摘要:

AbstractRecent void shrinkage models are reviewed and refined. The role of surface selfdiffusion is discussed for modelling void shrinkage by selfdiffusion along the void surface and bond interface. The refinement of the existing models makes it possible to discuss the effect of void crushing by power law creep, the validity of combining models of diffusion and creep, and the applicability of the existing models. The discrepancies between the various models are demonstrated by reference to the stress dependence of void shrinkage rate (log–log plots). The void crushing rate due to power law creep of the surrounding matrix is highly dependent on the degree of bulk deformation, i.e. the severity of bulk constraint. The applicability of the combined models of creep and diffusion are therefore limited by this condition.MST/1502

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.953

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe transition between two steady states of unidirectional solidification of Al–Si eutectic modified with 0·5 wt-%La has been investigated experimentally by abruptly changing the solidification rate. The addition of lanthanum results in only partial modification of the eutectic microstructure, fiakelike and fibrelike silicon phases being always present after solidification. The interflake spacing and the interfibre spacing are shown to have a continuous but retarded response to an abrupt change of solidification rate, the retardation of the interflake spacing being the greater. A model of the response dynamics governing the transition has been developed to interpret the results of the experiments.MST/1237

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.965

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAn Al/TiC composite has been developed using a melt infiltration technique. Green preforms of TiC were partially sintered to densities ranging from 50 to 85%. They were then infiltrated with molten aluminium in argon at atmospheric pressure, at temperatures ranging from 950 to 1350°C. The variations in mechanical properties of this composite material with ceramic content and fabrication conditions are presented and the resulting microstructures are discussed. The composite exhibited excellent tensile strength values of ~475 MN m−2and up to 5% elongation. Fracture behaviour mechanisms are also described in relation to the stress–strain curves. High infiltration temperatures were found to be detrimental to the mechanical properties since the TiC particle network, which formed during sintering, was broken down by the metallic phase.MST/1601

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.971

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

Abstracthe mechanical properties of extruded particulate composites of an enhanced 7000 series alloy have been examined and have been related to a macromodel of composite behaviour. The best tensile properties were found in the T6 condition: the 10 vol.-%SiC composite was found to have 624 MN m−2proof stress, 690 MN m−2ultimate tensile strength, 10% ductility (elongation), and 87 GN m−2Young's modulus. As would be expected, the Young's modulus was found to increase with volume fraction of reinforcement and, at a level of 25 vol.-%SiC, was 112 GN m−2. The tensile modulus of the unreinforced alloy was found to be 73 GN m−2. An explanation for the variation of tensile property behaviour with heat treatment is proposed. The fracture toughness of the composites was determined via the short bar method; toughness values were high, ranging from 34 MN m−3/2for 10 vol.-%SiC in the underaged temper to 19 MN m−3/2for 20 vol.-%SiC in the overaged temper. The relationships between properties and microstructure are discussed.MST/1505

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.977

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractAn earlier model for the overall transformation kinetics of bainite has been corrected and modified to be consistent with known details of the mechanisms of bainitic nucleation and growth. A comparison with published experimental data shows that the model is capable of accurately representing the development of transformation as a function of alloy chemistry and temperature.MST/1627

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.985

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe carbon concentration trapped in films of austenite between parallel platelets of bainite is often found to be much larger than that in the larger blocks of austenite between sheaves of bainite. The effect of this non-uniform distribution of carbon on the overall transformation kinetics of bainite is examined theoretically. It is found that the trapping of carbon in the films of austenite accelerates the bainite transformation. This effect increases with increasing film thickness and with decreasing average carbon concentration.MST/1628

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.994

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA brief rationalisation is made of the isothermal decomposition kinetics of supercooled austenite in steels. From the experimental evidence of the past several decades, it is concluded that each type of isothermal decomposition product, i.e. grain boundary allotriomorphs, Widmanstätten ferrite (and cementite), pearlite, upper bainite, lower bainite, lath martensite, and twinned martensite, has its own independent C-curve in time–temperature–transformation (TTT) diagrams. Special emphasis is placed on the isothermal transformation kinetics of martensite. It is demonstrated that martensite transformation follows C-curve kinetics in isothermal conditions; this is a general rule and holds for all steels. The reason why most experimental TTT diagrams fail to display separate C-curves for different products is briefly explained. A temperature–composition–product (TCP) diagram is constructed for Fe–C alloys (plain carbon steels) to depict the general pattern of the decomposition process and to display the conditions for the formation of the various decomposition products.MST/1623

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.1004

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe microstructural development during rolling is compared in two Hadfield steels, one having low carbon content (0·65 wt-%) and the other high content (1·35 wt-%). Differences in substructure are observed which are due not to small changes in stacking fault energy, but to carbon segregation, which occurs in the low carbon steel (through vacancy diffusion) but not in the high carbon steel. This is demonstrated using Mössbauer spectroscopy and is in agreement with systematic characterisation of microstructures by optical and transmission electron microscopy. In the low carbon steel mixed microstructures are formed which contain intrinsic stacking faults, deformation twins, and brass type shear bands. In the high carbon steel mixed substructures of dislocation tangles, deformation twins, and shear bands (both copper and brass type) are found to develop. In spite of the difference of substructure development during rolling in the two steels, the difference in stacking fault energy is measured to be small (~2 mJ m−2, i.e.<10% of the stacking fault energy).MST/1417

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.1011

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA homogeneous set of Cr–3·5Ni low alloy steel samples has been made to enable laboratories studying grain boundary segregation by Auger electron spectroscopy to interrelate their studies. This steel has P, Sn, and Ni segregated at the grain boundaries. Data are provided of the effect of variation of signal intensities across a grain, on one grain as a function of the electron emission angle, on many grains, etc. for both unidirectional (concentric hemispherical) and multidirectional (cylindrical mirror) spectrometers. Reference spectra recorded from the sample allow the spectrometer transmission function to be calibrated so that data from all instruments may be interrelated. After correction for the transmission function, the Auger electron peak-to-peak height ratios, for a 5 eV Savitzky and Golay differentiation, are found to be P120/Fe703=0·33±0·06 and Sn430/Fe703=0·12±0·02. Calibrations from the literature show these signals can be attributed to 33 and 31% of a monolayer of P and Sn, respectively.MST/1684a

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.1023

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA batch of low alloy reference material for the study of grain boundary segregations of P and Sn has been studied using eight Auger electron spectrometers in six laboratories. The instruments include both cylindrical mirror and concentric hemispherical analysers. Measurements in the differential mode using 5 eV Savitzky and Golay differentiation show that peaks close in energy, such as the ratio of the Sn 430 eV and Fe 651 e V peak-to-peak heights, can be compared directly to demonstrate a reproducibility of 8%. For peaks more widely separated, the scatter of intensity may exceed a factor of 2. However, using reference spectra from the material, all the spectrometers can be calibrated for their intensity/energy response function. After this calibration, the P and Sn peak-to-peak height ratios, with respect to Fe, show scatter of only 15%. In addition to this reduction in scatter, the mean values for the ratios can be corrected by up to a factor of 2. This work shows that the reference materials and methodology are suitable for relating the segregation spectra for P and Sn in low alloy steels from laboratory to laboratory on an absolute and traceable basis.MST/1684b

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.11.1036

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor