摘要:

AbstractThe present work was initiated in order to obtain a better understanding of the nucleation mechanism of cube oriented grains during recrystallisation of hot deformed aluminium. Investigations included: the stability aspect of cube oriented grains during deformation, a characterisation of cube oriented areas in the as deformed condition, and partly recrystallised states. Commercial purity aluminium, plane strain compressed at various deformation conditions, was investigated mainly using the electron backscattering pattern (EBSP) technique in a scanning electron microscope (SEM). The following deformation and nucleation pattern was observed: cube oriented grains present in the starting material remain orientation metastable during deformation and are smeared out to bands. The cube bands have a unique subgrain size distribution with a long tail towards large subgrains, making them potent nucleation sites. The observed preferred nucleation from cube bands surrounded by the S deformation texture component, is discussed both in terms of a microgrowth selection mechanism and differences in stored energy between the cube and S oriented regions.MST/3247

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.201

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractAmorphous titania particles (10–12μm in diameter) prepared by oxidation of metallic Ti in an aqueous solution of H2O2and ammonia werefound to be porous agglomerates of 0·25×0·08μm rodlike particles having a finer internal structure. The thermal treatment of the particles in CCl4can produce single crystal particles (10 nm in diameter) with no internal structure. This is thought to be due to the presence of CCl4in a supercritical state, and steric inhibition of CCl4between the primary particles during the treatment.MST/3072

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.211

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractFor near-αtitanium alloys IMI 834 and TIMETAL 1100 oxidation behaviour was investigated as a function of microstructure. Isothermal thermogravimetry was performed at 750°C for 100 h in air. The morphologies and compositions of the scales produced were examined using scaninng and analytical electron microscopy and X-ray diffraction to establish the nature of the scales. The oxidation behaviour of IMI 834 depends less on microstructure than TIME TAL 1100, but both alloys were found to be most oxidation resistant with lamellar, and least with globular structure. The weight gain depends on scale adherence which is generally better on IMI 834. Scale adherence is markedly influenced by the formation of Ti3AlN during oxidation.MST/3136

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.213

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA novel technique known as combustion assisted synthesis was utilised for the fabrication of titanium carbide + titanium boride reinforced titanium matrix composites. This technique resulted in a homogeneous distribution of rod like (TiB) and equiaxed (Ti2C) reinforcements in a fine grained (1–2μm) titanium matrix, with a clean matrix/particle interface. The deformation behaviour of the composites and the control sample of titanium were studied in the temperature range 298–873 K and strain rate range 2×10−5−2×10−2s−1. Tests indicated that the composites were more deformable in compression and the values of yield strength of the composites increased with volume fraction of reinforcements, being approximately×3–5 that of the control titanium. Fractographic analysis indicated that the composites failed in tension due to particle cracking, whereas the failure mode of the control titanium was dimpled fracture.MST/3255

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.219

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractAlthough metal matrix composite (MMC) layers have been successfully produced by a single laser track on aluminium alloys, a critical step in the application of this technique in industry is overlapping of the laser tracks to produce an MMC layer on specific areas of materials. The present work investigated overlapping laser tracks using prep laced SiC p and a mixture of SiCpand aluminium powder preplaced on AA6061 aluminium alloy surfaces, and describes the success achieved in both situations. The dependence of the surface smoothness on the overlapping technique, microstructures, and phases formed in the laser processing was studied. The effect of the spacing of two overlapped laser tracks is discussed and the laser processing conditions considered. In addition, post heat treatment on the laser glazed material was found to give rise to a significant increase in the hardness and the abrasive wear resistance of the MMC layer.MST/3236

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.227

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractMetallographic observations of steel samples transformed isothermally to lower bainite at temperatures well below the bainite start temperature have revealed that it is possible for separately nucleated platelets to coalesce during prolonged growth. The circumstances conducive to the coalescence process are discussed, and a mechanism is proposed to explain why a bimodal size distribution of plate thickness is sometimes observed for lower bainite and martensite.MST/3370

