Growth kinetics of antiphase domains in the alloy Ni4Mo

Using the methods of transmission and diffraction electron microscopy, we analyze the laws governing the growth kinetics of antiphase domains in the alloy Ni₄Mo during its isothermal ordering at 840, 800, and 700°C. The size distributions of the antiphase domains as well as the mean size and central moments of the distributions are determined. It is shown that the growth of the antiphase domains obeys the equation Dⁿ-D ₀ ⁿ =Ae^–Q/kT. The value of the parameter n is 2.5 for 840 and 800°C, and 5 for 700°C. By considering the isochronous cross section of the kinetic curves, we calculate the activation energy for the growth of antiphase domains; it equals 65 kcal/mole.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 84–89, January, 1977.     

Temperature and N energy dependence on nano-structural modifications and characteristics of Mo surface

The surface modifications of Mo massive samples (0.5 mm foils) made by nitrogen ion implantation are studied by SEM, XRD, AFM, and SIMS. Nitrogen ions in the energy range of 16-30 keV with a fluence of 1 × 10¹⁸ N⁺ cm⁻² were implanted in molybdenum samples for 1600 s at different temperatures. XRD patterns clearly showed MoN (0 3 1) (hcp) very close to Mo (2 0 0) line. Crystallite sizes (coherently diffracting domains) obtained from MoN (0 3 1) line, showed an increase with substrate temperature. AFM images showed the formation of grains on Mo samples, which grew in size with temperature. Similar morphological changes to that has been observed for thin films by increasing substrate temperature (i.e., structure zone model (SZM)), is obtained. The density of implanted nitrogen ions and the depth of nitrogen ion implantation in Mo studied by SIMS showed a minimum for N⁺ density as well as a minimum for penetration depth of N⁺ ions in Mo at certain temperatures, which are both consistent with XRD results (i.e., I_{Mo (2 0 0)}/I_{Mo (2 1 1)}) for Mo (bcc). Hence, showing a correlation between XRD and SIMS results. This phenomenon is explained on the basis of residual gas, substrate temperature, dissociation of water in the chamber and the ion energy.     

Orientation dependence of the surface segregation kinetics in Cu-6 at % Ge alloy

The surface segregation kinetics of germanium on the (110), (111), and (100) faces of Cu-6 at % Ge alloy has been investigated in the temperature range of 525–700 K by electron spectroscopy. In the initial annealing stage, Ge is accumulated on the surface, forming a phase similar to a supersaturated solid solution. When the Ge concentration reaches 25–40 at % (depending on the face), it forms well-ordered 2D phases, whose structure is determined by the face orientation. In the surface region the bulk diffusion parameters exhibit anisotropy; the Ge diffusion activation energy is minimum near the (110) face.     

Kinetics of ordering in Ni3Mn alloy with additions of copper

Neutron-diffraction analysis and measurements of electrical resistance were used to investigate the kinetics of ordering in Ni₃(Mn, Cu) alloys preliminarily tempered at 900°C, containing 0.45–9.29 at.% copper. It was established that introducing copper atoms in place of manganese atoms in the alloy Ni₃Mn leads to slowing of the ordering process. The degree of long-range order inside antiphase domains in Ni₃(Mn, Cu) alloys is less than in the binary alloy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 35–39, March, 1977.     

Mössbauer study of radiation ordering in Ni3Mn alloy

An ordering process in disordered Ni₃Mn alloy. irradiated with fast neutrons at different doses and isothermally annealed. has been investigated using Mössbauer spectroscopy.     

Thickness dependence of magnetization in FeNi invar alloy film

The thickness dependence of magnetization of FeNi Invar alloy films was observed by means of small angle Lorentz electron diffraction. A remarkable reduction of magnetization at room temperature was observed for films with thickness below 400 Å. This may be ascribable to the instability of the ferromagnetic state in Fe-Ni Invar alloys.     

Orientation dependence of texture evolution in cold-rolled Ni3Al single crystals

Texture evolutions of cold-rolled thin foils of binary stoichiometric Ni₃Al single crystals were examined as a function of the initial crystal orientation. In the cases of the initial rolling direction (RD) close to ?001?, a double {110} {112} texture associated with a banded structure tends to develop irrespective of the initial foil normal direction (ND). The macroscopic shape of these foils with the banded structure is straight and simply elongated along RD, keeping their rectangular shape. In contrast, when the initial RD is close to {112}, the texture and the microstructure are rather uniform without the texture splitting and the banded structure formation. The foils of group B are macroscopically curved, twisted and eventually cracked from the side edge of the samples. Tendencies of the lattice rotations vary with the initial ND in the latter case. According to the plastic strain analysis, the formation of the banded structure is found to be essential for fabricating the thin straight foils in the case of the cold rolling of Ni₃Al single crystals.     

