An extremely fine lamellar structure formed in a Ti-48at.%Al alloy, which was heat treated in the high-temperature α-Ti (disordered hcp) single phase field (1683K), followed by ice water quenching, has been examined by high-resolution and analytical transmission electron microscopy. The microstracture consists of thin plates of ordered α2-Ti3Al (D019: ordered version of hcp) and γ-TiAl (Ll0: ordered version of fcc) phases, and interfaces of lamellae are atomically flat in a wide range. From detailed analyses of the microstructure and composition in nm scale, the α→γ phase transformation, which occurs during quenching and produces the extremely fine α2-γ lamellae, has been discussed.

The surface modification induced by nitrogen ion implantation on the Al-alloy 7075 has been studied with the aim of understanding the microstructural evolution and the phase separation during the implantation process. 150 keV N2+ ions have been implanted at different temperatures from 373 K to 473 K, with a current density of 5–15 µA/cm2 on previously polished samples. The implanted dose was in the range 1 × 1017 N/cm2 - 5 × 1017 N/cm2. Vickers micro-hardness tests and friction coefficient measurements show a real improvement in the mechanical behaviour of the alloy after the treatment.

TEM observations of specimens treated at low temperature with different ion dose have been carried out at 200 kV on cross-sectional samples, prepared by ion beam milling. First results show the presence of small AlN hexagonal precipitates whose evolution is followed as a function of the implanted dose.

The present paper is aimed at studying the physics of a nickel nanophase at the atomic level. A dense polycrystal has been designed by ideally growing many nano-crystals from randomly distributed seeds and truncating them through a Voronoi construction. The sample has been brought to thermodynamic equilibrium and quenched to its local minimum energy thus leading to a mechanically stable system. The dynamic evolution has been simulated by means of classical molecular dynamics employing a Finnis-Sinclair interactive potential. Owing to the large number of atoms required, a parallel code has been developed. Elastic and plastic behaviour of the simulated sample has been compared with that of a perfect crystal. Evidence of an enhanced plastic behaviour has been observed when severe tensile stresses are applied.

Nano-grained Fe-29Al-2Cr intermetallic and Fe-Cu two-phase composites have been consolidated to full density from powders produced by high-energy ball milling, using a sinter forging procedure developed recently in our laboratory. Grain sizes remained within nanophase range (<100 nm) after consolidation. Microhardness tests of Fe-29Al-2Cr samples consolidated to different density levels indicate a significant strengthening effect due to nanoscale grain size and a monotonic microhardness increase with decreasing residual porosity. Fully dense Fe-Cu composites exhibit enhanced microhardness as compared with rule-of-mixtures predictions, which may be attributable to interface strengthening at fcc-bcc interphase boundaries.

While gas condensation and mechanical alloying have been used to produce nano-phase powders, an effective method of applying these powders as coatings is still lacking. Furthermore, fundamental studies of the mechanical properties of nano-phase powders may be complicated by the porosity associated with consolidation processes. Recently, we have made nano-crystalline composite thin films of Ag-Mo and Ag-Ni by depositing two immiscible elements simultaneous onto substrates. We found, using XRD and TEM, that the average grain size varies from 10 to 100 nm by choosing an appropriate substrate temperature. Nanoindentation measurements showed the hardness of the composite is increased four times by reducing the grain-size of both phases from 100 to 10 nm. The load vs. displacement curves were simulated using a finite element method (ABAQUS). A relationship between the hardness of the two-phase composite and the yield strength of each phase is obtained.

Mechanical properties of nanostructured intermetallic Ni3Al synthesized by the inert-gas condensation technique are studied by means of instrumental indentation using the ICT-CSEMEX indenter. This instrument is a microindenter which continously measures load and displacement. Load-displacement curves are performed as function of grain size, consolidation- and annealing temperature. The mean grain size of the samples are studied by means of x-ray diffraction and small-angle neutron scattering.

X-ray, magnetism and electron loss spectroscopy data were obtained for a series of coherent Fe-Cu face-centred multilayers which suggest that there is a lattice parameter anomaly in the structure. The use of high resolution electron microscopy (HREM) and dark field imaging to measure spacing changes along the layer normal are compared. Experimental dark field images suggest that the Fe has expanded lattice spacings in the growth direction in contradiction to the predictions of a conventional elastic model for a coherent multilayer structure.

In this work we compare the ferromagnetic behavior of ultrathin FexNi(1-x) and CoxNi(1-x) films grown on Cu(100) epitaxially with varying stoichiometry. The thickness regime chosen was 1 to 5 ML over a wide range of alloy composition. Using a finite-size scaling law we proposed for the Curie temperature vs. film thickness measurements, we extrapolate and plot the bulk fee Curie temperature as a function of composition. The results suggest that the growth of these films is pseudomorphic with the films adapting a fee structure and the Cu lattice constant. Besides, the Invar effect is not observed in these ultrathin films of FexNi(1-x) alloys and the magnetic phase of Fe atoms is the low-spin ferromagnetic phase. The CoxNi(1-x) films show the expected monotonic decrease in Tc with increasing Ni content.

Heterogeneous alloys CoxAg1-x with atomic concentrations x=0.20 and 0.35, presenting giant magnetoresistance properties, have been studied by Total Electron Yield X-ray absorption spectroscopy at liquid nitrogen temperature at the Co K edge after annealings at various temperatures. For both sample concentrations, the Co atoms are mainly in small filament agglomerates for the as-deposited and low temperature annealed samples (T<150°C). In this temperature range, the local Co atomic environment is very stable and disordered. A structural change has been detected by XANES and EXAFS analysis between the 250 and 400°C annealings. After a 400°C annealing during 10 min, the nanostructures evolve towards larger, more compact and well ordered granules. The Co-Co distance varies from 0.246 to 0.248 nm as the annealing temperature increases indicating that the small filament-shaped agglomerates are under strain in the Ag matrix. The Debye-Waller factor of the Co0.35Ag0.65 samples decreases continously as the annealing temperature increases, as this factor drops suddenly after a 250°C annealing for the Co0.20Ag0.80 sample. The Co agglomeration is steadily larger for the Co0.35Ag0.65 sample than for the Co0.20Ag0.80 one. The Co-Ag contribution is negligible for the Co0.35Ag0.65 sample, as it represents approximately one third of the nearest neighbors for the Co0.20Ag0.80 sample from the as-deposit up to a 250°C annealing stage.

The experimental results of research of structural modifications in amorphous magnetic alloys (AMAs) under thermotreatment obtained by angular and spectroellipsometric methods are presented and discussed. The ductile-brittle transition was observed for the ribbons of some 3d-metal-based amorphous alloys. The relationship between the principal angle of incidence φ0 and annealing temperature Ta of alloys was obtained for the ribbons of AMAs. The observed behaviour of φ0 is connected with appearance of the novel amorphous phase’s clusters inside the surface’s layers of alloys.

The influence of melt’s overheating on the atomic and electronic structure of AMAs was studied. It was found that the increase of melt’s overheating temperature leads to the decrease of absorption index within the whole spectral range (ħω=0.5–4.38 eV). The structural anisotropy of AMAs and its changes after annealings were determined by reflectometric and ellipsometric measurements.

The magnetic properties and hyperfine fields were investigated at low temperatures on amorphous Fe80B20 ribbons crystallized at the end of the nucleation-and-growth process without involving coarsening process. The results obtained by SQUID magnetometer and Mössbauer spectrometer show that saturation magnetization and mean magnetic hyperfine field values are greater than those in both the parent amorphous phase and in the fully crystallized structure where coarsening and grain growth processes are involved. Below 200 K irreversibility is observed in low field magnetization measurements. Transmission electron microscopy measurements reveal that spherulites of Fe3B include a radial structure made of small bcc-Fe acicular crystals about 200 nm long and 10 nm wide. In our opinion, magnetic properties and hyperfine fields are ruled by both high magnetic anisotropy of small monodomain acicular bcc-Fe crystallites and the structure of Fe atoms located at their surfaces.

SiO2 thin films containing fine Fe particles were prepared by a co-sputtering method. α-Fe particles were then formed by heat-treating the film at 650°C to 700°C. The average size of the particles was controlled by changing heat-treatment time and temperature. The magnetic properties of these samples were investigated and discussed in terms of the size of the particles. It was found that the coercivity of the sample containing α-Fe particles (average particle size = 24nm) is as large as 36 Oe which is much higher than that of the bulk Fe.

Selected glass compositions in the Pb5Ge3O11-PbTiO3 (PG-PT) and Pb5Ge3O11-Pb(Zr1/2Ti1/2)O3(PG-PZT) systems were prepared by quenching from the molten state. After different heat treatments, a multiple ferroelectric composite crystallized at low temperatures, PG-PT or PG-PZT. In this paper the results obtained on the dielectric constant, dissipation factor, ferroelectric hysteresis loop, and pyroelectric coefficient of different bulk and thick-film samples of compositions in the PG-PT and PG-PZT ferroelectric glass-ceramic system are presented and discussed.

Dense nanocrystalline CeO2-x. of ∼10 nm grain size exhibits enhanced, PO2-dependent electronic conductivity indicative of intrinsic nonstoichiometric behavior under conditions where coarse-grained counterparts are extrinsic. The enthalpy of reduction is lowered by over 2.4 eV per oxygen vacancy. The nanocrystals also exhibit greatly reduced grain boundary resistance, attributed to grain-size-dependent segregation. We propose that interface doping by selected low energy defect sites dominates the defect and transport properties of nanocrystalline ceria, and possibly other nanocrystalline compounds.