ChCl-urea-NiCl_2-FeCl_3离子液体电沉积Ni-Fe合金

以ChCl-urea-NiCl2-FeCl3离子液体为电解质在Fe基体上电沉积得到了Ni-Fe合金镀层。循环伏安测试表明电沉积过程中由于金属Ni的生成诱导金属Fe发生欠电位沉积,从而实现了Ni-Fe合金的共沉积。同时研究了电流密度对镀层成分、形貌和耐蚀性能的影响,结果表明:电流密度由2mA/cm2增加到5mA/cm2时,合金镀层中Fe含量从10.74at%升高到39.21at%。当Fe含量为24.89at%时,镀层最为平整致密,耐蚀性能最好。此外,镀层的组成主要为FeNi3固溶体和Ni,还存在FeNi和Fe0.64Ni0.36合金相。     

通过离子掺杂剂界面偏析来提高氧化物弥散强化合金的机械性能

氧化物弥散强化钨合金(ODS-W)因具有显著提升的抗辐照能力、高温强度以及抗蠕变性能而展现出巨大的高温应用潜力.然而,分散在合金中的氧化物第二相颗粒容易在钨晶界处团聚并长大(甚至到微米尺寸),这大大抑制了它们对钨合金的强化效果.目前,如何有效细化和分散钨晶界处的氧化物第二相颗粒一直是人们面临的巨大挑战.在本文中,我们通...     

Effect of electronic energy dissipation on strain relaxation in irradiated concentrated solid solution alloys

The effect of energy deposition by energetic particles on Ni and two single-phase concentrated solid solution alloys (NiFe and NiCoCrFe) is investigated through combined experimental and modelling efforts. Damage evolution as a function of increasing ion fluence is monitored via elastic strain developed in the irradiated crystals. We show that damage produced from displacement collision cascades is sensitive to subsequent highly ionizing irradiation that the strain generated by elastic nuclear collisions undergoes partial relaxation upon high-energy irradiation. This finding indicates a change in the damage structure upon electronic energy deposition due to both predominant defect annealing and growth of small defect clusters. Strain relaxation, more pronounced in the alloys than in Ni, is ascribed to both higher thermal conductivity and weaker electron-phonon coupling in Ni.     

Equi-axed growth and related segregations in cast metallic alloys

Full-scale trials of DC ingots and laboratory scale directional solidification experiments have been performed to study the effect of grain structure on macro-segregation in industrial cast products. An Al alloy sheet ingot was cast with constant casting conditions (speed, superheat, cooling rate) except for the grain refiner: the first half of the ingot was non-inoculated, while the second half was inoculated. The results indicate that the extent and intensity of the centreline segregation is modified via the grain-refinement treatment: the finer the grains are, the more intense is the macro-segregation.

Numerical simulations of directional solidification of binary Al-Cu alloys have been carried out with the help of a 2D finite volume software which takes account of the movement of the liquid with respect to the solid in the mushy zone. It is possible to account for the segregation pattern of the directionally solidified ingots that exhibit columnar or coarse equi-axed grain structures. Contrarily, the intense segregation of the fine-grained ingots is not yet understood.     

Radiation-induced solute segregation in metallic alloys

The subject of radiation-induced solute segregation (RIS) in metallic alloys is reviewed. RIS manifests itself in several different ways, including diffusion to point-defect sinks (dislocations, grain boundaries, voids, etc.), which can induce precipitation in undersaturated alloys, as well as self-organization of solute clusters and precipitation in defect-free material. Diffusion in dilute and concentrated alloys is highlighted, as are theories of RIS that include new ideas on diffusion of complexes involving coupling between fluxes of point defects and of solute atoms. Many important experimental observations are presented, including up-to-date findings using atom-probe tomography, with special emphasis on solute segregation in austenitic and ferritic steels. Results from computational modeling and theory are also presented and discussed in light of experimental findings. Examples illustrating the factors affecting RIS are shown and some important outstanding issues that impact the current understanding of RIS are described and discussed.     

