The aluminum-lithium alloy 2090-T8E41 undergoes delamination along certain high-angle boundaries parallel to the rolling plane when subjected to torsional loading. Weak boundaries were located by comparison of fracture surface replicas and thin foils in the electron microscope. Grain boundary orientation was determined from Kikuchi patterns obtained by convergent beam electron diffraction.

This paper summarizes recent research on intergranular fracture and alloy design of L12 ordered Ni3X intermetallics. The grain boundaries in Ni3AI, Ni3Ga, Ni3Si, and Ni3Ge are intrinsically brittle, and boron additions are effective in ductilizing the first three alloys but not in Ni3Ge The beneficial role of boron is to increase grain-boundary cohesive strength, to enhance plastic flow in the boundary region, and to disorder grain boundaries. Boron is ineffective in ductilizing Ni3X alloys with × > 25%. The room-temperature ductility of undoped Ni3Al can be improved also by change in grain shape from equiaxed to columnar.

The importance of grain boundary character distribution (GBCD) for the grain boundary design of polycrystalline materials with desirable properties is discussed. The GBCD which describes the type and the frequency of grain boundaries is regarded as the most important microstructural parameter controlling the bulk properties of polycrystals. This parameter can link the bulk properties with intrinsic or extrinsic properties of individual grain boundaries. The recent experimental work on GBCDs in metallic and ceramic polycrystalline materials is discussed. Particularly the relationship between texture and GBCD is discussed in detail in the light of recent studies on several polycrystalline materials with different types of texture. It is pointed out that we are now in a position to quantitatively design and precisely control GBCD in order to endow polycrystalline material with desirable or new properties.

Grain Boundaries in two specimens of Ni4Al of different compositions and mechanical behavior were studied by electron microscopy. SEM was used to determine the distribution of Σ values in both samples. TEM results were combined with CSL theory to completely characterize the nature of the boundaries, including Σ values and the grain boundary plane orientation. The boundaries most commonly observed in the experiments were also studied using a computer simulation technique and the results correlated with the experimental observations.

Grain boundaries in both pure and boron doped Ni3A1 have been studied using a variety of electron microscopy techniques. Small angle boundary structures were examined in both bicrystal and polycrystalline specimens. Dislocations with Burgers vector a/2<110> are observed in the presence of boron, while dislocations with Burgers vector a<100> are observed in the absence of boron. A possible explanation for this behaviour is the presence of a disordered layer at the interface in boron doped Ni3A1. The addition of boron to Ni3A1 was seen to induce faceting of grain boundaries, and to afford the boundaries some protection from etching. Using electron backscatter diffraction patterns, the frequency of occurrence of grain boundary types was found to be unchanged by the addition of boron.

Given the recent interest in the element boron as an intergranular “glue” in intermetallics it is important to recognize that it also has a strong effect on intergranular fracture in more conventional structural alloys. The best documented examples are Fe-Mn alloys. It was shown some years ago that the introduction of a minor alloying addition of boron can reduce the ductile-brittle transition of Fe-12Mn ferritic steel by nearly 200 degrees centrigrade; more recent work has shown similar results in austenitic Fe-Mn steels. The effect is due to the suppression of intergranular fracture. The basic mechanism has been worked out in some detail and will be described.

The fracture toughness and failure mode of ceramic materials are highly sensitive to the presence of impurities at grain boundaries. Magnesium oxide serves as a model material to investigate fracture with respect to impurity levels at grain boundaries. Lithium fluoride, added to MgO as a sintering aid, is retained as an intergranular phase. By post-fabrication heat treatment, the LiF is removed and a change in fracture mode follows. Transmission and scanning electron microscopy, along with analytical (atomic absorption spectroscopy and selective electrode analysis) and microanalytical (scanning Auger microprobe) techniques are used to follow the progression of LiF with heat treatment. The results of this study are compared to other oxides and carbide systems in which the fracture toughness has also been found to be sensitive to the amount and location of segregants.

The application of controlled-geometry interfacial pore structures to fundamental kinetic studies in alumina is described. Results from studies of the morphological stability of high aspect ratio pore channels, crack healing, pore coarsening and pore elimination in sapphire are presented.

