Ni-based fcc alloys are frequently used as critical structural materials in nuclear energy applications. Despite extensive studies, fundamental questions remain regarding point defect migration and solute segregation as a function of grain boundary character after irradiation. In this study, a coupled experimental and modeling approach is used to understand the response of grain boundary character in a model Ni–5Cr alloy after high temperature heavy-ion irradiation. Radiation-induced segregation and void denuded zones were experimentally examined as a function of grain boundary character, while a kinetic rate theory model with grain boundary character boundary conditions was used to theoretically model Cr depletion in the alloy system. The results highlight major variations in the radiation response between the coherent and incoherent twin grain boundaries, but show limited disparity in defect sink strength between random low- and high-angle grain boundary regimes.

A crystal plasticity finite element constitutive model combined with Bassani and Wu hardening law has been developed to investigate the effects of grain/phase boundary (GB/PB) on mechanical properties and microtexture evolution of Cu bicrystals and Cu–Al bicrystals during nanoindentation process. The simulated load–displacement curve for the Cu single crystal with Goss initial orientation has been analyzed and compared with the result from the experiment to validate the parameters. The numerical results indicate that the effects of GB/PB on load–displacement curves, indentation Young's moduli, Mises stresses, pile-up patterns are insignificant for Cu bicrystals while they are significant for Cu–Al bicrystals. The main reason is that PB works as a very effective barrier to resist the plastic slip propagation of the deformed material. The effects from different misorientations of GBs/PBs are insignificant for both Cu bicrystals and Cu–Al bicrystals. The effects of GB/PB on lattice rotation angles for both Cu bicrystals and Cu–Al bicrystals are significant.

The carburizing behaviors and mechanisms for Cr35Ni45Nb alloy subjected to different service conditions were studied in a high-temperature vacuum environment. Generally, the carburizing process of an alloy is always accompanied by diffusional heterogeneous reactions regardless of the service condition of the alloy. For a carburized original tube, there is a layered structure at the inner wall of the tube, which is comprised of a M7C3 zone, a M7C3–M23C6 mixed zone, and a M23C6 zone with different morphologies. However, for a 6-year tube (short for a tube serviced for 6 years), the composite oxide layers formed previously act as effective barriers to carbon infiltration. Moreover, the Cr2O3 scale tended to be carbonized to form carbide scale to spall from the surface in a reducing environment, while the SiO2 kept stable all along. Once the oxide layers were removed or carbonized enough, inconceivable internal carburization occurred widely.

This research article investigates the effect of SiO2 flux on Nd:YAG laser welding of 5 mm thick plates of super-austenitic stainless steel, AISI 904L. Microstructure studies revealed multidirectional grain growth comprising columnar and cellular dendrites along with a prominent, fine equiaxed dendritic growth at the centerline of the fusion zone. Tensile studies showcased the fracture at the fusion zone in all the trials. The average tensile strength reported for the flux assisted laser weldments was found to be 587 MPa which was slightly lower than the parent metal. The impoverishment of tensile strength could be attributed to the formation of centerline equiaxed grains. Similarly the impact toughness of the joints was found to be 58 J. The studies demonstrated the possibility of using a 2 kW Nd:YAG laser welding machine to weld 5 mm thick plate with the use of SiO2 flux. A detailed study on the structure–property relationship of flux assisted Nd:YAG laser weldment was carried out using the combined techniques optical microscopy, scanning electron microscopy, and energy dispersive x-ray analysis.

The peculiarities of the Seebeck coefficient and power factor are studied in porous thermoelectric materials with spherical hollow pores of varying diameter from nanometer to micrometer length scales. The pores are assumed to be randomly dispersed throughout the matrix material. The influence of trap centers situated at pore interfaces on the power factor is investigated. Using the model based on gamma distribution of the pore sizes, the analytical expression is obtained for the power factor at the arbitrary level of the Fermi energy. Limiting cases of nondegenerate and degenerately doped porous semiconductors are examined as well. The results are compared with calculations for a multilayer composite in which each layer contains pores of a single length-scale. It is shown that the presence of hollow pores with multiscale hierarchical disorder leads to more considerable enhancement in the thermopower over its value in the bulk. Necessary conditions for the enhancement of the power factor are found.

