Relative grain boundary free energy and surface free energy of some metals and alloys

By the method of thermal etching measurements were carried out of the ratio of grain boundary free energy _GB to the surface free energy _s in silver, copper, nickel, gamma-iron and cobalt of 99·999 pct. purity each, three copper-aluminium alloys and eight nickel-cobalt alloys, the total concentration of impurities in each alloy not exceeding 0·01 pct, as a function of the temperature and sometimes of the annealing medium.     

Structural and phase changes in metals during formation of the fatigue fracture surface in metals and alloys

The mechanisms of deformation-induced structural and phase changes, which accompany crack nucleation and growth during fatigue fracture of metals and alloys, are considered. It is shown that the crack steady growth phase is determined by the processes of local melting of the material in extension phase, and melt crystallization processes with formation of shrinkage pores in front of the crack tip in the unloading phases and crack narrowing.     

Elastic-plastic deformation and fracture of shock-compressed single-crystal and polycrystalline copper near melting

The Hugoniot elastic limit, the yield strength, and the spall strength of polycrystalline M1 copper and single-crystal (110) and (111) copper are determined during shock compression up to 8 GPa in the temperature range 20–1080°C from an analysis of the free-surface velocity profiles recorded with VISAR laser velocimeter. The measurements show that all copper samples exhibit strong athermal hardening (increase in the Hugoniot elastic limit) near the melting temperature. Copper single crystals have a very low elastic limit in the temperature range up to 600°C, this limit increases sharply as the temperature increases to 1000°C, and it depends on the crystallographic orientation of a single crystal. The temperature dependence of the spall strength has a threshold character for all copper samples. Copper single crystals demonstrate higher resistance to spall fracture; however, near the melting temperature, the difference between the spall strengths of the copper single crystals and M1 copper becomes insignificant, 50% of the initial level.     

Surface free energies of solid metals: Estimation from liquid surface tension measurements

An equation is derived on semi-theoretical grounds which expresses the solid-vapour surface free energy as a function of the liquid surface tension and the solid-liquid interfacial free energy. A means of calculating reliable values for the solid-liquid energy is presented, which then allows an accurate estimate of solid surface energy at the melting temperature, T_m, to be made for the large number of elements for which dependable liquid surface tension data exist. A method of estimating surface entropy is presented, and has been used to calculate the energies typical of “average”, high-index surfaces at temperatures ranging from 0 K to T_m. It is felt that this paper describes the most accurate method presently available for the calculation of the surface energy of solids in the absence of direct experimental measurement.     

On the theory and methods of calculation of surface state energies in nearly free electron metals

Intrinsic Heine-type surface states are discussed analytically for the nearly free-electron metals. It is shown, that if one constructs the wavefunctions corresponding to the real loops exactly, while the wavefunctions corresponding to the real lines are constructed in an approximate, free electron-like manner, the general N-band, M-beam surface state matching determinant can be solved exactly in the closed form, and the problem is no more difficult than the N-band, 2-beam calculation. The resulting surface state equation has a very simple form and is easily adaptable to computer calculations. It includes all of the special cases discussed previously by other authors.     

Fermi surface of the noble metals

We report calculations of extremal areas of four Fermi surface (FS) orbits of the noble metals using the linear muffin tin orbital method in the atomic sphere approximation. Our calculations indicate that thel = 3 potential parameters and increase in the number of k-points in the Brillouin zone (BZ) summation from 240 to 916 have no significant effect on the FS. All calculations were performed self-consistently including up tol = 2 potential parameters and with 240 k points in the BZ summation. Calculations were performed with the exchange, correlation potentials (XCP) of Barth-Hedin, Barth-Hedin modified by Janak, SlaterX _α, and the Vosko-Wilk-Nussair. Results compared with other theoretical calculations indicate that none of the above XC potentials give an accurate representation of the FS for all the noble metals. We feel that the inclusion of the non-locality of XCP may give a better account of the FS geometry.     

Critical crack size in the fracture of metals

A physical approach developed by I.I. Novikov is applied for estimating and predicting critical crack lengths in metals. Experimental data obtained for single crystals are considered. The necessity of taking into account the critical crack lengths in J integrals is demonstrated.     