The destabilization of zirconia thermal barriers has been monitored by directly exposing thin films of ZrO2 (+Y2O3) to V2O5 vapor. The growth of YVO4 and the transformation of cubic ZrO2 (+Y2O3) into tetragonal and/or monoclinic ZrO2 polymorphs are monitored by selected-area diffraction and energy-dispersive x-ray spectroscopy in the transmission electron microscope. The structure of a special YVO4 - ZrO2 (+Y2O3) interface is discussed.

The influence on electrical properties of yttria-fully-stabilized zirconia with low contents of lanthana (up to 5 mol%) were studied. Phase transformation by XRD, lattice parameter, crystallite size, and chemical composition after 4h sintering at 1400°C were adopted for the characterization of the synthesized solid electrolyte. Electrical conductivity from 350°C to 800°C and frequency dependence by complex impedance method were measured to analyze the role of grain-bulk and grain boundary on the electrical conductivity respectively. Nicrostructures of the synthesized sample were observed by SEM(EDS) and TEM for the confirmation of segregation phenomena at grain boundary. Sinterability was improved in the limited amount of La2O3 addition up to 0.5 mol%. The electrical conductivity decreased with increasing the La2O3 addition overall, but slightly increased up to 1 mol% due to the substitution of La3+ for Zr4+. The overall electrical conductivity was much dependent on the contribution of grain-bulk. However, both the potential barrier in the lower La2O3 contents and segregation of second phases in the higher La2O3 contents influenced the electrical conductivity.

Internal interfaces in YBa2Cu3O7 superconductors are characterized using electron microscopy. A number of specific examples of boundary structures are presented. The observations are used to discuss the role of boundaries on superconductivity in these Cu-O based ceramics.

Grain boundaries in as-sintered high-Tc YBa2Cu3O7-x were often found to contain thin amorphous layers up to 2nm in thickness. planar grain boundaries parallel to the c plane of one of the crystals tended to have thick layers, while the other boundaries were with layers of negligible width. The boundary width apparently increased in the specimens sealed in a quartz tube, re-heated at 773K and slowly cooled, even though the chemistry of the boundary layer was preserved except oxygen. Even a thin layer of other compounds was found in the c-plane type boundary when the specimen was re-sintered at above 1200K. These phenomena may be explained by the cracking of the interface and a liquidus valley between YBa2Cu3O7-x. The deterioration of the resistivity characteristics of the specimen is attributed to these changes of the grain boundaries.

Comparison of Auger electron spectra for intergranular and transgranular areas on fracture surfaces of sintered YBa2Cu3O7-x indicates the presence of a grain-boundary layer which is copper-rich and oxygen-poor compared to the bulk. This layer is believed to be an important factor limiting the critical current density in sintered material. The composition of the grain-boundary layer is strongly affected by small changes in sample composition, as might be expected for a line compound. These small deviations from the stoichiometric composition also affect the critical current density and the electrical resistivity above the transition temperature.

Bicrystal specimens of accurately controlled orientation and interface purity are critical for research into the structure and properties of interfaces. An apparatus is described which allows single crystals of a metal and an oxide to be bonded in exact, predetermined azimuthal orientation in an ultra high vacuum after sputter cleaning. Provisions for the monitoring of surface cleanliness by Auger spectroscopy and for controlled deposition of impurities on the mating surfaces are described.

Interfacial bond strength is assessed by measuring the work of propagation of a crack along the interface, and the fracture mechanical background of such measurements is discussed.The structure of the interfaces is studied by conventional and high resolution TEM. Such studies have been performed on interfaces created by diffusion bonding and by in-situ growth of oxide particles in metal matrices. Systems studied include Nb/A120 3, Cu/A12O3, Pd/A12O3, Pd/ZnO, Ag/ZnO, and Ag/CdO. All interfaces were found to be atomically sharp and to have densely packed planes and directions of the metal parallel to those of the oxygen sublattice; residual misorientation is accommodated by dislocations. For Ag/CdO and Pd/ZnO, HREM and hydrogen trapping experiments show that the outermost plane of the oxide consists either of oxygen or metal ions, depending on the relative activities of the two components in the matrix.

The earliest stages of epitaxy between metals and ceramics have been characterized using a novel transmission electron microscope experiment. Metal particles were deposited onto ceramic substrates which were previously thinned to electron transparency. Illustrations of epitactic relations, the influence of surface defects on particle nucleation and the growth of metal particles on single-crystal ceramic substrates are provided for the Cu / A12O3, W / β-SiC and Cu / MgO systems.

Chemical profiles of interfacial (transition) regions in InP-based heterostructures, fabricated by (1) vapor levitation epitaxy (VLE), (2) liquid phase epitaxy (LPE), and (3) molecular beam epitaxy (MBE), have been measured with a high degree of resolution on inclined surfaces by Auger electron microscopy (AES). This particular technique involves production of a chamfered wedge, characterized by a surface inclined by angle ø(≈ 0.02°) with respect to the interface, by controlled chemical etching and subsequent scanning across the trace of the interface on the (inclined) surface by AES, thereby allowing enhanced magnification of the interface by a factor of cot ø (≈ 2,000X) without deleterious effects associated with mechanical polishing and/or ion milling. Results indicate that corresponding transition widths δ between adjacent layers vary according to δLPE < δMBE < δVLE and may be explained by a combination of inherent surface roughness and interdiffusion of various chemical species across the original interface during and subsequent to the deposition process. It is concluded that the chamfered wedge technique provides a reliable and sensitive method to determine chemical profiles across a wide variety of heterojunctions, provided that a suitable chemical etch is available.

Zn film electrodeposited on a steel sheet is of hexagonal n-phase and comprises the packets of hexagonal platelets. The addition of either Fe or Ni ions to the plating solution produces fine bcc r- or Y-particles within the η-phase deposits and changes the n-phase morphology into more massive form. Further increase of Fe or Ni content yields large amounts of r- or Y-particles which can no more be absorbed within η-phase and the granular structure forms. Such morphological change can be explained partly in terms of the deposit/substrate and the deposit/deposit interface structures.

We will briefly describe the latest developments in the field of epitaxial silicide. Our present understanding of important issues in epitaxial silicide will be reviewed. Attention will be given to one epitaxial system, CoSi2 on Si(111), where considerable understanding of the silicide reaction has been gained recently.

Evolution of stress during interfacial reactions between thin films of nickel and (001) silicon substrates has been determined at temperatures ranging from 250 to 325° C by a levered optical beam reflection technique. This technique allows accurate and in situ measurement of composite specimen curvature, thereby providing a continuous measure of stress during ongoing interfacial reactions. In addition, microstructure and phase morphology associated with these reactions have been determined by x-ray diffraction and transmission electron microscopy. Initially, Ni2Si forms and grows at the original Ni/Si interface, accompanied by an increasing net compressive stress in the composite film. Subsequently, NiSi forms and grows at the Ni2Si/Si interface, accompanied by an increasing net tensile stress in the composite film. The initial compressive stress is attributed to localized formation and growth of Ni2Si into the adjacent silicon substrate, whereas the subsequent tensile stress is attributed to formation and growth of NiSi into the adjacent Ni2Si layer. Time required to effect transition from compressive to tensile stress decreases and magnitude of both stresses decreases with increasing temperature, due to thermally activated reaction processes.

Preimplantation of phosphorous is used in this work to promote the lateral uniformity of the interfacial WSi2 layer that grows upon subsequent thermal annealing of a thin W film sputter-deposited on a monocrystalline Si substrate. A phosphorous dose of 7.5x1015 P/cm2 yields an intermixed layer at the interface and the formation of the low-temperature hexagonal WSi2 phase. Subseqent vacuum furnace annealing at temperatures from 630°C to 715°C leads to a laterally uniform growth of tetragonal WSi2. The kinetics concur with those of previous reports for diffusion-limited growth of WSi2. All the available data fit well with a common growth law of x2 =kt, in which x is the thickness of the silicide layer, t is the annealing duration and k is the growth constant. The growth constant is given by k=1.5x104(cm2/s)exp(Ea/kBT), where the activation energy Ea=3.5±0.3 eV. Possible factors responsible for the beneficial effect of ion mixing on the interfacial silicide growth is discussed.