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.233

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractA critical investigation into the role of non-metallic inclusions in the nucleation of acicular ferrite in low alloy C–Mn–Ni weld metals was carried out using rapid in situ quenching, transmission electron microscopy, energy dispersive X-ray spectroscopy analysis, and dilatometric techniques. The relationship between the transformed acicular ferrite, the inclusions, and the chemical nature of the inclusions which had actually nucleated ferrite laths was examined in detail. By employing weld metals with either intermediate (200–350 ppm) or low (15–30 ppm) oxygen levels, the inclusion chemistry and nucleation behaviour of acicular ferrite in welds with different oxygen contents were compared. In addition, the influence of the [Al]/[O]ratio in lower oxygen content weld metals was also examined. It was found that the first acicular ferrite laths nucleated from the inclusions at both oxygen levels, and the chemical composition of the active inclusions varied considerably. The inclusions nucleated acicular ferrite by acting simply as inert substrates with the ability to reduce the free energy barrier to nucleation. The number and size distribution of the inclusions appeared to be the dominant factors; the thermal stress-strain fields and lattice disregistry were less important. The most favourable type of inclusions were within the size range 0·3–0·9μm for the higher oxygen content weld metals and 0·35–0·75μm for the lower oxygen level weld metals. A high [Al]/[O]ratio depresses the formation of acicular ferrite by increasing the soluble matrix aluminium content, which encourages extensive ferrite sideplate formation; the concurrent variation in inclusion chemical composition did not appear to influence the nucleation of acicular ferrite.MST/3209

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.237

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractThe present paper describes a study of the combined effects of velocity and applied electrochemical potential on the erosion of mild steel in an aqueous carbonate/bicarbonate slurry. The erodent used was alumina; the velocity was varied between 2 and 10m s−1and the potential between−1·0 and 0·2 V (saturated calomel electrode). Measurements were made of the erosion rate in the absence of corrosion (when the surfaces were cathodically protected), the instantaneous corrosion rate, and the overall erosion–corrosion rate. The results showed that the effect of velocity varied as a function of the applied potential. Velocity exponents were evaluated for the various erosion–corrosion conditions, and the trends in the variation of the exponents were discussed for each of the applied potentials. Criteria for the existence of erosion–corrosion regimes in aqueous environments were suggested, and were used to generate an erosion–corrosion map based on the experimental data.MST/3364

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.261

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractOver the past two decades there has been increasing interest in the use of the concept of a quality factor Q, introduced by Drouzy and co-workers, as a single parameter for assessing the‘quality’of Al alloys. This quality factor is defined as Q=σUTS+150 log E, whereσUTSis the ultimate tensile strength and E is the elongation, and has so far been used mainly for the description of the Al–7Si–Mg alloys A356 and A357. The current study was carried out to assess whether the concept could be extended to the higher strength Al–4·5Cu casting alloys A201 and A206. It was concluded that the quality factor does not apply to A201 and A206 in an analogous manner, and thus the concept is not transferable at the present time. It is recommended that the use of the quality factor for A201 and A206 be discontinued until it has been more fully investigated. In the meantime, an alternative definition, Q=σ0·2+kE, whereσ0·2is the 0·2% proof strength, as proposed in the present paper, seems useful and appropriate. This new definition may have wider applicability, but requires further investigation. The use ofσ0·2versus E maps is recommended to encompass the whole range of properties of interest to the designer. The area defined byσ0·2×E, and clearly shown on theσ0·2versus E map, is proportional to the energy required for ductile fracture. This is revealed to be over an order of magnitude greater in A201 than in A356 and A357 alloys.MST/3279

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.269

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor

摘要:

AbstractSemisolid metal (SSM) processing is a novel way of producing near net shape components by forming them in the semisolid condition. The potential of processing high melting point alloys, such as tool steels and Stellites, through the SSM route has previously been demonstrated, and this work also highlighted the necessity of uniform heating and partial melting of slugs before forming. Electromagnetic induction heating is a much more effective and versatile method for commercial production applications in this technology. A programme of computer modelling the induction heating and partial melting of high melting point alloy slugs, coupled with experimental verification, has been set up between EA Technology and the University of Sheffield. The aim of this paper is to demonstrate the agreement of experimental and calculated data, and show how once a model has been set up and verified, it can prove an extremely useful tool in providing the appropriate induction heating conditions for alloys whose thermal, electrical, and magnetic properties are known and determining sensitive features of the process.MST/3259

ISSN:0267-0836    

DOI:10.1179/mst.1996.12.3.274

出版商:Taylor&Francis    

年代:1996

数据来源: Taylor