The martensitic transformation of Fe–22 wt% Ni austenite was investigated by high-resolution dilatometry as well as differential thermal analysis. Macroscopically discontinuous formation of lath martensite was observed, manifested in a train of transformation-rate maxima. It is proposed that the modulation of the transformation rate is caused by simultaneous formation of blocks in different martensite packages. The origin of simultaneity is ascribed to the interplay of chemical driving force, developing strain energy, and its relaxation upon sufficiently slow cooling. The transformation-rate maxima become more distinct with decreasing cooling rate (CR), clearly indicating the involvement of a thermally activated process in martensite formation. Quantitative analysis of the microstructure of differently cooled specimens revealed smaller martensite block sizes for higher CRs. All observations are compatible with athermal nucleation and thermally activated growth. (Local) strain relaxation in the austenite was identified as the involved thermally activated mechanism.

The M-type hexaferrite Sr1−xLaxFe11.75Co0.10Zn0.15O19 (0 ≤ x ≤ 0.7) magnetic powders and magnets were synthesized by the ceramic process. The phase constituents of the magnetic powders were analyzed by x-ray diffraction. There is a single magnetoplumbite phase in the magnetic powders with La content (0.2 ≤ x ≤ 0.4). For the magnetic powders containing La content (0 ≤ x ≤ 0.1) or (0.5 ≤ x ≤ 0.7), magnetic impurities coexist in the structure. The microstructures of the magnets were characterized by field emission scanning electron microscopy. The magnets consist of homogenously distributed ferrite particles with the hexagonal structures. The magnetic properties of the magnets were measured by a permanent magnetic measure equipment. The remanence, maximum energy product, and Hk/Hcj ratio of the magnets at x = 0.3 reach the maximum values. However, the intrinsic coercivity and magnetic induction coercivity of the magnets at x = 0.2 reach the maximum values.

Polymethylmethacrylate (PMMA) and polyimide (PI) samples are implanted by 40 keV Cu+ ions with high fluences to synthesize copper nanoparticles in shallow polymer layers. The produced metal/polymer nanocomposites are studied using atomic force and scanning electron microscopies as well as optical transmission spectroscopy. It is found that nucleation and growth of copper nanoparticles are strongly fluence-dependent as well as they are affected by the polymer properties, in particular, by radiation stability yielding different nanostructures for the implanted PI and PMMA. Shallow synthesized nanoparticles are observed to partly tower above the sample surface due to a side effect of high-fluence irradiation leading to considerable sputtering of polymers. Implantation and particle formation significantly change optical properties of both polymers reducing transmittance in the UV–visible range due to structural and compositional change as well as causing an absorption band related to localized surface plasmon resonance (LSPR) of the nanoparticles. The role of polymer type and its degradation under the implantation on LSPR is studied to optimize conditions for the formation of nanoplasmonic materials.

Amorphous and nanocrystalline soft magnetic alloys have garnered interests in academia and industry due to their potentials for applications, such as power transformers, electric motors, and sensors. To achieve good glass formability, thermal stability, and prevent grain overgrowth, elements such as B, Nb, Ta, and Hf are used in many soft magnetic systems. However, the high price of these precursors results in expensive soft magnetic alloys. Herein, we report on substituting Ta and Hf with TaC and HfC, respectively, to significantly reduce the cost of Fe-based FINEMET and Co-based HTX005 alloys. Soft magnetic properties of these alloys are studied. The effect of thermal annealing and strain annealing on TaC and HfC substituted alloys are also investigated. Lastly, we discuss the cost analysis on these alloys. Using the synthesis route presented here, a cost reduction of up to 74% can be achieved.

