Creep in lead alloys. II

A study has been made by optical microscopy of the effects of small amounts of Sb, Te, and Cu on the creep of lead; copper has a very advantageous effect on account of its blocking of dislocation motion. Tellurium suppresses grain-boundary deformation and hinders dislocation collapse. Antimony is largely ineffective because it facilitates recovery although it hinders grain-boundary processes and movement of dislocations within grains.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 92–95, November, 1973.     

Creep of beryllium. I

Creep characteristics of beryllium have been determined in the temperature range 600–800°C and the stress range 0.25–5 kgf/mm². The rate of the process is controlled by the Herring —Nabarro mechanism in the range of stresses less than 1 kgf/mm². The creep activation energy (39±1 kcal/mole) hence agrees with the energy of self-diffusion. The creep rate for stresses greater than 1 kgf/mm² is determined by the simultaneous progress of dislocation creep and slip, where the slip contribution grows with the increase in stress. An approximate picture of the deformation mechanisms of creep is constructed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 68–73, March, 1976.     

Twinning in Be-Cu alloys. Part I

Mechanical twinning has been examined for 99.99% beryllium and for alloys of Be with 0.4 at. % and 2.3 at. % Cu. The yield points have been measured for single twins, and also studies have been made of the behavior of the twin boundaries under pulsating and sign-varying loads. The concentration dependence of the yield points for single twins has been used to estimate the interaction energy for the twinning dislocations with impurity atoms. The Bauschinger effect occurs at the boundaries of the mechanical twins, and the characteristics of this are dependent on the angle of the twin wedge, the impurity concentration, and the number of twinning cycles.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 104–108, December, 1972.We are indebted to G. F. Tikhinskiy for providing the alloy crystals used here.     

Theory of ordering effects in ternary alloys. I

Several problems of ordering theory are considered in the Gorskii-Bragg-Williams approximation for fcc-lattice ternary alloys, including atomic interactions in the first two coordination spheres. Possible types and existence conditions of superlattices are investigated.Translated from Izvestiya VUZ. Fizika, No. 1, pp. 17–22, January, 1972.     

Creep mechanism of gas-pressure-sintered silicon nitride polycrystals I. Macroscopic and microscopic experimental study

The creep behaviour and microstructure of two silicon nitride ceramics have been investigated. Compressive creep tests were performed at temperatures between 1450 and 1700°C at stresses between 6 and 90?MPa in an Ar atmosphere. The creep behaviour was characterized by a stress exponent lower than one for both materials, with an average value n?≈?0.6 over the whole range of stresses and temperatures, and with apparent activation energies between 470 and 530?kJ?mol^?1. The study of the microstructural evolution revealed the absence of dynamic grain growth and, in some cases, evidence of grain rearrangement. Partial coalescence of cavities was observed only at the highest stress, but this did not result in accelerated creep.     

Peritectic transformations in crystallization of alloys of the Al-Cr system. I

Established laws of the nonequilibrium crystallization of aluminum-chromium alloys permit the conclusion that each peritectic horizontal on the diagram of the Al-Cr system (at 725, 930, and 1000°C) corresponds to a region of structural transformation to a liquid extending from aluminum is the vertical of an intermediate compound. Retention of the stability of the high-temperature structural state of the liquid during its cooling predetermines the possibility of a delay in the peritectic transformation, crystallization according to metastable diagrams and, in individual cases, the formation of supersaturated solid solutions based on aluminum.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 53–58, March, 1980.     

Lattice vacancies in binary alloys: I. Equilibrium concentration of-vacancies in alloys with short range order

The influence of the short-range order parameter, of the alloy composition and of the exchange interaction on the equilibrium concentration of vacancies in binary alloys is studied with help of a simple model, taking in account the pair interaction between nearest neighbouring atoms. It is shown, that there is an anomaly of concentration of equilibrium vacancies near the Curie temperature.     

The effect of scale factor on mechanical properties of lead alloys

The effect of scale factor on mechanical and physical properties of metals and alloys is of both scientific and practical interest. Its study permits determination of the role in formation of physical properties of such factors as surface quality, character and distribution of internal and surface defects, types of processing, grain size, etc. As is well known, scale factor manifests itself to a greater degree, the stronger the material in question. Possibly because of this, data on the effect of scale factor on the properties of lead alloys with their relatively low mechanical strength are absent from the literature. However, such an omission is not justifiable, since lead, which is widely used in industry, is a scarce and expensive material, and proper determination of optimum dimensions for lead products is of major importance. The present study will clarify in greater detail the role of grain size and general level of mechanical properties on the relative effect of scale factor. The practical value of the study lies in the following. The alloys studied are used in manufacture of protective cable shields. The shield thickness can vary over wide limits, depending on the properties of the alloy, construction of the cable, and conditions of transportation and use. Therefore, by increasing the strength and other desirable properties of the alloy, significant reductions can be made in shield thickness, producing considerable economic savings. However, this cannot be done without a knowledge of the dependence of the alloy's mechanical properties on dimensions of the final product or specimen. Commencing from conditions of cable shield transportation and use, the effect of scale factor on alloy properties was studied for tensile loading, creep, and cyclical bending. The data gathered permit evaluating the validity of calculations for change in cable shield thickness for replacement of one alloy by another.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 103–109, July, 1977.     

