摘要:

AbstractThe acoustic microscope has the advantage of being able to detect microstructurally short cracks and to locate crack tips exactly. However, due to scattering of the sound waves and fringe interference effects, the surface texture relationship with the crack tip is not so clear. The optical polarising microscope on the other hand can clearly exhibit surface texture following a specimen surface treatment such as anodising of an Al–Li alloy. However anodising produces a thin layer of a brittle oxide on the surface of the specimen which will reduce the accuracy of the acoustic microscope in exactly determining the crack tip position. Whereas the acoustic microscope does not need any treatment of the specimen surface, and so does not affect the material properties, some materials such as carbon steels and anodised aluminium alloys can be very sensitive to corrosion pitting due to the lens water couplant. It follows that both of these microscopes have complementary advantages and disadvantages and therefore combining both microscopes in the same facility can permit more data to be gathered on the behaviour of very small fatigue cracks and their interactions with microstructural barriers. The present paper reports on these developments using the SIRIUS acoustic microscope facility.MST/2048

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.265

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe phase equilibria between the titanium aluminides, Ti3Al and TiAl, and V have been investigated in the temperature range 1473–873 K. Microstructures were characterised using light, scanning electron, and transmission electron microscopy and the nature of the phases present was established via X-ray diffractometry, electron diffraction, and energy dispersive X-ray analysis. A series of isothermal sections have been determined and are compared with those obtained in earlier studies. Ordering of the high temperature bccβphase to a simple cubic B2 (β2) structure was observed: the ordering temperature was found to decrease with increasing V content, whereas the opposite effect was observed with Al. The effect of oxygen is to stabilise theαphase and to shift theα2+β2+γfield in the V rich direction. The lattice parameters ofα2andβphases decrease with additions of Al and V: empirical equations have been developed to predict these changes.MST/1881

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.272

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe textures of austenite and ferrite in a duplex steel X2CrNiMoN225 were studied via X-ray and electron diffraction. This latter method was also used to determine the orientation difference distribution of grains and phase boundaries. The mechanical properties, e.g. hardness, microhardness, ultimate tensile strength, etc. were also measured. It was found that the hot rolled material was only partially recrystallised. Even after annealing at 1030°C the austenitic phase was not fully recrystallised. In addition, no change in texture was observed after aging in the two embrittlement ranges. Tensile deformation changed both textures due to plastic deformation in the two phases. During deformation at 45°to the rolling direction, rigid rotation of the phase particles may have contributed to the observed texture changes. The grain boundary distribution function revealed a large amount of low angle boundaries in both phases.MST/1396

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.289

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractPure Ta has been cold rolled and annealed at various temperatures. The crystallographic textures were studied by measuring X-ray pole figures and subsequently calculating the orientation distribution function. The microstructure was investigated via optical microscopy. The rolling textures were explained by dislocation glide on {110}〈111〉, {112}〈111〉and {123}〈111〉glide systems. Corresponding simulations were carried out using relaxed constraints Taylor theory. Interpretation of the annealing textures was carried out via continuous recrystallisation in the case of weak deformations and temperatures and via discontinuous recrystallisation for higher rolling degrees and temperatures, respectively.MST/1886

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.299

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe decomposition of a duplex stainless steel during aging at 600°C has been investigated using analytical transmission electron microscopy with the intention of elucidating the nucleation sites of the new phases arising from ferrite decomposition. The first transformation product to be formed is M23C6. This carbide, having a cube–cube orientation relationship with the parentγgrain, is found only on certainγ/αboundaries and its nucleation is shown to be strongly dependent on theγboundary plane of theγ/αinterface. Chromium depletion in the vicinity ofγ/αboundaries caused by M23C6precipitation initiates theα→γtransformation by migration of existingγ/αboundaries. Another mechanism for this bcc→fcc phase change is observed through the growth of Widmanstättenγplates intoα. Precipitation ofσbegins after M23C6formation has stopped. The existence of M23C6onγ/αboundaries is crucial toσformation because the majority ofσparticles are found to nucleate on nodes in migratingγnew/αboundaries caused by M23C6particle pinning. Another less common nucleation site forσis migratingγnew/αboundaries. Theσparticles nucleated on either of the sites have the Nenno orientation relationship with the parentγ. In the latter stages, theσand newγconsume theαgrains via a cellular growth mechanism.MST/1905