Order-disorder phase transition in Ni4W alloy

The order-disorder phase transition in Ni₄W alloy with a D1 _a superlattice was studied experimentally by x-ray structural analysis and theoretically by the Green function method. An experimental temperature dependence was obtained for the equilibrium parameter of long-range order for Ni₄W alloy. It was established that the order-disorder phase transition in the alloy is a first-order transition; the transition occurs through the two-phase region D1_a + A1. The Green function technique, with account for the pair-correlation functions, was used to describe the order-disorder transition for the D1 _a superlattice. The theoretical temperature dependence obtained for the equilibrium parameter of long-range order is in satisfactory agreement with the experimental curve.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 92–97, April, 1978.     

Phase segregation and crystallization in the amorphous alloy Ni70Mo10P20

Structural evolution of the amorphous alloy Ni₇₀Mo₁₀P₂₀ has been studied by x-ray diffraction, and by following transmission and high-resolution electron microscopy annealing both above and below the glass-transition temperature. When annealed above this temperature, the amorphous phase undergoes segregation into regions about 100 nm in size having different chemical composition. Diffraction from such samples produces diffuse rings, and the scattering vector corresponding to the maximum intensity varies from point to point within the interval of 4.88 to 4.78 nm⁻¹. When occurring between the glass-transition and crystallization temperatures, crystallization produces groups of nanocrystals, 20–30 nm in size, which are in direct contact with one another and form a polymorphic mechanism. The crystallization mechanism changes when the annealing temperature is brought below the glass-transition point. At these temperatures the amorphous matrix crystallizes entectically with formation of eutectic colonies. Fiz. Tverd. Tela (St. Petersburg) 40, 1577–1580 (September 1998)     

Temperature dependence of the yield point of the alloy Ni3Al

A study was made of the effect of variations in the Ni₃Al composition on the temperature dependence of the yield point. It was found that the yield point has an anomalous rate dependence: the yield point decreases as the rate of strain is increased. From an analysis of these results it is concluded that the anomalous temperature dependence of the yield point of Ni₃Al can be attributed to the same dislocation-retardation mechanisms as are apparently responsible for the anomalous temperature dependence of strain hardening.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 2, pp. 68–74, February, 1971.The authors thank V. Lunev and V. M. Barsanov, students at Tomsk State University, for participation in the experiments.     

Orientation dependence of the solid/liquid interfacial free energy in binary systems

A first-order theory of compositional segregation at solid/liquid interfaces, based on a pair-bonded, lattice-liquid interfacial model, has been applied to predict the effect of segregation on the orientation dependence of the interfacial free energy in binary metallic systems. The results show that the sharpness of the cusps in the gamma plot is reduced due to preferential segregation at layer edges as compared to layer faces, and cusps may be eliminated under certain conditions. The reduction in cusp sharpness is the greatest when the composition difference of the solid and liquid phases is large and the solutions are appreciably non-ideal. The relative reduction of sharpness due to segregation is less pronounced for cusps which are sharper in the unsegregated condition, so segregation tends to smooth the form of the gamma plot. Graphical results are presented for calculation of segregational anisotropy effects in general systems.     

Size dependence of the surface energy and surface tension of metal nanoparticles

The specific surface energy of small nanoclusters of transition fcc metals is calculated using the many-particle tight-binding potential and its earlier analog, the Gupta potential. The calculations are performed using both a theoretical model and computer simulations based on the Monte Carlo method. The equimolecular surface is considered as the dividing surface. It is found that at short radii of the nanoclusters, the surface energy and surface tension grow linearly as the particle radius increases. The values of the coefficient of proportionality in the dependence of the specific surface energy on the radius of a nanocluster are compared to the available literature data, experimental and otherwise.     

Investigation into the kinetics of ordering of the Au4Zn alloy

The kinetics of ordering of the Au₄Zn alloy is investigated using X-ray diffractometry. It is established that the ordering and growth of domains inside the ordered phase are multistage processes. These processes are characterized by nucleation and growth of the ordered phase. The kinetics of growth of domains involves the nucleation and growth stages, as well as stages in which the crystal lattice axes have preferred or equally probable directions. The stages are more pronounced at low annealing temperatures. The duration of particular stages of the evolution of antiphase domains and their sizes depend on the annealing temperature.     

Orientation dependence of surface critical phenomena in antiferromagnets: exact results in two dimensions

For an Ising antiferromagnet, we analyze exact expressions for the one- and two-point correlation functions for spins on the edge of a square lattice with a magnetic field applied to the surface sites. Two different edge orientations, with respect to the crystal axes, are treated. At bulk criticality, we confirm that the surface universality class depends on the edge orientation and show the importance of having the bulk phase in a pure state. For the two-point function, we find a singularity in the correlation length due to depinning effects which we argue is also present in higher dimensions.     

Orientation dependence of surface enhanced raman intensities: results from abinitio calculations

Time dependent Hartree—Fock methods have been used to calculate Raman intensifies for H₂ adsorbed onto a model lithium cluster as a function of the orientation of H₂ relative to the cluster surface. The intensity is found to be largest for perpendicular adsorption, dropping to a small value at an intermediate angle, and then rising to a second but smaller maximum for parallel adsorption. The results are interpreted using a model which correlates enhancement to lithium cluster orbital energy shifts induced by the static quadrupole field Of H₂.