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The initial reaction between Pt and molten Sn has been studied by dipping tests of 1 and 2 s. It was found that both PtSn and PtSn 4 formed in the first second of contact. PtSn formed 7 nm (1 s) and 20 nm (2 s) thick layers on top of the Pt substrate but PtSn 4 formed scattered particles in the liquid Sn. No orientation relationship was found between Pt and PtSn. PtSn nucleates heterogeneously on Pt by its larger energy of formation than PtSn 4 and PtSn 4 nucleates in liquid Sn by the very low solubility of Pt in molten Sn.

The dislocation structure in front of crack tips for various crack propagation rates and the redevelopment of the dislocation structure after reducing the fatigue load (i.e., after decreasing the crack propagation rate from approximately 5×10 −5 to 5×10 −7 mm/cycle) are investigated in this study. Pure polycrystalline copper with large grains was used in this study. The materials were annealed at 800 °C for 4 hours in a 10 −5 Torr vacuum and then cooled in a furnace. The specimen preparations followed the ASTM E647 instructions for compact tension (CT) specimens. Fatigue crack propagation was achieved using a computerised Instron 8801 hydraulic testing machine at R =0.1 at a frequency of approximately 20 Hz. The results are as follows: (1) The dislocation structure includes misoriented cells next to the crack tips for propagation rates greater than 5×10 −5 mm/cycle. When the crack propagation rate is less than 5×10 −7 mm/cycle, the dislocation structure next to the crack tips is dominated by a loop patch structure. (2) When crack tips have the same steady crack propagation rate, the dislocation structures are similar regardless of the load history. (3) The dislocation evolution presents an anti-sequence between positive and negative.

The dislocation structural evolution in polycrystalline copper at constant strain amplitude during low cycle fatigue is well understood. However, the dislocation structural development at variable strain, which changes from high to low strain amplitude, has seldom been reported. Scanning electron microscope (SEM) back-scattering electron imaging was used in this study. Dislocation structure fatigue research was conducted on many copper materials in the literature. Hence, OFHC with an ultra-large grain was used in this work. The fatigue is completed using the Instron 8801 hydraulic fatigue test machine. After fatigue was instituted the microstructures were investigated using BEI of SEM and TEM. The results show that; (1) the S – N curve at reduced strain amplitude reveals softening after hardening at the initiation stage and up to fracture. No plateau area and secondary hardening occurred. (2) A special microstructure with mis-orientation cells embedded in a vein structure was observed in the ultra-large grain. (3) With small strain amplitude from high–low strain amplitude in the ultra-grain specimen, the fracture microstructure includes mis-oriented cells embedded in a loop patch structure. Under this load the micro-cracks are initiated at a small band with a mis-oriented cell structure.

The TiO to anatase phase transformation has been studied by transmission electron microscopy in this Article. It is shown that prior formation of TiO from Ti film can induce the formation of anatase by thermal oxidation in air; otherwise only rutile is formed. Ti film deposited on the NaCl (001) surface is induced to form epitaxial TiO film by thermal oxidation in air. Further thermal oxidation in air partially transformed TiO into anatase (A) with a parallel orientation relationship of {200}A//{200}TiO. Detailed analysis of the lattice fringes image of the specimen reveals the presence of very high density of misfit dislocations. The TiO to anatase transformation is reversible as further annealing in a vacuum can turn the anatase back into TiO and eliminates the misfit dislocations. The transformation is analyzed in terms of the crystal structure, orientation relationship, and the dislocation distribution, which show that the TiO to anatase transformation is due to the close similarity between their stru...

A nanofilm method has been developed to study the formation of low-energy interfaces by the rotation of nanograins. Ion-beam sputtering was used to prepare very thin epitaxial NiO nanofilms on the (100), (110), (111), and (112) surfaces of NaCl single crystals. When two different NiO nanofilms were overlapped at different angles and annealed at 300 °C, the nanograins were found to rotate until a stable interface was reached. The stable interfaces were analyzed by transmission electron microscopy. Several previously unreported interfaces were found that belong to the asymmetric [110] tilt boundaries on different low-index planes. The orientation relationships and the structures of the interfaces were analyzed.

