Low temperature specific heat of transition metals and alloys

The article reviews experimental results on the low temperature specific heat of the transition metals and their alloys. Particularly discussed are the variations of the electronic part on the basis of a complete compilation of measurements given.     

Local degrees of freedom and nuclear quadrupolar spin relaxation in liquid metals and alloys

We discuss the temperature dependence of the nuclear quadrupolar spin relaxation rate in metals and alloys. Four different relaxation processes must be distinguished: Hard collisions, diffusion, decay of associates and rotational diffusion. The latter two processes are important in alloys of strongly interacting alloying partners, the former in pure metals (collision) and ideal or regular mixtures. Diffusion is important if the alloying partners produce different electrical field gradients.     

Nonmonotonous relaxation processes in nonequilibrium nanoforming alloys of Al with transition and rare-earth metals

The temporal dependences of viscosity in Al₈₇Ni₈Y₅, Al₈₆Ni₈Ce₆, and Al₈₆Ni₈La₆ melts were measured at various temperatures after the solid-liquid phase transition. A nonmonotonous change in viscosity with the passage of time was found, due to the destruction of the nonequilibrium microheterogeneous state of melts inherited from the initial multiphase melts. We propose a mechanism of nonmonotonous relaxation of nonequilibrium microheterogeneous melts within the dynamical theory of a molecular field, assuming the emergence of a hierarchy of different relaxation times in the system. A theoretical temporal dependence of viscosity of melts is proposed that is qualitatively consistent with the experimental data.     

High temperature paramagnon modifications in nearly magnetic metals

The standard paramagnon structure in nearly magnetic metals is shown to be drastically modified at high temperatures. Qualitative consequences for the electron paramagnon temperature dependence of the electrical resistivity are considered. Behavior like that exhibited in αPu resistivity might be expected.     

Nb-Al合金高温氧化机理

通过自编软件建立了铝氧化膜与基体铌界面的原子集团模型,用递归法计算了合金的原子埋置能、原子结合能等电子参数,从电子层面分析铌合金高温氧化机理.研究表明:铝通过晶界扩散偏聚在合金表面,并与氧结合生成致密的Al2O3氧化膜,阻挡氧向铌基体扩散.晶界和稀土元素能提高氧化膜与基体间的原子结合能,增加其界面的结合强度,加强氧化膜与基体铌间的黏附性.因此,通过在合金中添加稀土元素或细化合金晶粒均能提高铌合金的抗高温氧化性能.     

High temperature embrittlement of metals by helium

The present knowledge of the influence of helium on the high temperature mechanical properties of metals to be used as structural materials in fast fission and in future fusion reactors is reviewed. A wealth of experimental data has been obtained by many different experimental techniques, on many different alloys, and on different properties. This review is mostly concentrated on the behaviour of austenitic alloys—especially austenitic stainless steels, for which the data base is by far the largest—and gives only a few examples of special bcc alloys. The effect of the helium embrittlement on the different properties—tensile, fatigue and, with special emphasis, creep—is demonstrated by representative results. A comparison between data obtained from in-pile (-beam) experiments and from post-irradiation (-implantation) experiments, respectively, is presented. Theoretical models to describe the observed phenomena are briefly outlined and some suggestions are made for future work to resolve uncertainties and differences between our experimental knowledge and theoretical understanding of high temperature helium embrittlement.     

Pseudopotential in metals and alloys

In this communication, the pseudopotential investigation of, the various properties of non-transition metals and alloys, is discussed. Various one parametric model pseudopotentials, derived from well known spherical functions s_l(x), are employed in the calculations. Many recurrence relations of the s_l(x) function have been described. The effects of exchange and correlation on conduction electrons are also considered separately by using different dielectric screenings in various properties. The ion-ion interaction, force constants, phonon spectrum, temperature coefficient of Knight shift and electronic transport coefficients of certain metals and alloys are evaluated. The results are compared with available experimental values. Generally good agreement is achieved. The screening charge density of certain metals in low and high density region are also determined.     

Low temperature 93Nb nuclear spin-lattice relaxation in Nb and NbMo alloys

High accuracy ⁹³Nb nuclear spin-lattice relaxation data are presented for Nb, Nb_0.75Mo_0.25, and Nb_0.70Mo_0.30 between 1.7 and 4.2 K. (T₁T)^?1 is independent of temperature and scales as the square of the density of states at the Fermi level.     

Structural relaxation in metastable alloys

A mechanism of stress relaxation in metastable alloys is considered. It is demonstrated that structural transformations during a relaxation test lead to anomalously high stress relaxation. Two stages of structural relaxation are revealed: formation of defect-free channels and decomposition of a solid solution. A new method of program hardening of metastable alloys based on the structural relaxation processes is suggested. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 56–61, November, 2007.     

Structural instability in metals and alloys

An analysis of features of the electron structure required to produce the spectrum of structural states in alloys indicated a number of relationships inherent to such systems. The types of structural states that can occur under the conditions of instability of the system as a whole or of an individual structural phase component are considered theoretically and experimentally. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 16–25, August, 1998.     

Quadrupole interactions in metals and alloys

The contributions of the perturbed charge density of conduction electrons due to quadrupole moments of impurity paramagnetic ions and nuclei to the electric field gradient at the nuclei in metals and alloys are analyzed. The indirect multipole interactions of nuclei in metals via the mediation of conduction electrons is investigated. The influence of these interactions on the NMR parameters is studied.     

Positron annihilation in metals and alloys

This review article summarizes the present knowledge of positron-annihilation research in metallic substances. Including a short historical survey, the annihilation processes in metals and alloys are discussed and various physical conditions such as ordering processes, magnetic phenomena, liquid state, superconductivity and lattice imperfections are considered. Finally, the present state of theoretical investigation is given and the outlook for the new and very useful technique in metal physics is pointed out.     

Interatomic distances in liquid metals and alloys

X-ray diffraction patterns of liquid tin and liquid mercury are unlike those of simple liquid metals such as Na, K, Cu and Au in that the intensity patterns show considerable asymmetry, or a distinct shoulder, on the high angle side of the main peak. The position of the main peak gives the average interatomic distance in the melt; for Sn and Hg the additional detail of the pattern gives a special close distance of approach. It is shown that this distance is related to that occurring in the low temperature allotropes of the solid metals.

In diffraction patterns of liquids of the Au-Sn alloy system the main intensity peak is resolved into two distinct maxima. One component occurs at a position corresponding to a simple random mixture of the component elements, the other to a close interatomic distance. The relative heights of the peaks are composition dependent. The close-packed component persists across the diagram, being strongest at composition Au₃Sn and decreasing to a shoulder at pure Sn. As for Sn and Hg the short distance can be correlated with a short distance occurring in the crystalline solids of the system.

A similar scheme may be applied to the systems Cu-Sn, Au-Ga and Au-In where double-headed diffraction patterns have been observed in the liquids.

It is postulated that the origin of the close distance occurring in the liquid in each system is the same as that of the strong bond existing in the crystalline compounds.     

Nuclear orientation and spin-lattice relaxation in Pd-Fe-Co alloys

Hyperfine field on⁵⁷Co nuclei in the system Pd-Fe-Co has been studied by very low temperature nuclear orientation technique. Low temperature spin-lattice relaxation was measured on the same set of samples by thermal cycling method. The Co hyperfine field and Korringa constant is studied in dependence on external magnetic field and on the constitution of the sample.