Magnetic viscosity in Nd60Fe30Al10 amorphous alloys

Ferromagnetic amorphous Nd₆₀Fe₃₀Al₁₀ alloys melt spun at wheel speeds between 5 and 20 m/s exhibit hard magnetic properties, which are found to be very sensitive to the cooling conditions. The magnetization reversion mechanisms leading to the rather high coercive forces found are investigated by thermally activated magnetic relaxation experiments; the mean fluctuation field and the activation volume are measured—in specimens cooled at different rates—at the critical field for extensive magnetization reversion. These preliminary results show a qualitative agreement with the predictions of a ferromagnetic cluster model.     

Enthalpy and heat capacity of titanium based alloys

Light metal alloys, as aluminium- and titanium based alloys, are of great interest to aerospace industry but thermodynamic information, mainly heat capacity, is often missing. Then we measured on heating the heat content of seven industrial titanium alloys from room temperature to 600°C with the help of a high-temperature Calvet calorimeter (drop method). Their heat capacities were deduced by derivation of the enthalpy with respect to temperature. The departures from Kopp-Neuman law were calculated.     

Analysis of ground states of fcc thin film of binary alloy under confinement

In this paper, we have investigated the ground states of a few-layered fcc thin film of binary alloy with two surfaces in the (001) direction under symmetric surface confinement. The phase diagram of the ground states is given according to the energy analysis of binary alloy thin film composed of six atomic layers in the (001) direction. Surface confinement field (SC field) is introduced as a term to describe the confinement on the two surfaces in the (001) direction. Using Monte Carlo simulation, we have found that there are 17 different ground states occurring when both SC field and chemical potential vary from - ∞ to + ∞. Antiphase boundary(APB) was found in 12 of the 17 ground states, and only nine configurations with different symmetry were found among the 17 ground states. Received 6 November 2001 and Received in final form 25 January 2002     

High-Energy Ball-Milling of Alloys and Compounds

Hyperfine Interactions - After outlining some characteristics of high-energy ball-milling, we discuss selected examples of phase transformation and of alloy synthesis which focus on deviations from...     

金刚石生长过程中Fe基合金催化机制的研究

 用X光衍射、电子能谱及Mossbauer谱实验方法，测量了高温高压条件下Fe基合金中Fe原子的3d壳层电子状态的变化，揭示了人造金刚石生长过程中，Fe原子3d壳层未成对电子与2P_z电子之间的键合。     

On the Fremond’s constitutive model for shape memory alloys

The remarkable properties of shape memory alloys have increasing the interest in applications in different areas varying from biomedical to aerospace hardware. Despite the large number of applications, the modeling of SMA is the objective of many researches developed in order to describe all details of its thermomechanical behavior. The present contribution revisits a constitutive model presented by Savi et al. (2002), which is built up on the classical Fremond’s model, in order to contemplate the horizontal enlargement of the stress–strain hysteresis loop. Numerical simulations present qualitative agreement with experimental data, showing pseudoelastic, one-way and two-way shape memory effects.     

Predictable behavior of smart materials (Cu-Zn-Al SMA)

Reliability is a critical word in industrial applications of Shape Memory Alloys. Accurate and reproducible transformation hysteresis cycles and internal loops were obtained in single crystals using a high resolution automatized equipment. From a mechanical model formulated for a single martensite plate, the shape of the hysteresis cycle is obtained by generalizing the representation toN plates. The observed time effects on the hysteresis loops related to diffusion processes were also taken into account. It allows to explain the martensite recoverable creep and the micromemory effects. Also, the room temperature effects on the parent phase (for instance, summer to winter) acting over the transformation temperature are quantified.Research carried out under the project NATO 920452. Partial support from CICYT is gratefully acknowledged. V. T. acknowledges Dir. Pol. Terr. (Generalitat of Catalonia) for useful support. Fruitful discussions with Drs. F. C. Lovey and J. L. Pelegrina of CAB-Argentina (EEC-ALA/MED contract) are acknowledged.     

Diffusion mechanisms in the Fe_3Si alloys

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A comment on the cooperative-ring-exchange theory on the fractional quantum hall effect

Summary It is shown that the functional integral formulation of the cooperative-ring-exchange theory of Kivelson, Kallin, Arovas and Schrieffer contains some serious uncontrolled approximation. The formulation does not reproduce the correct value of the partition function even in the simple case of a two-dimensional electron with a strong magnetic field and a harmonicoscillator potential.     

Solute-atom segregation/structure relations at high-angle (002) twist boundaries in dilute Ni−Pt alloys

Monte Carlo simulations, utilizing embedded atom method (EAM) potentials, are employed to investigate in detail solute-atom segregation behavior at high-angle symmetrical (002) twist boundaries, at T=850 K, in Pt-3 at.% Ni and Ni-3 at.% Pt alloys. Solute enhancement in those alloys occurs on both sides of the phase diagram, although it is considerably higher on the Ni-rich side. The distributions of solute concentrations within the first and the second planes are very inhomogeneous, with the sites highly enhanced in solute being in the minority. The remaining sites exhibit little or no enhancement. The highest level of solute concentrations at individual sites continues to increase with the value of the rotations angle, , until saturation occurs at about the =5 misorientation. The large differences in concentrations between different types of sites suggest the possibility of an ordered grain-boundary phase. The correlation between the structure and solute species concentrations in most cases follows the trends observed for low-angle boundaries: Pt as a solute prefers the structural units of the perfect crystal type, while Ni as a solute tends to segregate at the filler units associated with the cores of the primary grain boundary dislocations. A strong correlation is observed between the position of a site in the first or second (002) plane and the plane of the interface. Rigid-body translations are detected for two boundaries on the Pt-rich side of the phase diagram. Roughening and possible structural multiplicity occur in the =5 boundary on the Ni-rich side. The same boundary on the Pt-rich side of the phase diagram exhibits a considerable amount of structural and chemical disorder.