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Formation of β′ phase in long-period stacking ordered (LPSO) structures in an Mg88Co5Y7 (at.%) alloy after aging at 200 °C for 24 h or electron beam (EB) irradiation has been studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). β′ phase was precipitated only in the Mg matrix but not in LPSO structures after aging at 200 °C for 24 h. LPSO structure containing stacking defects transforms into the β′-long phase during EB irradiation, which plays a key role in accelerating solute atoms’ diffusion. New complex β′(LPSO) structures formed in the alloy after EB irradiation, such as β′(12H) structure with an orthorhombic lattice (Mg7Y, Cmcm, a = 2a0 = 0.642 nm, b = 4 3 a0 = 2.27 nm, c = 6c0 = 3.12 nm).

Passive films on duplex stainless steels are heterogeneous, with properties depending on the two-phase microstructure. Accordingly, the interaction of chloride ions with the passive films on either of the two phases ought to vary. These issues have been investigated by some indirect methods, not sufficiently nor directly corroborated by experimental evidence. Using aberration-corrected transmission electron microscopy, we simultaneously investigate the films on the ferrite and austenite phase near the phase boundary, as well as the film evolution in chloride-containing media. This study provides some virtual experimental insights into the features of chloride attack on the passive film of duplex alloys.

The microstructures in B4C-6061Al composite hot-pressed at different temperatures (560 °C, 620 °C) are characterized, and the corrosion behavior of the materials is studied using electrochemical tests and quasi in-situ TEM observations. The composite fabricated at 620 °C is composed of more matrix-reinforcement reaction products (Al3BC at the interfaces and MgB2 in the alloy matrix). Corrosion occurred slightly in boric acid but severely in Cl−-containing solution. The B4C/Al interface in both samples is preferentially attacked and the MgB2 dispersions in the high-temperature-pressed composite remarkably promoted the pitting. Dealloying of Mg2Si precipitate does not obviously deteriorate the corrosion resistance of the composite.

The deformation mechanisms and microstructure evolution of Mg88Co5Y7 (at.%) alloy with long period stacking ordered (LPSO) phase during compression at 373–673 K have been studied using transmission electron microscopy. The alloy consists of α-Mg matrix, interdendritic LPSO phase, and other Mg-Co-Y intermetallic compounds. Increasing temperature leads to a general decrease in strength of the Mg88Co5Y7 alloy. A large number of {10 1 ¯ 2 } tension twins and deformation bands are activated in the matrix, whereas basal slip and deformation kink dominate in the LPSO structures during compression at 373 and 473 K. Non-basal slip in matrix and almost no dynamic recrystallization are responsible for high strength and the good ductility of sample deformed at 573 K. Recrystallization of Mg matrix occurs upon deformation at 673 K, dramatically lowering the corresponding strength. Further, the grain boundary pinning effect from LPSO phase, MgYCo4 phase, and broken Mg3(Co, Y) segments is supposed to account for the relatively high strength of Mg88Co5Y7 alloy at high temperatures.

Generally, minor elements such as carbon and boron are added in superalloys to strengthen grain boundaries. However, effects of carbon and boron on single crystal superalloys remain disputed. Here we demonstrate that M23B6 (where M is mixture of W, Mo, Cr and Ni) can induce dislocation channeling in a Ni-based single crystal superalloy. The M23B6 has a cube-on-cube orientation relationship with the matrix, forming a majority of {1 1 1} plane interfaces. Furthermore, the atomic stepped {1 1 1} interface could facilitate dislocation nucleation. Dislocations emitted from the interface glide forward and pile-up in the channel, resulting in strain localization and creep micro-crack initiation.

Element Cr imparts non-crystallinity effect on the oxide film on iron. Therefore, in contrast with the oxidation of iron, the oxidation process of Fe-Cr alloys is more complicated. By means of high angle annular dark field scanning transmission electron microscopic (HAADF-STEM) imaging combined with electron-energy loss spectroscopy (EELS) and super-X electron dispersed spectroscopy (Super-X EDS) techniques in an aberration-corrected TEM, we have clarified the evolution in the oxide film formed on an FeCr15Ni15 alloy. The oxide film is identified to be amorphous at the initial oxidation stage, but tends to become crystalline in the inner layer after aging in air.

Twinning-induced plasticity (TWIP) steels can exhibit high ultimate strength and ductility, but low yield strength and thermal stability. Here we approach this problem by introducing a heterogeneous microstructure comprised of soft, hard and thermally stable regions in a model composition of Fe-22Mn-0.6 C TWIP steel. This target microstructure is achieved via a three-step processing route: cold rolling to introduce nanotwin bundles, an aging treatment to transform highly defective regions to thermally stable pearlite nano-lamellae, and an annealing step for relatively large, ductile grains. We show that this microstructure generates a good balance between high yield strength, good ductility, high ultimate tensile strength, and good thermal stability. The main deformation mechanism of this unique heterogeneous structure is deformation twinning. The high thermal stability can be attributed to the transformation of the shear bands, introduced by cold rolling, into pearlite during the aging process, and into the composite of nanograined austenite and nanograined cementite formed during the subsequent isothermal annealing.

Using scanning transmission electron microscopy, we uncover the interaction between { 10 1 ¯ 3 } twin and stacking faults (SFs) enriched with solute atoms in an Mg97Zn1Y2 alloy at atomic scale. The pyramidal-basal (PyB) and basal-pyramidal (BPy) interfaces along SFs make faceted { 10 1 ¯ 3 } twin boundary deviate appreciably from { 10 1 ¯ 3 } twin plane. { 10 1 ¯ 3 } twin associated with shear can reorient one unit of SF, but engulf two successive SFs. { 10 1 ¯ 3 } - { 10 1 ¯ 1 } twin segment generated upon twin-SFs intersection region, and is proposed to arise from dislocation dissociation. The direct observations unravel some of the fundamental characteristics of interaction between compression twin and precipitates in magnesium alloys.

Interface engineering is an important strategy for developing radiation tolerant materials. In prior work, bulk nanolayered composites fabricated by accumulative roll bonding (ARB) showed outstanding radiation resistance. However, the effects of layer thickness and radiation conditions on damage distributions and their effect on hardness have not been explored. Here, we use transmission electron microscopy (TEM) and nanoindentation to investigate the effects of radiation on the distribution of radiation-induced cavities and post-radiation hardness in ARB nanolayered Cu-Nb composites. We show that whether the cavities cross the interface depends on layer thickness and temperature, and that, remarkably, radiation could generate softening, not always hardening. We posit that the softening mainly results from the recovery of dislocations stored in the crystal after the bulk forming ARB processing due to He radiation and this phenomenon offsets radiation-induced hardening as layers become finer and temperatures rise.

By atomic-scale high-angle annular dark field scanning transmission electron microscopy, we characterized a long period stacking ordered (LPSO) phase, 654R, in an Mg 88 Co 5 Y 7 (at.%) as-cast alloy, which is an ordered intergrowth of 15R and 12H LPSO phases. The unique stacking sequence of 654R LPSO phase can be described as [(T2) 10 (T3 T ¯ 3) 14 ] 3 , with lattice parameters of a = 0.321 nm, c = 170.4 nm, and a space group of R 3 ¯ m . T/ T ¯ refers to AB′C/AC′B building blocks, while normal and subscript number respectively represent the number of Mg layers sandwiched between T/ T ¯ and the number of sub unit cells. The formation mechanism of 654R LPSO phase is also proposed.

Stacking disordered (SD) structures in Mg–Co–Y as-cast alloys have been examined using atomic-scale high-angle annular dark-field scanning transmission electron microscopy. All these SD structures mainly consist of F-blocks, T-blocks, 2-Mg, 3-Mg, and 4-Mg, which are the structural components of previously observed 15R, 12H, 21R, and 18R LPSO structures. These components can further form complex structures with similar stacking characters, which are disordered or locally ordered. The stacking sequence, periodicity, and symmetry of these SD structures were characterized and illustrated by our previously introduced notation. The structural similarity and difference between the SD structures and LPSO structures featuring various stacking layers were analyzed by comparing their stacking sequences, the arrangement of clusters in the basal plane and along the stacking directions.

The magnesium alloys containing long-period stacking ordered (LPSO) structures exhibit excellent mechanical properties. Each LPSO structure is known to contain either AB′C′A or AB′C building block and feature its own stacking sequences. By atomic-scale high-angle annular dark field scanning transmission electron microscopy, we find the co-existence of AB′C′A and AB′C building block in a single LPSO structure of the as-cast Mg92Co2Y6 (at.%) alloy, leading to the formation of six new polytypes of the LPSO structures determined as 29H, 51R, 60H, 72R, 102R and 192R. The lattice parameter of each LPSO structure is derived as and (n presents the number of basal layers in a unit cell). The stacking sequences and the space groups of these newly identified LPSO structures are proposed based on the electron diffraction and atomic-scale aberration-corrected high-resolution images. A random distribution of Co/Y elements in the basal planes of AB′C′A and AB′C structural units is also observed and discussed.

The effect of alloying copper on the dissolution of manganese sulphide which triggers the pitting corrosion of stainless steels was studied by in-situ ex-environment transmission electron microscopy (TEM) with an atomic resolution. It was found that the benefits of Cu addition act in two ways: Cu ions replace the Mn ions in the surface layer of MnS and insoluble copper sulphide compound forms; on the other hand, Cu ions could stabilize harmful surphur species released from dissolved MnS. The two processes are supposed to be helpful to reduce the detrimental effect of MnS on the corrosion resistance of stainless steels.

Twins or multiple twins occur frequently in the orthorhombic Al20Cu2Mn3 approximant of decagonal quasi crystal (DQC). Due to the specific structural units, the twins in the Al20Cu2Mn3 approximant usually exhibit the glide-reflection characteristics. Using aberration-corrected transmission electron microscope at the atomic scale, we have observed not only glide-reflection twins but also simple mirror-reflection twins in the Al20Cu2Mn3 approximant. The two twinning modes are found to coexist in the present sample. These twins exhibit variant configurations at the twin boundaries where the tessellations of local subunits are imaged at an atomic scale. At the twin boundaries, diversified tiles such as star-like (S), bowtie-shaped and boat-shaped (B) are observed. The diversified tiles stacking with various manners allow the coexistence of the DQC and the approximant. Furthermore, the variants of B and S tiles are also found.

Using transmission electron microscopy, we investigate microstructural evolution at interfaces of a plasma sprayed thermal barrier coating system with an yttria–stabilized zirconia top coat and a NiCrAlY bond coat after isothermal oxidation at 1100 °C for up to 50 h. Interestingly, thermally grown oxide (TGO) layers split into two sub-layers. In principle, one of the two sub-layers comprises a mixture of α-Al2O3, Cr2O3 and Ni(Al, Cr)2O4, while the other one consists of dense α-Al2O3 and Cr2O3. Main microstructural evolution of the TGO layers follows a similar sequence that: original phases → α-Al2O3 + Cr2O3 → α-Al2O3 + Cr2O3 + Ni(Al, Cr)2O4. Particularly, after 50 h oxidation, γ-Ni and NiO form in the upper TGO sub-layer at the top coat–bond coat interface, and γ-Ni and α-Cr form in the upper TGO sub-layer at the bond coat-substrate interface. Moreover, γ-Al and β-Ti precipitate at the TGO-substrate interface after 50 h oxidation.

We explored the very high cycle fatigue (VHCF) behavior of solution treated Mg–10Gd–3Y–1Zn–0.5Zr (wt. %, GWZ1031K-T4) alloy containing long-period stacking ordered (LPSO) structures. The fatigue strength of GWZ1031K-T4 alloy at 109 cycles is about 115.0 MPa, and the corresponding fatigue ratio is approximately 0.44. Crack initiation that causes fatal failure was found to occur primarily from the specimen surface in the high cycle fatigue regime and the subsurface in the very high cycle fatigue regime, accompanied by crystallographic facet formation irrespective of a lifetime. Our results reveal that the basal slip activated in the matrix grain substantially alleviated strain localization during VHCF testing. The unique microstructure, featuring block-shaped LPSO structures scattered at the grain boundary, a large amount of thin LPSO phase and stacking faults enriched with solute atoms (SFs) homogenously distributing in the alloy matrix, and supersaturated Gd and Y atoms in the nano-scale Mg layers in the grain, is proposed to account for the enhanced fatigue failure resistance of GWZ1031K-T4 alloy.

The precipitates inside deformation twins may block the dislocation motion and consequently affect the mechanical property of materials. Herein, at the atomic level, we directly visualize that the basal dislocation slips shear the twinned stacking faults (TSFs) within the deformation twins in an Mg–Zn–Y alloy containing long-period stacking ordered (LPSO) structures. The TSFs, enriched with solute atoms, could be considered as precipitates inside deformation twins. They are sheared by a single step or multiple shearing steps on the basal plane. The microstructural fingerprints, i.e., the width of basal shearing steps, enable a quantitative assessment of the local and total plastic shear strain due to the basal dislocation within the deformation twins. The TSFs can block dislocation slip, while the dislocation shearing induces large lattice distortion and even solute atoms redistribution at local intersection. The TSFs-dislocation interaction is expected to lower the basal dislocation motion and resultantly modulate the mechanical properties of magnesium alloys. These results may offer a novel strategy for strengthening and toughening magnesium alloys via tailoring the shearable precipitates.

To develop facile, rapid and low-energy route for metal-organic framework (MOF) formation is of great importance. Here a water-alkane interface strategy was proposed for the MOF formation at room temperature. The content and molecular structure of alkane phase were found to have remarkable effect on regulating the porosity properties of MOFs. For example, the MOF synthesized in 1:1 (v/v) water/n-hexane mixture has the largest BET surface area (1474.1 m(2)/g) and total pore volume (0.7030 cm(3)/g). The mechanism was discussed from the competitive adsorption of water and alkane in the micropores of MOF building blocks during formation process. (C) 2015 Elsevier Inc. All rights reserved.

The hierarchical porous metal oxide combines the advantages of each class of hierarchical pores and has potential applications in different fields. Here we proposed an emulsion-calcination route for producing porous metal oxide. The porous metal-organic complex was first synthesized in CO2-in-water emulsion, then the metal-organic complex was calcined to remove the organic linker and form porous metal oxide. The hierarchical macro- and mesoporous assemblies of Co3O4 nanoparticles were produced. The hierarchical macro- and mesoporous assemblies of Co3O4 nanoparticles were produced, with the macropores in size of hundreds of nanometers and the mesopores in 9-15 nm. The porosity properties and nanoparticle size of Co3O4 can be modulated by controlling CO2 pressure. The as-synthesized Co3O4 is an excellent candidate catalyst for the methylene blue degradation. By taking advantages of the high porosity and small particle size, the Co3O4 have potential applications in catalysis, gas separation, and controlled drug release. The strategy proposed in this work can be applied to the synthesis of different kinds of porous metal oxides. (C) 2015 Elsevier Inc. All rights reserved.

The pit initiation and growth processes occurring in austenitic stainless steel are included in the passive region of polarization curve. However, polarization measurements do not yield surface morphological insights, which limit the ability to provide a comprehensive picture of the corrosion process. A quasi-in-situ ex-polarized TEM observation method is designed to elucidate the microstructural evolution corresponding to the characteristic regions of the electrochemical polarization curve. This work shows the potential and advantage of combining TEM technique and the traditional electrochemical methods in investigating the initiation of localized corrosion.

The formation of a water-sensitive metal–organic framework (MOF), Cu3(BTC)2 (BTC = 1,3,5-benzenetricarboxylate), in a water/ethanol solvent system was studied systematically. The X-ray diffraction results prove that the MOF cannot form in pure water or in a water/ethanol mixture with a small amount of ethanol. As the ethanol content exceeds 30 vol%, a crystalline MOF can be obtained. The scanning electron microscope images of the as-synthesized MOFs show the formation of MOF nanoparticles with an average size of 20–300 nm. The MOF particle size decreased with increasing ethanol content in the mixed solvent. The FT-IR spectra further support that the MOF formation occurs in water/ethanol mixtures with ethanol volume ratios higher than 30 vol%. Thermogravimetric analysis showed that the MOF is stable up to 300 °C. Moreover, the FT-IR spectra and thermogravimetric analysis gave consistent information on the solvent amount entrapped in the MOF pores. The porosity of the MOFs was determined using a N2 adsorption–desorption method. When the ethanol volume ratio reached 75%, the largest SBET value of 1067 m2 g−1 and Vt value of 0.52 cm3 g−1 were obtained. The possible mechanism for MOF formation in water/ethanol solvent systems and the dependence of the MOF size on the solvent composition was discussed from the view of hydrogen bond strength between solvent molecules and the ligands in different water/ethanol solvent systems.

Herein it was found that gas can be utilized as an activator to promote metal-organic framework (MOF) crystallization in IL at room temperature. The ultra-small MOF nanoparticles were obtained, and their size and porosity properties can be easily modulated by controlling gas pressure. The as-synthesized nano-sized Cu-MOF is an excellent candidate catalyst for the solvent-free oxidation of cyclohexene with oxygen.

CuO nanoleaves with a mesoporous structure were formed in an aqueous solution of triethylamine at room temperature. The growth process of the CuO nanoleaves in a triethylamine solution was investigated by varying the reaction time. It is shown that the CuO nanostructures form by reconstructive transformation from Cu(OH)2, going through a 0D nanoparticle → 1D nanowire → 2D nanoleaf dimensional transition process. The mechanism for the amine-induced formation of CuO at room temperature was studied by using different aliphatic amines. It is revealed that the amines play multiple roles on CuO formation, i.e. acting as an alkali, dominating the Cu(OH)2 to CuO transformation, and directing the oriented crystal growth of CuO. This route is simple, rapid, involves no additional alkalis or directing agents, and can proceed at room temperature. The as synthesized CuO exhibits excellent catalytic activity for cyclohexene oxidation with oxygen under solvent-free conditions.

Engineering of novel functional nanocomposite as like as the metallic nanocrystals supported non-stoichiometric perovskite nanomaterial in controlled parameters (size, shape and ratio of chemical characteristics) is a challengeable task. In this context, we present a facile route to fabricate and study its physicochemical property at real time mode in this report. Nanoscale pure Pb crystals surfaced on non-stoichiometric A-site deficient Pb1-xTiO3-y nanoparticle were fabricated when a precursor lead titanate (PbTiO3) nanoparticle was exposed to an electron beam irradiation (EBI) in a transmission electron microscope (TEM) at ambient temperature. In the state of the art, the chemical states and electronic structure of non-irradiated and irradiated PbTiO3 were studied by X-ray photoelectron spectroscopy (XPS). Electron bombardment resulted in a new visible feature at low binding energy in the Pb 4f core level, while Ti 2p and O 1s line shape showed slight changes. The Fermi level of the corresponding materials was determined to be 1.65 ± 0.1 eV and 2.05 ± 0.1 eV above the valence band maximum, respectively. The normal, weakly p-type PTO exhibits peculiar n-type feature after EBI process (The Fermi level moves near to the conduction band). A feasible mechanism is proposed involving the electron-stimulated local bond-breaking phenomenon in PbTiO3.

The interfacial segregation plays an important role in affecting the mechanical performance of various materials. Here we study the segregation behaviors along deformation-induced interfaces in the matrix of an Mg97Zn1Y2 (at%) alloy compressed at 473 K using atomic-scale high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging techniques. The kink boundary, twinning-like boundary, and tilt boundary within the matrix grain are detected to be segregated with both solute Zn and Y atoms. The segregation along kink boundary and twinning-like boundary is closely linked to the associated partial dislocations, and these boundaries also could be regarded as the nucleation sites for the formation of long period stacking ordered (LPSO) structures of nanometer scale and stacking faults (SFs) during deformation. For the various tilt boundary, the segregation could be explained based on either the O-lattice theory or partial dislocations. The experimental results may shed some new light on tailoring microstructures for improving mechanical properties and thermal stability of magnesium alloys.

In the work, we report a theoretical and experimental study of the {1 1 1} twin boundaries in the rock-salt MnS using aberration-corrected transmission electron microscopy (TEM) and density functional theory. The experimental TEM images are supported by first-principle calculations. In comparison with magnesium oxide, we also explained why it is comparatively more stable for twins to exist in MnS rather than in MgO, which may help us better understand the properties of different ionic compounds.

A novel interpenetrating C/Mg-Zn-Mn composite was fabricated by infiltrating Mg-Zn-Mn alloy into porous carbon using suction casting technique. The microstructure, mechanical properties and corrosion behaviors of the composite have been evaluated by means of SEM, XRD, mechanical testing and immersion test. It was shown that the composite had a compact structure and the interfacial bonding between Mg-Zn-Mn alloy and carbon scaffold was very well. The composite had an ultimate compressive strength of (195 ± 15) MPa, which is near with the natural bone (2-180 MPa) and about 150-fold higher than that of the original porous carbon scaffold, and it still retained half of the strength of the bulk Mg-Zn-Mn alloy. The corrosion test indicated that the mass loss percentage of the composite was 52.9% after 30 days' immersion in simulated body fluid (SBF) at 37 ± 0.5 °C, and the corrosion rates were 0.043 mg/cm(2)h and 0.028 mg/cm(2)h after 3 and 7 days' immersion, respectively. The corrosion products on the composite surface were mainly Mg(OH)2 and hydroxyapatite (HA).

Ferroelectric thin films grown on high index substrates show unusual structural and switching dynamics due to their special strain states. Understanding the misfit relaxation behavior is crucial to facilitate the high index thin film growth with improved quality. In this paper, ferroelectric PbTiO3 thin films were grown on LaAlO3 (111) substrates by pulsed laser deposition technique. The microstructures were investigated by combinations of conventional and aberration-corrected transmission electron microscopy. Diffraction contrast analysis and high resolution imaging reveal that high density interfacial dislocations were distributed at the interfaces. These dislocations have mixed character with Burgers vectors of a and line directions of . The edge components of the dislocations, with the Burgers vectors parallel to the interface, accommodate the lattice mismatch and are the main contributor to the misfit relaxation of this system. The formation mechanism of these dislocations is proposed and discussed to elucidate the novel mismatch relaxation behavior of oriented perovskite films.