摘要:

AbstractThe effects of the addition of rare earth metals on the electrical conductivity and mechanical properties of commercial purity aluminium have been investigated both in the laboratory and in industrial trials. The electrical conductivity of commercial purity aluminium is increased by about 1% on the international annealed copper standard by the addition of lanthanum, and both its tensile strength and elongation are improved considerably by the addition of cerium. Investigation of the microstructure of the alloys containing rare earth metals shows that the apparent improvement in the electrical conductivity of commercial purity aluminium is caused by a decrease in the solid solubility of impurities in the aluminium.MST/2032

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.933

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe effect of solution treatment temperature on both the morphology of grain boundary carbides and the creep rupture behaviour of Inconel alloy X-750 has been investigated. Solution treatment at 1050°C led to precipitation of Ti/Nb carbide along grain boundaries, and as a result the formation of chromium carbide during subsequent aging treatment was considerably affected. This led to changes in the morphology of the grain boundary carbide and reduction in the width of‘clear’zone. This modification in the morphology of grain boundary carbide reduced the creep resistance of the alloy, leading to a reduction in rupture lifetimes, whereas strains tofracture were unaffected.MST/1981

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.936

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe design and development of the future generation of nickel base superalloys for the demanding environments of rocket engines should be based on the metallurgical and structural characteristics of theγ′phase. The distinctive features of this phase (e.g. strength, stability, size, shape, amount, distribution, uniformity, and order) can be controlled when a superalloy is appropriately designed and subsequently processed by an innovative solidification processing method. This concept has been successfully applied in the design and development of a superalloy. The resulting microstructure is almost perfect requiring no further treatment or processing.MST/1954

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.941

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe thermal and thermomechanical behaviour of the relaxation of the residual stresses of a shot peened Astroloy superalloy under tensile cyclic loads has been evaluated by X-ray diffraction and investigated. The stress relaxation under purely thermal conditions (550 and 650°C) and thermomechanical conditions (pulsating tensile loading at 650°C) as afunction of the exposure time is presented. The purely thermal relaxation is interpreted by annihilation and reorganisation of the crystalline defects induced by shot peening, whereas the mechanical relaxation is linked to cyclic plasticity of materials. In consequence, the thermomechanical relaxation is essentially due to the complex mechanism of the concurrent thermal and mechanical effects. A model is used to predict the residual stresses induced by the specified shot peening conditions and their relaxation under the specified thermal/thermomechanical conditions.MST/1963

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.947

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe influence of vanadium addition on the microstructure of high carbon steels has been investigated. A careful examination of the initial stages of austenite decomposi~ion has been made, using a range of high resolution metallographic techniques. It has been confirmed that vanadium addition results in the formation of grain boundary ferrite films, even in the eutectoid composition range. It is argued that this ferrite is the product of eutectoid transformation, and is not proeutectoid ferrite. This is because the first event is the nucleation of carbide particles along the grain boundaries. These carbides have been identified mainly as cementite. The presence of vanadium appears to change the morphology and distribution of the grain boundary cementite, so that rather than forming a grain boundary network, the cementite occurs in the form of a high density of small discrete particles along the boundaries. It is proposed that this occurs because vanadium increases the driving force for cementite nucleation. The formation of the grain boundary cementite depletes the surrounding region of carbon and encourages the formation of ferrite, but because of their discrete and fine dispersion, the cementite particles are engulfed by the more voluminous ferrite phase. In such regions, the onset of afully cooperative growth regime is delayed. Pearliteforms later at the ferrite/austenite interfaces.MST/1923

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.955

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA series of highly ductile, high strength steels exhibiting transformation induced plasticity due to retained austenite was developed by varying the carbon content in the range 0·01–0·4 wt-% in 5 wt-%Mn based steel. For up to 0·l%C the mechanical properties are insensitive to cooling rate after intercritical heating, but afurther increase in carbon content causes a large sensitivity to the cooling rate, owing to carbide precipitation occurring during slow cooling. By suppressing this carbide precipitation with water quenching after the intercritical holding, an excellent combination of tensile strength (1580 MN m−2) and uniform elongation (21%) was attained at 0·3%C in this series.MST/1964

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.964

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractCrack initiation behaviour of low carbon, manganese steels (containing ferrite, pearlite, and martensite) during wire drawing, was investigated to identify the crack initiation site. The results demonstrated that crack initiation mechanisms were similar to those of ferrite–martensite dual phase steels, at a low drawing strain. Crack initiation by interface decohesion was mainly observed at globular martensite islands or the tip of elongated martensite islands, whereas, that by shear fracture was preferentially observed at elongated martensite islands. Crack initiation by the decohesion of ferrite/martensite interfaces was more frequently observed than that by shear fracture of martensite islands at a low drawing strain. As the drawing strain increased, small martensite islands and other areas such as pearlite/martensite interfaces and the interfaces of pearlite nodules could participate in crack initiation. The results show the importance of avoiding the presence of martensite in order to reduce the incidence of crack initiation during wire drawing.MST/1868

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.971

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe increased use of microsoldered circuits has brought with it concern over the reliability of the Pb–Sn solder joints in such assemblies. It is well known that bulk samples of the eutectic Pb–Sn alloy solidify as a lamellar eutectic. This has often been assumed to be the microstructure of considerably smaller volumes of the same alloy, although studies of atomised drops in the Pb–Sn and other systems have shown that non-equilibrium structures commonly develop in alloy systems during the solidification of small volumes. In the present work the solidification of small volume truncated sphere flip-chip microsolder bonds was studied using differential scanning calorimetry of the arrays of bonds, and the microstructures were assessed. Cooling traces obtained using differential scanning calorimetry revealed under coo lings up to 31 K before solidification, although the integrated solidification exotherm is insufficient to encompass the solidification of the entire array of bonds examined. Metallographic examination revealed non-equilibrium microstructures, and none of the bonds examined contained a lamellar eutectic structure. This is attributed to the bonds solidifying via a metastable reaction, involving the nucleation of a lead rich phase which enriched the remaining liquid in tin, resulting in a final microstructure of massive lead dendrites in a pure tin matrix.MST/2007

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.977

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe parallel heat welding process has been proposed recently as an effective method of reducing process induced residual stresses. Extensive test data have been provided by previous authors to prove the efficacy of the process. To examine the feasibility of theoretically analysing the residual stresses in the parallel heat welding process, finite element analyses have been carried out and compared with the results obtained by previous authors.MST/1927

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.981

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA finite difference model has been developed to study the effects of polymer degradation on the temperature of the liquid metal during the formation of the casting in the expendable pattern casting process. The model has been used to estimate the endothermic losses in the liquid metal during the mould filling process. The calculations have been conducted for pure aluminium and a commercial aluminium alloy. The results indicate that the temperature of the metal front decreases continuously during the formation of the casting. The degradation of the polymer establishes thermal gradients in the bulk of the casting of the order of 2–2·5 K cm−1. Thermal gradients as high as 50 K cm−1may be achieved in a zone near the metal front. The heat transfer coefficient at the metal/mould interface has been estimated to be 420 Wm−2K−1. The model suggests that the thickness of the gas layer at the metal front is negligibly small. The model confirms the experimental observation that a large fraction of the polymer is converted to a viscous residue during the thermal degradation of the polymer. The data from the model are in good agreement with experimental resultsfor a variety of conditions.MST/1922

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.11.986

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor