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espanolEn este trabajo se estudia la posibilidad de preparar aleaciones de alta entropia del sistema Al-Sc-Ti-V-Cr. Para ello se han seleccionado los elementos y la composicion utilizando los criterios conocidos y disponibles en la literatura y se han preparado mediante fusion por arco tres aleaciones con contenidos que varian entre el 10 y 35 at.%. Las tres aleaciones tienen una microestructura dendritica bifasica similar, siendo las dendritas una solucion solida bcc enriquecida en Ti, V o Cr. El escandio aparece unicamente en el espacio interdendritico formando el intermetalico Al2Sc. La dureza de las dendritas crece con el contenido en Ti y se hace menor a medida que es mayor el contenido en Cr. Ademas, la tenacidad de las aleaciones depende de la dureza de las dendritas siendo esta mayor cuanto mas blandas son las dendritas. Los resultados obtenidos demuestran que ni los criterios empiricos utilizados ni los calculos mediante THERMOCALC permiten predecir la formacion de una unica solucion solida ni la naturaleza de las fases observadas experimentalmente. EnglishThe feasibility of preparing high entropy alloys in the Al-Sc-Ti-V-Cr system has been evaluated taking into account the different criteria reported in the literature. Based on such criteria, three Al-Sc-Ti-V-Cr alloys were chosen with contents of each element varying from 10 to 35 at. %, and prepared by arc melting. All alloys exhibit a two-phase dendritic microstructure, with the major dendritic phase being a bcc solid solution enriched in Ti, V, or Cr. Scandium is strongly rejected from the dendrites towards the interdendritic regions to form Al2Sc in the three alloys. The bcc solid solution dendrites become harder with high Ti content and lower with high Cr content. The toughness of the alloys depends on the hardness of the dendrites, with alloys with harder dendrites becoming more brittle. The results indicate that neither empirical criteria used nor THERMOCALC calculus tool can predict properly the formation of a single solid solution nor the nature of the existing phases respectively.

The goal of the Complex Trait Consortium is to promote the development of resources that can be used to understand, treat and ultimately prevent pervasive human diseases. Existing and proposed mouse resources that are optimized to study the actions of isolated genetic loci on a fixed background are less effective for studying intact potygenic networks and interactions among genes, environments, pathogens and other factors. The Collaborative Cross will provide a common reference panel specifically designed for the integrative analysis of complex systems and will change the way we approach human health and disease.

The cast-in network of continuous Laves phase in a Fe-15%Al-5%Nb alloy has been converted to a dispersion of coarse Laves phase particles by high temperature forging, and the room temperature and high temperature deformation behaviour examined. The material shows good room temperature tensile ductility and good creep strength at temperatures up to 700 °C. The good high temperature strength is explained by the refinement of substructure by the dispersion of Laves phase particles and load and strain partitioning between the stiff and hard phase and the softer matrix. The relatively coarse microstructure is expected to be highly stable against coarsening at high temperatures, which should allow retention of creep properties even for long exposure times. © 2012 Elsevier B.V.

The microstructure and mechanical behaviour of an Al-Cu-Li alloy has been examined after processing over a wide range of conditions involving severe deformation at elevated temperatures with prior or subsequent heat treatments. Dislocation cellular or subgrain structures are obtained, with varying degrees of precipitation. High strength, as well as poor ductility, can be correlated with the presence of a high density of fine T1 phase precipitates, with the dislocation substructure playing a smaller role. Careful control of processing conditions allows a suitable combination of good strength with ductility to be obtained. © 2011 Elsevier B.V.

Recovery and recrystallization have been examined on annealing Fe3Al alloy initially cold rolled to strains in the range 0.47-3.8. The cold worked microstructure is composed of poorly recovered dislocation cells of submicron size and lying in orientations near {001} 〈110〉 and {111} 〈110〉. A large drop in hardness accompanies recovery on annealing, as dislocation cells change to subgrains with lower dislocation density, with the hardness further falling slightly during recrystallization. Recrystallization occurs readily in regions with {111} 〈110〉 orientation but more slowly in the rotated cube oriented regions. Grain size of fully-recrystallized material decreases at high strain and for low annealing temperatures, but is always larger than several microns. Strength and ductility combinations are greatly increased for materials of submicron cell/subgrain microstructure. © 2010 Elsevier B.V.

