The equilibrium surface composition of some indium-lead and indium-tin alloys

Auger electron spectra have been obtained from the near surface region of six equilibrated, solid, single-phase alloys — four in the In-Pb system and two in the In-Sn system — at temperatures ranging from 20°C to near the melting point of each. For dilute solutions, the surface is enriched in the solute, the amount increasing with decreasing temperature. As the bulk solute concentration is increased, the relative enrichment in the surface decreases, and at a sufficiently high solute concentration the surface becomes depleted in the solute. These results are consistent with an earlier study of the tin-lead alloy system and with the thermodynamics of non-ideal solutions. Together with the results from the tin-lead system, they represent the first systematic study of the equilibrium surface composition of a series of non-ideal solutions covering several alloy systems.     

亚稳相的高压暴露

 很久以前,便有人指出,气态冷凝成固态时,要连续经历液相及各种高温相,才达到平衡结晶相。但是,液态及高温相往往需靠很大的冷却速度才能冻结下来,这在当时对绝大多数合金,是不可能的。近些年,随着超急冷等技术的进步,关于非晶等亚稳相得研究十分活跃。当超过一定临界冷却速度时,液态合金可固化为非晶态。虽然,亚稳结晶相较非晶应更容易冻结,但是,由于产生各种亚稳相所需的过冷条件各不相同,以及对冷却速度的选择不能是任意的,因此有时它们较非晶还难于形成。与液相凝固过程相似,非晶合金的晶化也服从构型最小重排原理,即在晶化完成之前,存在某些亚稳相变态阶段。但是,限于热力学上的不稳定性及动力学因素,在常压下这些亚稳相同样是难以发现的。作者根据对多种合金系的研究,提出高压暴露亚稳相的设想,并利用非晶等亚稳相的高压变态过程,将进行液态急冷时的速度控制方式,改为便于掌握的高压退火方式,来获得新亚稳相。本文对压力暴露亚稳相的原理和实践,加以论述。     

New phenomena in the adsorption of alkali metals on Al surfaces

Recent studies of the adsorption and co-adsorption of alkali metals on Al surfaces have revealed a wealth of hitherto unexpected phenomena, including: order-preserving phase transformations between metastable and stable structures; reconstruction of the substrate by adsorption at room temperature; and formation of binary and ternary surface alloys. The results of experimental structural determinations are reviewed, with the major emphasis on Low-Energy Electron Diffraction (LEED) studies of the ordered structures formed by adsorption of the alkalis on Al(111). The experimental results are compared where possible with corresponding results of ab initio calculations of total energy by Scheffler and co-workers. The experiment-theory comparisons provide valuable insight into the adsorption mechanisms, including the possible role of surface steps as both sources and sinks.     

亚稳态FeCu固溶体微粉原子相互作用势的计算

本文介绍了亚稳态Fe50Cu50固溶体晶格常数的测量结果,应用金属结构的经典概念并考虑到原子核周围电子密度的高斯型球对称分布,导出了计算金属中一个原子的平均内能和两种不同金属原子相互作用势的普遍公式.对亚稳态Fe50Cu50合金原子相互作用势作计算,得到平衡时fcc-FeCu的晶格常数为0.36433 nm与实验测量结果接近,也与H.R.Gong等人对亚稳态FeCu合金的研究结论一致,证实了亚稳态Fe50Cu50合金是以fcc结构形式存在的固溶体.     

Mechanomaking of nanostructure in nitrided Fe–Cr alloys by cyclic “dissolution–precipitation” deformation-induced transformations

Structural-phase transformations in surface layers of iron and Fe? Cr? (Ni) alloys subjected to ion-plasma nitriding and subsequent cold plastic compression shear deformation in Bridgman anvils have been investigated by the methods of Mössbauer spectroscopy, transmission electron microscopy and X-ray analysis. It has been shown that the deformation-induced cyclic phase “dissolution–precipitation” transformations of nitrides in alloys lead to the formation of nitrogen oversaturated solid solutions, precipitation of secondary nitrides and nanostructurization of the metal matrix.     

Atomic transport in ionic solid solutions

Summary This paper examines certain aspects of the relation of tracer diffusion coefficients to the corresponding so-called intrinsic diffusion coefficients arising in chemical interdiffusion in binary solid solutions. Although no exact general relation between these quantities is to be expected, the existence of such a relation for the solute species is to be anticipated in dilute solid solutions. In metallic alloys they become equal in the dilute limit, but in solid solutions of ionic conductors the ratio depends on details of the system (in particular on the solute and solvent ion charges and the degree of association between solute ions and charge compensating defects). Both the macroscopic and microscopic theories of these ionic solutions are described. A rather clear conflict exists between the theoretical predictions and some existing experimental results on the system Cr₂O₃ in MgO. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

Calculation of the solvus temperature of metastable phases in the Al-Mg-Si alloys

A procedure has been proposed for the self-consistent calculation of the solvus temperatures of metastable phase precipitates in Al-Mg-Si alloys and the specific energy of their interface with the aluminum matrix. The procedure is based on the results of experimental studies on the kinetics of formation of these precipitates during decomposition of supersaturated solid solutions of quenched Al-Mg-Si alloys, which were carried out by measuring the Young’s modulus and electrical resistivity. On the basis of the obtained set of solvus temperatures of the β″-phase, an empirical formula has been proposed for calculating this temperature as a function of the chemical composition of the initial solid solution.     

Microstructural evolution and thermal stability of Fe–Zr metastable alloys developed by mechanical alloying followed by annealing

The effect of Zr (up to 1 at.%) addition on the formation of Fe–Zr metastable alloys and their thermal stability were investigated for their possible nuclear applications. Fe–xZr (x = 0.25, 0.5, 1%) alloys were synthesised by mechanical alloying under a high-purity argon atmosphere using stainless steel grinding media in a SPEX 8000M high energy mill. The milling was conducted for 20 h with a ball-to-powder weight ratio of 10:1. The formation of metastable solid solutions after milling was confirmed from the change in the Gibbs free energy analysis as per Miedema’s model. The microstructural characterisation was carried out by analysis of X-ray diffraction, atomic force microscopy and transmission electron microscopy. The effect of Zr on the thermal stability of Fe–Zr alloys was investigated by extensive annealing experiments followed by microstructural analysis and microhardness measurements. The stabilisation was found to occur at 800 °C and thereafter, no significant change in the crystallite size was observed for the samples annealed between 800 and 1200 °C. The supersaturated solid solution, especially 1% Zr alloy, found to be highly stable up to 800 °C and the microhardness value of the same measured to be as high as 8.8 GPa corresponding to a crystallite size of 57 nm. The stabilisation effect has been discussed in the light of both the thermodynamic and kinetic mechanisms and the grain size stabilisation is attributed to the grain boundary segregation of Zr atoms and/or Zener pinning by nanoscale precipitation of the Fe₂Zr phase.     

Structure and magnetism of Fe-rich nanostructured Fe–Ni metastable solid solutions

New futures on the physical properties of ferromagnetic FeNi alloys have been found combining in situ neutron diffraction experiments and magnetic measurements in mechanical milled Fe-rich Fe–Ni metastable solid solutions. Apart from the well-known Invar effect, on heating these materials are characterised by the existence of a first-order martensite–austenite transformation that takes place at some system-dependent temperature. On cooling, the transformation occurs at a lower temperature than on heating; for Fe₈₀Ni₂₀ the size of the effect being larger than 100 °C, much more than the values found in conventional FeNi alloys. These results are discussed considering intrinsic features as magnetovolume effects and/or extrinsic effects such as small grain size and the existence of defects.     

On the effect of concentrated solid solutions on properties of clusters in a model binary alloy

In a series of papers aimed at better understanding precipitation in binary alloys, it was shown that Cluster Dynamics (CD) is a valuable tool to bridge the gap between microscopic and macroscopic scales, provided that cluster-free energies are carefully derived from Monte Carlo calculations. Indeed, in such conditions, CD predictions compare well with Atomistic Kinetic MC simulations. Nevertheless, in a recent work, the authors pointed out some limitations of this approach at high solute concentration. The present work aims at revisiting the notion of cluster-free energy in the context of concentrated solid solutions at thermal equilibrium.     

