In order to develop programs in education, technology transfer and research to achieve these goals, a partnership between the University of Minnesota, industries and government was established. The Center for Interfacial Engineering was born and the strategic plan is shown in Figure 1. Some statistics for this year are as follows. The budget is $6.5 M of which 41% is contributed by the NSF, 25% by the University of Minnesota and 34% by 54 industrial members. Sixty four faculty members from 6 departments are involved in the Center with 18 core CIE faculty. There are 244 graduate students and postdoctoral fellows, 41 undergraduates and 69 industrial researchers directly involved in center projects.

We have used a Tight Binding model to calculate the surface energies of various (111) stacking faults in TiC1.0 and TiC0.5. Based upon our preliminary results we have identified the stable stacking faults and have examined possible dislocation dissociation reactions.

The atomic and electronic structure of the Ag/MgO interface are calculated using the ab initio Hartree-Fock approach and a supercell model. The electronic density distribution is analyzed in detail for isolated and interacting slabs of a metal and MgO. The energetically most favorable adsorption position for Ag atoms is found to be above the O atoms. The binding energy is 0.20 eV (0.41 eV) for one and three Ag layers atop MgO substrate, respectively. The relevant equilibrium Ag-O distance is 2.64 Å(2.41 Å). Neither appreciable charge transfer in the interfacial region, nor considerable population of bonds between the silver layer and the insulating substrate take place. The adhesion energy arises mainly due to the electrostatic interaction of substrate atoms with a complicated charge redistribution in the metal monolayer, characterized by large quadrupole moments and electron density redistribution towards gap position in the middle of nearest Ag atoms.

Using embedded atom potentials and molecular statics we calculate the structure and energy of [001] tilt grain boundaries in NiAl for 25 orientations with Σ values from 5 to 185. For three structures (stoichiometric, Ni-rich and Al-rich) of the Σ = 5 (210) boundary we simulate tracer self-diffusion by the vacancy mechanism both parallel and perpendicular to the tilt axis using the Monte Carlo technique. The effective activation energy calculated in a wide temperature range is compared with the spectrum of individual jump energies in the boundary core. The results are interpreted in terms of the grain boundary structure-diffusion relationship and the role of the jump correlation effect in grain boundary diffusion.

Elastic constants of metallic multilayered film have been calculated using MEAM (Modified Embedded Atom Method) potential. Structural relaxation has been performed to obtain relaxed model structure of (111) stacked multilayers which consist of two fee metal elements. The composition modulation wavelength dependence of elastic constants was found to be large, and we could not observe any large enhancement of elastic modulus in the calculated systems.

Ab initio calculations of grain boundaries in SiC have been performed for the first time by using the first-principles molecular dynamics (FPMD) method. Four-fold coordinated models of polar and non-polar interfaces of the {122}Σ = 9 boundary in SiC have been examined. Interfacial C-C and Si-Si wrong bonds have bond lengths and bond charges similar to those in bulk diamond and Si. The C-C bonds generate greatly localized states at the valence-band edges, which have features similar to the bulk band-edge states of diamond. The wrong bonds have significant effects on the properties of grain boundaries in SiC.

This paper describes the current experimental knowledge base concerning the geometry and property relationships at the gram boundary plane. In order to analyse the data the interface-plane scheme is used, and its application is described here. The most important points to emerge from the data are that particular boundary properties - energy, mobility, segregation, precipitation and cracking - correlate with boundary plane types. Recent data illustrating the high occurrence of asymmetrical tilt grain boundaries and importance of low-index grain boundary planes are discussed in more detail.

We have used a two-step (low and high temperature) strain-annealing process to evolve the grain boundary character distribution (GBCD) in fully recrystallized oxygen-free electronic (OFE) Cu bar that was forged and rolled. Orientation imaging microscopy (OIM)[1–4] has been used to characterize the GBCD after each step in the processing. The fraction of special grain boundaries, “special fraction,” was ∼70% in the starting recrystallized material. Three different processing conditions were employed: high, moderate, and low temperature. The high-temperature process resulted in a reduction in the fraction of special grain boundaries while both of the lower temperature processes resulted in an increase in special fraction up to 85%. Further, the lower temperature processes resulted in average deviation angles from exact misorientation, for special boundaries, that were significantly smaller than observed from the high temperature process. Results indicate the importance of the low temperature part of the two-step strain-annealing process in preparing the microstructure for the higher temperature anneal and commensurate increase in the special fraction.

It is expected that the grain boundary diffusion is the principal contributor to the transport properties of nanocrystalline zirconia, and that it controls the oxidation kinetics and hydrogen permeation. This process depends on the grain boundary character distribution (i.e. the fractions of different grain boundary types) and on the topological characteristics of the grain boundary network. Modeling of the random walk problem on a planar honeycomb network for different types of the grain boundary misorientation distributions (GBMD) in nanocrystalline zirconia film is presented in the current paper. The GBMD was calculated using the model texture. Changes of the oxidation rate for different types of the grain boundary character distribution and different ratios of the bulk and grain boundary diffusion coefficients are analyzed. In this study it was found that an increase of the frequency of low energy boundaries lowers the oxidation rate.

Intergranular glass phases can have a significant influence on the fracture resistance (R-curve behavior) of silicon nitride ceramics and appears to be related to the debonding of the β-Si3N4/oxynitride-glass interfaces. Applying the results from β-Si3N4-whisker/oxynitride-glass model systems, self-reinforced silicon nitrides with different sintering additive ratios were investigated. Silicon nitrides sintered with a lower Al2O3:Y2O3 additive ratio exhibited higher steady-state fracture toughness together with a steeply-rising R-curve. Analytical electron microscopy studies suggested that the different fracture behavior is related to the Al content in the SiAlON growth band on the elongated grains, which could result in differences in interfacial bonding structures between the grains and the intergranular glass.

High-purity HIPed Si3N4 ceramics doped systematically with Ca additives are analyzed quantitatively by EELS. Using an ELNES related method to obtain film composition, we found that the composition difference from film to film is less significant than segregation. This is interpreted as a change of film width related to grain surface faceting. The hexagonal structure associated with anisotropie dielectric function can alter van der Waals attraction for different surface structures to produce variations in film thickness with a uniform film composition. These grain boundary films are better described as a high pressure amorphous oxynitride phase that allows higher but still limited solubility of calcium nitrogen.

Changes in the electron energy-loss near-edge fine structure (ELNES) of the O-K and Co-L edges have been characterized in cobalt oxide in the vicinity of a boundary between periclase-(CoO) and spinel- (Co3O4) structured phases. The data were acquired with a conventional transmission electron microscope (CTEM) equipped with an imaging filter and operated in spectrum-line mode. Independent spectral features were identified by multivariate statistical analysis (MSA) of the raw data. The MSA of the spectrum-image acquired at the Co-L edge indicated a transition over ∼12 nm in the spectral features at the phase boundary. The variation of the ELNES at the O-K edge varied appreciably only in the interface region, whereas that at the Co-L edge also indicated subtle gradients in both phases adjacent to the interface area. These gradients are consistent with a change in the average oxidation state of the cobalt cations in the vicinity of the interface. A second independent component of the ELNES was also identified at the Co-L edge. Possible interpretations of this second component are discussed.

The embrittlement of materials through the segregation of impurities to the grain boundaries is a common and industrially important problem. Despite considerable investigation, the mechanism by which the impurity elements cause embrittlement is not well understood. A change in the electron energy loss near edge structure (ELNES) has been observed at Cu grain boundaries containing Bi. This result provides experimental evidence that a change in the electronic structure at the grain boundary is responsible for embritdement.

Grain boundary segregation of phosphorous in model reactor steels has been measured using EDX Spectroscopy in the FEG-STEM. The results have been compared with Auger spectroscopy measurements made on similar materials. The results were in excellent agreement.

Phase contrast techniques in the transmission electron microscope are used to measure directly the electrostatic potentials at θ = 24° [001] symmetrical tilt grain boundaries in both undoped and Nb-doped SrTiO3 bicrystals. The boundaries are all found to have significantly lower scattering potentials than the surrounding bulk material. The depths and the shapes of the potential wells at the boundaries are discussed in the light of both theoretical models of the grain boundary chemistry of pure and doped strontium titanate and other experimental data that we have acquired on these boundaries from high resolution transmission electron microscopy, diffuse dark field imaging, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy.

Using a new EELS analysis method the local chemical and structural changes induced by Fe segregation to two types of grain boundaries in SrTiO3 were studied. At Σ5 boundary in bicrystals Fe segregation lowers O/Ti ratio but increases substantially Ti and O concentrations in boundary region. Sr-O bond has been severely changed by the segregation as revealed by ELNES. Grain boundaries in a polycrystalline sample were covered with titania-based amorphous films where Fe content is higher but Ti and O concentrations are both lower than the bulk levels, which are strikingly different from the bicrtysal. More dopants segregated to glass pockets at triple junctions. SiO2 was detected in one of the large pocket but not at the grain boundary films within the detection limit. These observations suggest the equilibrium defect chemistry and the related space charge theory may not be the only explanation for the grain boundary segregation in SrTiO3 Local structure modification at gram boundaries can trigger dramatical change of the chemistry to a degree higher than the segregation level. The existence of titania-based amorphous films at general grain boundaries makes it better to understand Fe segregation from the two phase (SrTiO3-TiO2) equilibrium.

In this study, three different Ni-base superalloy / heat treatment combinations are studied in an attempt to assess the role of grain boundary morphology, composition, and phase distribution on mechanical properties, particularly time-dependent fatigue crack growth. The alloys chosen include one in which crack growth can be slowed by slow-cooling, and one in which crack growth is slow in the fast-cooled state. Both x-ray spectroscopy and energy-filtered imaging in the analytical electron microscope were used to measure grain boundary composition. The x-ray spectroscopy showed some enhancement of Cr, Mo, and W in the γ matrix at grain boundaries in the fast-cooled state, which was not present after slow cooling. Energy-filtered imaging showed no significant enhancement in alloying elements at interfaces in any of the samples studied. The results did show the tendency for the γ matrix to quickly equilibrate by second-phase precipitation, and a preference to avoid γ ‘- γ’ interfaces. The conclusions of this study are that time-dependent fatigue crack growth behavior in these alloys cannot be completely explained on the basis of grain boundary composition of major alloying elements.

Grain boundary segregation in cerium dioxide doped with varying amounts of gadolinium oxide and tantalum oxide has been measured with x-ray energy dispersive spectroscopy using a Vacuum Generators HB603 Scanning Transmission Electron Microscope (STEM). The data has been analyzed in the framework of both elastic relaxation and space charge segregation forces with a limited number of surface sites. Results show that multiple driving forces must be taken into account to explain aliovalent solute segregation.

TEM studies of the microstructure and of chemical reactions at interfaces in TiB2-ZrO2 composites are presented. Samples with 70 vol% of Y2O3-stabilized ZrO sintered at 1700 °C showed reaction zones around the TiB2 grains, that consisted of a solid-solution of TiO2 and ZrO2(Y2O3). In addition, nontransformable, tetragonal t'-ZrO2 was observed in these samples. In contrast, the interphase boundaries in composites sintered at 1450 °C contained no reaction products, and the ZrO2 matrix consisted of small, transformable tetragonal grains, as required for transformation toughening of the composites.

The electronic structure of electrode-thermistor interfaces will be related to the thermochemical properties of the interface. Sessile drop wetting experiments of metallic electrodes on commercial BaTiO3 PTCR ceramic devices in combination with measurements of the electrical contact properties of the interface through impedance spectroscopy measurements will be used to establish a fundamental perspective of the electrode-ceramic interface. It will be shown that the thermodynamic work of adhesion (Wad), which is the sum of the strengths of chemical interactions present at the interface, can be manipulated by the addition of chemically active elements to the electrode metal which can segregate to the interface and enhance adhesion. This same procedure will be used to modify the important electrical interfacial properties such as the contact resistance and capacitance.