The products and kinetics of solid state reactions between TiC and Ti3Al have been investigated using X-ray diffractometry (XRD) and Auger electron spectroscopy (AES) with Ar ion beam sputtering. Diffusion couples were prepared by sputtering TiC thin films onto polished Ti3AI substrates, and then isothermally annealed in vacuum in the temperature range of 800 to 1000°C for 0.25 to 2.25 hours. The thickness of the interfacial reaction layer was obtained from AES elemental concentration depth profiling, while the reaction products were identified from XRD spectra. In the TiC/Ti3Al system, the reaction product was primarily P(Ti3AlC) phase. The growth-rate of the reaction product was fitted to a parabolic growth law (dZ/dt = k1/Z) and the activation energy of the rate constant was about 36.16 kcal/mole. The reaction mechanism will be discussed on the basis of thermodynamical equilibrium in Ti-Al-C ternary system.

Thermodynamic and structural properties of coherent interphase boundaries (IPBs) in the Al-Li and Ag-Al alloy systems are studied using the cluster variation method (CVM) and low-temperature expansion (LTE) techniques. The energy parameters required as input for the CVM and LTE calculations were obtained by fitting to phase diagram data in the case of Al-Li alloys and from a fit to the results of first-principles total energy calculations for Ag-Al. Interphase energies are calculated as a function of temperature and composition profiles across coherent IPBs are computed for high-symmetry crystallographic orientations. It is demonstrated that the calculated temperature dependence of interphase energies and the “widths” associated with compositionally diffuse IPBs can be appreciable even at temperatures well away from critical points.

Excess free energies of solid Cu - Solid Sn and Solid Cu - liquid Sn have been calculated employing an adiabatic switching formalism in a Molecular Dynamics (MD) framework. The atomic interactions are described by modified embedded atom method (MEAM) potentials which includes the angular dependence of the electron density to describe bond bending forces necessary to model covalent materials.

The wetting behavior of a calcium aluminosilicate liquid in contact with sapphire of four crystallographically different orientations has been investigated using scanning electron microscopy and atomic force microscopy. Continuous layers of glass films heat-treated at 1600°C and 1700°C result in dewet pockets of glass on the surface. The heat treatment also causes the alumina surfaces to facet which presents interesting shapes to the glass pockets. The morphology of the pockets with respect to the orientation of the facets is useful in understanding qualitatively the liquid-solid interfacial energies relative to the orientation of the facets. This approach enables a sequential study of the interaction between the facets and the silicate liquid. Based on temperature, the equilibrium composition of the silicate changes by solution-precipitation and evaporation processes which affects the facet and step morphology. This experiment directly emphasizes the relevance of anisotropy in the α-Al2O3 crystal structure which may ultimately control some of the key issues of materials’ processing.

Multilayered difiiision couples consisting of alternating layers of titanium (Ti) and amorphous silicon (a-Si) have been fabricated using sputter deposition with a range of modulation lengths corresponding to an average composition of Ti33 Si67. We have used differential scanning calorimetry to measure the enthalpy evolved during the solid state reaction a-Si + Ti → C49-TiSi2 and have characterized the phases formed using x-ray diffraction analysis. An average measured enthalpy of formation, ΔΗ was found to be ΔΗ = -58 + 9 kJ/g atom for thin film samples. Using scanning and isothermal calorimetry measurements, we have also characterized the kinetics involved during the initial intermixing stage.

Using differential scanning calorimetry, supplemented by measurements from scanning electron microscopy images, we have investigated solid state reactions in Pd/Sn multilayer composites to form PdSn4 and PdSn3. Planar diffusion couples of Pd and Sn were prepared by means of mechanical co-deformation in a rolling mill. A phase formation sequence was determined using differential scanning calorimetry and x-ray diffraction. Growth of the PdSru phase was studied from room temperature to the melting point of Sn. For temperatures between 430 and 460K diffusion limited growth of PdSn4 was observed. From heat flow data over this limited temperature range, the form of the reaction constant was found to be k2 −k0 exp(−Ea / kbT), where k0= 0.16 cm2/s and Εn= 0.8 eV/atom. Also determined was a heat of formation, ΔHf = −27±1 kJ/mol for PdSn4 from Pd and Sn.

We find differential scanning calorimetry to be suitable for the characterization of the energetics and kinetics of interdiflusion in solder/metal diffusion couples. Differential scanning calorimetry studies of interdiffusion in Cu/Cu6Sn5 diffusion couples have shown that the driving force for interdiffusion is similar for thin film composites and for bulk diffusion couples. The heat of formation of Cu3Sn from Cu6Sn5 and Cu thin films was found to be ΔHr = −4.3 + 0.3 kJ/mol. Portions of our differential scanning calorimetry scans are identified with diffusion limited growth of Cu3Sn. From these calorimetry data we have estimated D(cm2 / s) = Do exp(−E / kbT), where kb is Boltzmann's constant, D0 = 3.2 × 10–2 cm2/s, and E=0.87 eV/atom.

Nanocrystallization by heat treatment of initially amorphous alloys occurs for high nucleation frequency I and low crystal growth rate u values. Calorimetrie data extracted, for instance, from differential scanning calorimetry are normally presented by the dependence of the crystallized fraction x, on: i) x=x(T,t) when obtained under isothermal annealing at temperature T as a function of time t; ii) x=x(τ,β) when obtained under continuous heating at a scan rate β as a function of temperature. Theoretical analysis of the crystallization kinetics is presented which accounts for nuclei either pre-quenched or created by homogeneous nucleation whose initial steps of growth are controlled by the interface formation between the nanocrystals and the matrix and subsequent growth is limited by diffusion.

Through mechanical alloying of pure elemental powders of Fe and Zn, true homogeneous alloys of Γ (Fe3Zn10), Γ1 (Fe5Zn21), δ (FeZn7) and ζ (FeZn13) intermetallic phases are formed. Based on nonisothermal kinetics analyses, the highest activation energies associated with the metastable to stable transformations of these phases are determined as follows: 170±1 kJ/mol, 2 51±2 kJ/mol, 176±1 kJ/mol and 73 7±4 kJ/mol for the Γ, Γ1, δ and ζ-phases, respectively. These values reflect different diffusion/thermally induced processes associated with the transition of each of these phases.

In an immiscible Cu-Nb system, an amorphous alloy and two metastable crystalline phases were obtained by solid-state reaction of Cu-Nb multilayered films, and the formation of the alloy phases was found to be quite sensitive to the average composition of the films. At Nb concentration of 75at%, amorphization was achieved by 250°C annealing for 50 min, while in the films with compositions of 70 and 80 at% Nb, a simple cubic (a=0.405±0.005nm) and an orthorhombic phase (a=0.421, b=0.334, c=0.291±0.005nm) were observed, respectively. Thermodynamic calculation was conducted for the Nb-Cu alloy phases and the energetic state of the multilayers, which consisted of 9 Cu/Nb bilayers. It turned out that the excess free energy originating from the interfacial atoms could raise the multilayers to an energy level being higher than that of the amorphous or/and metastable crystalline phases both with a convex shape, and thus provided a major driving force for alloy phase formation in such immiscible system.

We address aspects of hydrogen bonding and its thermal evolution in amorphous Silicon nitride films grown by Remote Plasma Enhanced Chemical Vapor Deposition (RPECVD) from SiH4 and NH3 (or ND3) source gases. Rapid Thermal Annealing (RTA) decreases the Si-H(D) and SiN-H(D) bond populations. The hydrogen bonds break, and H2 (HD, D2) forms and evolves from the film with the heat treatment. This molecular hydrogen release is accompanied by Si- and N- bond healing as detected by a SiN infra red stretch mode signal gain. The ex-situ RTA experiment temperatures ranged from 400 °C to 1200 °C, in 100 °C steps and the film structural changes were monitored by Fourier Transform Infrared spectroscopy (FTIR) after each incremental anneal. Gas flow ratios R=NH3/SiH4 > 2 produced films in which SiN-H(D) bonds dissociated, and a gas desorption rate equation estimated an activation energy barrier of Ea = 0.3 eV. The release of hydrogen from the films in the form of H2 (D2) and ammonia radicals was detected by mass spectrometry and is shown here. The re-bonding of nitrogen to silicon upon thermal dissociation of hydrogen's is consistent with the improvement of the electrical properties of a-SiN:H films following RTA treatment.

Ion-beam-induced amorphization in single crystal α-SiC has been studied as a function of temperature. Specimens have been irradiated with 1.5 MeV Xe+ ions over the temperature range from 20 to 475 K using the HVEM-Tandem Facility (ANL), and the evolution of the amorphous state has been followed in situ in the HVEM. Specimens also have been irradiated at 170, 300, and 370 K with 360 keV Ar+ ions, and the damage accumulation process followed in situ by Rutherford backscattering spectroscopy/channeling using the dual beam facilities at the Ion Beam Materials Laboratory (LANL). At 20 K, the displacement dose for complete amorphization is 0.25 dpa and increases with temperature in two stages. The activation energy associated with the simultaneous recovery processes above 100 K is 0.12 ± 0.02 eV. The critical temperature above which amorphization does not occur is 485 K under the 1.5 MeV Xe+ irradiation conditions. Ion channeling results suggest that the rate of simultaneous recovery increases with temperature only above a critical damage level. Raman spectroscopy indicates that rapid chemical disordering occurs during irradiation.

Relaxation processes in different amorphous transition metal-metalloid (TM-M)-type alloys have been studied using thermopower measurements. The migration of two types of atomic complexes has been considered. For Ti-based amorphous alloys the migration of TM atoms and TM-M complexes diffusion are at least two processes that define the structural relaxation. For Ni and Fe-based alloys the relaxation processes are determined first of all by isolated TM atom migration.

The heating-rate dependence of crystallization temperature, Tc, and the glass transition temperature, Tg, is studied from the view points of nucleation and fragmentation processes in disordered structures. Tc and Tg are expected to increase monotonically with heating rate. Such behaviors of Tc and Tg are classified into four characteristic regions with respect to the heating rate. Results are summarized in the Transient Phase Diagram where Tc and Tg are given as a function of heating rate. The scaling rule in the Transient Phase Diagram is given.

Glass transition phenomena for a fictive V2-VI3 compound have been described on the basis of fragmentation model in which glass materials begin to fragmentize at a certain temperature and the fragment size becomes small with increasing temperature. By a numerical calculation, the heating rate dependence of glass transition temperature was clearly presented, and fragment sizes at glass transition and melting temperature were estimated as 1.4μm and 20Å respectively. Further, thermodynamic aspects were discussed using the model and it was concluded that the glass transition is a sort of the first order transition.

The decomposition and crystallization above the glass temperature of the bulk metallic glass Zr41Ti14Cu12.5Ni10Be22.5 and the crystallization during solidification of the melt were investigated by means of different analytical methods, including Transmission Electron Microscopy (TEM), Small Angle Neutron Scattering (SANS), Field Ion Microscopy with Atom Probe (FIM/AP).

Dependent on the thermal history these phase transitions lead to different phases and different microstructures of the alloy. During annealing above the glass tremperature the decomposition of the alloy into two supercooled liquid phases is observed by the formation of nanosized precipitates, which differ from the matrix by their Be and Ti contents. This decomposition retards significantly the subsequent crystallization, however it does not inhibit the formation of the phases which crystallize if the decomposition is bypassed by appropriate heat treatment. By stepwise crystallization a nanosized microstructure is formed consisting of three metastable phases and of stable Zr2Cu. This microstructure differ significantly from the crystalline equilibrium microstructure resulting from slow cooling of the melt. Crystallization of the amorphous alloy by very fast heating causes totally different microstructures.

Titania films with two types of phase composition were sputter deposited on fused silica substrates: Type (I) amorphous+anatase+rutile and Type (II) amorphous+rutile. These films were subjected to various annealing procedures in air. We studied three relevant transitions: 1) amorphous→crystalline (anatase and rutile) at temperature <800 °C, 2) amorphous→mitile at an temperatures, and 3) anatase→rutile in the 750–800 °C temperature range.

X-ray diffraction was used for phase identification and crystallographic orientation. The films had a preferred orientation, with (101) anatase and/or (110) rutile planes parallel to the substrate. The activation energy for the amorphous-to-rutile transformation was 0.3 eV. The anatase-to-rutile transformation occurring at 750 °C was modelled using the Avrami relation, which yielded an exponent of unity.

From the results of this study, we propose a model for titania crystallization in which site saturation of rutile and/or anatase nuclei already exists in the as-deposited film. Further crystallization upon annealing occurs by one dimensional growth of these nuclei into the amorphous material. If no anatase seeds exist in the as-deposited material, then no anatase will form upon annealing, indicating again that no new nuclei are formed during annealing. In this manner, highly oriented rutile titania films can be produced at temperature below the bulk anatase-to-rutile transformation temperature (750 °C).

Solid Phase Crystallization of amorphous silicon films, deposited by the Low Pressure Chemical Vapor Deposition technique, is studied by in-situ monitoring the film conductance. The crystal growth rate VG, deduced from this measurement, was found to be thermally activated. The activation energy E behaviour for films with different doping varying in a great range, from undoped to 4×1019 cm−3, was then deduced. This behaviour, described for the first time in this work, shows a constant E for undoped and weak doping, then a high decrease after a doping value threshold. The undoped films show a decreasing E when the deposition rate increases i.e. when the structure of the amorphous deposited film tends to correspond to the relaxed amorphous network. All these new results are used to introduce a crystallization model based on a crystalline-amorphous double phase and on the charge of defects at the crystal-amorphous interface.

The solid-phase epitaxial growth of amorphized GaAs has been characterized to investigate the influence of both microscopic and macroscopic non-stoichiometry on the onset of twinning and subsequent interfacial non-planarity. Microscopic non-stoichiometry or equivalently, chemical disorder on an atomic scale, was produced by implanting samples with equal doses of both Ga and As ions. In such samples, the onset of twinning and interfacial non-planarity where independent of the energy deposited in vacancy production, the latter considered a first estimate of relative differences in microscopic non-stoichiometry between samples. Twinning and interfacial non-planarity are thus independent of microscopic non-stoichiometry or alternatively, microscopic non-stoichiometry may approach saturation over the given dose range. In contrast, macroscopic non-stoichiometry produced by implanting samples with Ga or As ions influenced both the onset of twinning and interfacial non-planarity. Excess Ga was observed to have a greater effect than excess As. The influence of a macroscopic non-stoichiometry may be indicative that the availabiltiy of a lattice constitutent and/or defect is rate-limiting during solid-phase epitaxial growth. Macroscopic non-stoichiometry may also yield preferrential nuclueation sites for twinning and in the presence of excess Ga, molten precipitates could contribute to an observed rapid amorphous-to-crystalline transformation.

Processing techniques were investigated to produce c-axis orientation, or texture, of ferroelectric Pb5Ge3O11-based glass-ceramic compositions during crystallization of amorphous thick-film printed samples from the Pb5Ge3O11-PbTiO3 (PG-PT) and Pb5Ge3O11Pb(Zr1/2Ti1/2)O3 (PG-PZT) systems. In these systems the PG crystallized into a ferroelectric phase, producing a multiple ferroelectric phase composite at low temperatures, PG-PT or PG-PZT. In this way the non-ferroelectric component of traditional ferroelectric glass-ceramics was eliminated.