Enhancement of solute self-diffusion in fcc alloys

Using a new simulation approach to the calculation of correlation factors in very dilute solutions, the present paper reports on results of the first calculations of the first and second solute enhancement factors for solute self-diffusion in the fourteen-frequency model postulated by Bocquet for describing the diffusion kinetics of paired and unpaired solute atoms in dilute fcc alloys. Bocquet's assumption that correlation effects do not contribute to solute self-diffusion enhancement is shown to have a fairly limited range of validity. Specifically, it is shown that this assumption is reasonable when the solvent–vacancy exchange frequency far from the solute is high compared with the others or when all of the solute–vacancy exchange frequencies are small compared with the others. The assumption is also reasonable when the vacancy is not attracted to the solute atoms and when the vacancy does not often alternate between two solute atoms. The present study would strongly suggest that many of the ratios of exchange frequencies that have been determined from experimental data on the basis of this assumption are likely to be in error.     

Diffusion, Solute Segregations and Interfacial Energies in Some Material: An Overview

We have shown a connection among the three important properties of interfaces, namely, the free energy, diffusion and solute segregation through the conjecture that the interface free energy is the difference between those responsible for diffusion in the lattice and the interface itself. The interface energy is known to decrease upon solute additions. We discuss the methodology and the thermodynamical analysis of the diffusion parameters which enable extraction of the interfacial energies and illustrate them by results obtained in a wide variety of materials. Investigations carried out in pure polycrystalline metals have yielded grain boundary energies comparable to those directly measured. Furthermore, we discuss the role of solute segregation at grain boundaries in alloys in altering diffusion. From the perturbations caused, the solute segregation parameters—the enthalpy and the entropy of binding—have been extracted and levels of solute concentrations estimated. It is shown that similar analyses when applied to complex materials, e.g. the Pb–Sn eutectic alloy, several intermetallic compounds, and oxide systems, also result in acceptable values of interface energies and segregation factors. Finally, some ad-hoc guidelines are provided to alter diffusion in interfaces through solute additions in order to achieve some end use engineering objectives.     

Fast solute diffusion in solid and supersaturated solid solutions

In this paper, we review the experimental data concerning fast diffusion of solute in Pb matrix and Pb (solute) solid solutions. Using both calorimetric and radiotracer techniques the temperature dependence of solute diffusion coefficients in Pb (solute) supersaturated solid solutions is determined. On the basis of experimental results it is shown that these coefficients can only be understood by assuming different defect states for solutes in solid and supersaturated solid solutions.     

Doping of ZrO2 by ion mixing

The morphology and structure of ZrO₂ films grown in steam-water medium on an ion-doped surface of zirconium and its E110 and E635 alloys have been studied. It has been found that the properties of oxide films are determined mostly by the conditions of ion-implantation doping at large oxidation times. It has been shown by the example of samples doped simultaneously with Al, Fe, Mo, and Y that the formation of a multiphase oxide film occurs due to the diffusion redistribution of implanted atoms during oxidation.     

Depth concentrations of deuterium ions implanted into some pure metals and alloys

Pure metals (Cu, Ti, Zr, V, Pd) and diluted Pd alloys (Pd-Ag, Pd-Pt, Pd-Ru, Pd-Rh) were implanted by 25-keV deuterium ions at fluences in the range (1.2–2.3) × 10²² m⁻². The post-treatment depth distributions of deuterium ions were measured 10 days and three months after the implantation by using Elastic Recoil Detection Analysis (ERDA) and Rutherford Backscattering (RBS). Comparison of the obtained results allowed us to make conclusions about relative stability of deuterium and hydrogen gases in pure metals and diluted Pd alloys. Very high diffusion rates of implanted deuterium ions in V and Pd pure metals and Pd alloys were observed. Small-angle X-ray scattering revealed formation of nanosized defects in implanted corundum and titanium.     

Physical and chemical phenomena occurring between solid ceramics and liquid metals and alloys at laser and plasma composite coatings formation: A review

The review describes the physical and chemical phenomena occurring between solid ceramics used as reinforcement and liquid metals and alloys used as matrix in the composite coatings. Initially, the properties of typical matrix metals as Ni, Co, Fe and alloys as Ni-based (NiCr, NiAl, NiCrAlY,…) and Co-based (Stellites) alloys in liquid state are described. Then, the phenomena related to the diffusion of some atoms such as nitrogen or carbon in liquid metals and alloys solidification are described. Subsequently, the phenomena at the interface between liquid metals and alloys and solid ceramics such as oxides or carbides during the coatings' formation are reviewed. Finally, the methods of composite coatings deposition using laser cladding and plasma transferred arc are described and the properties of the composite coatings related to their microstructure are discussed by taking into account the phenomena in melt-pool.     

Effect of temperature-induced solute distribution on stacking fault energy in Mg–X(X = Li,Cu, Zn,Al, Y and Zr) solid solution: a first-principles study

Stacking fault energies (SFEs) of Mg solid solutions at different temperatures are very significant for studying dissociation of dislocation, plasticity deformation and other mechanical properties. Our present work starts with the investigation of interactions between basal stacking faults (SFs) and solutes (Li, Cu, Zn, Al, Y and Zr) using first-principles calculations. It is found that the interactions between basal SFs and solutes can be extended to several closed-packed layers. Combined with Fermi–Dirac function of solute distribution at each layer, the temperature dependence of SFE for Mg–X(X?=?Li, Cu, Zn, Al, Y and Zr) solid solution has been investigated. This study predicts correctly the increase tendency observed in experiment. Then the SFEs of Mg solid solutions at room temperature of 300?K are investigated at different solute concentrations; the obtained concentration dependence of SFEs is in agreement with the available experimental values. So the solute distribution under finite temperature due to the basal SF–solute interactions plays a critical role in the variation of SFEs of Mg solid solutions.     

Softening and hardening of yield stress by hydrogen–solute interactions

Abstract

Hydrogen atoms have a wide variety of effects on the mechanical performance of metals, and the underlying mechanisms associated with effects on plastic flow and embrittlement remain to be discovered or validated. Here, the reduction in the plastic flow stress (softening) due to hydrogen atoms in solute-strengthened metals, previously proposed by Sofronis et al. is demonstrated at the atomistic level. Glide of an edge dislocation through a field of solutes in a nickel matrix, both in the absence of hydrogen and in the presence of H bound to the solutes, is modelled. The ‘solutes’ here are represented by vacancies, enabling use of accurate binary Ni–H interatomic potentials. Since vacancies have a misfit strain tensor in the Ni matrix and also bind hydrogen atoms, they are excellent surrogates for study of the general phenomenon. The binding of H to the solute (vacancy) reduces the misfit volume to nearly zero but also creates a non-zero tetragonal distortion. Solute strengthening theory is used to establish the connection between strength and solute/hydrogen concentration and misfit strain tensor. Simulations show that when a dislocation moves through a field of random vacancy ‘solutes’, the glide stress is reduced (softening) when H is bound to the solutes. Trends in the simulations are consistent with theory predictions. Trends of softening or hardening by H in metal alloys can thus be made by computing the misfit strain tensor for a desired solute in the chosen matrix with and without bound hydrogen atoms. Pursuing this, density functional theory calculations of the interaction of H with carbon and sulphur solutes in a Ni matrix are presented. These solutes/impurities do not bind with H and the complexes have larger misfit strains, indicative of H-induced strengthening rather than softening for these cases. Nonetheless, H/solute interactions are the only mechanism, to date, that shows nanoscale evidence of plastic softening due to hydrogen associated with the hydrogen-enhanced localised plasticity concept in fcc metals.     

A quantitative atom-probe field-ion microscope study of the compositions of dilute Co(Nb) and Co(Fe) alloys

The compositions of Co-1.0at%Nb and Co-1.0at%Fe alloys have been measured using the atom-probe field-ion microscope. The main purpose of this experimental work was to find a set of optimum conditions which gives the correct solute concentrations in these alloys. This information was necessary for measuring the absolute compositions, in our extensive investigations of solute atom segregation effects to individual stacking faults in these alloys. The dependence of each alloy's composition on the following parameters was investigated: (1) the specimen temperature; (2) the pulse fraction; (3) the field-evaporation rate; (4) the crystallographic plane; (5) the effect of the presence of hydrogen in the atom-probe on the measured Nb composition in a Co-1.0at%Nb alloy. It is shown that the composition determined by the atom-probe FIM is very sensitive to some of the parameters listed above. The effects of these experimental parameters on the measured Nb and Fe concentrations are discussed in terms of possible field-evaporation models. Under certain experimental conditions drastically different behavior has been observed in these alloys; preferential field-evaporation of solute atoms in a Co-1.0at%Fe alloy and preferential retention of solute atoms in a Co-1.0at%Nb alloy was observed. Correct solute concentrations were obtained by using the following experimental parameters: (1) a specimen temperature of less than or equal to 60 K; (2) a pulse fraction of greater than or equal to 0.10.