The microstructure of a cast Fe-35% Ni-20% Al alloy has been examined and changes occurring on annealing examined in relation to the ternary equilibrium diagram for these conditions. Significant changes occur with various precipitations inside the initial dendritic cast structure. As cast material is brittle due to cleavage across the B2 regions, despite the presence of ductile fcc interdendritic phase, precipitation on annealing softens the material and allows notable room temperature ductility. © 2006 Elsevier B.V. All rights reserved.

The creep behaviour of an Fe-Al-Zr alloy has been examined at 700 °C and compared with the behaviour of an Fe-Al-B alloy, as well as with previously reported creep data. The Zr-containing alloy is strengthened by the formation of Fe-Zr intermetallic precipitates during high-temperature exposure, which makes this alloy about as strong under such creep conditions as any iron aluminide previously examined. © 2007 Acta Materialia Inc.

An Al–Mg–Si alloy was annealed to various solutionized and aged states and was then severely plastically deformed by equal channel angular pressing (ECAP). These materials were subsequently annealed for a range of times and temperatures to induce precipitation, dislocation recovery, and grain growth, with changes of mechanical behavior followed by tensile testing. Precipitation of excess solute was seen to occur in all cases, independent of the initial heat treated state, but the particles present appear to play only a small role in stabilizing the deformation substructure, at least until significant particle and grain coarsening has occurred, when discontinuous grain coarsening can be provoked. The strength of materials is examined, and the respective contributions of loosely arranged dislocations, many grain boundaries, and dispersed particles are deduced. It is shown that dislocation strengthening is significant in as-deformed, as well as lightly annealed materials, with grain boundary strengthening providing the major contribution thereafter, Comunidad de Madrid (CAM) under Contract No. 07N/0087/2002

Equalchannelangularpressing (ECAP) is a materials processing method that allows very high strains to be imposed, leading to extreme work hardening and microstructural refinement, with minimal change of external sample dimensions. It offers possibilities of good mechanical properties, such as high strength and ductility, while allowing flexibility of choice of alloy composition for better corrosion behaviour, lower materials costs, and so on. The microstructure of an Al–3 wt.% Mgalloy is examined after processing by ECAP as well as its evolution during subsequent heat treatments for precipitation, recrystallization, or grain coarsening. Fine microstructures are produced by deformation which coarsen steadily on annealing. The nature of the grain boundaries after deformation and after annealing, as well as the grain sizes obtained, is reported. It is interesting to consider to what extent such heavy-deformation processing offers the possibility to achieve extremely fine grain sizes (towards the nano-scale) by the control of alloy composition, deformation conditions, and subsequent heat treatments, We should like to thank J. Chao for assistance with the ECAP processing and C. Moreno for X-ray texture measurements

Previous studies of crystallization in Al-based glasses show the early appearance of many nano-sized, pure Al crystals which thereafter grow much more slowly. The present study extends such annealing treatments and examines the early appearance of nano-sized Al crystals and their subsequent growth to very large sizes before, eventually, other intermetallic phases appear. The growth of the Al crystals to very large size appears to take place by a spherulitic destabilization of the Al crystal-glass interface and the formation of a glass-Al mixture. Changes of mechanical properties are discussed in terms of the structural changes. © 2003 Elsevier B.V. All rights reserved.

Trabajo presentado en el 9th International Symposium on Metastable Mechanically Alloyed and Nanocrystalline Materials (ISMANAM), celebrado en Seúl (Corea del Sur), del 8 al 12 de septiembre de 2002, ECAP (Equal Channel Angular Pressing) is a materials processing method that allows very high strains to be imposed, leading to extreme work hardening and microstructural refinement. The microstructure of an Al-Mg alloy is examined after processing by ECAP as well as its evolution during subsequent heat treatments for precipitation, recrystallization, or grain coarsening. Fine microstructures are produced by deformation which coarsen steadily on annealing. The grain boundaries present after deformation as well as after annealing are generally of very low angle misorientations, and different textures are obtained than after heavy deformation by conventional deformation processing. Much of the strengthening observed can be explained by Hall-Petch strengthening, with additional strengthening due to the high dislocation density of the deformed state.

We report the evolution of texture and microstructures during thermomechanical processing of roll compacted Fe-40A1 (at.%) sheets produced from water atomized powders. The oxide films present on the surface of the powder are transformed into discrete particles due to multiple cold rolling steps, and serve to pin grain boundaries leading to improved strength and ductility. In addition, oxide particles limit the grain growth when the sheets are exposed to temperatures in the range of 1000-1200 °C. The carbon present in the alloy remains in solution during the roll-anneal processing steps, but is precipitated as fine perovskite particles on ageing. Interestingly, FeA1 sheets manufactured by roll compaction followed by cold rolling and annealing treatments exhibit only very weak textures in the sheets with no differences between sheet centre and surface detected. © 2002 Elsevier Science B.V. All rights reserved.

The softening produced by the microstructural instability of the a TiAl intermetallic alloy containing three phases was examined. The lamellar microstructure exhibited faster softening kinetics than the globular one due to transformation taking place between the α2 and B2 phases. The globular structure softened by a coarsening/dissolution process of the respective B2 and and α2 globules initially present.

The hardening produced by quenching from high temperatures, and the evolution of hardness during subsequent low temperature annealing of a Fe-40Al-0.4C alloy prepared in strip form, 0.2 mm thick, by a powder rolling procedure starting with water atomized powders were examined. The composition of the material is Fe-39.2Al-0.4C-0.02B-0.19Mo-0.86O-0.05Zr (atomic %), with Zr and B are in the form of large dispersed boride particles, Mo in solid solution and O as coarse (50-500 nm) uniformly distributed oxide particles. These insoluble dispersoids are sufficiently coarse and widely spaced that they are not expected to play a major role in influencing C and vacancy solution and precipitation and neglecting the small amount of Mo solute.

In conventional metallurgy it is well accepted that preferred crystal orientations in a polycrystalline material can have significant effects in modifying properties, with notable examples found in γ-γ′ superalloy components and Fe(Si) transformer sheets. The same effects clearly should be obtained in intermetallics, but this aspect has hardly been considered until recently. The influence of textures will be examined in iron aluminide and in γtitanium aluminides. The first compound is highly elastically anisotropic and plastically relatively isotropic. The second compound is elastically more isotropic and shows severe plastic anisotropy, both as single phase γTiAl and in the more common two-phase (γ+α2) form. Control of texture and of its uniformity throughout a component can have a major effect on its response to mechanical stresses.

The corrosion behaviour of an Fe3Al-base intermetallic compound with different crystal structures in a chloride containing solution has been investigated. The corrosion current densities of this intermetallic were independent of the material crystal structure showing a passive state stable with time. These corrosion rates were of the same order of magnitude as for 316L stainless steel. The pitting corrosion resistance evaluated by means of cyclic anodic polarization curves was high for all different states. Amongst the different crystal structures of this intermetallic alloy, the two ordered states present the lowest pitting probability. This Fe3Al intermetallic shows higher pitting corrosion resistance than the 316L stainless steel but its capacity for repassivation is lower. A damaging factor of influence on the pitting corrosion behaviour is the presence of non-metallic inclusions on the surface which reduce the pitting corrosion resistance by almost a half. © 1999 Elsevier Science Ltd. All rights reserved., This work was carried out under the umbrella of CEASI, Iron Aluminides program. The authors thank Shell Research Laboratories, Arnhem for the kind supply of material, and CICYT (Spain) for financial support under projects MAT95-0249-CO3-01 and MAT95-0796.

Crystals of trimethylammonio-P,P-diphenylphosphinamidate hydrate, Me3NNP(=O)Ph2 ⋅ H2O, are held together by hydrogen bonds which link two Me3NNP(=O)Ph2 and two water molecules to form a centrosymmetric O4H4 ring belonging to graph set R2 4(8). Each P=O oxygen atom can thereby act as acceptor to two hydrogen bonds, rather than to only one, as in the two-fold symmetric P=O⋅⋅⋅H–O–H⋅⋅⋅O=P motif commonly found in phosphine oxide hemihydrates. The unusual P–N bond in Me3NNP(=O)Ph2 is short enough 1.614(3) Å to indicate some multiple character.

The high strains achieved during high temperature deformation of a Ti-Al rolled sheet have been evaluated by following the microstructural evolution of tensile samples tested along the transverse and rolling directions. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations have confirmed that in both types of samples extensive twinning activity occurs during deformation at temperatures of 700 and 800°C but not at 900°C. Microstructural refinement occurs by subdivision of the grains either by the twin interfaces or by subgrain formation followed by recovery/recrystallization processes. The lower strains achieved in the samples deformed along the transverse direction are a result of a more inhomogeneous microstructure due to the different deformation mechanisms involved, that include activation of superdislocations at high strains.

Refining grain size to the nanocrystalline level has been suggested as a way of improving strength while enhancing ductility and toughness. In the present study, nanocrystalline bulk FeAl has been prepared by mechanical alloying and hot forging. Powders quickly reach a state of partial order during milling, and low temperature annealing is sufficient to chemically homogenize and give full order. Contamination during milling leads to the formation of carbide and oxide particles, which stabilize fine grains during heating. Bulk materials show grain sizes of 20 nm to 100 nm depending on the consolidation temperature. Hardness and compression strength show little change over this grain size range. Fracture toughness stays high down to moderately small grain sizes, falling only for consolidation at the lowest temperatures. There appears to be a reasonable range of fine grain sizes (40-100 nm) where good interparticle bonding and high densities can be achieved leading to good strength and toughness.

Antiphase boundaries (APBs) in a rapidly solidified Ni3Al alloy have been examined by transmission electron microscopy in the as-solidified state and after annealing. Dark field imaging suggests that the APB thickness increases with temperature during annealing and that a dark, disordered phase appears at temperatures above about 800°C. The boundary region at high temperatures has a chemical composition close to that expected from the phase diagram for the disordered phase, namely containing about 15 al.% Al. Examination of APBs by high-resolution electron microscopy does not confirm the disorder. however, and the so-called disordered regions showing dark contrast may in fact be caused by the significantly modified chemistry of these ordered regions. It is not clear whether disorder may form at high temperature when the average alloy composition enters the two-phase ordered+disordered region, or whether simply extensive segregation takes place to the APB without the true appearance of a second, disordered phase. Similar effects occurring at grain boundaries would lead to a structure dependent on both composition and temperature, with the mechanical behaviour of the material depending on the structural state.

There is considerable interest in the development of high strength Cu-base composites with high conductivity for applications such as high field magnets 1, 2, 3, 4, 5, 6 and 7, and essentially two alloy types have been examined, where a phase distributed in the Cu matrix during solidification is transformed into fine filaments during cold working of the material to sheet or wire 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20. Some of these are Cu-Ag alloys 8, 9, 10, 11, 12, 13 and 14, with the Ag present as inter-cellular or inter-dendritic phase, or as part of a Cu-Ag eutectic. The other alloys are of the Cu-bcc element type 15, 16, 17, 18, 19 and 20, where the bcc element (Cr, Fe, Nb, etc.) is present as primary dendrites after solidification. For Cu-Ag alloys, it has been shown that the second phase Ag is transformed into fine filaments or rods during working, and it is the reduction of the distance between such matrix-Ag interfaces that is responsible for the increased hardening 8, 12 and 14.

Strong yield point effects are observed on reloading iron aluminides after deforming, unloading for a short time at low temperatures, and reloading. Such yield point effects are shown to be essentially independent of material microstructure and occur so quickly at room temperature that it is unlikely that diffusional effects play any role. The most important factor determining the extent of yield point stress change at a given stress and temperature condition seems to be the Al content with aluminides of composition near FeAl showing very strong yield drops and aluminides of composition near Fe3Al hardly showing any yield point effects. The likely cause of the yield point effects is dislocation locking occurring during unloading, which is believed to be due to core transformation–dissociation at the a/2〈111〉 dislocation cores.

Neutron powder diffraction measurements have been carried out in situ from room temperature to about 100°C in Fe28Al (28 at.% Al), Fe32.5Al (32.5 at.% Al) and Fe28Al15Cr (28 at.% Al, 5 at.% Cr) alloys. X-ray diffraction and TEM studies provided supporting information. The data were analysed to obtain information about the temperature dependence of the DO3 and B2 long range order parameters, the location of the Cr atoms and their effect on the ordering energies, and on the vacancy formation and migration properties in Fe28Al and Fe32.5Al alloys. The location of the ternary alloying addition in DO3 and B2 ordered Al-rich Fe3Al is shown to be consistent with considerations of interatomic bond energies.

The mechanical behaviour of an alloy based on Fe40Al prepared from mechanically alloyed powders was examined over a wide temperature range in the fine-grained, as-extruded state as well as after recrystallizing to a large-grained state. While the fine-grained material was strong and reasonably ductile at room temperature, in contrast with the weaker and more brittle large-grained material, at high temperature the strength fell to low values, similar for both materials. This behaviour is interpreted in terms of a contribution to strengthening due to the particles present, by Orowan hardening at low temperatures and by dislocation-particle interactions at high temperature, a contribution due to the grain size, which can harden at low temperatures and soften at high temperatures, and a contribution due to the matrix. The room temperature ductility seems to be dependent mostly on the grain size, since fine grain sizes can inhibit brittle crack formation.

The mechanical properties of an Fe-28 at.% A1 alloy have been examined in detail from room temperature up to 700°C. The solute additions contained in this alloy lead to higher strength at all temperatures than is shown by the binary alloy. These high strengths are associated with dissociated imperfect superdislocations from room temperature up to a stress peak. The anomalous stress peak is found at 500°C, somewhat below the temperature range where disordering of D03, order to the B2 ordered state occurs and the Burgers vector of the dislocations present changes from 111 to 100. The reason for the anomalous peak, the locking of the 111 superdislocations and the eventual change to 100 dislocations is a local climb-locking process operating on the 111 superdislocations.

The influence of annealing treatments over a range of temperatures encompassing the critical ordering temperature for the B2-DO3 change and inducing recovery and recrystallization have been examined for a deformed alloy based on the Fe3Al composition. The initial ordered state before heavy deformation plays no role on subsequent recovery and recrystallization, essentially because the heavy deformation destroys the prior order. Recovery occurs faster relative to the rate of recrystallization at higher temperatures. The extended period at lower temperatures where poorly recovered structures remain allows grain nucleation mechanisms to remain activated, in contrast to higher temperature situations where grain nucleation slows as grain growth dominates recrystallization. This evolution is slightly enhanced at lower temperatures as DO3 order appears, and leads to finer final grains after such lower temperature anneals. There is no evidence to indicate that dislocations influence the rate of ordering of this material.

The cubic titanium trialuminide alloys studied previously show limited ductility and toughness, which can be related to the difficulties of dislocation emission, multiplication and mobility and to the excessively high energies of faults associated with the dislocations. The present study examines several new alloys chosen in an attempt to reduce these fault energies and thereby improve the mechanical properties. The region of single phase L12 material is unfortunately so limited that only minor changes in composition are possible before second phases form and precipitation hardening occurs. Over the range of compositions of the L12 phase evaluated there are generally only small changes in fault energies. These changes, as well as the changes in dislocation configurations seen, may be rationalized in terms of the instability of the matrix towards the particular second phase forming.

Iron aluminides containing about 28 at.% Al have the D03 ordered structure in equilibrium below about 550°C and the B2 ordered structure above that, with the disordered state existing at temperatures above about 900°C. The transition from the D03 state to the B2 state has been examined for several alloys containing various alloying additions using X-ray diffraction, differential scanning calorimetry and in situ transmission electron microscopy. Some of the alloying additions investigated lead to changes in both the kinetics of ordering and disordering as well as modifying the temperature range of stability of the D03 state. While the alloys examined lose most of the D03 order at the critical transition temperature, there is clear evidence of remnant long range order for temperatures up to 100–200°C above this critical temperature, at least for some of the more complex alloys. The retention of this order may be caused solute remaining on specific lattice sites after disordering of the majority Fe and Al atoms.