Grain Boundary Orientation Research Articles

Grain boundary effects on the fatigue deformation and cracking behavior of copper bicrystals

Fatigue tests were performed on two types of [134] iso-axial copper bicrystals for studying the grain boundary (GB) effects on the cyclic deformation and fatigue cracking behavior and the corresponding mechanism in copper bicrystals. One bicrystal contains a perpendicular GB and the other contains a tilting one with respect to the loading axis. Both the grain boundaries are nearly 180° rotated. It was shown that both the perpendicular and tilting grain boundaries have little effect on the cyclic hardening and saturation behavior of the bicrystals, but show strong effects on the slip deformation and fatigue cracking behavior. The microcracks were found to prefer to nucleate and propagate at the GB, leading to intergranular cracking. However, the crack nucleation behavior was found to be different for the above two iso-axial copper bicrystals. Two types of intergranular fatigue cracking mechanisms were proposed based on the specimen geometry with respect to the dominant slip system and the GB orientation.

The etching behavior of tungsten (W) with respect to the orientation of the grain boundary and masking layers

In this paper, we present the study of the tungsten (W) etch rate as a function of different masking materials: Ti/TiN and SiO 2. In addition, the impact of the W grain boundary orientation on the etch rate is established. With the use of a SiO 2 masking layer, the W etch rate is five times higher compared to etching with a Ti/TiN masking film. The blanket W etch rate is the average of these two values. The difference of etch rate with respect to the orientations of grain boundaries is only detected in pure SF 6 plasma.

Novel Electromigration Failure Mechanism for Aluminium-Based Metallization on Titanium Substrate

AbstractIn this paper a phenomenological characterisation of an anomalous grain growth, observed after classical electromigration lifetests, on Al-l%Si-0.5%Cu multigrain stripes, deposited at high temperature (460°C) on a Ti substrate, is reported. Failure analysis, carried out by Scanning Electron Microscopy (SEM) and Focus Ion Beam (FIB), has detected an abnormal single-grain growth in the vertical direction, starting from the Ti/Al interface. Medium Time to Failure (MTF) data are compared with those of stripes on Ti/TiN substrate, on which no grain growth was observed. The growth of the anomalous grains has been related to the Ti/Al interface properties. Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM) analyses concurrently show a higher texture of the film on the Ti, compared with the film on the Ti/TiN substrate. The tight columnar orientation of grain boundaries strongly limits the mechanism of grain boundary diffusion during electromigration stress. The atomic flux is then forced to take place at the Ti/Al interface, where the epitaxial growth of the Al single grains is favoured.

Misorientation analysis and the formation and orientation of subgrain and grain boundaries

In contrast to the behaviour of individual grains, both inter- and intra-granular boundaries within rocks have received much less attention. However, many geological processes, particularly during deformation (e.g., yielding, dislocation creep, recrystallisation, superplasticity and various fracture mechanisms), and petrophysical properties depend to some extent on the nature of boundaries present in a rock. In this contribution, we consider the role of intergranular and intragranular crystal boundaries. A precise characterisation of such boundaries depends on defining the crystallographic and dimensional orientations of the boundary and the misorientation between the adjacent regions (i.e. grains, subgrains, etc.) separated by the boundary. Although several theoretical descriptions of boundary configuration are available, practical precision is lacking and approximations are necessary. We describe two specific approximations for boundary formation and orientation obtained using the SEM electron channelling technique. The first is a geometrical interpretation of electron channelling patterns (ECP) in terms of the likely formation and orientation of the intervening boundary. The second considers the misorientation between adjacent regions across a boundary. This involves a model which assumes a simple geometrical relationship between crystal slip systems responsible for the rotation and misorientation between adjacent regions, and the formation and orientation of the resulting boundary. These approximations are capable of: (a) identifying trends in the dispersion of crystallographic directions during deformation; (b) identifying active slip systems; (c) calculating the relative Schmid Factors for each crystal slip system (and therefore the most likely system to be activated); (d) modelling synthetic misorientations and predicting the crystal slip systems and boundary configurations to be expected; and (e) comparing real data with synthetic models. Our analyses are illustrated via natural examples of dynamic recrystallisation in quartzite and a theoretical simulation of the behaviour of an individual quartz grain during deformation.

Microstructures and reproducibility for several high-Tc Josephson junctions

We overview relationship between microstructures and reproducibility for several types of Josephson junctions which we have studied by transmission electron microscopy (TEM). For grain boundary type junctions, we found that although the orientation between two grains can be controlled, the detailed orientation of grain boundary is uncontrollable. Therefore, the critical current varies dramatically even prepared under the same conditions. When one of the grain boundaries is a basal-plane-facet (001) grain boundary, the grain boundary structure is always the same such that a good control of critical current becomes available. In the case of multilayer junctions, a growth of a-axis multilayer by homoepitaxy is proposed to challenge SIS junction, because recent results show that the substrate smoothness can be obtained less than 10Åwithin 5 μm area.

Grain boundary cracking in fatigued bicrystals

Compact tension (CT) shaped copper bicrystals containing the Σ3(111), Σ9(221), Σ41(338) or random [110] tilt boundaries either perpendicular or parallel to the tensile axis (TA) were tested to examine the effect of grain boundary (GB) structure on fatigue crack initiation and propagation. With both types of bicrystals, the GB resistance to intergranular cracking increases with the decrease in the Σ value. The effect of air on fatigue crack propagation is found to be of primary importance. It is shown that the GB is not necessarily a preferential site for crack propagation in vacuum. A crack introduced intergranularly in air may assume a stransgranular mode of growth in vacuum. The initial GB structure greatly affects the susceptibility of GBs to corrosion in air and this determines their resistance to crack growth. The relative importance of slip band cracking as compared to GB cracking in vacuum is examined. The dominant mechanism of fracture is seen to be determined by two factors: the GB structure in the non-equilibrium state and the geometry of slip with respect to GB orientation.

Effect of ambient air on fatigue crack propagation in copper compact tension bicrystals

The effect of environment on fatigue crack propagation in copper compact tension (CT) bicrystals was examined. The role of the initial grain boundary (GB) structure is analyzed for bicrystals having Σ9 and Σ41 grain boundaries. It is shown that the GB is not necessarily a preferential site for crack propagation in vacuum. A crack introduced intergranularly in air may change its mode of growth to transgranular in vacuum. The relative importance of GB cracking compared with persistent slip band (PSB) cracking in vacuum is examined. The dominant mechanism of fracture is determined by two factors: the GB structure and the geometry of slip with respect to the GB orientation.

Orientation relationships between grains and grain boundaries in Al-1 wt% Ga at the beginning of secondary recrystallization

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Quantitative TEM analysis of microstructural anisotropy

Preferred orientation of grain boundaries or interfaces in solids is an important indicator of anisotropy in boundary energy or kinetics. The present study is part of an ongoing investigation of faceting in thin films with the mazed bicrystal microstructure which possesses several unique features that are difficult to measure with standard parameters such as grain size distribution. One of the important characteristics of this microstructure is the degree and type of anisotropy. Figure 1 shows a micrograph with a typical mazed bicrystal microstructure. Only two grain orientations with about equal volume fraction are seen in black and white contrast, respectively. It is apparent that unlike a normal polycrystalline thin film, individual grains in this microstructure have unusual convoluted shapes with both concave and convex regions.The standard stereological method to measure microstructural anisotropy is the rose plot generated from a count of intersections with a reference grid overlaid on the micrograph at different angles.

Σ３｛１１１｝およびΣ９｛２２１｝粒界を有する銅双結晶の再結晶において結晶粒界が果たす役割

Copper bicrystals with Σ3{111} and Σ9{221} boundaries were deformed in tension and annealed for 900sec at temperatures between 773K and 1273K. Noticing grain and grain-boundary orientations of the specimens, the effects of grain boundaries on the recrystallization were discussed. In the case of the bicrystal where both of the primary slip planes in the grains were parallel to a grain boundary, the recrystallization behavior was almost the same with that of the single crystal of the component grain. On the other hand, in the bicrystals where the primary slip planes in grains were intersected at the grain boundaries, the grain boundaries in the bicrystals lowered the temperatures of appearance of new grains. The new grains were preferentially observed on the grain boundaries. In the case of the specimens where double slips took place in the grains from the early stage of deformation, no effect of grain boundaries on recrystallization was observed. The single crystal with double slips showed the lower temperature of appearance of new grains than those of the single crystals with single slips.Although the deformation behavior of bicrystals with Σ3{111} and Σ9{221} boundaries was almost the same at room temperature, the recrystallization of the bicrystal with the Σ9{221} boundary was easier. The difference in recrystallization behavior corresponded to the reported result that the grain-boundary diffusion coefficient of a Σ9{221} boundary was much larger than that of a Σ3{111} boundary.

Electromigration in Bicrystal Al Lines

We have developed a new experimental technique to study electromigration in bicrytal Al lines as a function of the type and location of the grain boundary as well as the testing temperature. The failure times of these lines are found to be lognormally distributed. The median time to failure (MTTF) depends more strongly on the boundary orientation than the type of grain boundary. The dependence of lifetimes on the type and orientation of grain boundaries, the location and appearance of the failure sites, and the measured activation energy (E.) of 0.94eV suggest that both interfacial and grain boundary diffusion contribute to failure in bicrystal lines, and likely in bamboo and near-bamboo lines as well.

Effect of grain boundary structure on sensitization and corrosion of stainless steel

This paper reports on the influence of misorientation angle and structure of a grain boundary on the sensitization and grain boundary corrosion of austenitic and ferritic stainless steels. To establish grain boundary atomic structure, orientation information of the adjacent grains, obtained with the electron backscattering (EBS) technique, was combined with the SEM image of the surface to obtain the orientation of the grain boundary. Modeling of the grain boundary structure was based on ideal crystallography and the coincident site lattice concept. The results support the concepts (1) of a threshold misorientation angle whose value is a function of the aging time and temperature, below which boundaries are of sufficiently low energy that sensitization does not occur, and (2) of a major role of grain boundary structure in explaining the wide variation in sensitization that occurs in grain boundaries of misorientation angle greater than the threshold value. It was also found that the grain boundary corrosion mechanism is not simply the dissolution of chromium depleted alloy since the observed groove widths were 10 to 100 times larger than the Cr-profile widths.

Natural Fractures, Mechanical Anisotropy, Stress, and Fabric in North-Central Oklahoma: ABSTRACT

The regional fracture pattern exposed on surface outcrops of Permian and Pennsylvanian limestones and sandstones in north-central Oklahoma consists of a systematic set striking east-northeast and an orthogonal set striking north-northwest. Both sets are normal to bedding and show no evidence of shear offset. Detailed mapping of fractures exposed in Permian limestone in a quarry at Vap's Pass, Kay County, Oklahoma, reveals that individual fractures of both sets are comprised of joined straight-line segments of slightly different strike. The systematic set strikes between N70E and N85E and the non-systematic set between N10W and N45W. Both the systematic and non-systematic fracture orientations are parallel to a (microcrack) fabric in the plane of bedding inferred from point load testing in the laboratory. Neither fracture set appears related to the depositional fabric as determined by thin-section analysis of the preferred orientations of grain boundaries and long axes. Results of point load tests on oriented (Pennsylvanian) shale core from Conoco's Borehole Test Facility, 3 mi southwest of the Vap's Pass exposure, indicate a different orientation for mechanical anisotropy N50E. That direction is roughly parallel to maximum horizontal in-situ stress determined from bore hole breakouts and to large-scale extensional fractures observed in the core. Themore » relations among surface and subsurface fracture orientation, depositional fabric, mechanical anisotropy, and the in-situ stress field are discussed.« less

Improved technique for the determination of low energy boundaries by the rotating-sphere-on-a-plate method: Results for grain boundaries in the Cu/Ni system

Using the rotating-sphere-on-a-plate method, the relatively low energy orientations of grain boundaries in Cu, Ni and two Cu-Ni alloys lying, on average, parallel to the (100) surface of the plate were measured. Pole figures were plotted by using an X-ray texture goniometer. The data were analysed to determine whether special Σ-value boundaries existed (up to Σ35b), and crystallographic parameters such as Σ-value, boundary plane, rotation axis and angle, twist and/or tilt components were tabulated. The measured low energy orientations were compared with previous measurements from other studies and with predictions from geometric criteria.

Simple shear experiments on calcite rocks: rheology and microfabric

Ideal simple shearing of Carrara marble and Solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35°. The experiments covered a wide range in temperatures (25–900°C) at confining pressures of 200 and 250 MPa and at strain rates between 10−3 and 10−5 s−1. Shear strains of up γ = 2.7 were achieved. The stress-strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing. This comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks. At the highest temperatures Carrara marble exhibited substantial work softening after high shear strains. A complete texture analysis was carried out with the U-stage and a texture goniometer. The following four distinct microfabric regimes were found. (1) Twinning regime: an oblique c-axis maximum deflected from the pole to the flattening plane towards σ1 and against the imposed sense of shear results directly from e-twinning. Extensive twinning (some grains are completely twinned) rapidly rotates the c-axes into near parallelism with σ1. This regime was observed for Carrara marble deformed at temperatures below 700°C and for Solnhofen limestone at room temperature. (2) Intracrystalline slip regime: three c-axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning. These c-axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear-zone boundary and the shear direction, respectively. This finding supports the idea of an ‘orientation for easy slip’ resulting from simple shearing. In addition to r- and -glide, basal glide is inferred to have been operative. (3) Grain-boundary sliding regime: a great circle distribution of c-axes approximately perpendicular to the direction of finite shortening is observed. This texture is weaker compared to the other regimes. It is interpreted to result from minor contributions of f-slip towards total strain. This regime is restricted to fine-grained Solnhofen limestone deformed at the highest temperatures. (4) Grain-boundary migration regime: only in Carrara marble deformed at the highest temperatures is there substantial grain-boundary migration recrystallization. The texture consists of a dominant c-axis maximum oriented perpendicular to the shear-zone boundary. This single maximum corresponds to an ‘orientation for easy slip’ for basal slip. Grain-boundary migration assists rapid lattice reorientation, and leads to (geometrical) work softening. Quantitative analysis of grain-boundary surface orientations gave the following results. Within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types. The strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures. At intermediate temperatures, and especially in Carrara marble, there is a consistent trend for the aspect ratios to indicate too little flattening, and for the angles between the long axis of the strain ellipse and the shear-zone boundary to be too small. In the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another (grain-boundary sliding or translations accommodated in the mantle regions of grains). At the highest temperatures, where extensive grain-boundary migration occurs in Carrara marble (grain-boundary migration regime), two preferred orientations of grain boundaries are observed: (1) parallel to the shear zone boundary; and (2) parallel to an oblique direction deflected 20° away from the normal to the shear-zone boundary in the sense of the imposed shear. The same pattern of grain-boundary alignment is observed in Solnhofen limestone deformed in the grain-boundary sliding regime. The geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general.

Velocity anisotropy in granodiorite and quartzite due to the distribution of microcracks

The spatial anisotropy of P-wave velocities was investigated in spherical samples of granodiorite and quartzite and correlated with the orientation of microcracks and grain boundaries, determined optically by universal stage techniques. The preferred orientation of normals to cleavage cracks of biotite and amphibole in granodiorite correlates well with the direction of maximum velocity increase under hydrostatic pressure, although the minerals form only nine per cent of the volume. Irregular microcracks in an almost monomineral quartzite have only a very small effect on the velocity anisotropy, although they are also preferentially oriented. The nature of the microdiscontinuities is of primary importance for the velocity anisotropy observed at atmospheric and low hydrostatic pressures.

Grain-Boundary Diffusion of 51Cr in MgO and Cr-Doped MgO

The grain-boundary diffusion product, D'δ, of 51Cr in MgO and Cr-doped MgO as a function of grain-boundary orientation and point-defect concentration was determined at T=1200° to 1450°C. A large degree of anisotropy was found in the grain-boundary diffusion behavior in MgO. The ratio of D'δ|| parallel to D'δ‖ perpendicular to the growth direction, D'||/D'‖, is 102 for a 5° (100) tilt boundary, decreased to ∼2 in boundaries with tilt angles > 10°. The decrease in D'||/D'‖ is due to a large increase in D'‖ with increasing tilt angle. The results indicate that grain-boundary diffusion in MgO is connected to the orientation of dislocations and the mechanism is one of dislocation pipe diffusion. The grain-boundary diffusion product D'δ increases with increasing Cr concentration in MgO and is ∼4 times larger for MgO containing 0.56 at. % Cr than for the undoped MgO. For all bicrystals studied, the activation energies are within 180 ± 20 kJ/mol which is 60% of the activation energy for 51Cr diffusion in undoped MgO.

Angle between grain-boundary Widmanstätten ferrite and grain boundaries in carbon steel

Results are presented of an investigation into the influence of grain-boundary orientation on habitplane variant selectivity in proeutectoid ferrite sideplate formation in carbon steel, as indicated by constraints on the range of angles which the grain-boundary ferrite sideplate habit can make with the grain boundary. A statistical approach was adopted.

一方向凝固したＡＣ７Ａの鋳造組織と機械的性質

Thermal expansion, tensile and fatigue tests were carried out on the castings having different structures. The coefficient of thermal expansion changes with temperature in a similar manner regardless of cast structures and of cooling rates. The castings having a columnar structure show a considerable anisotropic effect on tensile and fatigue properties regardless of cooling rates. This is attributed to the crystallographic orientation and geometry of grain boundaries. The castings having equi-axial crystals are free from anisotropy.

The use of accelerators to obtain channelling micrographs of polycrystalline foils

Abstract The very well-collimated proton beam from a Van de Graaff accelerator has been used to obtain micrographs of polycrystalline nickel foils. The graphs are obtained by registering those of the particles in the beam that are channelled nearly all the way. The micrographs carry information from the bulk about the presence of dislocations, orientation, and migration of grain boundaries.