Photoconductivity of lead telluride-based doped alloys in the submillimeter wavelength range

Persistent photoconductivity in a Pb_0.75Sn_0.25Te(In) alloy initiated by monochromatic submillimeter-range radiation at wavelengths of 176 and 241 µm was observed at helium temperatures. This photoconductivity is shown to be associated with optical excitation of metastable impurity states.     

Ordering of body-centered cubic ternary alloys with three types of site. I

The ordering theory of A-B-D alloys with body-centered cubic (bcc) lattices and three types of site is examined by the Gorskii-Bragg-Williams approximation. It is shown that under certain conditions there can be two critical temperatures (T₀) for the order-disorder phase transition. The case of alloys with a quasi-binary BA-BD section is examined in detail.     

Severe plastic deformation of amorphous alloys: I. Structure and mechanical properties

The basic regularities of variation in the structure and mechanical properties of amorphous Ni₄₄Fe₂₉Co₁₅Si₂B₁₀ alloy at severe plastic deformation (SPD) in a Bridgman cell at different temperatures are considered. It is shown that SPD is accompanied by homogeneous nanocrystallization, which is caused by the plastic flow mode. The transition from inhomogeneous mode of plastic flow to a qualitatively different one has been detected. The SPD structural model of deformational “dissolving” of crystals is proposed to explain why nanocrystals no more than 10 nm in size are observed during SPD. It is found that thermally activated nanocrystallization may occur at very low temperatures (77 K) under very high stress and with a high concentration of excess free volume.     

The growth of thin PbO layers on lead films: I. Experiment

The growth of ～ 10 to 100 Å thick, orthorhombic PbO layers on lead was investigated by ellipsometry, electron tunneling and X-ray diffraction. Oxides were grown on 2000 to 15000 Å thick, vacuum-deposited lead films, using: oxygen pressures from 10^?2 to 10⁺³ Torr; temperatures from ?90 to + 150°C; and, times up to several weeks. Apparatus is described for monitoring ellipsometric parameters during oxidation and fabricating PbPbOPb tunnel junction devices in situ. The results indicate that lead recrystallization processes can accelerate the oxidation, so that the rates depend complexly on temperature, lead thickness and microsctructure. The refractive indices provide an indication of the extent of lead recrystallization effects on the oxidation process as well as the accuracy of the oxide thickness determination. X-ray findings indicate that the PbO has the orthorhombic PbO structure, is highly strained while being epitaxially related to the lead, and has a thickness close to that obtained ellipsometrically. Electron tunneling data provide a measure of oxide thickness fluctuations from the average or ellipsometrically-derived values.     

Onset of magnetism in concentrated ternary alloys I

The onset of magnetism and the magnetic propreties of concentrated substitutional ternary alloys A(Fe_1?xB_x)₂ (A = Y, Zr, U; B = Mn, Co, Ni and Al), Y₂(Ni_1?xCo_x)₇, Y(Ni_1?xCo_x)₃, Y₆(Fe_1?xMn_x)₂₃ and Ti(Fe_1?xCo_x) as well as the amorphous alloy system (Fe_1?xNi_x)₇₇Si₁₀B₁₃ are discussed in terms of homogeneous and heterogeneous models based on the Stoner-, Edwards- Wohlfa arth- and the Landau theory of phase transitions of second order. For a detailed comparison of the nine ternary systems A(Fe, B)₂ (A = Y, Zr, U; B = Mn, Co, Al) we refer to a following paper. From the results obtained on alloying UNi₂ with Fe, Co and Cu we propose that the magnetic moment of UNi₂—contrary to UFe₂—resides mainly on U rather than on the Ni site. The appearance of magnetism in YNi_x compounds by either changing the Y : Ni ratio or substituting Ni by Co in YNi₃ and Y₂Ni₇ is mainly attributed to band effects for which a schematic N(E) curve is proposed. The breakdown of long-range magnetic order in Y₆(Fe, Mn)₂₃ seems to be caused by a lack of delocalized electrons and a preferential site occupation of Mn and Fe. The magnetic properties of Ti(Fe_1?xCo_x) change from an itinerant to a localized moment behaviour above and below x = 0.5 due to the occurrence of Fe antistructure atoms which drive the onset of long-range magnetic order. The occurrence of magnetism in amorphous alloys compared with that of crystalline alloys with a high degree of disorder may be characterized in a similar way.     

Recent advances in the metallurgy of aluminium alloys. Part I: Solidification and casting

The goal of these review papers is to summarize the recent advances in the metallurgy of aluminium alloys and from this analysis, to try to outline future developments in this field. Part I deals with the transformation of aluminium alloys from the liquid to the solid state, while Part II will focus on solid-state transformations. These papers are by no means exhaustive since the literature is very abundant, but the authors wish to give a personal view of what they think are the most relevant scientific contributions that can impact future technological developments.