Time-dependent interfacial failure in metallic alloys

Time-dependent intergranular brittle fracture has now been studied experimentally in a number of alloy systems, and the generic features are becoming clear. Mobile surface-adsorbed elements are caused to diffuse inward along grain boundaries under the influence of a tensile stress, and this can lead to sub-critical crack growth by decohesion. Oxygen is found to play this role in nickel-base superalloys and intermetallics, as well as in a precipitation-strengthened Cu–Be alloy. Crack-growth rates lie in the range 10⁻⁷–10⁻⁴ m sec⁻¹. The same kind of cracking is found in steels treated so that free sulfur is able to segregate to the surface, as well as in Cu-Sn alloys, in which the embrittling element is surface-segregated Sn. The latter has been studied in bicrystals, and the importance of the variation in diffusivity with grain boundary structure has been documented. Hydrogen-induced cracking is a special case of an extremely mobile embrittling element and is responsible for much of the brittleness found in intermetallics. The effect of boron in retarding brittle behavior in Ni₃Al has been shown to result partly from its interaction with hydrogen. This is a prime example of how segregated solutes can be used to ameliorate the tendency for diffusion-controlled brittle fracture.     

Magnesium diffusion,surface segregation and oxidation in Al-Mg alloys

Auger electron spectroscopy (AES) has been used to follow the surface segregation behaviour of magnesium at the surface of Al-Mg alloys in the temperature range up to 600° C as a function of time. The evaporation rate of magnesium from the magnesium-rich surface has also been measured. The combination of the competing processes of segregation and evaporation has been treated theoretically and compared with the experimental measurements. The measured equilibrium surface enrichment of magnesium fell from a factor of 24 at 100° C to 12 at 200° C. At higher temperature the evaporation rate exceeded the segregation rate and the surface layer became magnesium-depleted. The data also lead to a low-temperature determination of the diffusivity of magnesium in aluminium. The same Al-Mg alloys have been heat-treated, within a similar time-temperature regime, in air. The oxide films have been composition-depth profiled using AES with ion sputtering, and measurements of the rate of oxide growth lead to information about the diffusivity of magnesium through the oxide films.On leave of absence from Laboratoire de Thermodynamique et Physico-Chimie Metallurgiques, ENSEEG Domaine Universitaire, St. Martin d'Hères, France.     

Microstructure,phase stability and properties of CoCr0.5CuxFeyMoNi compositionally complex alloys

Liquid-phase separation occurred in CoCrCu_xFeMoNi (x?≥?0.5) alloys when the mixing entropies are positive in our previous work. So in this work, CoCr_0.5Cu_xFe_yMoNi alloys are designed to investigate the microstructure, component phases and properties. FCC and BCC were detected in CoCr_0.5Cu_xFe_yMoNi alloys, accompanied with a topologically close-packed μ phase. A parameter, V_R, was defined, where V_R is the ratio of the volume fraction of BCC plus μ phases and that of FCC phase. The maximum strength and the ductility were obtained at the minimum V_R of the alloys, whereas the hardness increased with the increasing V_R. It can be presumed that the strange balance between strength, ductility and hardness is an indirect result of the degree of brittle failure.     

Coupled visco-mechanical and diffusion void growth modelling during composite curing

Most critical processing step during long fiber reinforced epoxy matrix composite laminate manufacturing is the polymerization stage. If not optimized, it gives birth to defects in the bulk material, such as voids. These defects are considered as possible sources of damage in the composite parts. The aim of this work is to model the evolution of void growth in thermoset composite laminates after ply collation (autoclave processes) or resin impregnation (RTM, LCM process). A coupled mechanical and diffusion model is presented to better predict the final void size at the end of polymerization. Amongst the parameter investigated, onset of pressure application and diffusive species concentration where found to have a major effect on void size evolution during curing process.     

