams of the Au–Sn and Au–Pb binary systems, the constitution of the Au–AuSn–Pb partial ternary system has been redetermined using thermal analysis, metallography, and X-ray techniques. The equilibria consist of four ternary transition reactions at 63·5Au–26·0Pb–10·5Sn, 382·5°C; 42·5Au–47·5Pb–10·0Sn, 254°C; 30·5Au–60·5Pb–9·0Sn, 224°C; and 20·5Au–75·5Pb–4·0Sn, 214°C; a ternary eutectic equilibrium at 15·0Au–84·0Pb–1·0Sn, 211°C; and a four-phase monotectic equilibrium at 64·0Au–9·0Pb–27·0Sn, 257·5°C (compositions are given in atomic per cent). The phase assemblage of the partial ternary system is characterized by a region of true ternary liquid immiscibility that covers much of the composition triangle. The composition of the second liquid phase at the monotectic reaction temperature is 45·0Au–40·0Pb–15·0Sn. Solid solubilities were not determined.MST/620

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.621

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe constitution of the Ni–Cr–Al–Mo system has been investigated at 1273 and 1073 K using alloys containing 60 and 50 at.-%Ni. The alloys were initially annealed at 1523 K, resulting in structures containing combinations of two or three of the phases:γ(nickel-base solid solution),γ′(based on Ni3Al),β(based on NiAl),σ, P, and Mo–Cr base solid solution. On annealing at 1273 and 1073 K, equilibrium conditions were not achieved but the solid state transformations occurring during the approach towards equilibrium included the fine scale precipitation ofσ- and P-phases. Data are reported of phase compositions determined by electron probe microanalysis and by energy dispersive X-ray analysis of thin foils. Theγ/γ′mismatch values in the alloys studied ranged from−0·17 to−0·75%.MST/605

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.629

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractAn examination by transmission electron microscopy has been made of the austenite→ferrite + carbide reaction in an Fe–C–V low-alloy steel over the transformation temperature range 550–850°C. Thin films of interlath retained austenite in the untransformed martensite regions of partially transformed specimens have been used to investigate the crystallographic relationships between parent and product phases. Grain boundary ferrite allotriomorphs nucleate with a rational orientation relationship to at least one, but also occasionally to both, of the two adjacent austenite grains. Interphase precipitation of vanadium carbide can occur in the ferrite irrespective of the austenite–ferrite crystallographic relationship and, in particular, it is shown that the single habit plane adopted by the carbide is not a consequence of a three-phase crystallographic relationship between parent austenite and the product ferrite and carbide phases. It is thought that the precipitate adopts that habit plane which lies at the smallest angle to the plane of the transformation interface, and additional experimental evidence to support this is presented.MST/664

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.642

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractThe conditions for martensite formation in the intercritical heat affected zone (HAZ) of two low-carbon microalloyed steels have been investigated using optical and transmission electron microscopy. Based on Charpy V-notch testing of a large number of thermally cycled specimens, it is concluded that embrittlement within the intercritical HAZ of such steels is closely related to the development of twinned martensite during the weld cooling cycle. The reduced HAZ toughness probably arises from the associated stress concentrations developed in the surrounding ferrite matrix, which give rise to the initiation of brittle fracture in the ferrite.MST/634

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.649

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractA general model for constrained cavity growth is developed for cavitation during creep deformation. The model incorporates the effect of the separation between cavitated facets, the contributions of local power-law creep in the cavitated regions of a specimen, and the possibility of coupled cavity growth. A detailed analysis of the model reveals that, during constrained cavity growth at low stresses, interaction effects enhance the cavity growth rates when L/d<10, where L is the separation between the cavitated facets and d is the grain size. An assessment of the stress redistributions occurring during cavity growth indicates that constrained cavity growth may lead to increases in the specimen creep rate by significantly increasing the stress in the uncavitated regions of a specimen when L/d<5. It is also demonstrated that, under the appropriate limiting conditions, the present general model gives results similar to those obtained in previous studies on constrained cavity growth.MST/610

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.656

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor

摘要:

AbstractRectangular and round cross-section test bars of Zn–Al alloy containing (wt-%) 27·67%Al; 2·30%Cu; 0·13%Mg; 0·04%Fe;<0·0025%Pb, Cd, and Sn; balance Zn were cast in metal moulds. The variables studied were: bar cross-section 3–25 mm thickness and 14·5–28 mm dia., pouring temperature 550–700°C, feeder location at bar shoulders or over full gauge length, and cast iron mould preheating temperature 100 or 200°C. The results show that the above variables can lead to variations of 0·14–1·72% bar porosity, 18–0·5% elongation, 428–305 MN m−2tensile strength, and 108–128 Brinell hardness. Metallographic examination leads to the conclusion that these properties are influenced by the volume, distribution, and morphology of shrinkage porosity and of eutectic constituent. The observed variations in the microstructure and their effects on the mechanical properties are related to the cooling and feeding conditions of the bars.MST/549

ISSN:0267-0836    

DOI:10.1179/mst.1987.3.8.665

出版商:Taylor&Francis    

年代:1987

数据来源: Taylor