Changes In Grain Structure Research Articles

Position Normalization as a Tool to Extract Compositional and Microstructural Profiles from Backscatter and Secondary Electron Images

Abstract Position normalization is a method of manipulating data from any image source so that the effective information to noise ratio is dramatically increased. In this paper we present two very different examples of the application of position normalization used in the study of high current density superconductors. In the first example we use FESEM fractography to analyze grain boundary density and grain shape in micron-diameter filaments and then normalize the data obtained from individual grains to their positions with respect to the filament-matrix interface. In this way we extract the change of grain structure with position in apparently inhomogeneous microstructure. In the second example we analyze the backscattered electron intensity, BEI, from the cross-section of a superconductor filament with respect to its proximity to phase boundaries. In this way we extract small trends in the mean atomic number with a spatial resolution of better than 100 nm.

Effects of substrate temperature and ion irradiation on the formation and structure of Co films on NaCl(100)

The effects of substrate temperature and ion irradiation on the formation and the structure of thin Co films during vacuum deposition onto air-cleaved NaCl(100) single crystal surfaces were investigated using transmission electron microscopy (TEM). Both rise in the substrate temperature and the ion irradiation, caused considerable changes in average grain size, structure and orientation of the Co films. In particular, a well pronounced cubic (fcc) phase was established from ion irradiation, whereas the physical vapour deposited room temperature Co films without ion irradiation show a hexagonal (hcp) structure. The effects of ion irradiation during the growth of Co films on NaCl(100) substrate at room temperature were found to be identical to the effects of raising the substrate temperature to the range of 80°C–90°C during the physical vapour deposition.

Visual‐stratigraphic dating of the GISP2 ice core: Basis, reproducibility, and application

Annual layers are visible in the Greenland Ice Sheet Project 2 ice core from central Greenland, allowing rapid dating of the core. Changes in bubble and grain structure caused by near‐surface, primarily summertime formation of hoar complexes provide the main visible annual marker in the Holocene, and changes in “cloudiness” of the ice correlated with dustiness mark Wisconsinan annual cycles; both markers are evident and have been intercalibrated in early Holocene ice. Layer counts are reproducible between different workers and for one worker at different times, with 1% error over century‐length times in the Holocene. Reproducibility is typically 5% in Wisconsinan ice‐age ice and decreases with increasing age and depth. Cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50,000 years. Visible observations are not greatly degraded by “brittle ice” or many other core‐quality problems, allowing construction of long, consistently sampled time series. High accuracy requires careful study of the core by dedicated observers.

Equiaxed-grain size analysis in the mushy zone during solidification via an in-situ method based on the electrical sensing zone principle

This paper addresses dendritic equiaxed growth during grain structure formation in alloy solidification, and focuses on the growth and interaction of primary dendrite arms, which drive and limit grain development, respectively. Dedicated solidification experiments on Al–10 wt.% Cu alloy were carried out at the European Synchrotron Radiation Facility, enabling live observation by in situ and real-time synchrotron X-ray radiography. Equiaxed solidification was achieved by cooling nearly isothermal samples, and the growth of the grains was continuously monitored from the very early stages of solidification up to a state where changes in grain structure were no longer visible to the observer’s naked eye. The time evolution of individual equiaxed grains is analysed through measurements of the lengths and tip velocities of the primary dendrite arms driving grain growth. It is found that equiaxed dendrite propagation is characterized by two growth regimes. The first regime, in which a gradual increase in the tip growth rate is observed, corresponds to free dendritic growth, when the relative distance between grains is large enough to consider a grain as isolated. During this regime, the far-field liquid concentration ahead of the advancing dendrite tip remains constant, equal to the initial alloy composition, and the driving force for growth is the undercooling applied by cooling of the sample, in agreement with three-dimensional models of free dendritic growth. The second regime shows a decrease in the tip velocity towards zero and is attributed to grain interaction when the solute diffusion field in front of the advancing dendrite tip under consideration overlaps with the solute field associated with the growth of the grain(s) facing it. Solute concentration profiles are measured in the extra dendritic liquid ahead of dendrite tips interacting with neighbour grains, from which the far-field solute concentration and neighbour–interaction distance are deduced. These measurements confirm that impingement of the solute boundary layers is the main cause of dendrite growth being slowed down and stopped.

Copper Migration and Precipitate Dissolution in Aluminum/Copper Lines During Electromigration Testing

AbstractWe have used transmission electron microscopy to examine in detail how microstructural changes take place in aluminum/copper lines adjacent to tungsten contacts. A structure that could be powered in a probe station was deposited directly on an electron transparent silicon nitride window to allow direct observation of the structure of the line after different intervals of electromigration testing. Observations made on aluminum-4% copper lines show that significant changes in the grain structure surrounding precipitates occur during testing even under conditions where no normal grain growth is observed in the lines. Elecromigration testing at 260°C resulted in grain coarsening and the formation of new diffusion blocking structures in the lines. By making measurements of the volume of individual precipitates as a function of time, the flux of copper through specific segments of the microstructure of the line could be measured. The results indicate that the presence of a single grain boundary can increase the electromigration flux of copper along the line by an order of magnitude. In line segments where a bamboo grain occurred copper diffusion appears to be controlled by diffusion along the Al/oxide interface at the surface of the lines. It is also shown that, in polycrystalline lines, the rate of copper depletion frorr the cathode is largely determined by the rate of dissolution of the precipitates. In mixed structure lines the migration of copper can become quite complex as changes in diffusion paths can occur as precipitates dissolve or grow.

Crystallographic contribution to the formation of columnar grain structure in iron films deposited at oblique incidence

The columnar grain structure and the texture were investigated for Fe films vapor-deposited at various deposition rates R. The incidence angle was 65° and the substrate temperature was 473 K. From the X-ray analysis using the Schulz method and the observations of replica electron microscopy it was revealed that the change in columnar grain structure with R can be understood by considering the exhibition of the {100} habit.

Thermal and Electromigration Effects on the Surface and Aluminum/Aluminum Oxide Interface of Aluminum Metallizations

ABSTRACTThermal and electromigration effects on the thicknesses of aluminum oxide at the aluminum-1% silicon/thermal silicon dioxide interface were quantitatively determined by AES. Void sites corresponded with thinner aluminum oxide thicknesses at this interface. Changes in surface topography and grain structure were quantitatively determined for thermally annealed aluminum-1% silicon metallizations by AFM.

Effect of microstructure on tensile and fatigue properties of superplastically formed Al–Li–Cu–Mg–Zr 8090 alloy sheet

The effect of super plastic deformation on the microstructure of the low density Al–Li–Cu–Mg–Zr (8090) alloy has been investigated. Changes in grain structure, grain misorientation, and texture were observed with increasing superplastic deformation. These observations are consistent with strain enhanced grain growth accompanied by grain boundary sliding and rotation. The tensile and fatigue properties of superplastically formed (SPF) 8090 depend on superplastic strain, post-form heat treatment, and copper content. It is shown that, in the heat treated condition, the continuous loss in strength with superplastic strain can be attributed to grain growth and solute depletion at the surface. The changes in grain structure lead to increased surface roughness and a consequent reduction in fatigue life. In alloys of high copper content precipitation during age hardening is additionally dependent on the rate of cooling after SPF.MST/1286

Effect of microstructure on tensile and fatigue properties of superplastically formed Al–Li–Cu–Mg–Zr 8090 alloy sheet

AbstractThe effect of super plastic deformation on the microstructure of the low density Al–Li–Cu–Mg–Zr (8090) alloy has been investigated. Changes in grain structure, grain misorientation, and texture were observed with increasing superplastic deformation. These observations are consistent with strain enhanced grain growth accompanied by grain boundary sliding and rotation. The tensile and fatigue properties of superplastically formed (SPF) 8090 depend on superplastic strain, post-form heat treatment, and copper content. It is shown that, in the heat treated condition, the continuous loss in strength with superplastic strain can be attributed to grain growth and solute depletion at the surface. The changes in grain structure lead to increased surface roughness and a consequent reduction in fatigue life. In alloys of high copper content precipitation during age hardening is additionally dependent on the rate of cooling after SPF.MST/1286

一方向凝固マグネシウム中を伝ぱする単一応力波パルスの減衰特性

Pure Mg plate cast by heated mold continuous casting method (O.C.C-Mg) have layer structure of the columnar crystals parallel to the casting direction. The acoustic proparties of O.C.C.-Mg is compared with that of pure Mg cast by conventional casting method (polycrystal Mg). One dimensional stress wave which formed the single pulse (stress pulse) was used for investigation of their properties. The stress wave was generated by a gas-gun and the stress wave was detected by strain gages. The amplitude and duration time of the stress wave dependence of the attenuation constants obtained from both peak value and energy of the strain are confirmed. Moreover, attenuation characteristics of the specimen after annealing is compared with that of specimen as cast to confirm the influence of the change in grain structure of O.C.C.-Mg and polycrystal-Mg by annealing on the attenuation characteristics. In addition, frequency distribution which is connected to attenuation of stress wave in O.C.C. or polycrystal Mg is studied by Fourier analysis.

Superplasticity in A Zn-1·1 wt.% Al alloy III. The influence of grain size

The paper represents the third instalment of the series dealing with the superplastic deformation in a Zn-1·1 wt. % Al alloy and is devoted to the influence of grain size on the deformation behaviour of this alloy. Deformation characteristics were measured at two temperatures — 293 and 500 K. The grain size dependence of the flow stress observed was found opposite to that predicted by the Hall-Petch relation. Such a behaviour was explained under the assumption that grain boundaries might act as sites of rapid recovery of lattice dislocations. The results obtained at temperature 293 K proved that the transition between the regions of “abnormal” behaviour (with the flow stress increasing with increasing grain size) and “normal” behaviour (with the flow stress decreasing with increasing grain size) was not directly connected with the transition from the superplastic to the nonsuperplastic state. The results obtained at 500 K revealed dynamic recrystallization and a grain refinement in samples with initially coarser structures. Such a change in grain structure was accompanied with a development of superplastic characteristics.

Magnetic investigation of the columnar grain structure in obliquely deposited iron films

The columnar grain structure in obliquely deposited iron films has been magnetically investigated by measuring the anisotropy field and the effective saturation magnetization. The incidence angle was 60 ° and the substrate temperature T s range from 473 to 698 K. At low temperatures ( T s < 650 K) columnar grains are sparse but they align along the direction perpendicular to the incidence plane. On the other hand the packing of columnar grains at high temperatures ( T s ≥ 650 K) is dense and isotropic. The electron microscopic observation supported these results and the X-ray analysis found out two-degree and one-degree orientations at low and high temperatures, respectively. The change in columnar grain structure with T s and the evolution of texture are discussed on the basis of the adatom movement due to momenta.

Effect of post-oxidation anneal temperature on radiation-induced charge trapping in metal-oxide-semiconductor devices

Polycrystalline silicon-gate metal-oxide-semiconductor (MOS) capacitors have been fabricated with high-temperature anneals from 800 to 950 °C after gate oxidation and polycrystalline silicon deposition. Temperatures from 800 to 875 °C are found to have very little effect on the radiation response of these devices. However, a rapid increase in radiation-induced oxide-trapped charge, ΔVot, is observed for anneal temperatures above 875 °C. This increase in ΔVot coincides with an experimentally observed change in the polycrystalline silicon grain structure. The anneal temperature was found to have a much smaller effect on radiation-induced interface-trap charge. The correlation of these results to other properties, e.g., stress, is discussed.

Thermal recovery processes in deformed aluminum

The effects of recovery on both microstructure and subsequent stress vs strain behavior were studied in pure aluminum single crystals prestrained at room temperature in 〈111〉 compression; they are presumed to be representative of polycrystal behavior, avoiding changes in grain structure. Transmission electron microscopy showed that two distinct dislocation processes occur: 1. (1) a rapid tightening of tangles and loose cell walls, eventually into subgrain boundaries, without a noticeable change in the scale of the structure, and 2. (2) subsequent coarsening of the subgrain structure. These two processes of microstructural change were correlated respectively with two distinct types (I and II) of stress vs strain behavior during postanneal straining. After ‘Type I recovery’, the relation between the strain-hardening rate, θ = dσ/ dϵ (σ: true stress, ϵ: true strain), and the true stress is identical to that of an unrecovered specimen, after a transient of a few percent of post-anneal straining. Type I recovery encompasses all of ‘metarecovery’ and part of ‘orthorecovery’, and bears resemblance to ‘dynamic recovery’ processes during stage III strain-hardening. Type II recovery, which succeeds Type I recovery, shows long-lasting effects on the mechanical behavior which are characterized in particular by unusually low θ values compared to unrecovered specimens deformed to the same stress. It may correspond to some transition stage between recovery and recrystallization.

Tempering behavior of iron-carbon sputter deposits with 0 to 5 wt pct C

Iron-carbon sputter deposits with 0.06, 0.18, 0.66, 2, 3, and 5 wt pct C were tempered at temperatures from 100° to 550°C. The 0.06, 0.18, and 0.66 wt pct C sputter deposits were similar to severely cold-worked martensite, both as-deposited and in tempering response. Specifically, these three deposits were much harder than water quenched steels of the same composition, and the deposit hardnesses decreased less than martensite hardnesses on tempering below 400°C. The hardnesses of the 2 and 3 wt pct C deposits increased 40 to 50 Dph units upon tempering at low temperatures (150° to 250°C) and decreased for higher tempering temperatures. The hardness of the 5 wt pct C deposit remained constant (920 Dph) after tempering at 150°C, but increased to 1170 Dph upon tempering at 250°C when monoclinic Hagg carbide (Fe5C2) formed. Cementite (Fe3C) was the only other carbide detected in the tempered deposits, and it formed only at 475°C and above. The columnar grains of the sputter deposits transformed to equiaxed grains upon tempering above 250°C. This change in grain structure was due to recovery and not recrystallization. Some grain growth occurred in the 0.06, 0.18, 0.66, and 2 wt pct C deposits above 300°C, but the grain size of the 3 and 5 wt pct C deposits remained submicron. The hardnesses of the deposits after tempering at 550°C increased with carbon content, the 5 wt pct C deposit having the highest hardness (960 Dph) and the 0.06 wt pct C deposit the lowest (360 Dph).

Rate Dependence in a Solarizing Commercial X-Ray Emulsion: Sensitometric Properties, Number, and Structure of Developed Grains*

A comparison was made of optical density, mass of developed silver, number, projected area, and structure of the grains of a solarizing radiographic bromo-iodide emulsion exposed to Co60 gamma radiation at two different intensities, and developed in a surface developer. In contrast to the optical density and the mass of silver developed for a given exposure, which show only little dependence on intensity, before solarization sets in, the dependence of the number of developed grains on intensity of exposure is quite marked. Another anomaly is observed in the re-reversal region for exposure to high-intensity radiation. There, mass of silver does not vary with exposure in the same direction as optical density.Associated with the changes in photometric behavior are marked changes in grain structure, while the changes in the projected area of developed silver are small. The photometric properties cannot be correlated uniquely with grain structure over the entire exposure range.