摘要:

AbstractMethods for diffusion bonding of Al–Li alloys in the solid state and via a transient liquid phase are described and the factors that affect bond quality are discussed. Bond shear strength values at room temperature and peel strength values at room temperature and at superplastic forming temperatures are compared. The possibility of combining diffusion bonding with superplastic forming to manufacture multiple sheet structures is considered. It is concluded that under the most favourable processing conditions and on a small scale, combined diffusion bonding and superplastic forming of Al–Li 8090 alloy is now possible. Future developments will involve the optimisation of the process for cost effective commercial applications.MST/1608

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.385

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA simple levitation dispersion test has been developed to provide a qualitative assessment of the conditions of dispersion of solid reinforcing particles in liquid metals. The test has been used to assess the degree of dissolution and dispersion that occurs when TiC and Ti(O,C) powders are melted in contact with liquid iron based alloys with the ultimate aim of developing a liquid based route for the production of iron based TiC composites. Dissolution of TiC was found to occur for low carbon and low titanium contents in the iron. Dispersion of TiC was found to occur for high contents of dissolved carbon and/or dissolved titanium in the liquid iron. Under such conditions, excellent dispersions can be obtained as a result of wetting of the TiC by the liquid iron alloy.MST/1476

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.399

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractTo control austenite grain growth in high strength low alloy (HSLA) steels, additions of micro alloying elements showing chemical affinity for interstitial elements (C and N) are used. These elements have a significant effect on the mechanical properties of the steels. The mechanical properties of HSLA steels depend both on the amounts of the microalloying elements dissolved in the austenite and on undissolved carbonitrides. In the present work, a thermodynamic model enabling calculation of the composition of the austenite as well as the composition and quantity of the carbonitrides in HSLA steels containing up to four microalloying elements is presented. This model can be a useful tool in determining the optimum chemical compositions for steels as well as the heat treatment parameters required to maximise hardenability and to control austenite grain growth.MST/1471

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.406

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA thermodynamic model has been coupled with simplified kinetic theory, so that, subject to a number of assumptions, the one-dimensional parabolic thickening constantα1for allotriomorphic ferrite growing from austenite can be estimated as a function of temperature and composition. To do this, kinetic theory for ternary Fe–C–X systems (where X represents a substantial alloying element) is extended to multicomponent alloys. Values ofα1calculated assuming local equilibrium and paraequilibrium are compared. Consistent with recent calculations, the slope of theα1versus temperature plot is found to change abruptly on entry into the negligible partitioning local equilibrium regime, consistent with an increase in interfacial velocity. At very high supersaturations, the effect of the cross-terms in the diffusivity matrix appears to be small and only then can their effect be ignored. At temperatures below the Ae3′, the value ofα1, calculated assuming local equilibrium, is less than that calculated assuming paraequilibrium. Classical nucleation theory is used to model the ferrite allotriomorphs as discs growing from prior austenite grain boundaries. It has been demonstrated that the model developed here can reproduce the C-curve behaviour typical of those parts of the time–temperature–transformation diagrams that are due to allotriomorphic ferrite, provided the paraequilibrium mode of transformation is assumed to be operative. This work therefore suggests that in multicomponent alloys, the state of true local equilibrium does not exist at the advancing interface. Some problems associated with the paraequilibrium mode of transformation during reconstructive growth are discussed.MST/1452

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.421

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe effect of additions of the stabilising elements aluminium, niobium, titanium, and zirconium on the formation ofσphase in the experimental ferritic stainless steel Fe–39Cr–2Mo–2Ni (wt-%) has been studied. It was found that additions of titanium and zirconium increased the overall rate of formation ofσphase, whereas additions of aluminium and niobium decreased the rate. Precipitation ofσphase can be significantly retarded by making an addition of from 1 to 3%Al. The morphology of theσphase formed in these alloys is discussed. Time–temperature–transformation curves for some of the alloys are presented.MST/1567

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.437

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractTwo recently developed mechanical tests–a stress versus strain rate relaxation test and a constant displacement rate notched bar test–are described as a basis for measuring the effect of prior creep exposure on 2·25Cr–1Mo steel. These tests were used to monitor property changes resulting from prior creep, in both laboratory tests and also following service exposure in T-pieces of fossil plant main steam piping. Significant changes of properties were measured. These post-exposure tests may be used to monitor damage evolution during service and could form the basis of a life management methodology.MST/1501

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.443

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe effect of vanadium (0–4%) on the morphology and amount of eutectic and eutectoid carbides in high speed steels has been investigated using scanning electron microscopy and image analysis. It was found that vanadium promotes the formation of MC carbide and M2C carbide, but inhibits the formation of M6C carbide. In the vanadium free steels, the eutectic carbide consists solely of skeletal M6C. For each steel composition, there is a critical vanadium content at which the skeletal eutectic changes to lamellar eutectic and the critical value decreases as the molybdenum content of steel increases. The effect of vanadium on the total amount of eutectic carbide differs in tungsten alloyed and molybdenum alloyed high speed steels. Theδeutectoid has a rodlike morphology in tungsten high speed steels;δeutectoid is not present in Mo–W or molybdenum high speed steels. Increasing the vanadium content leads to an increase in the size of eutectic and eutectoid carbides.MST/1264

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.449

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractA study has been performed on an Al–7Mg–2Cr (wt-%) rapidly solidified alloy as a candidate for engineering applications requiring low density and high strength. The objective of the work was to investigate the development of microstructure during extrusion with respect to the consolidation conditions used and this was achieved by employing a combination of X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The rapidly solidified powder was found to be cellular in structure with drastic segregation of magnesium during solidification, which resulted in a heterogeneous distribution of magnesium rich intermetallics in the as atomised condition. However, it was observed that the atomisation process had successfully prevented the formation of coarse chromium containing intermetallics. Owing to the stability of a ternary chromium containing phase at the lower consolidation temperatures used (450°C) the severity of this inhomogeneity was reduced and the desired homogeneous distribution of chromium rich intermetallics in a magnesium rich solid solution was produced. The mean dispersoid diameter increased with extrusion temperature, as did the volume fraction of dispersoids, this being a result of the rapid increase in the diffusivity of chromium in aluminium over the temperature range employed for consolidation. Owing to a high dispersoid density, the substructure formed by dynamic recovery during deformation was refined, with the extruded material exhibiting subgrains of the order 0·4–1·0μm mean diameter. The consolidation temperature that yielded the optimum microstructure was found to be 500°C.MST/1488

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.455

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

摘要:

AbstractThe calculation of the temperature field T(r) in a heat treated cylinder requires a knowledge of the heat transfer coefficient h(Ts) which may show a highly non-linear dependence on the surface temperature Ts. Since h(Ts) can very often not be explicitly determined, measurement of a temperature Tinear the surface is employed. As a result the analysis becomes an inverse (‘ill posed’) problem which cannot be handled using standard finite element codes that are applicable only to direct problems. By implementing a procedure for an explicit estimation of the surface temperature Tsthe problem can be overcome via two direct calculations. Diagrams are presented for calculation of both the surface temperature Tsand the heat transfer coefficient h(Ts). The method is applied to the investigation of a duplex steel cylinder which is quenched in cold water. The accuracy of the method is discussed and the complex nature of h(Ts) is demonstrated.MST/1497

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.468

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor

ISSN:0267-0836    

DOI:10.1179/mst.1992.8.5.475

出版商:Taylor&Francis    

年代:1992

数据来源: Taylor