Measurement of dense plasma temperature of the shock-compressed silicon

Measurements of the brightness temperature and compressibility of a dense silicon plasma formed by powerful shock waves (SWs) passing through a single-crystal sample have been carried out. Plane SWs were created using an explosive technique: the traditional plane acceleration of a steel driver plate made it possible to obtain pressures in silicon up to 133 GPa, and the use of “Mach” cumulative generators realized the pressures up to 510 GPa. The shock Hugoniot of silicon was determined by the impedance matching with α-quartz as the reference. The intensity of emitted thermal radiation was measured in the infrared range λ ∼ 1.5 μm, where silicon is optically transparent, and in the visible range of the spectrum. A significant (up to five times) understatement of the measured values of the brightness temperature in comparison with the values calculated by the equation of state was found. Taking into account the reflective properties of the SW in silicon does not lead to an agreement with the experiment. The estimates of relaxation processes behind the shock front suggest the presence of a zone of the establishment of ionization equilibrium with a width of ∼10 μm.     

Mechanisms of the strain-induced dissolution of phases in nanostructured metals

The possible mechanisms of the strain-induced dissolution of phases in metals subjected to severe plastic deformation have been investigated. The mechanisms of impurity absorption by new interphase and grain boundaries formed under severe plastic deformation and the high-temperature phase at its strain-induced nucleation are shown to be the most effective. The possible dislocation mechanisms of phase dissolution are low-efficient. In carbon steels, the strain-induced dissolution of cementite continues until the limiting nanostructure absorbs about 10–12 at % carbon from the mixture volume.     

Mechanisms of deformation and fracture of the Al-Zn-Mg alloy

Laws of dislocation substructure evolution in the Al-Zn-Mg alloy subjected to compression and tension in different structural states are compared with laws of forming a deformation relief. It is established that long aging of the alloy changes the deformation localization mechanisms compared to its evolution in the alloy subjected to short-term aging. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 62–67, November, 2007.     

Correlation effects in the surface energy of metals

It is argued that the correlation energy plays a minor role in the surface energy of metals, compared to kinetic, electrostatic and exchange energies. Recent work in which the surface energy is attributed primarily to changes in plasmon zero point energy during the creation of the surface is criticized.     

Unoccupied surface states and surface barrier in metals

Recent progress in the spectroscopy of empty electronic states at metal surfaces allows for measuring the energy vs. momentum dispersion of both crystal-induced and image-potential surface states with high precision. This allows for deriving the effective barrier potential for an electron near a metal surface with considerable accuracy by comparing the experimental data with corresponding calculations based on the one-step model of inverse photoemission. The method is demonstrated for Cu(100) where four empty surface states are known experimentally.     

Structure at the free liquid surface

The singlet Born-Green-Yvon equation yields surface density profiles. A new pressure related relocation procedure during iteration yields oscillatory density profiles, as well as monotonic profiles similar to previous works. The type of profile depends upon the closure approximation of the BGY equation.     

On the nonintegrability of the free surface hydrodynamics

The integrability of the compact 1D Zakharov equation has been analyzed. The numerical experiments show that the multiple collisions of breathers (which correspond to envelope solitons in the NLSE approximation) are not pure elastic. The amplitude of six-wave interactions for the compact 1D Zakharov equation has also been analyzed. It has been found that the six-wave amplitude is not canceled for this equation. Thus, the 1D Zakharov equation is not integrable.     

The investigation of the optics of shock-compressed strongly correlated plasma

Rare gas plasmas at high temperatures and pressures, produced by explosive shock fronts, are explored using laser diagnostics. The analysis of the response of a dense plasma to an electromagnetic wave of moderate-intensity proves successful for investigating properties and the validity of physical models describing the behaviour of dense and non-ideal plasmas. We present new experimental data for the reflectivity of oblique incidence of polarized electromagnetic waves on the front of shock-compressed xenon plasmas. The optical properties of strongly correlated plasma were studied in the near-infrared and green spectral regions at a plasma mass density ρ = 0.83 g/cm³ and temperature T = 32900 K. The spatial parameters of the plasma transition shock-front layer are determined by solving numerically the electromagnetic field equations.