Both irradiation and plastic deformation can induce the stabilization of non-equilibrium phases in alloys. A simple kinetic atomistic model is used for describing these two situations, when the external forcing is acting in competition with thermally activated diffusion. Monte Carlo simulations are performed on alloys with positive heats of mixing. Both situations share common features : random solid solutions are stabilized at high enough forcing intensity (i.e. irradiation flux or shearing rate), while at moderate forcing intensities interfaces exhibit kinetic roughening. However, major differences are observed : alloys under irradiation undergo dynamical transitions between steady-states, such as a dynamical roughening transition at interfaces and a precipitation-dissolution transition in the bulk ; in alloys under shear such transitions are not observed ; instead the steady-state microstructure of a two-phase alloy is continuously refined on increasing the shearing rate. These differences originate from the size of the perturbation induced by the external forcing : the perturbation is of microscopic size for alloys under irradiation, while it is of macroscopic size for alloys under shear. Results obtained for the shearing case provide a rationalization scheme of ball milling experiments showing chemical mixing of immiscible elements. The fact that such systems consist of nanograins should also contribute to prevent the existence of 1st order phase transitions on varying the milling conditions.

The evolution under sustained shear of an ordered crystal with B2 structure is studied by Monte-Carlo simulation: the effect of shearing is modelled by shifts of atomic planes, while thermally activated atomic diffusion is promoted by the motion of one vacancy. The tricritical point expected in the dynamical phase diagram from mean field theories and from Monte-Carlo simulations in the limit of weak driving (few atoms shifted at once) does not appear in such simulations, much in the same way as for "large cascade size" in alloys under irradiation. However an unexpected bifurcation in microstructures is observed which could be related to the order-disorder transition experimentally observed under ball-milling.

The process of mechanical alloying in binary metallic systems is discussed in a microscopic picture. Special emphasis is put on systems with large positive heat of mixing. In these systems, a competition between thermal diffusion and forced transport takes place. Based on results from Monte Carlo studies of the effect of combined shear and diffusion processes on an atomistic scale, a simple rate equation approach is developed. The approach can reproduce the phase evolution in the simulation and the main features of the temperature dependence of the alloy phase fraction in steady state. The results are further compared with experimental data.

Powder blends consisting of prealloyed FCC Ag-Cu solid solutions and elemental Fe powders were ball milled in overall compositions of Ag25Cu50Fe25, andAg40Cu20Fe40. The phase evolution with milling time was investigated by x-ray diffraction and differential scanning calorimetry. For the sample with higher Cu concentration, a ternary FCC alloy phase was formed, while milling the other sample resulted in a two phase mixture consisting of a Ag-rich FCC and an Fe-rich BCC solid solution. About the same amount of enthalpy between 12 and 13 kJ/g-atom is stored in the final states for the two different compositions. Two models based on kinetic and energetic considerations will be discussed and compared to the results. The kinetic model is based on the competition between forced atomic motion during shearing, which is driving the system towards a homogeneous alloy, and thermally activated diffusion, which favors phase separation. For the energetic model, the energy balance is calculated and a phase transformation is expected, if the required energy can be stored in phase boundaries.

Cryogenic attritor milling (cryomilling) is used to synthesize nanocrystalline Fe-10wt.%Al powders. Following consolidation in a rigid die at 823 K and heat treatment for 1 hour at 1223 K, an average grain size of 16±7 nm is maintained. This level of thermal stability is shown to exceed that of pure Fe processed under identical conditions. The significant increase in thermal stability is attributed primarily to the presence of nanometer-scale γ-Al2O3 and AIN dispersoids formed during cryomilling and subsequent heat treatment.

Cryogenic ball milling of Fe-10 wt.%Al in liquid argon is shown to produce a nanocrystalline microstructure with high thermal stability against grain growth. The experimental evidence suggests that this stability may originate from the presence of fine γ-Al2O3 particles which pin the Fe grain boundaries. In contrast, Fe3O4 particles formed during cryomilling of Fe in liquid nitrogen were not able to impede grain growth during consolidation at 823 K. The interactions between the γ-Al2O3 particles and the grain boundaries during growth may be described by Gladman's theory. Additional stabilization against grain growth may have been provided by the presence of Al at the Fe grain boundaries. Following annealing at 1223 K, the grain size of the Fe-10 wt.%Al powders cryomilled in liquid argon was 13.3 ± 7.9 nm, but it exceeded 1700 nm following annealing at 1373 K. The loss of nanocrystalline structure may be attributed to the Ostwald ripening of γ-Al2O3 particles, resulting in abnormal grain growth.

The present study investigated the synthesis of nanocrystalline high speed steel M50 (4.5% Mo, 4.0% Cr, 1.0% V, 0.8% C, balance Fe) by cryogenic high energy ball milling (cryomilling). Pre-alloyed M50 steel was spray atomized, and subsequently cryomilled in liquid nitrogen for 25 hours. Elemental Al powder was added prior to cryomilling in order to promote the formation of nanoscale Al2O3 and AlN particles, which improved the thermal stability of the nanocrystalline M50 steel. Following annealing at 1373 K, the M50 steel was found to retain its nanocrystalline microstructure with the average grain size of 40–80 nm.

The synthesis of nanostructured multicomponent (Fe-Mo-Cr-V-C) M50 type steel has been carried out by two chemical routes: the sonochemical decomposition of organometallic precursors and the co-reduction of the respective metal halides. Both methods produce amorphous nanopowders, but the co-reduction method requires an additional heat treatment in vacuum at 700 °C to remove the by-product LiCl. In this paper we describe the synthetic methods and the characterization of the powders by XRD and SEM-EDAX. The powders exhibit a composition very close to that of M50 steel with an average grain size in the nanometer regime. In both cases the powders have been compacted in a vacuum hot press after they were heat treated in hydrogen. The characterization of the compacted specimens by XRD and SEM-EDAX is also discussed. The TEM characterization is presented for the sonochemically produced powders and compacts. A similar characterization of the co-reduced powders and the compacts is in progress. The consolidated specimens are homogeneous and dense, with an average grain size of ∼30 nm. Their hardness is higher as compared with that of the conventional M50 alloy.

Granular films were prepared by simultaneous cluster beam and physical vapor deposition. The clusters are formed by high pressure sputtering and have an average size between 2 and 5 nm. This method makes it possible to control the granule size and concentration, which is not possible using precipitation synthesis of granular alloys. Most importantly, a diverse set of granule/matrix systems are accessible by this system. The method is illustrated for systems of interest for giant magneto-resistance applications: Co/Cu (miscible), and Co/Cr (immiscible.) Synthesis of films with isolated embedded clusters of more complex structures, e.g. intermetallics Ni3Al and Cu3Au, are also discussed.

We have produced metal clusters with a molecular beam apparatus based on a Pulsed Arc Cluster Ion Source. The source has been optimized in order to generate intense and stable cluster beams of various elements, with a mass distribution ranging from the monomer up to several thousands of atoms. The source operation conditions can be varied in order to control the mass distribution, intensity and velocity of the aggregates. Preliminary results on the synthesis of granular thin films with this technique are also presented.

Nanoparticle synthesis by condensation from the vapor is a versatile process which allows control of both particle size and composition. We have developed a novel aerosol source for producing nanoparticles of metals and metal oxides, nitrides and carbides with controlled mean size. Metal is vaporized by heating a liquid metal pool by means of an atmospheric pressure d.c. arc. The evaporated atoms are entrained in a steady stream of inert gas and are quickly transferred to a quench region where the hot stream from the arc plasma is mixed with a second stream of cold gas. The role of the quench gas is to suppress aggregation by both rapid cooling and dilution. Metal oxide, nitride, and carbide particles are formed by the addition of oxygen, nitrogen, and methane respectively to the inert gas flow in either the arc or the quench region. The size of the primary particles is controlled by varying the metal atom density and residence time in the arc plasma and in the quench region. Cluster aggregation is controlled by varying the cluster density in the flow downstream from the quench region.

This study focuses on the optical characterization of a novel method of forming nanoscale titanium and boron particles, which can be used to form ceramic precursors such as TiB2. TiCl4 or BCl3 reacts with heated Na vapor in a counterflow diffusion flame reactor. After Na strips the Ti or B of its Cl atoms, nanosize Ti or B particles form and become encased in NaCl, which helps to prevent agglomeration and oxidation. The two-dimensional spatial distribution of the Na dimer has been optically interrogated using planar laser-induced fluorescence (PLIF) to clarify the influence of the concentration distributions and transport on particle formation rates.

A new technology for obtainment of amorphous single-component metals is presented.

For the first time the reduction of molybdenum oxide with formation of its amorphous phase is realized in conditions of a given quantum-chemical technology by means of vibrationally excited to the third quantum level hydrogen molecules with 1.5 ± 0.2 eV energy. The evidences of formation of this nonequilibrium amorphous phase are presented along with certain physicochemical properties of the obtained amorphous molybdenum.

A model is proposed for the origin of amorphous phase under the influence of nonequilibrium quantum-chemical technology.

Nanocrystalline BaTiO3 has been synthesized for the first time by a gas-condensation process using an electron beam evaporation system. BaTiO3 and Ti sources are vaporized simultaneously in either a mixed helium-oxygen or pure helium environment. Nano-BaTiO3 particles have an average particle size of approximately 18 nm. The processing parameters of the evaporation process are reported.

In this work we firstly established the optimal conditions to preferentially form nanosized β-Sn inclusions from a supersaturated solid solution of Sn in Si, formed by a high dose ion implantation. Afterwards we tried to elucidate the origin of the strongly enhanced recoilless fraction of Sn nuclei inside these precipitates, thereby making a link to the observed shift in isomer shift value. This is tentatively interpreted in terms of a local compression of the inclusion to about 200 kbar.

A series of different nano-sized silver particles has been prepared using r.f. magnetic plasma co-sputtering apparatus. A combination of high-resolution lattice images and optical diffractograms has been used to characterize the atomic structures during nucleation and growth of silver particles embedded in a silica matrix. For particles with diameter of 2 ∼ 5 nm, most have single crystal structures, but some have singly twinned morphologies and a few have multiply twinned morphologies. In those particles, there are many defects such as dislocations, stacking faults, twin boundaries and lattice fringe bends. For particles with diameter of 5 ∼ 9 nm, we can detect some single crystals, singly twinned particles and multiply twinned particles including decahedral and icosahedral particles. Anomalous meta-stable structured particles with 90° cross {111} lattice fringes have been also found. For particles with diameters of larger than ∼ 9 nm, most have multiple lamellar twins and sometimes there are macroscopically irregular shaped particles.

A detailed characterization was performed of the particles produced under various Pb:Si molar feed ratios in a flow reactor at a maximum temperature of 1000 °C. The silica particles formed in the high temperature region coagulated and only partially coalesced to form large agglomerate structures of high specific surface area. For a lead only feed, the resulting particles were hydrocerussite with small but detectable amounts of massicot. As the silica precursor was inlet in excess amounts (Pb:Si ≤ 1:12), the crystalline lead compounds disappeared and amorphous lead-silica complexes predominated. The particle morphology also changed from cylindrical, polygonal and spherical shapes to large agglomerate structures composed of several size modes of primary particles. At Pb:Si molar feed ratios of 1:12 and 1:29, the particles making up the chain-like agglomerate structure were primarily spherical with larger lead silicate spherical particles (≈ 0.5 μm) attached to the agglomerate. The lead was found to be distributed throughout the large agglomerate structures.

X-ray scattering at small angles (SAXS) is used to study the structure and the thermodynamic properties of dispersions of CdSe nanocrystallite particles. In particular, this study allowed us to probe the inter particle interactions, and their dependence on several relevant parameters, such as the nature and size of the capping units attached to the crystallite surface and solvent.

Atomistic simulations show that high-energy grain boundaries in nanocrystalline copper and nanocrystalline silicon are highly disordered. In the case of silicon the structures of the grain boundaries are essentially indistinguishable from that of bulk amorphous silicon. Based on a free-energy argument, we suggest that below a critical grain size nanocrystalline materials should be unstable with respect to the amorphous phase.

With the CALPHAD approach based on the regular solution model, the thermodynamic functions of the Cu-Co system can be extrapolated to compositions where the homogeneous fee solid solution is thermodynamically unstable. Up to now it has been unclear how reliable such extrapolations are in view of the driving forces for decomposition and whether the Gibbs energy is well described by the model in the unstable region. Therefore, electromotive force measurements were performed to determine directly the chemical potentials of highly supersaturated Cu-Co alloys. Under the prerequisite that time scales of the electrochemical exchange reaction are fast compared with the kinetics of decomposition, the thermodynamics of the alloys can be investigated quasi statically. Within the experimental accuracy the results for both a metastable and an unstable alloy agree well with the calculated chemical potentials. In addition, the experiments demonstrate that the electrochemical cell reaction is reversible upon small external concentration fluctuations of the investigated alloys. Possible reasons for this unexpected stability are discussed taking the kinetics of the decomposition into account.