Influence of vanadium on grain boundary segregation of phosphorus in iron and iron-carbon alloys

The influence of vanadium on grain boundary segregation of phosphorus has been studied in iron and iron-carbon alloys by means of fracture experiments in a scanning Auger microprobe. The emphasis here is to study the effects of vanadium on the interaction processes operative under circumstances when structure in the interior of the grain (in the present case carbide formation) and grain boundary segregation form simultaneously. It is emphasized that to predict and analyse the behaviour of an alloy, it is important to consider atomic interactions both at the grain boundaries and in the grain interior and that between the constituents and the grain boundaries. The study suggests that the principal determining factor in the scavenging or retardation of migration of phosphorus to the grain boundaries is whether vanadium is present in the combined form (say, carbide) or is available in solid solution form. When vanadium is present in solid solution form, grain boundary segregation of phosphorus is low because of the chemical interaction of vanadium and phosphorus. However, as carbon is increasingly introduced in the alloy, vanadium now preferentially reacts with carbon in view of higher interaction for carbon as compared to phosphorus. A consequence of this is the increase in the grain boundary concentration of phosphorus. In such a situation the presence of excess carbon in addition to what is stoichiometrically required to precipitate the entire vanadium as vanadium carbides, serves as a palliative with regard to the reduction in the intergranular concentration of phosphorus. This palliative behaviour is explained in terms of the sitecompetition model. An effort is also made to examine the behaviour of segregating elements in terms of whole range of probable interactions (both at the grain boundaries and in the grain interior) and chemical interaction energies.     

Bulk and porous metastable beta Ti-Nb-Zr(Ta) alloys for biomedical applications

In this work, metastable beta Ti-Nb-Zr(Ta) ingots were manufactured by vacuum arc melting. The ingots thus obtained were divided into two batches: the first subjected to cold rolling (CR) from 30 to 85% of thickness reduction and subsequent annealing in the 450 to 900 °C temperature region, and the second atomized to produce 100 μm size powders. This powder was used to manufacture open-cell porous material. Regardless of the CR intensity, Ti-(18…20)Nb-(5…6)Zr (at.%) samples subjected to 600 °C (1 h) annealing showed a significant material softening due to the stress-induced martensitic transformation. The Young's modulus of these alloys varied between 45 and 55 GPa, and the yield stress, between 300 and 500 MPa. The obtained Young's moduli, which are comparable to 55-66 GPa of concurrent beta-titanium alloys and 45-50 GPa of superelastic Ti-Ni alloys, come close to those of cortical bones. Compression testing of the porous material as a function of porosity (from ~ 45 to 66%) and interconnected cell size (d₅₀ from 300 to 760 μm) showed the following properties: Young's modulus from 7.5 to 3.7 GPa, which comes close to that of trabecular bones, and ultimate compression strength, of from 225 to 70 MPa.     

An analysis of measurement of solute segregation in Ni-base superalloys using X-ray spectroscopy

The extent of solute segregation in a multi-component Ni-base superalloy, IN713LC, is analysed using X-ray spectroscopy techniques. It is demonstrated in this study that such an analysis is strongly influenced by the volume averaging of γ and γ′ phases sampled by the electron beam; the γ′ having precipitated from the γ phase below the γ′ solvus temperature in the solid-state. It is found that the size of the precipitate (γ′) in relation to the interaction volume is crucial; volume averaging is dominant when the precipitate size (γ′) is comparable to the interaction volume. Accurate interpretation of the measurements is essential when they are used to infer the micro-segregation and solute partitioning during solidification. Implications of this analysis in the assessment of segregation during solidification in Ni-base superalloys are addressed.     

Calculation of solute-vacancy binding energy in dilute fcc and bcc alloys by diffusion

Due to excess charge of the solute with respect to solvent, the free energy of vacancy formation and migration in the neighbourhood of the solute will change. This results in a change in the solvent diffusivity. A relation for the solute vacancy binding energy for fcc and bcc lattices using enhancement factor has been derived considering the solute vacancy interactions to be limited to first neighbour and neglecting the changes in the solvent correlation factor.     

Diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couples

The diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couple method were investigated. Results demonstrate that Al_2Ca is the only phase existing in the diffusion reaction layers.The volume fraction of Al_2Ca in diffusion reaction layers increases linearly with temperature. The standard enthalpy of formation for intermetallic compounds was rationalized on the basis of the Miedema model. Al-Ca intermetallic compounds were preferable to form in the Mg-Al-Ca ternary system under the same conditions. Over the range of 350–400?C, the structure of Al_2Ca is more stable than that of Al_4Ca, Al_(14)Ca_(13) and Al_3Ca_8. The growth constants of the layer Ⅰ, layer Ⅱ and entire diffusion reaction layers were determined. The activation energies for the growth of the layer Ⅰ, layer Ⅱ and entire diffusion reaction layers were(80.74 ± 3.01) k J/mol,(93.45 ± 2.12) k J/mol and(83.52 ± 1.50) k J/mol, respectively.In layer Ⅰ and Ⅱ, Al has higher integrated interdiffusion coefficients D~(Int, layer)ithan Ca. The average effective interdiffusion coefficients D_(Al)~(eff) values are higher than D_(Ca)~(eff) in the layer Ⅰ and Ⅱ.     

Effects of Sn segregation and precipitates on creep response of Mg‐Sn alloys

Mg‐Sn alloys are promising for the development of new cheap creep resistant magnesium alloys. In the present paper, the creep behaviours of Mg‐Sn and Mg‐Sn‐Ca alloys were examined at the constant temperature and different stresses. The measurements of stress exponents indicate that the dislocation climbing is the dominant mechanism during the creep of Mg‐3Sn or Mg‐3Sn‐2Ca alloys. The poor creep resistance of the binary Mg‐3Sn alloy is caused by the easy movement of dislocation and the segregation of Sn at the boundaries. Both T4 and T6 heat treatments improve the creep resistance of Mg‐3Sn alloy due to the alleviation of Sn segregation at grain boundaries and the precipitation of Mg₂Sn particles, respectively. Ca is an effective alloying element to increase the creep resistance of Mg‐Sn alloys. The Ca addition leads to the formation of thermal stable phases Mg₂Ca and CaMgSn in Mg‐3Sn‐Ca alloys. These two phases effectively hinder the movement of dislocations and the sliding of grain boundaries. On the other hand, the addition of Ca alleviates the segregation of Sn by the interaction of Ca with Mg and Sn to form the phase CaMgSn.     

Grain growth and grain orientation distribution of Al-Mg alloys

Grain growth behaviour of Al–Mg alloys containing 0.3, 2.7 and mass% Mg was investigated focusing on the spatial distribution of grain orientation and grain boundary character. In Al–0.3 mass% Mg alloy the cube texture developed at the first stage and then the texture declined accompanied with abnormal grain growth of non-cube grains at the second stage. The development of cube grains was suppressed by an increase of solute Mg atoms. The texture change depended strongly on spatial distribution of grain boundary character and cube clusters.     

Effect of ion irradiation in an Al90Fe2Ce8 metallic glass

Here the irradiation effect of an AlFeCe metallic glass under nitrogen ions was investigated. Ion irradiation induced crystallization can be observed in the studied metallic glass. The surface morphologies have been also examined by atomic force microscopy prior to and after ion irradiation. It is found that the surfaces have been smoothened after ion irradiation. The nanohardness and Young’s modulus of metallic glass increase after ion irradiation, which can be attributed to the formation of crystalline phases. The results obtained here clearly suggest that ion irradiation can be a useful method to tailor the microstructure and mechanical properties of metallic glasses.     

Experimental studies of oxygen and carbon segregation at the interfacial boundaries of a 90W–7Ni–3Fe tungsten heavy alloy

The paper presents the results of a study of the heat treatment effect on the segregation in a 90%W–7%Ni–3%Fe alloy by an X-ray microanalysis and nanoSIMS technique. The measurements revealed oxygen and carbon segregations as well as enrichment of interfacial boundaries with nickel and iron.     

Micromechanisms of fatigue crack growth in aluminium alloys

The fatigue crack growth characteristics of high-strength aluminium alloys are discussed in terms of behaviour during mechanical testing and fracture surface appearance. For a wide range of crack growth rates, the crack extends both by the formation of ductile striations and by the coalescence of micro-voids. Dimples are observed at stress intensities very much less than the plane strain fracture toughness, and this is explained in terms of the probability of inclusions lying close to the crack tip. The striation formation process is described as a combination of environmentally-enhanced cleavage processes and plastic blunting of the crack tip.