Application of electromagnetic processing for development of high-performance sintered powder metal parts

Electromagnetic processing was used to study the effects of electro-magneto forming on the dimensional control and thermal stability of sintered powder metal (PM) parts. The investigation was carried out on sinter-hardened, low chromium-molybdenum bainitic steel. The results show an increase in the microhardness of about 14% for the electromagnetic processed parts compared to the as-sintered parts. This was attributed to the 2% increase in the density, 17% and 29% reduction in the volume fraction of porosity and width of the bainitic lath, respectively, due to the electromagnetic processing. Dimensional characterization was carried out using a vertically aligned push-rod dilatometer. After four thermal cycles of heating and cooling, at a controlled rate of 5 °C/min to 1000 °C, the electromagnetic processed parts exhibited reduced dimensional change of about 44% lower than for the as-sintered parts. This is significantly important for applications that demand high dimensional tolerance and performance, especially at elevated temperatures.     

Ultrasound absorption due to electrons and phonons in alkali liquid metals

The excess longitudinal ultrasonic absorption over and above the classical value in four alkali liquid metals near their melting points has been accounted for by the mechanisms of interaction of sound waves with the conduction electrons and the thermal phonons (Akhieser mechanism), both exhibiting a quadratic dependence on sound frequency. An expression, similar to the Bridgman relation for liquids, for the phonon conductivity in the liquid metals has been developed. This approach briefly reported here yields good results.     

Three-half harmonic generation in laser-plasma interaction: Evidence for plasmon propagation

Summary Side emitted 3ω/2 radiation was studied by interacting 1.064 μm laser light with plasmas obtained from exploding thin foils. Both focusing (f/8) and collecting (f/7) optics were designed in order to reduce the instrumental bandwidth of the 3ω/2 spectrum. Time-resolved spectra and time-resolved images were obtained and analysed. All the observed spectral features, including the substantial lack of a ?blue? component, the amount of red shift and bandwidth, are consistent with the Karttunen theory of half-integer harmonics generated in plasmas. This theory takes into account the propagation of ω/2 plasmons produced by ?two plasmon decay? and their coupling with laser light.     

Evidence for a crossover in the frequency dependence of the acoustic attenuation in vitreous silica

We report measurements of the sound attenuation coefficient in vitreous silica, for sound waves of wavelength between 50 and 80 nm, performed with the new inelastic UV light scattering technique. These data indicate that in silica glass a crossover between a temperature-dependent (at low frequency) and a temperature-independent (at high frequency) acoustic attenuation mechanism occurs at Q approximately equal to 0.15 nm(-1). The absence of any signature in the static structure factor at this Q value suggests that the observed crossover should be associated with local elastic constant fluctuations.     

Surface plasmon propagation in a pair of metal nanowires coupled to a nanosized optical emitter

The coupling, propagations, and far-field emissions of surface plasmons in a pair of Au nanowires with a dipole emitter have been investigated using the finite-difference time domain method. The surface plasmon wavelength is tunable from 650 to 380 nm by adjusting the distance between the two wires, which leads to an enhancement of coupling constant and density of states of the surface plasmon. The converted energy from the dipole emitter to the propagating surface plasmon as well as the far-field emission intensity of a pair of Au nanowires increase to approximately four times as large as those of a single nanowire.     

Surface of a 3He crystal: crossover from quantum to classical behavior

3He crystals start to show facets on their surface only at about 100 mK, well below the roughening transition temperature. To understand the reason for that, we have performed the first quantitative investigation on the growth dynamics of the basic (110) facet at 60-110 mK. The obtained values of the step free energy suggest an extremely weak coupling of the solid-liquid interface to the crystal lattice which we show to be the result of quantum fluctuations of the interface. The renormalization group approach by Nozières and Gallet, modified to incorporate quantum fluctuations, explains well the temperature dependence of the step energy measured in this work and at ultralow temperatures by Tsepelin et al., where the coupling is known to be strong. We have thus shown that, paradoxically, the role of quantum fluctuations is at higher temperatures much larger than at low temperature.     

Critical behaviour of two slightly uniaxial ferromagnets: Evidence for crossover with anisotropy

The critical exponents β, γ, δ and the scaling function of ferromagnetic Cu(NH₄)₂Br₄, 2H₂O and CuRb₂Br₄, 2H₂O have been determined. The experimental scaling function is close to the theoretical one of three-dimensional Heisenberg model and the scaling laws are approximately fullfilled. The measured susceptibilities agree well with theoretical results for slightly anisotropic Heisenberg ferromagnet. The predicted cross-over effect, well observed on the perpendicular susceptibility, allows to explain the low experimental value of γ.     

Dimensional crossover in quantum networks: from macroscopic to mesoscopic physics

We report on magnetoconductance measurements of metallic networks of various sizes ranging from 10 to 10(6) plaquettes, with an anisotropic aspect ratio. Both Altshuler-Aronov-Spivak h/2e periodic oscillations and Aharonov-Bohm h/e periodic oscillations are observed for all networks. For large samples, the amplitude of both oscillations results from the incoherent superposition of contributions of phase coherent regions. When the transverse size becomes smaller than the phase coherent length Lphi, one enters a new regime which is phase coherent (mesoscopic) along one direction and macroscopic along the other, leading to a new size dependence of the quantum oscillations.     

Flow equations for Hamiltonians: crossover from Luttinger to Landau-Liquid behaviour in the n-orbital model

Flow equations for Hamiltonians are a novel method for diagonalizing Hamilton operators. They were applied by one of the authors to a one-dimensional SU(n)-symmetric fermionic system, solving the occuring equations to first order of a $\tfrac{1}{n}$ -expansion. In this paper, we generalize the procedure to an arbitrary number of spatial dimensions. Although the resulting equations cannot be solved analytically, some information can be extracted about the particle number near the Fermi surface. The results suggest a nonuniversal behaviour for d = 1 which breaks down in favour of that of a Landau liquid in any dimension ? 1.     

Evidence for a two-magnon process in the linewidth of thin metal films

The temperature dependence of the spinwave resonance linewidth in thin ferromagnetic metal films has been observed at 35 GHz in the temperature range 4 °K to 300 °K. The data are analyzed in terms of a two-magnon relaxation process induced by a planar inhomogeneity in the internal field of the film. The inhomogeneity is due to imperfections in the film structure introduced during deposition. The linewidth is found to decrease with increasing temperature in a manner similar to the temperature dependence of the magnetization with a mode dependence that is in reasonable agreement with the model proposed.Supported in part by the National Science Foundation.     

Role of decay processes in the propagation of slightly nonequilibrium thermal-pulse phonons in YAlO3:Lu crystals

Data on the propagation of slightly nonequilibrium phonons, ΔT≪T _b (T _b is the cryostat bath temperature) in Y_0.9Lu_0.1AlO₃ crystals with effective elastic scattering by rare-earth metal atoms are analyzed. The experimental results are interpreted on the basis of the “quasidiffusion” model, where three-phonon inelastic decay processes play a decisive role in the phonon kinetics. Monte Carlo calculations with these processes taken into account yield good quantitative agreement with the experimental data. Zh. éksp. Teor. Fiz. 112, 325–331 (July 1997)