The onset of a diffusive phase transformation in thin film Zn0.70Mg0.29Ga0.01O deposited on c-oriented sapphire (α-Al2O3) was explored using dynamic heating experiments in a laser pulsed atom probe tomography (APT) instrument and correlated with transmission electron microscopy (TEM). Specimens were laser irradiated using 100–1000 pJ pulse energies with initial temperatures between 50 and 300 K for up to 8.64 × 1010 pulses. Using a finite element model, it was possible to estimate the temperatures reached by the specimen during laser pulsing, which were calculated to be 300 K to above 1000 K. Due to the small sample volume, quench rates were estimated to be 1013 K/s, allowing for nanosecond temporal resolution during the in situ heating experiments. The formation of Mg-spinel (MgAl2O4) at the transparent conductive oxide/α-Al2O3 substrate interface was observed using electron diffraction and confirmed by atom probe analysis. Subnanometer spatial resolution in the atom probe data reconstructions allowed for near atomic level diffusion to be observed. This work demonstrates the feasibility of conducting these experiments in situ using a combined TEM and APT instrument.

A micro-indentation system integrated with an acoustic emission (AE) sensor is used as a damage test method for crack detection of the specimen during the indentation loading–unloading cycle. The specimens investigated are the Si die, and various stacked structures of metallization (Al or Cu) deposited over the dielectric layers (SiO2 or Si3N4) on the Si substrate. The 1st AE event detected during the loading stage corresponded to the ‘pop-in’ observation in the force–displacement curve, which was related to the brittle cracking in the dielectric or Si substrate. However, during unloading, a 2nd AE event was detected, but no “pop-out” was observed, which was mainly due to the delamination between the dielectric and Si substrate. It was also found that for Si die, “pop-out” was observed without any AE event during the unloading stage, which was related to the Si phase transformation. This observation is unique to sharp indenter tip but not for a blunt indenter tip.

Crystalline Au nanoparticles embedded in epitaxially grown SrTiO3 layers were prepared by an annealing and coating procedure of Au seed layers on SrTiO3 (STO) substrates. X-ray diffraction and transmission electron microscopy measurements were performed to investigate the size, shape, and deformation of the particles and their crystal orientation. The shape and size of the crystalline Au nanoparticles can be tuned by controlling the Au seed layer thickness and single crystalline elliptically shaped Au nanoparticles have been generated. Furthermore, the orientation of the surrounding SrTiO3 matrix changes significantly from homoepitaxially grown (001) to secondary (111) and (011) orientations for Au seed layers that are thicker than 4 nm. This is of great interest for modifying the electrical properties of SrTiO3 layers, whereas the anisotropically shaped crystalline particles are relevant for optical applications, due to localized surface plasmon resonances.

To investigate the effect of Y element and hot-extrusion on microstructure and mechanical properties of the three alloys which are Mg–4Zn–xY (x = 1, 2, 3 in wt%). All the three alloys are hot-extruded and analyzed. The results show that as Y is increased, the microstructures of the as-cast alloys are more refined and the phase compositions are changed from both I-phase and W-phase to single W-phase whose structure is changed from mix of net and spheroidization to continuous net. The mechanical properties are increased to a small extent mainly due to the refining effect of Y. After hot-extrusion, coarse dendrite crystals are broken and dynamic recrystallization appears which obviously refine the microstructure. Second phases are redistributed along the extrusion direction. W-phases are twisted and broken, while I-phases are spheroidized. Tensile strengths and elongations are all increased by around 100% compared with the as-cast alloys.

The effects of trace La additions on the microstructures and mechanical properties of Cu–0.2 wt% Zr alloy have been investigated. Traditional thermo-mechanical processing was applied to the Cu–Zr alloys. Isochronal aging and isothermal aging were used to optimize the aging conditions. According to the hardness and conductivity tests, the optimized aging condition should be 150 min isothermal holding at 400 °C following 85% cold-rolling. If the as-cast sample is subjected to aging, the addition of La obviously refines the microstructures. After cold-rolling, however, the La addition has no significant effects on the grain size of the aged sample. SEM and TEM are combined to observe the distribution and morphology of the precipitates, which are identified to be Cu5Zr. The addition of La can improve the hardness and conductivity simultaneously in the as-cast samples after aging, while it improves the hardness and strength and decreases the conductivity slightly in the cold-rolled samples after aging. XRD and TEM results show that the lattice parameter and the dislocation density are increased by the addition of La.

In this study, scanning electron microscope, electron backscatter diffraction, and transmission electron microscope have been used to investigate the microstructure evolution of Cu–0.2Mg alloy during continuous extrusion in mass production. The continuous extrusion could change the size and orientation of as-cast crystallite grains of the alloy. Hardness increased gently in upsetting zone and dropped sharply in adhesion zone. Hardness reached the maximum value in right-angle bending zone; and it decreased rapidly in extending extrusion zone. Upsetting zone was mainly composed of cell blocks and microbands, and adhesion zone mainly consisted of discontinuous recrystallize grain. Shear band and subgrains were formed in right-angle bending zone due to polygonization during shear deformation. In extending extrusion zone and extrusion rod zone, recrystallize microstructures were predominant.

The forming limit strains (FLSs) of zircaloy-4 sheets are studied. After having obtained the true stress–strain curve of zircaloy-4 using the weighted-average method, limit dome height (LDH) tests are performed to establish experimental FLSs. We summarize related theoretical forming limit curves (FLC) and discuss their limitations. Two finite element (FE) models are established for determining FLSs; an LDH test FE model for the negative minor strain sector, and a biaxial tensile FE model for the positive minor strain sector. The numerical FLSs are found to agree well with experimental data. Since the numerical FLC gives the strain at the onset of local thinning (whereas the experimental FLC provides the strain between local necking and ductile fracture), resulting FE FLS values are slightly lower than the experimental ones so that results can be regarded as conservative. Our FE approach substitutes the expensive and time-demanding experimental LDH tests.

The finite element method is used to simulate indentation with a 100 nm spherical indenter on Al/Pd multilayer thin films and Al and Pd monolayer thin films. The elastic/plastic properties of bulk Al and Pd and the material formulation are obtained by molecular dynamics simulations of tensile and indentation loadings. Hill's plasticity with isotropic hardening is found to best represent the stress–strain response of both bulk Al and Pd. The Pd monolayers appear the hardest and the Al monolayers the softest. The indentation hardness of both monolayered and multilayered films is found to increase with the indentation depth and appears independent of the layer order and thickness in the multilayer films. The hardness values determined by the finite element method simulations are close to those obtained using the well-known formula of Field and Swain. No hardness enhancement in very thin multilayered films (3–5 nm per layer) is evident, in contrast to experimental reports.

Some Fe-rich amorphous alloys of Fe–B–P–Si and Fe–B–P–Si–C systems were found to exhibit simultaneously good soft magnetic properties with high-saturation magnetization values near 1.7 T, which are higher than those for previously reported Fe-based amorphous and glassy alloys, in addition to rather good amorphous ribbon formability, good bending ductility, and rather high corrosion resistance. The corrosion resistance increased with increasing P content, accompanying by the increase in thermal stability of the amorphous phase. The decrease in the outer surface velocity of the wheel, which results in the increase of ribbon thickness, also causes an improvement of surface smoothness of the melt-spun amorphous alloy ribbons. The syntheses of new high-saturation Fe-based soft magnetic amorphous alloys without any other transition metals hold promise for future extension of Fe-based soft magnetic amorphous materials.

Self-energy correction density functional theory local density approximation–1/2 (LDA-1/2) method was successfully applied to predict the electronic structure and optical properties of the N-doped, Ti-vacant Ti3−δO4N oxynitride [G. Hyett et al., J. Am. Chem. Soc.129, 15541–15548 (2007)], which was shown experimentally to be more photocatalytic than titania. The procedure takes into consideration of the two possible types of Ti vacancies (with different numbers of nitrogen and oxygen neighbors) and their formation energies, according to the experimental data on fractional occupancies, with potential effects on the electronic structure and photocatalyst mechanisms analyzed. Different defective model structures were calculated for optimal final configuration, whose optical calculations revealed massive damping in infrared spectrum, while transparency in green region. The band gap determined by our methodology is 2.5 eV, in close agreement to the experimental value of 2.6(1) eV. Results presented in this work represent the first report of an electronic structure modeling of Ti3−δO4N, which is a starting point to help provide an understanding of its photocatalytic activity.