ZnO nanofilms of (01 1 ¯ 1) texture have been prepared by ion beam sputtering on the (001) surface of single-crystal NaCl. The orientation relationship between them is determined by transmission electron microscopy. Analyses of electron diffraction patterns and interface confirm that the ZnO (01 1 ¯ 1) plane is the interface with the NaCl (001) surface. The photoluminescence spectrum from the ZnO (01 1 ¯ 1) surface shows a near-band-edge UV emission and a broad green emission. The result indicates that the inherent high surface defects of oxygen vacancies on the (01 1 ¯ 1) surface are the probable origin of the green emission.

The aluminized coating on type 310 stainless steel prepared by high-activity Al pack cementation method has been annealed at 900 °C for 12 h to transform the brittle δ-Fe2Al5 phase into the more ductile β-FeAl phase. The microstructure is studied in detail with transmission electron microscopy. The thick outer layer has β-(Fe, Ni)Al as matrix with cube-like Cr2Al precipitates. The interfacial layer has a thin layer of metastable FCC phase (layer I) and then mixed β-(Fe, Ni)Al grains and α-(Fe, Cr) grains (layers II and III). The Cr2Al precipitates are present in the β-(Fe, Ni)Al grains in layer II but not in those in layer III, while β-FeAl precipitates are present in the α-(Fe, Cr) grains in both layers. The orientation relationships between various phases, the formation of the layers, and the precipitation of Cr2Al in β-(Fe, Ni)Al are discussed.

This work examines the evolution of the dislocation structure in large grains of polycrystalline copper with decreasing strain amplitude. The experimental results show that (1) dislocation reversal is initially triggered by the operation of a final slip system, which is formed by the previously high strain amplitude when the strain amplitude is reduced; and (2) the region that is occupied by the dislocation reversal structures called loop patches. It is small in large grains because a more homogenous internal stress distribution induces a more uniform evolution of dislocations in large grains.

Low-temperature preparation of transparent conducting electrodes is essential for flexible optoelectronic devices. Tin-doped In2O3 films with high transparency and low electrical resistance were prepared at room temperature using a radiofrequency ion beam sputtering system. Specimens with a low sheet resistivity of 10−4 Ω cm and a high visible-light transmittance of 85% to 90% were obtained. Hall measurements were used to determine mobility and carrier concentration, and the effects on resistivity are discussed.

Temperature dependent oriented growth of ZnO thin film deposited on NaCl (001) substrates using ion beam sputtering was studied by transmission electron microscopy (TEM). Thin films showing a texture due to parallel epitaxy with NaCl (001) as deposited at 100 oC, whereas thin films deposited at 400 oC can form a texture. The microstructure and the epitaxial relationship with the NaCl (001) plane were studied by a high-resolution TEM. The possible causes for the orientation changed with temperature are discussed. The optical transparency of the nanofilms grown from room temperature to 400 oC was measured.

There are three types of cyclic hardening for cyclically deformed interstitial-free (IF) steels. The magnitude of cyclic hardening was unobvious and dislocation cells smaller than 2 μm were very hard to find when total strain amplitude (Δe/2) was controlled to within 0.1 pct. When Δe/2 is increased to 0.125 to 0.3 pct, secondary cyclic hardening takes place prior to fatigue failure. Δe/2 = 0.6 pct, following an initial rapid-hardening stage. Dislocation cells smaller than 2 μm tend to develop near grain boundaries and triple junction of the grains while cycling just above Δe/2 = 0.125 pct. Such dislocation development results in secondary hardening. However, no failure occurs if cycling just below Δe/2 = 0.1 pct; hence, the fatigue limit for IF steel should be very close to Δe/2 = 0.1 pct.

Low-temperature growth of undoped ZnO films with high transparency and low electrical resistance was performed by ion beam sputtering. After systematic testing, resistivity as low as 2.95 × 10−3 Ω cm was obtained at a substrate temperature of 150°C, ion source voltage of 850 V, and ion beam current of 30 mA. The transmittance of the ZnO films was in the range of 85% to 90%. Hall measurements showed that a high mobility of 21.41 cm2/Vs was obtained for films less than 200 nm thick. The related microstructures and physical properties were measured and are discussed.

In order to clear the relationship between dislocation development and endurance limit in fatigued body-centered cubic (BCC) metals, the automotive grade interstitial-free steel (IF steel) was fatigued near the endurance limit in this study. When cycling just below the endurance limit, the dislocation structures are mainly composed of loop patches, moreover, a few large dislocation cells and dislocation walls can also be found, and thus these structures have no significant effect on fatigue failure. However, once cyclic strain slightly exceeds the endurance limit, the small dislocation cells tend to develop near grain boundaries and triple junction of the grains, and which provide a more appropriate structure for crack growth than do large dislocation cells.

This study aimed to understand the relationship between gliding behavior of dislocations and reversed evolution of dislocation structures in pure body-centered cubic metals, using automotive-grade interstitial-free steels under strain ratio = 0 for case studies. Dislocation cells were converted into loop-patch structures, and the gilding behavior of dislocations would have changed from the original multiple-slips to single-slip when the maximum strain was reduced from 1.2 to 0.15 or 0.2%. The extent to which the reversed evolution of dislocation structures occurs is lower for maximum strain = 0.15% as compared to that of maximum strain = 0.2%. However, once the maximum strain is reduced to 0.1%, dislocation cells would persist, showing no signs of reversed evolution. A strain threshold for reversed evolution of dislocation structures was inferred to fall between maximum strain = 0.1% and maximum strain = 0.15%.

Strain controlled fatigue experiment was employed to evaluate automotive grade interstitial-free ferrite steel. Hundreds of grains were examined by scanning electron microscope under electron channeling contrast image technique of backscattered electron image mode for comprehensive comparison of micrographs with those taken under transmission electron microscope. The cyclic stress responses clearly revealed that rapid hardening occurs at the early stage of cycling as a result of multiplication of dislocations to develop loop patches, dipolar walls and dislocation cells at various total strain amplitudes. After primary rapid hardening, stress responses varied from being saturated to further hardening according to dislocation structure evolution at various strain amplitudes. The fatigue failure was always accompanied with further hardening including secondary hardening. The corresponding dislocation structures with the three types of hardening behaviors are discussed. Once the secondary hardening starts, dislocation cells began to develop along grain boundaries in the low strain region and then extended into grain interiors as strain amplitudes increased and cycling went on. The secondary hardening rates were found to be directly proportional to their strain amplitudes.

This work aimed to understand the relationship between gliding behavior of dislocations and reversed evolution of dislocation structures in pure BCC (body-centered cubic) metals, using automotive-grade interstitial-free steels (IF steel) under strain ratio (R) = 0 for case studies. The corresponding dislocation structures for ɛmax = 0.2% and 1.2% are loop-patch structure and dislocation-cell structure, respectively. However, dislocation cells were converted into loop-patch structures and the gilding behavior of dislocations would have changed from the original multiple-slips to single-slip when the ɛmax was reduced from 1.2% to 0.2%.

ZnO nanofilm of the (2 1 ¯ 1 ¯ 0) surface was prepared by ion beam sputtering deposition. The nanofilm was prepared on NaCl (0 0 1) surface at 200 °C to produce nearly pure (2 1 ¯ 1 ¯ 0) ZnO texture and the orientation relationship was determined and the interface discussed. Transmission electron microscopy lattice images were used to find the interface formed between ZnO nanocrystals. The ZnO nanocrystals coalesced to form a straight (0 1 ¯ 1 ¯ 2) interface. The photoluminescence spectrum from the (2 1 ¯ 1 ¯ 0) ZnO surface showed only a near-band-edge UV emission peak.

The cyclic stress–strain curve (CSSC) of cyclically deformed polycrystalline interstitial-free steels (IF steel), divided into regions A, B and C, have been correlated with the fatigue test conditions. No dislocation arrangement can be found when plastic strain amplitude is controlled in region A. For region B as revealed as a plateau, the plastic strain amplitude is located in the range between ɛ pl = 7.5 × 10 −5 (Δ ɛ /2 = 0.05%) and ɛ pl = 5 × 10 −4 (Δ ɛ /2 = 0.1%). Loop patches prevail in region B. If the strain amplitude is close to the upper limit of the region B, the loop-patch structure is also predominant in the dislocation structures despite the existence of dislocation walls and a few dislocation cells larger than 2 μm. However, these structures have no significant effect on fatigue failure. The dislocation cells rapidly developed once the plastic strain amplitude is elevated into region C.

Strain-controlled fatigue experiments were employed to evaluate automotive-grade interstitial-free ferrite steels under R = 0. Hundreds of grains were examined by scanning electron microscope (SEM) under electron channeling contrast image technique of backscattered electron image mode (BEI/ECCI) for comprehensive comparison of micrographs with those taken under transmission electron microscope (TEM). It is clearly revealed that cyclic hardening was virtually unobvious and dislocation cell structures were very rare when Δe/2 was controlled to within 0.1%. When Δe/2 was increased to 0.2%, the general dislocation structure exhibited a predominately dislocation wall structure prior to the secondary cyclic hardening, after which the formation of dislocation cells were observed. At Δe/2 = 1.0%, following an initial rapid-hardening stage, the dislocation cell structure of low-angle misorientation formed in the early stage was gradually converted into high-angle misorientation as the cyclic strain continued to be imposed.

The effects of annealing on the microstructure of first stage (high-Al activity pack) aluminized coating on Ni–15Cr alloy prepared by pack cementation method were analyzed by transmission electron microscope. The coating consists of a thin layer of γ′-Ni 3 Al, an interfacial zone of mixed β-NiAl and α-Cr, and a thick outer zone of β-NiAl (A layer) and mixed β-NiAl and α-Cr (B layer). Martensitic transformation was observed in the β-NiAl grains in the interfacial zone. Parallel crystallographic relationship was found at the γ/γ′ interface in the substrate and the α/β interface in the interfacial zone. Cr 2 Al was found to precipitate in the β-NiAl and α-Cr grains in the B layer of the outer zone. The formation mechanisms of the coating layers, the precipitates, and the observed crystallographic relationships are discussed.

Lattice images by transmission electron microscopy (TEM) were used to find new interfaces formed between c- and/or t-ZrO2 nanocrystals. The ZrO2 nanocrystals, prepared by ion-beam sputtering on a NaCl (100) plane, coalesced to form a straight {220}/{200} interface and a stepped {200}/{111} interface with misfit dislocations. The former is characterized by a good match of O2- lattice sites and smooth joining of low index planes across it without mismatch and dislocation. The special interfaces are applicable to fcc nanocrystals in general. The atomic structure of the new interface, however, can be studied further with an atomic-resolution TEM

Nanocrystalline -Zr condensates deposited by ion beam sputtering on the NaCl (1 0 0) surfaces and then annealed at 100–750 ◦ C in air. The phases present were identified by transmission electron microscopy to be nanometer-size -Zr + ZrO, -Zr + ZrO + c-ZrO2, c-ZrO2, c- + t-ZrO2, t-ZrO2, and t- + m-ZrO2 phase assemblages with increasing annealing temperature. The ZrO2 showed strong { 100 } preferred orientation due to parallel epitaxy with NaCl (1 0 0) when annealed between 150 and 500 ◦ C in air. The c- and t-ZrO2 condensates also showed (1 1 1)-specific coalescence among themselves. The c- and/or t-ZrO2 formation can be accounted for by the small grain size, the presence of low-valence Zr cation and the lateral constraint of the neighboring grains. © 2006 Elsevier B.V. All rights reserved.

In this experiment, a radio frequency dual ion beam sputtering (DIBS) system was used to prepare aluminum nitride (AlN) films with a bottom Al electrode on a Si (100) substrate. After systematic testing of the processing variables, a high-quality film with preferred c-axis orientation was grown successfully on the Si (100) substrate with an Al target under 700 eV energy flux, N2/(N2 + Ar) ratio of 55%, and 4 × 10−4 torr in vacuum. The characteristics of the deposited AlN thin films were studied by x-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), secondary ion mass spectrometry (SIMS), and electronic spectroscopy for chemical analysis (ESCA). The surface roughness was also measured. It was found that AlN films prepared by DIBS at room temperature are better than those prepared at 300°C, and those prepared with an Al target are better than those prepared with an AlN target. The inferiority of AlN films prepared with AlN targets is due to the AlN bond being broken down by the ion beam source.

The aluminized coating on 310 stainless steel was prepared by pack cementation method and the microstructure of the coating was studied by transmission electron microscopy. The coating consists of a thick outer zone and a thin interfacial zone. The matrix of the outer zone is δ-Fe 2 Al 5 with scattered Cr 5 Al 8 grains. The interfacial zone is made up of two layers; a layer of mixed α-(Cr, Fe) and β-FeAl grains with β-FeAl precipitates in the α-(Cr, Fe) grain, and a β-FeAl layer. A thin layer of polygonized γ phase is present in the γ substrate next to the coating/substrate interface. Dense dislocations are present in the interfacial zone and the substrate near the coating/substrate interface. No crystallographic relationship was found at any of the interfaces between the layers.

The siliconization of austenitic type 310 stainless steel was prepared by pack cementation method. The coating is adherent, free of voids and contains ∼5 wt.% Si. Both the coating and the substrate near the coating/substrate interface are turned into layered structure. The substrate remains to be the original face-centered cubic structure but the coating is turned into body-centered cubic (BCC) structure. In the interfacial zone the grain size is reduced to less than 20 nm and high density of dislocations is observed. In the outer zone of the coating the BCC grains are much larger than those in the interfacial zone and contain sub-micrometer precipitates of B2 structure and nanometer Fe3Si precipitates of DO3 structure. Rod-like precipitates of σ phase are also present.

Nanosized cubic and tetragonal ZrO 2 were formed as thin nanocrystalline film on NaCl (1 0 0) plane by radio frequency ion beam sputtering. The microstructure and the epitaxy relationship with the NaCl (1 0 0) plane were studied by a high-resolution transmission electron microscope. The epitaxy orientation was found to be [0 0 1] Z ∥[0 0 1] N , [ 1 0 0 ] Z ∥ [ 1 1 ¯ 0 ] N (group A), [0 1 1] Z ∥[0 0 1] N , [1 0 0] Z ∥[1 0 0] N (group B 1 ) and [0 1 1] Z ∥[0 0 1] N , [1 0 0] Z ∥[0 1 0] N (group B 2 ) between zirconia (Z) and NaCl (N). Groups B 1 and B 2 are the dominant type. The possible causes for the epitaxy relationship are discussed. Crystallites within the same group can merge by rotation and coalesce into a single crystal, whereas crystallites in different groups can form high-angle grain boundaries.

The N-polar GaN grown on c -plane sapphire with an indium-facilitated growth technique by RF-MBE has been studied. Upon the incorporation of indium during growth, the photoluminescence intensity and electron mobility of GaN have been enhanced by a factor of 15 and 6, respectively. The electron concentration drastically increases by several orders of magnitude. The biaxial strain of GaN film estimated with micro-Raman technique reduces from 0.6729 to 0.5044 GPa. The full-width at half-maximum of asymmetric (1 0 1 2) X-ray reflection which related to the density of overall threading dislocations (TDs) increases from 593 to 744 arcsec. In contrast, the symmetric (0 0 0 2) reflection related only to TDs having a non-zero c -component Burgers vectors reduces from 528 to 276 arcsec. The enhancement of GaN optical property is generally attributed to the reduction of non-zero c -component dislocations. The reduction in density is confirmed by cross-sectional transmission electron microscopy.

Aluminum nitride (AlN) thin films were reactively deposited onto Al layers on negatively biased glass substrates by radio frequency magnetron sputtering at a target-to-substrate distance of 17 cm. The microstructures and morphology of the films grown at different bias voltages on the substrates were investigated. Typical thickness of the deposited film is 600 nm. The films were amorphous when no bias was applied to the substrates. Diffraction peak of AlN (0 0 2) direction was observed at bias voltages of −180 and −210 V. At a bias voltage of −210 V, the (0 0 2) granular crystal with the maximum diameter of 80 nm was obtained. In addition to the AlN (0 0 2) direction, AlN (1 0 0) direction was observed when the bias voltage was increased to −240 and −270 V. The peak of (0 0 2) plane vanished at a bias voltage of −320 V. Moreover, the deposited AlN films have specular reflectance owning to the large target-to-substrate distance. The maximum roughness of the films was 47.2±5.0 nm at a bias voltage of −210 V.

The loading at a crack tip varies during fatigue crack propagation. As a result, overloading causes retardation of crack propagation, and underloading causes the acceleration of crack propagation. In addition, reducing the load range by changing either the minimum load or maximum load can cause a reduction or retardation of crack propagation to occur. Examining a fatigue cracked specimen made of polycrystalline copper with back scattered electron images (BEI) in a scanning electron microscope (SEM) revealed that (1) the dislocation structures close to the crack tips gradually evolved from a cell structure into a new loop patch structure during the crack retardation period which follows after reducing the maximum load; (2) restoring the crack propagation rate is a result of re-establishing the cell structure from new loop patches or PSBs; and (3) the evolution of the dislocation structure at the crack tip due to the maximum loading reduction is affected by residual active slip systems.

The dislocation structures evolution on the polycrystalline copper at constant strain amplitude during low cycle fatigue is well understood. However, the dislocation structures developments at variable strains, which change from high to low strain amplitude, are seldom reported. In order to realize the dislocation morphology evolution at reduced strain amplitude, the polycrystalline copper is used in this study. The results show that. (1) The S–N curve at reduced strain amplitude from high to low reveals softening, and it is lower than S–N curve which is fatigue in constant strain amplitude at low strain amplitude. (2) The dislocation structures of walls, labyrinth walls, cells or misorientation cells transfer into scattering walls, loop patches or cells. (3) The dislocation morphology development at decreased strain amplitude is determined by the magnitude of reduction in strain amplitude.

The purpose of this work is to investigate the dislocation structure in front of crack tips of a duplex (ferrite–austenite) steel at various crack propagating rates, and to investigate the influence of the dislocation structure on the threshold stress intensity. The experimental results show that the result in difference of threshold stress intensity factors for as-rolled 2205 duplex (ferrite–austenite) stainless steel along different crack directions is very slight, which is because the influence of grain boundary is greater than that of grain orientation for small grains. In front of crack tips, no dislocation cells were observed. Instead, persistent Luder bands embedded in a highly dense dislocation matrix were found, and the dislocation density increased with the increase of the crack propagation rates. Nucleation of fine CrN/CrC particles from many small amorphous domains, which evolved from a very high-density dislocation in the matrix, were also observed along the crack path close to the crack surface.

First-stage aluminized coating on pure Ni–Cr alloy are prepared by pack cementation aluminizing method at 750 °C. The microstructures were analyzed with scanning electron microscope, transmission electron microscopy and electron probe micro-analyzer. The coating consists of several layers which, in sequence from substrate to coating surface, are substrate γ, polygonized γ, γ′-Ni 3 Al, β-NiAl+α-Cr, δ-Ni 2 Al 3 , and δ-Ni 2 Al 3 +Cr 5 Al 8 layers. A high compositional gradient is present across these interfaces together with a high density of dislocations. No crystallographic relationship was found at the γ/γ′, γ′/β and β/δ interfaces. The γ′ and β+α layers consist of very fine grains with some scattered amorphous regions.

Thin ZnO nanofilms 25 nm thick with (0001), ( 11 2 ¯ 0 ) and ( 10 1 ¯ 1 ) as surfaces were grown epitaxially on the NaCl (111) and (001) surfaces. The room temperature photoluminescence (PL) spectrum from the ( 11 2 ¯ 0 ) nanofilm has a sharp UV emission but negligible green emission, indicating that it has good quality and low defect density. However, the PL spectra from the ( 10 1 ¯ 1 ) and (0001) surface nanofilms have a broad green emission, and that of the ( 10 1 ¯ 1 ) surface is stronger than the (0001) surface. The result supports that the surface oxygen vacancies are the probable origins of the green emission.

A1N thin films were reactively deposited onto Al layers on negatively biased glass and Si substrates at temperatures

During fatigue crack propagation there is large interaction effects of the fatigue cycle for different loading amplitudes. Two examples are the retarding effect of overload and the accelerating effect of underload on the crack propagation. In the former, the result is explained in terms of residual stress effects associated with the overload, and in the latter, the underload partially annihilates the residual stress built up by the positive load. However, at the microstructure level of material under fatigue, the crack propagation is caused by dislocation action. Assuming this, this paper reports studies of the crack propagation interaction effect by using microstructural examination of crack tips. Observations were made with the Back Electron Images (BEI) of the Scanning Electron Microscope (SEM). The results are: (1) the microstructure of cells close to the crack tips formed into vein or loop patch structures upon the overload, so that the crack propagation was reduced. (2) The region of cells s close to the crack tips become enlarged on the underload and the scale of the other microstructure (such as PSB, vein and loop patch) were also enhanced too, so that the crack propagation was accelerated.

During the past two decades, several studies on the crack initiation have shown that the crack initiation at high plastic strain amplitude is mainly started at the grain boundaries(GB), and at low plastic strain amplitude crack initiation is mainly started at the persistent slip band(PSB). However, the GB is still considered to be the preferred locations for crack initiation. It has also been pointed out that crack initiation started at GB results from the interactions between grain boundaries and persistent slip bands (PSB–GB), but only few studies has been devoted to finding the starting places for the following crack propagation, which may start at either the PSB or the GB. Moreover, most of the observations on the PSB–GB are done by scanning electron microscopy (SEM) — yet, observation by transmission electron microscopy (TEM) is seldom reported. In this paper, pure copper square specimens are employed in low cycle fatigue testing under strain-controlled condition. Optical microscopy (OM), SEM and TEM are used to investigate the initiation, propagation and the accompanied dislocation structures of the cracks. The results reveal that the mechanisms of crack initiation are the same as those in earlier studies. The dislocation structures, for crack initiated at the PSB, are ladder-like dislocation wall; and for those initiated at the GB, are dislocation cell. With regard to the crack propagation, crack initiated at the GB is the majority — no matter the crack was initiated at the PSB or the GB at the beginning.

This work is an investigation of the dislocation structures close to the crack tip near the stress intensity threshold, and the dislocation morphology of surface crack initiation. In these experiments, a material (Fe–Al–Mn–0.4% C alloy) with the planar dislocation structure at early stages in fatigue and wavy type at the later step in fatigue was used. The crack propagation was produced by the Instron hydraulic testing machine to obtain the near threshold of the crack propagation. The microstructure was observed by the JEOL 200CX transmission electron microscope. The results are (1) the dislocation structure in front of the crack tip at the stress intensity threshold is the cell with an average diameter about 0.5 μm and with a range of about 2–3 μm. Out of this range, the dislocation is similar to the dislocation of a planar type. (2) The surface crack initiates when the multiple slip system is created and the accomplishment of dislocation is triggering multiple ladder-like wall in persistent slipband (wavy dislocation) embedded in a matrix–planar dislocation (persistent slip Luder band).

In this work, the fracture surface of the crack paths in specimens of pure copper have been studied by secondary electron imaging and the dislocation structures in front of crack tip were observed by backscattered electron imaging. It was observed that the propagation of the cracks is mainly transgranular, but the behavior models change in accordance with the variation of dislocation structures located at the front of the crack tip. With a 10 −6 mm/cycle rate of cracking, the dislocation structures are in full development with a vast range of area. Therefore, a model for the propagation of cracks is transgranular along the sides of grain boundaries (GB). However, with a propagation rate of 10 −7 mm/cycle, the dislocation structures evolve incompletely, and the range of cell or ladder-like walls of persistent slip band is limited to a small area. The sequence of crack propagation is initiation, propagation in strain localization in front of the crack tip, and then coalescence with the crack tip. The crack propagation is transgranular, but the side of the GB is still the preferred path. A model is proposed to explain these behaviors. The major factors of the model are the evolution of the dislocation structures at the crack tips, and the interactions between the grain boundaries and persistent slip bands.

The purpose of this study is to investigate the dislocation structures in front of fatigue crack tips embedded at various propagation rates in copper. Back electron images with the scanning electron microscope were used for the observation. The results are, at a rate of 10−6 mm per cycle, that the dislocation morphologies are distinguishable and can completely to evolve into various dislocation structures. At a rate of 10−7 mm per cycle, the dislocation morphologies are the same as those of the 10−6 mm per cycle rate, but the ranges of the dislocation structures are too small to be distinguished. Regardless of the plastic strain amplitudes, the average diameter of the dislocation cell in front of the crack tip is about 0.7 μm. Therefore, once the low-energy dislocation cell was formed, the crack initiates and/or propagates. At a 10−8 mm per cycle rate, the crack tip is propagated toward the region of true strain localization. The dislocation structure threshold for propagating the crack tip is cell with an average diameter of less than 0.7 μm.

The connection between the chemical corrosion resistance and the microstructure of the Ta2O5 thin films prepared at room temperature by a RF magnetron sputtering technique on Si substrates has been investigated. We find that the microstructure of the films changes with different RF sputtering power, and is responsible for the degradation of the corrosion resistance in HF solutions. The deposited films are amorphous and porous when the RF power is low. A preferred orientation toward (200) β-Ta2O5 can be observed when the RF power is increased to 150 W. In addition, the films deposited under this condition are dense and are consequently more resistant to the attack of chemicals. AT an RF power of 300 W the corrosion resistance of the films declines due to an increase of the exposed pore surface to the HF solution.

The aim of this wok is to study the fatigue properties in relation to the microstructures of interstitial-free (IF) steel, a representative of body center cubic (BCC) materials, subjected to low cycle periodic stress. In order to compare the grain size effect on dislocation development, we used samples of two distinctive grain sizes, 70 µm and 210 µm, prepared by different thermo-mechanical processes. We found (1) there was an initial softening when the stain amplitude was lower than 1.6% and the microstructure of the fatigued samples are cellular independent of the grain sizes and the amplitude of strain. (2) A re-entrant hardening following an initial softening stage took place for strain amplitude range from 0.2% to 0.4% in the samples of 70 µm grains and 0.4% to 0.8% for those of 210 µm grains. Small cellular structures formed within a larger uncondensed cells structure at an initial stage. (3) While the mechanical behaviors of fatigue for both grain sizes are similar, differences do exist and are determined by strain localization as well as the multiple slip systems which can be triggered into active operation

In this paper, image processing techniques are applied to the analysis of near-infrared videos. The goal is to detect human activities in the videos. For detecting human activities, we implement the Gaussian mixture modeling (GMM) to construct background model and to perform foreground detection. Additionally, we pay attention to commonly use sensing lighting equipments used in nighttime environment because of its illumination and shadowing phenomena. Accordingly, a two-mode GMM is proposed which separately constructs background GMM for different lighting conditions and switches GMM modes by event detection. In order to cope with excessive shadowing phenomenon, an efficient way of searching footholds by using scan-lines is proposed to remove human shadow. The proposed approach will provide reasonable bounding boxes information of human regions as detection results which will be very helpful for a nighttime surveillance system.

The anatase TiO2(001) surface was shown to have superior photoreactivity. Epitaxial anatase (001) films used to be grown on single-crystal SrTiO3 and LaAlO3 substrates. It is shown in this report that these films can be grown also on the NaCl substrate, which is much cheaper and easily prepared. Epitaxial TiO(001) films were first grown on the NaCl(001) substrate. By testing the TiO-to-anatase transformation over temperature and time ranges, an epitaxial anatase (001) film was prepared by simple thermal oxidation in air. The formation of a single-variant anatase (001) film instead of a multiple-variant film is discussed in this report.

We report that a VCSEL operated in stable polarization was obtained with an intrinsic anisotropic semiconductor distributed Bragg reflector (DBR) grown on a (001) on-axis substrate by molecular beam epitaxy (MBE). All the VCSELs, with a square or a rectangular active region oriented in either the [011] or [011̄] direction, exhibited a stable polarization state toward the [011] direction.