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Microstructural evolution during friction stir welding (FSW) of a high-strength linepipe steel was studied. The various grain structures developed through a complex process including the rearrangement of low-angle boundaries, continuous dynamic recrystallization and phase transformation. In most parts of the stir zone (SZ), acicular-shaped bainitic ferrites were formed by the phase transformation during the FSW process. A fine-grained microstructure developed mainly in the thermomechanically affected zone (TMAZ), where continuous dynamic recrystallization occurs. The shear texture in the SZ became considerably weak due to the phase transformation during the FSW process. The hardness of the SZ was significantly higher than that of the other FSWed regions due to the bainitic ferrites.

Cycle stability of solid-state lithium batteries (SSLBs) using a LiCoO2 cathode is improved by atomic layer deposition (ALD) on active material powder with Al2O3. SSLBs with LiCoO2/Li3.15Ge0.15P0.85S4/77.5Li2S-22.5P2S5/Li structure were constructed and tested by charge-discharge cycling at a current density of 45 μA cm−2 with a voltage window of 3.3 ~ 4.3 V (vs. Li/Li+). Capacity degradation during cycling is suppressed dramatically by employing Al2O3 ALD-coated LiCoO2 in the composite cathode. Whereas only 70% of capacity retention is achieved for uncoated LiCoO2 after 25 cycles, 90% of capacity retention is observed for LiCoO2 with ALD Al2O3 layers. Electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM) studies show that the presence of ALD Al2O3 layers on the surface of LiCoO2 reduces interfacial resistance development between LiCoO2 and solid state electrolyte (SSE) during cycling.

An interstitial-free steel was austenitized and cooled in a high-pressure high-temperature apparatus. Despite its inherently negligible hardenability, an interstitial-free steel with a full martensitic structure could be obtained even without quenching. Under atmospheric pressure, the microstructure after austenitization and cooling at an even faster rate consisted of massive ferrite. The thermodynamic stabilization of austenite by high pressure (on the gigapascal scale) led to great retardation of ferrite transformation and resulted in a rare microstructure of martensite in interstitial-free steel.

A two-step rolling-annealing process has been developed to increase the //ND (γ fiber) component in the recrystallization texture of a copper-bearing bake hardening steel. The two step process comprises the first rolling by a low reduction in thickness and subsequent annealing at 780°C, followed by the second rolling by a high reduction and subsequent annealing at 780°C. The first rolling process aims at seeding the γ fiber oriented grains, so that they can grow at the expense of differently oriented grains developed in the second rolling process. In this way the density of γ fiber component in the recrystallization texture of the bake hardening steel much increases compared with that in the conventional one-step rolling-annealing process.

We performed the tensile test of an individual carbon nanofiber (CNF) inside a scanning electron microscope. The mechanical testing system was installed in a scanning electron microscope (SEM). The nano-manipulator was set up in the SEM, and the force sensor, which is formed as a cantilever, was mounted on the nano-manipulator. Then, the force sensor can be controlled by using the nano-manipulator. The CNFs were dispersed on the transmission electron microscope (TEM) grid, and the both end of the CNFs were welded on the TEM grid and the tip of force sensor by exposing electron-beam of the SEM. The tensile test of the CNFs was performed by controlling the nano-manipulator. The load response during the tensile test was obtained by force sensor. Stess-strain curve was obtained from force-displacement curve of CNF after tensile test. The elastic modulus of CNFs was calculated at ~12.5 GPa.

We present the mechanics of folding surface-layer wrinkles on a soft substrate, i.e. inter-touching of neighbouring wrinkle surfaces without forming a cusp. Upon laterally compressing a stiff layer attached on a finite-elastic substrate, certain material nonlinearities trigger a number of bifurcation processes to form multi-mode wrinkle clusters. Some of these clusters eventually develop into folded wrinkles. The first bifurcation of the multi-mode wrinkles is investigated by a perturbation analysis of the surface-layer buckling on a pre-stretched neo-Hookean substrate. The post-buckling equilibrium configurations of the wrinkles are then trailed experimentally and computationally until the wrinkles are folded. The folding process is observed at various stages of wrinkling, by sectioning 20–80 nm thick gold films deposited on a polydimethylsiloxane substrate at a stretch ratio of 2.1. Comparison between the experimental observation and the finite-element analysis shows that the Ogden model deformation of the substrate coupled with asymmetric bending of the film predicts the folding process closely. In contrast, if the bending stiffness of the film is symmetric or the substrate follows the neo-Hookean behaviour, then the wrinkles are hardly folded. The wrinkle folding is applicable to construction of long parallel nano/micro-channels and control of exposing functional surface areas.

Inhomogeneous microtexture evolution during the cold drawing process usually results in lean, sway, or sweep failure. The longitudinal fiber texture has higher stiffness than the texture and its proportion and distribution in the cross-section are critical for the bonding stability of fine gold wire. We investigated the inhomogeneous microtexture evolution of gold wire that was cold drawn through an asymmetric diamond die. In this study, the distributions of the and textures in a2 0μm diameter fine gold wire are the variables and their effects on the bonding stability of the wire were estimated by electron backscattered diffraction (EBSD) and finite element method (FEM) simulations. The use of a focused ion beam apparatus enabled a high quality of band contrast of the EBSD to be achieved in the exact half cross-sectional area of the fine gold wire. The detailed three-dimensional FEM results show that the asymmetric distribution of the textures plays a crucial role in increasing the spatial displacement of the gold bonding wire.

We report the direct observation of microstructural changes of LixSi electrode with lithium insertion. HRTEM experiments confirm that lithiated amorphous silicon forms a shell around a core made up of the unlithiated silicon and that fully lithiated silicon contains a large number of pores of which concentration increases toward the center of the particle. Chemomechanical modeling is employed in order to explain this mechanical degradation resulting from stresses in the LixSi particles with lithium insertion. Because lithiation-induced volume expansion and pulverization are the key mechanical effects that plague the performance and lifetime of high-capacity Si anodes in lithium-ion batteries, our observations and chemomechanical simulation provide important mechanistic insight for the design of advanced battery materials.

A two-step rolling–annealing process has been developed to increase the 〈1 1 1〉//ND (γ fiber) component in the recrystallization texture of a copper-bearing bake hardening steel. The two step process comprises the first rolling by a low reduction in thickness and subsequent annealing at 780 °C, followed by the second rolling by a high reduction and subsequent annealing at 780 °C. The first rolling process aims at seeding the γ fiber oriented grains, so that they can grow at the expense of differently oriented grains developed in the second rolling process. In this way the density of γ fiber component in the recrystallization texture of the bake hardening steel much increases compared with that in the conventional one-step rolling–annealing process.

The effects of Zr composition on the crystallization behaviors and reliability characteristics of atomic-layer-deposited Hf1-x ZrxOy (0 ≤ x ≤ 1) gate-dielectric films are examined. n-Channel metal-oxide-semiconductor field-effect transistor (nMOSFET) devices with ZrO2 gate dielectrics showed a much smaller Vth shift under the positive bias stress compared with the same device with HfO2 gate dielectrics. The impact of Zr composition on the crystallization temperature, crystalline phases, and surface morphology of Hf1-x ZrxOy films is studied. As the Zr composition in the Hf1-x ZrxOy films increased, the reduction of crystallization temperature and the transformation from a monoclinic to a tetragonal phase were observed. The grain size of the crystallized ZrO2 film is much smaller than that of crystallized HfO2. The Hatband voltage (Vfb) shift under positive gate-bias stress in p-channel MOS capacitor (pMOSCAP) devices show a similar trend to the Vth shift in nMOSFET devices. In addition, the annealed ZrO2 films show a large reduction in the Vfb, shift under the positive bias stress compared with as-deposited ZrO2 in pMOSCAP devices. The improved bias-temperature-instability characteristics of ZrO2 compared with that of HfO2 is related to the smaller grain size of crystallized ZrO2.

This study examined the effects of inclusions on the gold wire drawing stress using the Finite Element Method (FEM). Al2O3 and SUS304 are used as the model inclusion materials, which are frequently found on the fracture surfaces of drawn wire. The wire drawing stress showed a strong correlation with the size and yield stress of the inclusions. In the case of Al2O3, a larger diameter induced more drawing stress in the wire, whereas in case of SUS304, a larger diameter induced less drawing stress in wire. The difference was estimated quantitatively by comparing the amount of equivalent plastic strain (PEEQ) in the wire, which is the result of an interaction between the wire and inclusion. This result shows that the reason of difference in drawing stress variation is due to the yield stress of the inclusion.

