摘要:

AbstractThe properties of chemical vapour deposited diamond are reviewed and many properties are shown to approach or equal those for natural diamond. The manufacture of solid diamond fibres via chemical vapour deposition on various wire and ceramic cores and the production of hollow diamond fibres by removal of the cores is described. The potential values of Young's modulus of continuous and discontinuous diamond fibres, calculated using the rule of mixtures, are predicted to be substantially higher than for current commercial SiC fibres. Corresponding increases in compressive stiffness are expected, with significant increases in specific buckling loads for hollow fibres. Hollow fibres may also allow the use of sensors in smart structures. The factors affecting the cost of diamond fibres are discussed. It is concluded that chemical vapour deposited diamond fibres offer for the first time the possibility of exploiting the properties of diamond on a large scale via diamond fibre composites.MST/2098

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.177

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe Young's modulus of transition metal carbides has been calculated from their assessed thermal properties to explain why the modulus of steels and white cast irons can be only marginally altered by changes in composition or heat treatment. It is shown that the modulus of cementite (200 GN m−2) is virtually identical to the value calculated for pure ferrite (215 GN m−2). The predicted systematic variation for the modulus both with structure and position in the periodic table rationalises previous isolated experimental observations and confirms that the MC carbides of the group IV elements should have the most powerful strengthening effect in a matrix of their parent metal.MST/1909

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.190

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe microstructure of a power plant steel changes during elevated temperature service. These changes in effect provide a built in time–temperature recorder which can be used in remanent life assessments. Hence, extensive studies have been undertaken of cementite composition changes as a function of time and temperature in a 2·25Cr–1Mo steel with a fully bainitic microstructure. The results are interpreted theoretically using a model for the enrichment of carbides as a function of heat treatment and steel chemistry. The results confirm the validity of the model, although further work is needed to predict the onset of alloy carbide formation at the expense of cementite.MST/1895

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.193

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractIt is found that the carbide chemistry changes at a slower rate in a mixed microstructure of bainite and allotriomorphic ferrite when compared with carbides in a fully bainitic microstructure. These results are expected intuitively and confirmed theoretically.MST/1896

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.205

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractRecently published experimental data demonstrate that the strength of mixed microstructures of tempered bainite and martensite can peak at an intermediate volume fraction of martensite. In the present work, a quantitative interpretation of these observations is achieved by modelling the mechanical properties of bainite and martensite in their tempered states. It is found that the peak in the curve of the strength as a function of the volume fraction of martensite can be attributed to two factors. When bainite forms it enriches the residual austenite with carbon, so that the strength of the subsequent martensite increases. In addition, during its deformation, the strength of the bainite is enhanced via plastic constraint by the surrounding stronger martensite. Taking these effects into account, it is possible to predict accurately both the trends and the absolute values of published experimental data on the strength of mixed microstructures.MST/1901

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.209

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA quantitative study of variations in microstructure and texture evolution in the through thickness direction of industrially hot rolled AA 3004 aluminium alloy has been carried out. The microstructural features of the specimens were examined with the aid of the electron channelling contrast technique in conjunction with an image analysis system. The number of recrystallised grains and the size distributions of coarse and fine intermetallics were measured to evaluate the variation between surface and centre. Significant differences in the number of recrystallised grains and the average size of coarse intermetallics in the through thickness direction of the hotband were observed. After isothermal annealing of the hotband for various times the fine intermetallic area fraction increased and was higher at the centre than at the surface. Quantitative texture analysis was carried out on the specimens and various texture components estimated to characterise the through thickness texture evolution. The proportion of cube texture component was higher near the surface than at the centre and this difference increased after isothermal annealing. Since negligible change occurred in the cube content of the centre specimen, growth of cube grains was deduced to have taken place primarily near the surface region. These observations illustrate that mechanisms of cube texture formation, heterogeneous nucleation of precipitates causing retarded recrystallisation, and Zener drag are evidently applicable even to complex commercial alloys.MST/1849

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.215

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractMetastableδ′precipitates formed at 473 K in Al–1·9Li–2·5Mg alloy have been studied via specific heat measurements, analytical transmission electron microscopy, and atom probe field ion microscopy. The peak temperature of heat absorption associated with the resolution ofδ′into the matrix increases by more than 45 K after prolonged aging, i.e. the thermal stability ofδ′is enhanced by the aging treatment. The coarsening ofδ′obeys Ostwald ripening kinetics. However, the increase in the peak temperature is not related to the increase in size ofδ′but is instead attributed to an increase of the Mg content inδ′precipitates; presumably,δ′changes from Al3Li to (Al, Mg)3Li.MST/1846

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.222

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA method of computer simulation of the process of strain hardening in rods of circular cross-section subjected to deformation in a rolling–drawing process is presented. Such simulation allows the determination of the magnitude of the deformations induced by the rolling and drawing to obtain a particular cross-sectional hardness distribution in the rod. The application of this method permits, in particular, the determination of the conditions under which a rod subjected to combined rolling–drawing deformation will exhibit uniform hardness. The method was experimentally verified for Cu–30Zn rods.MST/1873

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.227

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractLaboratory tests were carried out on CR1 grade steel strip involving punch stretching without lubrication and with PQ6 oil or polythene as lubricant. The finite element code was then used to simulate the forming behaviour during the test. The effects of normal anisotropy of the material and the contact friction between punch/die and the specimen on the forming behaviour were studied systematically. The predictability of the finite element modelling was confirmed by direct comparisons between the experimental measurements and the computer predictions. The aspects of further refinements required in the finite element models are discussed.MST/1887

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.233

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractHeat treatments have been carried out on an annealed low alloy Cr–Mo–3·5Ni–V steel (J-steel) to investigate the effects of various normalising and hardening temperatures, before tempering, on the mechanical properties. It was observed that the 0·2% proof stress increased, whereas the impact toughness, as measured by the increase in transition temperature, decreased with increasing hardening temperature for both normalised and non-normalised material. For a constant hardening temperature, the 0·2% proof stress passed through a minimum and the Charpy upper shelf energy passed through a maximum, at a normalising temperature of 890°C. The variation in properties has been correlated with the observed variation in martensite packet size, dislocation density, precipitate size, and volume fraction. It was found that a 0·2% proof stress above 1100 MN m−2, and a Charpy impact energy of greater than 50 J at−40°C located within the upper shelf energy region, was attainable with the following heat treatment: normalising from 870°C and hardening from 850°C, followed by tempering at 620°C and oil quenching to room temperature.MST/1870

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.3.239

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor