Crystallographic characteristics of a large number of Σ3 boundaries have been investigated in a nickel superalloy. The results indicated that {111}, vicinal-to-{111} (within 10° of {111} planes) and not-{111} Σ3s were all present in the sample population. At Σ3/Σ3/Σ9 junctions a combination of one {111} and one vicinal-to-{111} Σ3 was more likely to occur than two {111} or two not-{111} Σ3s, and an explanation is proposed. An analysis of the interface planes for the not-{111} Σ3s indicated that more than half the boundaries in this category could not have {211}{211}, {774}{855}, {111}{511}, {001}{221} or {110}{411} planes.

Ferromagnetic thin films were combined with piezoelectric substrates with the purpose of obtaining voltage controllable magnetization behavior. The interface between the ferromagnetic and piezoelectric material was examined for optimized voltage controlled magnetic response. Magneto Optic Kerr Effect (MOKE) measurements, supported by atomic force microscopy (AFM), showed the need to polish the piezoelectric substrates to a roughness below 1nm RMS (1*1νm2scan) for a minimum coercivity of 3kA/m. The magnetic anisotropy dependence on deposition, and anneal temperature was determined, and was shown to cause temperature driven coercivity changes up to 45 A/Km. A buffer layer between the piezoelectric substrate and the ferromagnetic thin film doubled the relative importance of the voltage driven magnetic effects.

Superconductivity in high-Tc materials is often modeled as a percolation problem in which grain boundaries are classified as strong or weak-links for current transmission based on their disorientation angle. Using Monte Carlo simulations, we have explored the topology and percolation thresholds for grain boundary networks in orthorhombic and tetragonal polycrystals where the grain boundary disorientations are assigned in a crystallographically consistent manner. We find that the networks are highly nonrandom, and that the percolation thresholds differ from those found with standard percolation theory. For biaxially textured materials, we have also developed an analytical model that illustrates the role of local crystallographic constraint on the observed nonrandom behavior.

For visualization of orientation inhomogeneities in crystalline material orientation imaging maps are conventionally used, with different colors representing different orientations. Two different approaches are proposed to extract more information from the orientation data on deformation structures gathered by electron back-scattering diffraction. First, a statistical approach is introduced for obtaining the chord length distribution of a grain structure and, secondly, an evaluation scheme is presented to resolve the details of the deformation structure within individual grains.

We address the problem of calculating the long-time-limit effective diffusivity in stable two- phase polycrystalline material. A phenomenological model is used where the high diffusivity interphase boundaries are treated as connected “coatings” of the individual grains. Derivation of expressions for the effective diffusivity with segregation is made along Maxwell lines. Monte Carlo simulation using lattice-based random walks is used to test the validity of the expressions. It is shown that for the case analysed the derived expressions for the effective diffusivity are in very good agreement with simulation results. The equivalent of the Hart equation is also derived. It is shown to be in poor agreement with simulation results.

Bulk Ca2RuO4 is an antiferromagnetic Mott insulator with the metal-insulator transition above room temperature, and the Neel temperature at 113 K. There is strong coupling between crystal structures and magnetic, electronic phase transitions in this system. It exhibits high sensitivity to chemical doping and pressure that makes it very interesting material to study. We have epitaxially grown Ca2RuO4 thin films on LaAlO3 substrates by pulsed laser deposition technique. Growth conditions such as substrate temperature and O2 pressure were systematically varied in order to achieve high quality single-phase film. Crystalline quality and orientation of these films were characterized by X-ray diffractometry. Microstructure of the thin films was examined by transmission electron microscopy. The electrical transport properties were also measured and compared with bulk single crystal.

The use of reconstructed ceramic surfaces as templates for nanopatterning has been demonstrated recently. This technique differs from the surface decoration by Au on stepped surfaces of alkali halides which has been a topic of intense research in the past. Some of the intriguing aspects related to the physical origin of the phenomena have been considered here. Based on heterogeneous nucleation of Pt vapor on wedged alumina surfaces, it has been shown that the valley sites are the preferred sites for nucleation. However, the hill sites are decorated by the particles in the present study pointing out to a different physical origin for the formation of the nanoparticles. The role of electrostatic energy reduction on the formation of such nanopatterns is discussed.

The anisotropy in room temperature plastic deformation has been investigated in single α(HCP)/β(BCC) colonies of a commercial α/β titanium alloy (Ti-6Al-2Sn-4Zr-2Mo-0.1Si) oriented for activation of individual basal slip systems. Detailed transmission electron microscopy (TEM) studies of the slip transmission mechanisms through the α/β interfaces have been performed to elucidate the role of these interfaces in determining yield and strain hardening behavior. Significant anisotropy in the yield strengths and hardening rates for the 3 unique basal slip systems is measured, and is attributed to the different slip transmission mechanisms active due to the near-Burgers orientation relationship existing between α- and β-phases. These results are should be transferable to other alloy systems exhibiting this orientation relationship.

The strength of structural materials strongly depends on the structure and properties of grain boundaries. Interfaces usually act as barriers to dislocation motion and therefore strengthen materials with decreasing grain size, quantitatively described by the well-known Hall-Petch relation. However, interfaces in nanocrystalline materials are often covered with impurities or second phases, which may influence the mechanical properties. With nanoindentation testing it is now possible to probe the strength of interfaces like grain boundaries directly on a nanometer scale. Therefore this method was used to investigate the properties in the vicinity of grain boundaries in polycrystalline materials with conventional grain size and in ultrafine-grained metals prepared by equal channel angular pressing (ECAP), where no impurities are introduced during processing. Measurements on an austenitic steel clearly show a decreasing hardness close to the interface opposite to the general expected behavior of strengthening. In this case segregation effects strongly influence the mechanical properties near the boundaries. The nanoindentation investigations on ultrafine-grained Al and Cu show a strong strain rate sensitivity. Inelastic effects are also found between unloading-loading segments during indentations.

The phenomenon of dynamic embrittlement involves the stress-induced diffusion of a surface- adsorbed embrittling element into grain boundaries, leading to time-dependent decohesion along these boundaries. Here, the state of our understanding of this generic type of brittle fracture is reviewed, with the focus on cracking of nickel-base superalloys caused by oxygen, including recent and new results on cracking in bicrystals, thermo-mechanical processing to reduce the susceptibility to dynamic embrittlement, and quench cracking.

Monazite (LaPO4) was indented at room temperature. Deformation twin boundaries and stacking faults were characterized by high resolution transmission electron microscopy. Kinked deformation twins were also characterized and analyzed. Three types of stacking faults associated with climb-dissociated partial dislocations were observed. Two were found on twin boundaries, and a third in the lattice. Formation mechanisms are discussed. The superimposition of stacking faults along twin boundaries during deformation twinning and the glide of climb-dissociated partial dislocations allowed by stacking fault migration are discussed. The possible relationship between the formation mechanisms for these defects and the low- temperature recrystallization and self-annealing of defects in monazite is considered.

Interfaces control many properties in engineering materials, several of which are critical to the integrity of the engineering structure. In single phase, solid solution, austenitic alloys, grain boundaries are often the weak link, displaying susceptibility to creep, corrosion and stress corrosion cracking. As such, grain boundary structure control affords the opportunity to improve the overall performance of alloys in a variety of applications. The role of coincident site lattice boundary (CSLB) enhancement and grain boundary connectivity is examined for how it affects the response of an alloy to stress and the environment. Specifically, the effect of grain boundary character on creep, grain boundary sliding, intergranular stress corrosion cracking, and irradiation assisted stress corrosion cracking in austenitic nickel-base (high purity Ni-Cr-Fe and alloy 600) and iron-base (high purity Fe-Cr-Ni and 304 stainless steel) alloys and for ferritic- martensitic alloy T91 is discussed.

Two-dimensional (2D) cross sections through three-dimensional (3D) polycrystalline materials present a biased picture of the statistical properties of grain boundary networks. These properties are essential to many practical applications such as grain boundary engineering. We show a simple correction that will partly correct for the sampling biases by removing the effect of the correlation between grain boundary type and grain boundary area. This correction alters number fraction estimates by as much as ∼60% for σ3 boundaries in the highly-twinned copper samples we consider. We also estimate the bias introduced by the correlation between boundary type and boundary shape, which for many materials represents perhaps a 10% shift in the measured statistics, so that the simple method we propose should correct for the majority of the bias in favorable cases.

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Impurity segregation at grain boundaries in polycrystalline alloys is known to have a tremendous impact on the material properties such as mobility, cohesion.. But, direct measurement of grain boundary chemistry is quite complex and there are quite few results concerning polycrystals. In this paper we present an indirect method to measure segregation- misorientation dependence on polycrystalline Ni-S alloys using both EBSD and 3D reconstruction of etch grooves. Samples of Ni-S alloy (7.2 ppm at) have been annealed at different temperatures to get equilibrium segregation at grain boundaries. Then they have been etched near the transpassive potential to form etch grooves, whose geometry depends on the sulfur segregation level. Grain boundaries misorientation statistics and first results about the segregation-misorientation function are given here.

We have examined the effects of isothermal annealing, at a variety of temperatures, and directional annealing, under a range of conditions, on both primary recrystallization and secondary recrystallization in 90% cold-rolled 99.5% nickel of two different textures. The initial texture is shown to influence the rolling texture and, hence, the results of subsequent annealing. It was found that one alloy showed a cube texture after primary recrystallization, underwent abnormal grain growth upon annealing at high temperatures, and could be directionally (secondary) recrystallized to give large columnar grains. In contrast, the other alloy produce a weak cube texture after primary recrystallization, showed only normal grain growth upon annealing at higher temperatures, and could not be directionally annealed to produce columnar grains. The implications of these results are discussed for producing columnar grains.

The effect of strain on the surface magnetism of the manganite La0.7Sr0.3MnO3 has been studied as a function of temperature, using magnetic force microscopy. The non- uniform strain distribution in the film leads to a two-phase coexistence between ferromagnetic and non-ferromagnetic phases. This leads to a reduction of the surface curie temperature and the formation of ferromagnetic islands. Methods of controlling this behavior in order to fabricate arrays of magnetic nanodots are discussed.

Characterization of the TiN coatings oxidized in air at temperatures at 600 and 700°C for 30 min was carried out by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). TiN thin films with a Ti interlayer were prepared by hollow cathode discharge ion plating on AISI 304 stainless steel. Both XRD and TEM results show that the TiN coatings and Ti interlayer have columnar structure with (111) and (0002) preferred orientations, respectively. AFM results show the existence of pinholes on the surface of specimens due to electropolishing process of the steel substrate, and the surface roughness (Ra) changes from 3.5 nm for the as-deposited specimen to 11.6 nm after oxidation at 700°. After oxidation, the TiO2 oxide layer formed on the specimen surface was porous and retained the columnar structure as the original TiN coating. The microstructure of the Ti interlayer gradually changed from columnar to polycrystalline structure due to grain growth. The Auger elemental depth profiling indicated that interdiffusion of the Ti interlayer with steel substrate had occurred during the oxidation process.

Grain boundary structure and composition is assessed in austenitic stainless steels along with its influence on intergranular stress corrosion cracking (IGSCC) in high-temperature water. Brief examples are presented illustrating effects of grain boundary character and segregation on behavior in specific light-water-reactor environments. Although grain boundary engineering can produce an increased fraction of “special” boundaries in austenitic stainless alloys, practical benefits depend on the boundary orientation distribution. It is critical to recognize that only ∑3s appear to be more resistant to SCC and the behavior of other low ∑ boundaries is uncertain. Grain boundary composition can have a dominant effect on IGSCC under certain conditions, but altered interfacial chemistry is not required for cracking. In high-potential oxidizing environments, IGSCC susceptibility is a direct function of the boundary Cr concentration. Non- equilibrium thermal segregation of Cr and Mo is often present in mill-annealed stainless steels and may influence cracking susceptibility. This initial grain boundary composition alters subsequent radiation-induced segregation and delays irradiation-assisted SCC susceptibility to higher doses. Other alloying elements and impurities in 300-series stainless steels have been seen to enrich grain boundaries, but few have any significant impact on IGSCC susceptibility. One exception is Si that strongly segregates during irradiation. Recent results suggest that Si may accelerate crack propagation in both low- and high-potential water environments. Critical research is still needed to isolate individual grain boundary characteristics and quantitatively link them to IGSCC.

Dislocation-density based multiple-slip constitutive formulations and specialized computational schemes are introduced to account for large-strain ductile failure modes in polycrystalline aggregates. Furthermore, new kinematically based interfacial grain-boundary regions and formulations are introduced to account for dislocation-density transmission, absorption, and pile-ups that may occur due to grain-boundary misorientations and void interactions.

With the Three Dimensional X-ray Diffraction microscope (3DXRD) located at the European Synchrotron Radiation Facility (ESRF) full 3D spatial information of grains in the interior of a sample can be measured non-destructively. In this paper we discuss the possibility of an extension to this scenario, namely in-situ annealing studies, where the 3D spatial grain shape can be monitored as function of time. Consequently, local boundary migration rates can be estimated and compared to the deformed microstructure. Such information may reveal to what extend the deformed microstructure influences the growth of a grain during recrystallization.