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.306

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractExtensive interlamellar spacing measurements on directionally solidified Al–CuAl2eutectic alloys show that in this system the eutectic exhibits a limited range of spacings rather than a unique spacing during steady state growth at a constant velocity. The minimum spacing observed corresponds to the extremum spacing predicted by the Jackson–Hunt model. However, the maximum observed spacing is much less than the maximum spacing predicted by the theory. In this paper the assumption of a planar interface made by Jackson and Hunt is relaxed and the boundary element method is used to calculate the solute distribution for a curved interface. An iterative technique is used to calculate the maximum spacing for which a selfconsistent interface shape can be calculated for a range of velocities. This maximum selfconsistent spacing shows much closer agreement with the maximum observed spacing than that calculated on the assumption of a planar interface. The deepest point on the selfconsistent interface shape at the maximum spacing does not lie in a deep pocket. It is below the conjunction level but close to it.MST/1932

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.312

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA shape memory alloy powder was prepared using a mechanical alloying technique. Four stages of formation of the mechanically alloyed powder have been identified, namely, layered structure formation, deformation of the layered structure, disappearance of the layered structure, and the formation of alloyed powder. It was found from X-ray diffraction patterns that the alloyed shape memory powders started to form after mechanical alloying for 1·8 ks. Theγphase of the alloyed powders can be distinctively detected after 3·6 ks mechanical alloying. The shape memory effect has been observed in specimens prepared using this mechanical alloying technique. It was observed that a shorter diffusion time was required for the powder to be mechanically alloyed in comparison with conventional mixing.MST/1885

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.319

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe hot deformation of AA 6063 and AA 6005 Al alloys has been related to chemical composition and the microstructural evolution occurring during the various heat treatment procedures before extrusion. It was shown that a small addition of Mn significantly accelerates the homogenising process (transformation of the brittle platelikeβ-AlFeSi phase to the more roundedα-AlFeSi phase) which results in superior hot formability and ductility. The mechanical behaviour of Al–Mg–Si alloys during hot deformation can be explained in terms of a model of dislocations climbing around particles. Largeβphase particles increase initial work hardening rate and flow stress and impair hot ductility. The hot ductility of the material investigated via tensile testing was found to correlate with the density of particles covering grain boundaries. It was also shown that grain refinement in the billet leads to more uniform distribution of intermetallic constituents, which accelerates the homogenising process and improves the hot ductility. Full scale extrusion trials show that the results from hot formability tests in the laboratory correlate closely with the relative extrudability of the investigated alloys.MST/1877

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.323

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractTo explain a series of experimental data concerning low carbon, high manganese, microalloyed structural steels, a theory of cleavage fracture is presented, based on the assumption that cleavage initiation can occur in the ferrite lattice at the intersection of two slip bands, in the absence of brittle phases. The crack extension force acting on the propagating microcrack is controlled by the grain diameter d which, accordingly, is the microstructural parameter determining the tendency of the material to fracture. The cleavage fracture stressσcfis found to be strongly influenced by the amount of blunting produced during the stage of subcritical crack growth. Taking this effect into account,σcfis shown to depend on grain diameter according to a law of the type d−p, where p is close to 1/4.MST/1667

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.334

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractBoth the Larson–Miller and the Manson–Haferd parameters are used to extrapolate rupture data from high temperature creep. The first of these is in agreement with the theoretical equation for low temperature deformation only, and cannot describe the high temperature properties accurately. The second parameter has no physical basis. Starting from data taken from a theoretical stress–rupture time diagram, both extrapolation methods are tested. At the lower stresses the Larson–Miller method considerably overestimates the resistance of the material to rupture. Despite the lack of physical significance, the Manson–Haferd parameter coincidentally describes to some extent the complex deformation patterns due to the different deformation mechanisms, and is more reliable for high temperature predictions.MST/1882

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.4.340

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor