Diffusion Of Interstitial Atoms Research Articles

Theoretical analysis for diffusion of interstitial atoms in crystal

A new theory for analysis of diffusion of interstitial atoms in crystal is presented. The foundation of the theory is based on the fact that an interstitial atom experiences the action of a cyclic potential of lattice atoms when it moves along a channel of crystal. An equation for the motion of the interstitial atom is derived from this hypothesis. According to the characteristics of solutions of the equation, the diffusing process of interstitial atoms along the crystal axis 〈hkl〉 are described. Formulas for calculation of the openness of a channel in crystal for diffusion of interstitial atoms and diffusivity are obtained. The calculated results obtained by using this theory are close to those of experiments.

The effect of temperature on the low cycle fatigue of type 316L stainless steel over the range 20–200°C

Abstract Strain-controlled low cycle fatigue tests (with and without tensile hold) were performed on type 316L stainless steel over the temperature range 20–200°C. The results indicate that for strain ranges of less than 1%, the fatigue life was temperature independent. By contrast, for strain ranges of 1% or more, fatigue life decreased significantly as temperature was increased from 20 to approximately 50°C. It then increased with further increases in temperature until approximately 100°C and beyond when it became relatively temperature insensitive. Fatigue life at all temperatures was reduced with the superimposition of a speak tension hold of 50 s. A model based on the temperature-assisted diffusion of interstitial carbon atoms is proposed to explain the phenomenon.

Structure Peculiarities and Annealing Mechanism of the Red Flash-Like Luminescent Centre in CdS Single Crystals Irradiated with 1.2 MeV Electron Beam

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Long-range migration of self-interstitials and dislocation pinning in niobium

The authors present experimental evidence for pronounced dislocation pinning in niobium beginning at 6 +- 0.2 K due to defects introduced by 2.3 MeV electron irradiation. This indicates long-range diffusion of radiation-induced interstitial atoms in niobium at 6 K. On the other hand, resistivity results to be presented elsewhere.

Pinning of a Bloch wall by diffusion of carbon atoms in a silicon-iron single crystal: an experimental study by means of an autoregressive spectrum analysis method

Diffusion of interstitial carbon atoms in iron creates the phenomenon of the 'diffusion after-effect'. After a review of the main features of this effect, this paper reports on an experimental study of this phenomenon in a SiFe crystal. The various waveshapes generated by the motion of a single Bloch wall are analysed by an autoregressive signal processing technique which allows the study of the 'instantaneous' power spectrum. A simple model is proposed in order to account for the experimental results.

Low-field viscomagnetic behavior of annealed, quenched, and cold-worked polycrystalline nickel

Behavior of aftereffect in magnetization process of annealed, quenched, and cold-worked ferromagnetic polycrystalline nickel under constant applied fields is studied. The effect of relaxation of electronic circuit response of measurement system in the experiment is eliminated. The present results do not conform with the proposed early stage magnetization mechanisms such as interstitial atom diffusion, interstitial dumbbell rotation and dislocation interaction. The relaxations of all samples followed the Voigt–Kelvin-type viscoelastic behavior with a short unique time constant τ=1.50 sec for all samples.

Trapping of Interstitials in Metals

The term trapping is used extensively to refer to the fact that interstitial atoms often find interstices associated with lattice imperfections to be energetically preferable to normal sites. This preference results in a delay of diffusion of interstitial atoms near these sites. As understanding of the details of lattice imperfections has improved, understanding of the effect of traps on the diffusion process has increased. Trapping is often illustrated by the use of a potential energy diagram. This simple model is characterized by a potential energy well deeper than those of surrounding interstitial sites. The energy required for the interstitial to jump into the trap is the same as that required for jumping into other adjacent interstitial sites, but that required for jumping out is greater. The additional energy required to leave the site is often designated as the trap binding energy, E/sub B/. Potential energy diagrams appropriate for most traps in metals are likely to be more complicated, but this simple model is a starting point for more sophisticated models of trapping. Imperfections may occasionally produce interstitial sites less favorable than normal sites and thus be less preferred. Little experimental exploration of this anti-trapping phenomenon has been carried out, however.more » Developments in understanding at various levels of trapping of interstitial impurities by lattice imperfections are examined.« less

A Modified Quasistationary Model of Uphill Diffusion of Interstitial Atoms

A Modified Quasistationary Model of Uphill Diffusion of Interstitial Atoms

Solubility, diffusivity and trapping of hydrogen in dilute alloys. Deformed and amorphous metals—II

The chemical potential and diffusivity of interstitial solute atoms was calculated for disordered materials in a general way. Disorder may be of chemical nature as in alloys or caused by a strain field as around dislocations and a crack tip or disorder may be as total as in an amorphous alloy. For these examples of disordered systems relations were derived from a general expression and compared with corresponding special theoretical results which are mostly related to attractive interaction (trapping) and repulsive interaction (antitrapping) between interstitially and substitutionally dissolved impurity atoms. A comparison with experimental results is namely made for the solubility and diffusivity of hydrogen in dilute alloys, deformed Fe and Pd and amorphous Pd 77.5Si 16.5Cu 6 and Ni 64Zr 36.

Volume effects in solid solutions

This review presents an outline and discussion of recent developments in the study of volume effects in the thermodynamics and kinetics of solid solutions. Such effects may be defined generally in a somewhat loose manner as all effects describable as resulting from the fact that, in contrast to most of the statistical mechanical treatments of solid solutions, the specific volume of the system is a function of composition. A compilation of formal relationships between constant-pressure and constant-volume thermodynamic relationships is given and their application to binary and ternary solid solutions is presented. Specific examples of binary solid solutions include carbon-: austenite and several hydrogen-metal systems. The thermodynamics of ternary solid solutions is also considered, with special emphasis given to ternary systems containing a substitutional solute and an interstitial solute at low concentration. A consideration of the effects of lattice dilation on the diffusivity of interstitial atoms in solid solutions is also presented. A specific case treated is the diffusion of carbon in face-centred cubic iron.

Diffusion in iron, iron solid solutions and steels

Systematic experimental and theoretical studies of the diffusion in iron, iron solid solutions and steels have been carried out at the Institute of Physical Metallurgy, Czechoslovak Academy of Sciences, Brno, for several years. The aim of this review is to present some results achieved in the Institute and to complement them by the results published in journals and monographs, in a complete well-organized format that gives a basic idea of the problem and enables certain technological applications to be made. In the four sections we deal with self-diffusion and heterodiffusion in iron and in iron solid solutions. The investigations have shown, as well as other facts, that three types of bulk diffusion in iron-based materials should be distinguished: (i) diffusion in the ferromagnetic b.c.c. structure, (ii) diffusion in the paramagnetic b.c.c. structure and (iii) diffusion in the f.c.c. structure. In Section 3 we demonstrate that the effect of magnetic order on diffusion, creep and high temperature yielding has a common base: the atomic spin-spin interaction which influences the variation in the elastic constants with temperature. The results concerning substitutional diffusion in steels are presented in Section 6. It can be concluded from the compiled data that the self-diffusion and heterodiffusion values measured in f.c.c. iron may be used as a good approximation in austenitic steels, if the data for these particular materials are not available. Examples of diffusion applications in related material branches are introduced in Section 7 on the homogenization of alloys and steels and in Section 8 on diffusion and creep. In Section 9 we deal with the diffusion of interstitial atoms in iron and steels and particularly with carbon diffusion and redistribution in steel weldments. It is shown that the concept of the carbon activity gradient as a chemical “driving force” in carbon diffusion and redistribution is well established and has been applied successfully.

High temperature elastic properties of polycrystalline niobium, tantalum, and vanadium

A pulse-echo technique has been used to measure the temperature variation of the velocity of extensional and torsional acoustic waves in polycrystalline Nb(Cb), Ta, and V up to ∼2000 K. The concomitant temperature variation of the elastic moduli do not show any anomalies which would be consistent with a “lattice softening” theory for the departure from linearity of the Arrhenius plots for the diffusivity of interstitial atoms in the Group V metals.

The diffusion of heavy interstitial solute atoms in body-centered cubic metals

This paper discusses recent observations of the diffusivity of nitrogen, carbon and oxygen in a series of body-centered cubic metals in which positive deviations from Arrhenius behavior have been seen in some cases at high temperatures. Several models involving both single-stage and two-stage diffusion mechanisms are presented and discussed in terms of the individual systems and current high temperature measurements of the elastic properties o of the solvent metals.

Interstitial solute diffusion in metals

The diffusion of interstitial solute atoms, which were subject to nearest neighbour solute-solute interactions, was simulated by means of a modified Monte Carlo method. Solute correlation factors, nearest neighbour vacancy availability factors and effective jump frequency factors were calculated as functions of composition and temperature. Compared with non-interacting atoms attraction between solute atoms always retarded diffusion whereas repulsion always enhanced diffusion except within the ordered region.

Diffusion of interstitial atoms in ordered Pt2Mo-type alloys (II)

Diffusion of interstitial atoms in ordered Pt2Mo-type alloys (II)

Diffusion of Interstitial Atoms in Ordered Pt2Mo-Type Alloys (I)

The tensor diagonal components of the diffusion coefficients for interstitial atoms in laminated superlattice structures of Pt2Mo type are calculated. The crystal lattice is shown to be diffusively anisotropic if interstitial atoms interact mainly with the adjacent atoms of the alloy. When thermodynamic equilibrium exists, the degree of anisotropy is claimed to rise quickly with the decrease of temperature. [Russian Text Ignored].

Ti-2 at%Zr合金の多重降伏現象

Serrated yielding was clearly observed between 330 and 460°C at a strain rate of 2.22×10−4 sec−1 in Ti-2 at%Zr alloy, while in a commercially pure titanium it was not so clear. Two types of serrations were observed in the alloy. One type is the serrations with a regular periodicity and the other is the serrations with relatively large stress drops which occur intermittently. In cases where the strain increases, the strain rate decreases or the grain size decreases, the stress amplitude of the regular serrations increases. Examination of the temperature and strain rate dependence of the regular serrations suggests that serrated yielding in Ti-2 at%Zr alloy is probably dominated by the diffusion of both zirconium and interstitial impurity atoms. The regular serrations, therefore, must be closely related to the strong interaction between a dislocation and an interstitial impurity atom which is at the octahedral site distorted locally by a zirconium atom.

Trapping effect in diffusion of interstitial impuritl atoms in B.C.C. lattices

Diffusion of interstitial impuritl atoms is considered in the presence of substitutional impuritl atoms lhich act as trapping centers. The unit process of diffusion is regarded to consist of tlo steps: escape from a trap (escape process); and trapping bl a trap (trapping process). The mean first passage time (m.f.p.t.), lhich is a lell knoln concept in the theorl of stochastic processes, is calculated for the tlo processes bl considering the connectivitl of interstices. The apparent diffusion constant is defined in terms of m.f.p.t. for escape and trapping processes. The expression for the apparent diffusion constant is derived lith a special attention to the effect of the change in saddle point energl near traps ( ΔE). The expression agrees lith those of previous investigators onll lhen ΔE = 0.

Trapping effect in diffusion of interstitial impurity atoms in B. C. C. Lattices

Trapping effect in diffusion of interstitial impurity atoms in B. C. C. Lattices

Diffusion of interstitial and substitution atoms in a strain hardened matrix

Diffusion of interstitial and substitution atoms in a strain hardened matrix