Differentiation of dynamically and statically transformed ferrites in SIDT (Strain-Induced Dynamic Transformation) steel was carried out by various image-based analyses of EBSD (Electron BackScattered Diffraction) maps. Various identification methods were tried on the basis on the grain size, and the intra- and inter-granular misorientations. The grain-size-based method was valid only when a bimodal grain size distribution in the ferrite phase, due to the large prior austenite grain size, appeared in the specimen. On the other hand, using the proposed method based on both intra- and inter-granular misorientations, the dynamically transformed ferrite could be effectively extracted from SIDTed steel, even in steel in which the grain sizes of the dynamically and statically transformed ferrites were alike.

EBSD mapping was used for phase analysis of multi-phase steels. Some products of austenite decomposition could be discriminated using a range of grain-average functions and properties derived from the map data. In DP steels, martensite could be extracted from the ferrite matrix using the average band contrast or a set of geographic information. Bainite in TRIP steel was identified with the local variations of band contrast and orientation inside a grain. As the proposed method reproduced a phase map, a visual confirmation of the result and additional analyses were possible.

If plasma technology can come out of the vacuum chamber and plasma can be extruded through a small pencil-type torch, it can be applied widely to dental practices. For this study, we designed a small pencil-type non-thermal atmospheric-pressure glow discharge plasma torch. The purpose of this study was to determine the effect of plasma polymer coating on the adhesion of composite resin to feldspathic porcelain. The effect of plasma polymer coating was evaluated using shear bond strength (SBS) test. Contact angle measurements and fracture mode analysis were also performed. Among the groups treated with plasma polymer coating, the SBS of the adhesive (Adper Scotchbond Multi-Purpose, 3M ESPE) to the ceramic surface pre-treated sequentially with water plasma and triethyleneglycol dimethacrylate (TEGDMA) plasma in helium gas was significantly higher than that of the adhesive to the untreated surface (p < 0.05). In this group, the predominant fracture mode was mixed fracture, where small cohesively fractured fragments of ceramic were dispersed on the adhesively fractured flat adhesive surface. However, the SBS values of all the plasma polymer-coated groups were lower than those obtained through a routine porcelain bonding procedure with HF acid and silane coupling agent (p < 0.05). The non-thermal atmospheric-pressure plasma polymer coating technique was found to have a potential promoting adhesion to dental materials.

마찰교반 접합 시, 공구는 빠른 회전을 하면서 동시에 진행을 하기 때문에 복잡한 유동현상이 발생하게 된다. 따라서 적절한 공정변수에 의해 접합이 이뤄지지 않으면 재료내부에서 결함이 많이 발생하게 된다. 결함형성은 공구의 회전에 의해 발생되는 마찰열과 함께 재료유동의 시작점과 끝점을 변화시켜주는 공구의 진행속도에 의해서 지배된다. 일반적으로 공구의 회전은 마찰열을 발생시키기 때문에 회전속도는 접합하고자 하는 판재에 열량을 공급하기 위한 변수에 해당하며, 건전한 접합이 이뤄지기 위해서는 공구의 진행속도가 적절히 조절되어야 한다. 공구의 회전속도와 진행속도는 판재의 종류에 따라 결정된다고 할 수 있다. 접합 시 발생하는 재료내부의 결함은 공구의 진행속도와 더 밀접한 관련이 있는데, 이것은 재료유동이 공구를 따라서 완전한 회전을 이루지 못하였을 때 발생하는 것으로 볼 수 있다. 재료 내부의 유동변화는 미세집합조직의 해석을 통해서도 이해할 수가 있다

A numerical modeling, which is hierarchically coupled with the crystal plasticity finite element method and discrete dislocation dynamics, was performed to examine thermal fatigue behavior of via pattern in ultra-large-scale copper interconnections. The pattern had a pillar shape and one of three crystallographic orientations, 〈0 0 1〉, 〈1 1 0〉 and 〈1 1 1〉, along its longitudinal direction. The internal stress and surface morphology on via patterns could be obtained considering the generation of dislocations and their motion. A robust via pattern in terms of crystallographic orientation was suggested.

Strain-induced martensitic transformation of metastable austenite was investigated by nanoindentation of individual austenite grains in multi-phase steel. A cross-section prepared through one of these indented regions using focused ion beam milling was examined by transmission electron microscopy. The presence of martensite underneath the indent indicates that the pop-ins observed on the load-displacement curve during nanoindentation correspond to the onset of strain-induced martensitic transformation. The pop-ins can be understood as resulting from the selection of a favorable martensite variant during nanoindentation.

We applied the crystal plasticity finite element method (CPFEM) based on a rate sensitivity model to examine the subgrain texture evolution of FCC metals under shear deformation. We used two kinds of microstructure models with the same orientation distribution function (ODF) but different spatial arrangements or misorientation distributions (MDs). One contained a great high frequency around low misorientation angles and the other a great high frequency near high misorientation angles. Different misorientation angles among neighboring crystals caused different interactions among them, particularly at the subgrain scale. The difference in MD affected the evolution of texture and average misorientation angles during deformation. The average misorientation angles of the subgrain boundaries increased with shear strain.

The influence of additives on the reaction kinetics and microstructure refinement in LiBH4–MgH2 composites is investigated in detail. Indications of the rate-limiting processes during the reactions are obtained by comparison of the measured reaction kinetics with simulations with one specific rate-limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in situ X-ray diffraction measurements. During desorption, the hydrogen is released at a constant rate, which is possibly correlated with the one-dimensional growth of MgB2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of microstructure on the reaction kinetics.

Microstructural changes in NbF5-doped MgH2 during the dehydrogenation reaction (MgH2 → Mg + H2) have been investigated by in situ heating transmission electron microscopy. Nanocrystalline MgH2 shows fast hydrogen sorption kinetics, as well as a high density of defects induced by high-energy ball milling. Since the network-structured Nb layer covering Mg grains acts both as an impediment to grain growth of Mg and a gateway for hydrogen diffusion by forming metastable NbH1−x, the improved kinetics can be maintained during hydrogen cycling.

We report β - Ga2O3/diamond-like carbon (DLC) core–shell heterostructure nanowires fabricated by vapor–liquid–solid method and radio frequency plasma enhanced chemical vapor deposition (PECVD). As-synthesized β - Ga2O3 nanowires have widths of 30–150 nm and outer shell DLC thickness was in the range of 20–30 nm. The products were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersed spectrometry (EDS). In addition, outer DLC layer was confirmed by Raman spectroscopy, which shows typical two Raman bands at 1550 cm−1 (G peak) and 1330 cm−1 (D peak) corresponding to disordered graphite peak.

A 250-nm-thick Al2O3 film was deposited on a Si(100) by a radio-frequency magnetron sputtering and annealed at 1100 °C for various periods of time in air. In the matrix composed of fine metastable-Al2O3 grains of 50–100 nm in diameter, large α-Al2O3 grains of about 2–10 μm in diameter appeared, interestingly aligning themselves along various directions. The compressive stress developed in the alumina films because the thermal expansion coefficient of the film was higher than that of the silicon substrate. The stress distribution in the film is expected to be inhomogeneous due to some discontinuities or defects, such as arrays of dislocation pits and steps on the surface of the Si substrate, which could be generated by intersections of the substrate surface and the slip and twin planes in the Si substrate. The enhanced phase transformation into α-Al2O3 along various directions is suggested to arise from such discontinuities or defects.

The material flow and crystallographic orientation in aluminum alloy sheets joined by friction stir welding (FSW) were investigated by electron back scattered diffraction (EBSD). The microstructure and microtexture of the material near the stir zone was found to be influenced by the rotational behavior of the tool pin. It was found that, during FSW, the forward movement of the tool pin resulted in loose contact between the tool pin and the receding material at the advancing side. This material behavior inside the joined aluminum plates was also observed by an X-ray micrograph by inlaying a gold marker into the plates. As the advancing speed of the tool increases at a given rotation speed, the loose contact region widens. As the microtexture of the material near the stir zone is very close to the simple shear texture on the basis of the frame of the tool pin in the normal and tangent directions, the amount of incompletely rotated material due to the loose contact could be estimated from the tilt angle of the shear texture in the pole figure around the key hole.

For a flexible electronic device integrating inorganic materials on a polymer substrate, the polymer can deform substantially, but the inorganic materials usually fracture at small strains. This paper describes an approach to make such a device highly stretchable. A polyimide substrate is first coated with a thin layer of an elastomer, on top of which SiNx islands are fabricated. When the substrate is stretched to a large strain, the SiNx islands remain intact. Calculations confirm that the elastomer reduces the strain in the SiNx islands by orders of magnitude.

The mechanical properties of dynamically and statically transformed ferrites were analyzed using a nanoindentater-EBSD (Electron BackScattered Diffraction) correlation technique, which can distinguish indenting positions according to the grains in the specimen. The dilatometry and the band slope and contrast maps by EBSD were used to evaluate the volume fractions of two kinds of ferrite and pearlite. Fine ferrites induced by a dynamic transformation had higher nano-hardness than the statically transformed coarse ferrites. Transmission electron microscopy (TEM) showed the dynamic ferrites to have a higher dislocation density than the statically transformed ferrites.

The preparation of Li11 BD4 from Al11 B2, LiD and D2 and several subsequent hydrogen sorption cycles according to 2LiD + AlB2 + 3D2 ↔ 2LiBD4 + Al starting from the desorbed state are investigated by in situ neutron diffraction. Absorption is carried out at T = 450 ◦ C and at p = 50 bar D2, while desorption is performed at T = 450 ◦ C using a back-pressure of 1 bar. Compared to the Al free system, the absorption is observed at much lower temperatures and pressures. We attribute the increased deuterium uptake to the enhanced chemical reactivity of the elemental boron released in the dissociation of AlB2. The desorption process on the other hand is similar to the desorption of pure LiBD4 and seems not to be influenced by the present aluminum. The hydrogen capacity decreases from cycle to cycle, due to an incomplete re-formation of AlB2. We attribute this to a phase separation of Al and B during the decomposition of LiBD4.

Single crystalline titanium nitride (TiN) nanopowder is synthesized by a mechano-chemical reaction between titanium chloride (TiCl3) and lithium nitride (Li3N) by means of high-energy ball milling. The TiN nanopowder has an average particle size of 6 nm and is introduced into sodium alanate (NaAlH4) as a catalyst. During hydrogen sorption cycles, TiN-catalyzed NaAlH4 exhibits a greater hydrogen desorption rate and higher hydrogen capacity than TiCl3-catalyzed NaAlH4. Contradicting thermodynamic predictions, in situ X-ray diffraction results reveal that TiN nanopowder remains stable and produces no by-products (e.g., Ti–Al compounds) in the reaction with NaAlH4 during hydrogen desorption. In situ Raman spectroscopy also confirms the stability of TiN nanopowder in NaAlH4. This implies that the sustained hydrogen sorption kinetics and hydrogen capacity of TiN-catalyzed NaAlH4 originate from the structural and chemical stability of TiN nanopowder in NaAlH4 for the given conditions of the hydrogen cycle test.

Finite element micromagnetic studies on the magnetic behaviors of granular structures are performed to investigate the magnetostatic contributions of the curved surfaces of grains with various film thicknesses. From the result, it is found that the magnetization reversal process in one grain is much faster when the grains have convex surfaces. The magnetization vectors of all convex models are stabilized in shorter time by factor of 10 compared to those of flat models. And, the reversals of each grain are carried out by nucleation and domain wall propagation in the entire granular structure, whereas the grains in flat model are individually reversed. Moreover, the magnetization behaviors of the convex models are closer to the experimental results. Since the geometric and magnetic conditions are same for the two models, the only origin of the more realistic magnetic behavior is the magnetostatic interaction between the grains, enhanced by introducing the convex surfaces. From the further analysis, it is found that the convex surface induces pinning field that suppress other parts' reversal.

Using transmission electron microscopy, microstructures of 2LiBH4/Al are investigated during the hydrogen cycling (2LiBH4 + Al ↔ 2LiH + AlB2 + 3H2). Mechanically, ball milled 2LiH/AlB2 mixture shows a homogeneous phase distribution. For the hydrogen absorption, the decomposition of AlB2 and the formation of 2LiBH4 occur simultaneously. During the hydrogen cycling, the incomplete formation of AlB2 results in a spatial separation of Al and B. A lack of reactive B from AlB2 results in a limited formation of LiBH4, which leads to the capacity loss of the system.

The deformation behavior within the deformation zone of a workpiece during equal channel angular pressing (ECAP) was investigated using the finite element method. The effects of die geometry on the variations of normal and shear deformations were studied with a deformation rate tensor (D). The zero dilatation line, at which the normal components (D11 and D22) of the deformation rate tensor (D) are zero, in the die coincided with the line of intersection of the two die channels irrespective of die geometry such as curvature angle (Ψ) and oblique angle (Φ), while the maximum shear line, at which the shear components (D12 and D21) of the deformation rate tensor (D) have maximum value, is dependant on the die geometry

This paper examines the mechanics of ball shear testing with the objective of understanding the mechanism by which the maximum shear force and the rate of crack growth is dependent on the solder bump size. For this, Pb-Sn solder bumps with diameters between 460 lm and 760 lm are soldered to 400 lm-diameter Cu pads and subjected to ball shear testing. In spite of the constant interface area, the bump size significantly impacts the measured shear fracture force and the crack growth rate. Both the fracture force and the crack growth rate increase with bump size, and in the case of the fracture force, the increase is almost linear. Our analysis finds that the linear increase in the fracture force is a result of the bump deformation force, which increases with bump size. A simple model that accounts for the deformation force component is developed and used to extract the true interface fracture force. The estimated true interface fracture force is found to vary little with bump size, tightly converging to the 40 MPa to 48 MPa range. On the other hand, the dependence of crack growth rate on bump size is found to result from the higher degree of rotational moment associated with larger bumps.

We report self-assembly of highly aligned GeTe nanowires epitaxially grown on octahedral GeTe microcrystals in two well-defined directions by using one-step vapor transport process. The epitaxial relationship of nanowires with underlying microcrystals along with the growth orientations of nanowires were investigated in detail by electron microscopy combined with atomic unit cell models. We demonstrate that maximizing atomic planar density to minimize energy of the exposed surfaces is the determining factor that governs the unique growth characteristics of micro/nanostructures that evolve from three-dimensional octahedral microcrystals to tetrahedral bases to finally one-dimensional nanowires. The crystallographic understanding of structuring of crystalline nanomaterials obtained from this study will be critical to understand, predict, and control the growth orientation of nanostructures in three-dimensions.

The effects of thermal annealing and Si incorporation on the structure and properties of diamond-like carbon (DLC) films were investigated. As-deposited DLC film (DLC) and Si incorporated DLC film (Si-DLC), both with and without thermal annealing, were analyzed for bonding structure, residual stress, film thickness, elastic modulus and fracture properties using Raman spectroscopy, wafer curvature, nanoindentation, four-point bend fracture testing, and X-ray photoelectron spectroscopy (XPS). Raman spectroscopy clearly showed that thermal annealing of DLC films promotes more sp2 bonding character, whereas Si incorporation into the films promotes more sp3 bonding character. Interfacial fracture energies, film hardness and elastic modulus, and residual film stress were all found to vary strongly with the degree of sp3 bonding in the DLC film. These changes in mechanical properties are rationalized in terms of the degree of three dimensional inter-links within the atomic bond network.

The mechanical stability of diamond-like carbon (DLC) films coated on nitinol vascular stents was investigated under cyclic loading condition by employing a stent crimping system. DLC films were coated on the vascular stent of a three dimensional structure by using a hybrid ion beam system with rotating jig. The cracking or delamination of the DLC coating occurred dominantly near the hinge connecting the V-shaped segments of the stent where the maximum strain was induced by a cyclic loading of contraction and extension. However the failures were significantly suppressed as the amorphous Si (a-Si) buffer layer thickness increased. Interfacial adhesion strength was estimated from the spalled crack size in the DLC coating for various values of the a-Si buffer layer thickness. © 2008 Elsevier B.V. All rights reserved.

Nano indentation analysis and transmission electron microscopy observation were performed to investigate a microstructural evolution and its influence on the hardening behavior in Fe–Cr alloys after an irradiation with 8 MeV Fe4+ ions at room temperature. Nano indentation analysis shows that an irradiation induced hardening is generated more considerably in the Fe–15Cr alloy than in the Fe–5Cr alloy by the ion irradiation. TEM observation reveals a significant population of the a0 dislocation loops in the Fe–15Cr alloy and an agglomeration of the 1/2a0 dislocation loops in the Fe–5Cr alloy. The results indicate that the a0 dislocation loops will act as stronger obstacles to a dislocation motion than 1/2a0 dislocation loops.

ARTICLE I NFO It has been recently shown that ordered wrinkles can be created on the surface of polymers using focused ion beam irradiation. Here, we provide an overview of the techniques developed for controlled creation of nanoscale wrinkling patterns on the polymer surface using focused ion beam. Moreover, some of the key experimental challenges for precise fabrication of wrinkling patterns were investigated by exploring the role of pixel dwell time and fluence on the morphology of the created patterns. It was demonstrated that precise modification of the polymeric surface can be achieved with high pixel dwell time at low ion fluence.

The present investigation was carried out on hypoeutectic Al-Si alloys containing two levels of Fe, 0.5 and 1.1 wt pct, and Sr in the range of 30 to 500 ppm. The addition of Sr in excess of 100 ppm significantly reduced the number of eutectic grains and also resulted in the formation of polygonal-shaped Al2Si2Sr intermetallics. Transmission electron microscopy studies revealed that the Al2Si2Sr phase surrounded the P-rich particles. This may suggest that the otherwise potent nuclei for the Al-Si eutectic, aluminum phosphide (AlP), become poisoned or deactivated by the formation of the Al2Si2Sr phase around the particles. At the high-Fe level (1.1 wt pct Fe), pre-eutectic formation of β-Al5FeSi platelets further reduced the number of eutectic Al-Si nucleation events. It is proposed that both eutectic silicon and β-Al5FeSi are preferentially nucleated on AlP particles. Nucleation of eutectic silicon, therefore, becomes more difficult when it is preceded by the formation of Al2Si2Sr or β-Al5FeSi, because fewer nuclei are available to nucleate silicon. Addition of up to 60 ppm P to the alloys increased the formation temperature of the β-Al5FeSi platelets but did not significantly alter the size, whereas the addition of Sr decreased the β-Al5FeSi nucleation temperature by reducing the potency of the AlP particles.

A novel method for the synthesis of transition-metal boride nanopowder has been developed using a mechanochemical reaction between LiBH 4 , LiH and transition-metal chloride (TiCl 3 and VCl 3 ) by high energy ball milling. This method successfully produces TiB 2 and VB 2 particles dispersed within a soluble LiCl matrix. Subsequent washing with distilled water, ethanol and acetone to remove the LiCl matrix phase yields TiB 2 and VB 2 nanopowders of 15–60 nm particle size. From the X-ray diffraction patterns and high resolution transmission electron microscopy image, it is found that each particle is polycrystalline consisting of 3–5 nm crystallites. Neither particle nor crystallite size are increased significantly after heating at 680 °C.

Bending fatigue behavior of eutectic Sn-3.5Ag solder bump bonded on FR4-PCB was characterized by experimental and finite element method (FEM). To investigate an effect of stress state on bump failure, which had not been weighed in conventional Coffin-Manson model of Nf=K ⋅εp -1~-2, ‘fatigue frequency variable’ and ‘bump viscoplasticity’ were included in analysis procedure. As experimental results, with increasing fatigue cycles from 3,000 to 10,000, bond strength decreased from 98.9% to 76.5%, and from 97.5% to 67.1% at the fatigue frequencies of 2.5Hz and 5.0Hz, respectively. Stress state could be critical components to determine fatigue life, which should be combined in Coffin-Manson criteria. FEM calculation showed that higher bending frequency led to higher normal stress development at the solder and IMC interface, but smaller plastic strain in bump. However, bending fatigue experiment revealed discrepant results from that of Coffin-Manson criteria. Higher bending frequency, which was predicted to give rise to smaller εp at solder, showed dramatic bond deterioration of solder bump on UBM (under bump metallurgy). This was confirmed experimentally through SEM (scanning electron microscopy) observation as cracks were found at the solder bump and UBM interfacial IMC, Ni3Sn4, in case of the higher bending frequency.

The friction stir welding (FSW) process of aluminum alloys has been modeled using a two-dimensional Eulerian formulation. Velocity field and temperature distribution are strongly coupled and solved together using a standard finite element scheme. A scalar state variable for hardening is also integrated using a streamline integration method along streamlines. A viscoplastic constitutive equation to consider plastic flow and strength variations was implemented for the process modeling. Precipitates inside AA6061 alloys are sensitive to elevated temperatures and affect strength evolution with temperature. The overall effects of the precipitate variations with temperature on strength were reflected using temperature-dependent material parameters. The material parameters of constitutive equations were obtained from isothermal compression tests of various temperatures and strain rates. The effects of FSW process conditions on heating and hardening were investigated mainly near the tool pin. The microhardness distribution of the weld zone was compared with the prediction of strength. In addition, crystallographic texture evolutions were also predicted and compared with the experimental results.

On the other hand, post-processingof indium nanowires (e.g., by oxygen or nitrogen plasma treat-ment) can be used to create composite nanowires made fromindium compound materials on the outer surface layer of thewire. Such composite nanowires have versatile applicationsin electronics and optoelectronic devices, for example in build-ing biosensors, solar cells, electrodes, and even memorydevices.

The microstructure of MgH 2 with 1 mol% NbF 5 , prepared by high-energy ball milling (HEBM), was studied using high resolution transmission electron microscopy (HR-TEM) with an X-ray energy dispersive spectrometer (EDS) before and after hydrogen sorption cycles. The TEM samples were prepared without any air exposure by a novel, focused ion beam (FIB) system specially designed for highly air sensitive materials. During HEBM, the doping agent, NbF 5 , was distributed as an extremely thin, film-like, amorphous phase along the grain boundaries of the nanocrystalline MgH 2 . After 10 sorption cycles, amorphous Nb-F phase was transformed into crystalline Nb hydrides. It is believed that the Nb hydride played a decisive role in improving the sorption kinetics of MgH 2 .

Ag-incorporated diamond-like carbon (DLC) films were prepared on Si substrate using a hybrid deposition system composed of an end-Hall-type hydrocarbon ion gun and a silver DC magnetron sputter source. Ag was selected due to their potential values of biomaterial. The concentration of Ag in the films was varied from 0.1 to 9.7 at.% by controlling the fraction of Ar in the reaction gas mixture with benzene. In order to understand the influence of incorporated Ag on wettability, the surface energy and the protein adsorption as an indirect haemo-compatibility were measured. The surface energy of the Ag-incorporated DLC film decreased gradually with the increase of the Ag concentration. The haemo-compatibility was examined by the adsorption ratio of albumin/fibrinogen as an indirect method and improved with the increase of Ag concentration. The surface and biological behaviors of the films will be discussed in terms of the atomic bond characteristic and microstructure induced by Ag incorporation. Our results demonstrate that the Ag-incorporated DLC films are potentially useful as biomedical devices having good haemo-compatibility and hydrophobic characteristics.

We have investigated the effect of plastic deformation of diamond-like carbon (DLC) coated and uncoated stainless steel on the corrosion resistance in a simulated body fluid environment to measure its protective efficiency as a biomedical coating material. We deposited the DLC film on 304 stainless steel specimens by radio frequency plasma assisted chemical vapor deposition(R.F.-PACVD) method, followed by a tensile test to apply plastic strain on the coated specimen. Corrosion behavior in the simulated body fluid environment was studied by a potentiodynamic polarization test. As the tensile deformation progressed, the cracks of the film were observed to be perpendicular to the tensile axis. Further deformation increased both cracking and the spallation. Estimated porosity and corrosion current density increased, and thus the protective efficiency decreased at a strain of 2%. In spite of the degradation, the anti-corrosion properties were significantly improved relative to the uncoated stainless steel. However, a significant increase in porosity and corrosion current density was observed at a strain of 4%. This study showed that increasing the thickness of the Si interlayer of film improved the corrosion resistance with reduction of spallations and cracks.

In a transformation-induced plasticity (TRIP)-assisted multiphase steel, the phases around a micro-crack at the initial stage of cracking during wire drawing were observed by a focused ion beam (FIB), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). A novel FIB method, which is termed as “In-plane lift-out” technique, was applied to obtain an overall plan-view of the TEM specimen containing the micro-crack. The equilibrium concentration ratio of Mn in austenite and ferrite was calculated for the alloy and compared with the EDS line profile of Mn concentration across the micro-crack in the TEM specimen. The interface between the ferrite and martensite was identified as the crack initiation site during drawing of this multi-phase steel.