Scripta Materialia

Published by Elsevier
Online ISSN: 1359-6462
Publications
Article
The property degradation observed in thin Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT) crystals is believed to relate to large domains and subsequent clamping induced by surface-boundary. In this work, the properties were investigated as function of domain size, using controlled poling. The degraded piezoelectric and dielectric properties of thin PMN-PT were found to increase significantly, by decreasing domain size. Furthermore, the fine domain structure was found to be stable at 3kV/cm after 7.0×10(5) negative-pulse cycles, hence, enabling PMN-PT crystals for high-frequency (>20 MHz) ultrasound-transducers.
 
Relative length change Δl/l of Fe 55 Al 45 as function of time due to annealing of remnant vacancies at 723 K after heat treatment at 966 K (2 h) and subsequent water-quenching. Specimen length l = 20 mm.
Relative length change Δl/l of HPT-deformed Fe as a function of temperature T. Heating rates: 1.5 K min −1 (-), 3 K min −1 (-), 6 K min −1 (······). Specimen length l = 7 mm.
Relative length change Δl/l of HPT-deformed Fe as a function of temperature T. Heating rates: 1.5Kmin−1 (—), 3Kmin−1 (- - -), 6Kmin−1 (······). Specimen length l=7mm.
Relative length change Δl/l of HPT-deformed Fe (—) and undeformed Fe reference sample (- - -) upon heating and cooling at a constant rate of 3Kmin−1 (time t). Dotted line: difference (enlarged by a factor of 3) between deformed and undeformed specimen due to annealing of deformation-induced free volume upon first heating cycle.
Relative length change Δl/l of Fe55Al45 as function of time due to annealing of remnant vacancies at 723K after heat treatment at 966K (2h) and subsequent water-quenching. Specimen length l=20mm.
Article
A maximum excess volume ΔV/V ≈ 1.9 × 10(-3) in ultrafine-grained Fe prepared by high-pressure torsion is determined by measurements of the irreversible length change upon annealing employing a high-resolution differential dilatometer. Since dislocations and equilibrium-type grain boundaries cannot fully account for the observed released excess volume, the present study yields evidence for a high concentration of free volume-type defects inherent to nanophase materials, which is considered to be the main source of their particular properties, such as strongly enhanced diffusivities.
 
Surface energies for low-index planes of AlN allotropes. Red curves represent the calculated density of broken bonds, as discussed in the text. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Convergence of the Al-terminated {111} surface energy of B1-AlN.
Article
In this letter we present first-principles calculations of the surface energies of rock-salt (B1), zinc-blende (B3) and wurtzite (B4) AlN allotropes. Of several low-index facets, the highest energies are obtained for monoatomic surfaces (i.e. of only either Al or N atoms): [Formula: see text] and [Formula: see text]. The difference between Al- and N-terminated surfaces in these cases is less then 20 meV/Å2. The stoichiometric facets have energies lower by 100 meV/Å2 or more. The obtained trends could be rationalized by a simple nearest-neighbour broken-bond model.
 
Article
Experiments show that the rupture strain of gold conductors on elastomers decreases as the conductors are made long and narrow. Rupture is caused by the irreversible coalescence of microcracks into one long crack. A mechanics model identifies a critical crack length ℓ(cr), above which the long crack propagates across the entire conductor width. ℓ(cr) depends on the fracture toughness of the gold film and the width of the conductor. The model provides guidance for the design of highly stretchable conductors.
 
Cross-section of a parallel macro fracture surface HPT deformed at 25°C. The contrast has been increased to enhance the microdefects below the surface. An inclusion on the fracture surface is marked.
(a) Macro tensile curves for the HPT deformed disc at different deformation temperatures (testing direction parallel to the HPT shear direction). (b) Micro tensile curves for the HPT deformed disc at different deformation temperatures. The tensile test direction for the filled symbols is parallel to the HPT shear direction whereas the tensile test direction is perpendicular to the HPT shear direction for the open symbols.
Details of the fracture surface in the middle of a parallel macro sample HPT deformed at 200°C. Inclusions are visible in some of the pores.
Fracture surface of the micro and macro samples in the parallel and perpendicular orientations: (a) parallel macro sample, HPT at −196°C; (b) parallel macro sample, HPT at 25°C; (c) parallel macro sample, HPT at 200°C; (d) parallel macro sample, HPT at 400°C; (e) parallel micro sample, HPT at 25°C; (f) perpendicular micro sample, HPT at 25°C; (g) side view, parallel micro sample, HPT at 400°C; (h) parallel micro sample, HPT at 400°C.
Micro and macro tensile test results and their corresponding standard deviations.
Article
Nickel discs (>99.5 wt.%) were deformed by high pressure torsion (HPT) at different temperatures (-196 °C, 25 °C, 200 °C, and 400 °C) until saturation was reached. The strength and fracture behavior of microdefect-free samples and samples with inclusions were investigated using micro and macro tensile tests, respectively. The fracture behavior is not sensitive to the HPT deformation temperature but differs significantly in the two types of sample. The ultimate tensile strength is not affected by inclusions or grain texture.
 
Article
A new synthetic approach for fabrication of perforated hollow silica morphologies using colloidal template assemblies is demonstrated. As proof-of-principle, the polystyrene/silver colloidal assemblies had chemically modified surfaces. The template dissolution resulted in the fabrication of the sub-micron perforated hollow silica shells. The morphologies are characterized by transmission electron microscopy, energy dispersive spectroscopy and plasmon light extinction spectrophotometry. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
 
Conference Paper
Intrinsic thermal fatigue in a mechanically unconstrained Pb-free, Sn-rich Sn-3.8Ag-0.7Cu alloy has been investigated under cyclic thermal loading between 293 K and 353 K. Fatigue damage is shown to occur preferentially along high angle grain boundaries. From a combination of orientation imaging microscopy and finite element modelling it appears that this fatigue damage and stresses resulting from the thermal anisotropy of Sn are highly correlated. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
 
Conference Paper
A sheet of fully dense nanocrystalline (nc) Ni with a thickness of 350 μm was obtained by a direct-current electrodeposition method. The nc Ni has an average grain size of 40 nm and an evident {200} texture as revealed by X-ray diffraction analysis. TEM observations show that the microstructure of the nc Ni consists of the grain clusters of about 150-300 nm surrounding by nano-grains of about 10-20 nm. Moreover, the clusters are also composed of the nano-grains of about 30-50 nm possessing the small misorientation angles. The room temperature tensile test performed at a strain rate of 1.04×10<sup>-3</sup>s<sup>-1</sup>indicates that the nc Ni has a combination of high tensile strength of 1220 MPa and enhanced elongation to failure of 7.2%. The optimized mechanical properties of our nc Ni is discussed by connected with its special micro-structures.
 
Article
Oxidation of a model β-phase Ni–40Al–5Cr–0.03Y (at.%) was studied in the temperature range 1000–1100 °C. Numerous voids formed at the oxide/alloy interface, and the coalescence of those interfacial voids caused extensive spallation of the thermally grown oxide during isothermal oxidation. The density of interfacial voids depends on the orientation of the bond coat alloy substrate, which suggests that the epitaxial Al2O3/alloy interface structure plays an essential role in the formation of interfacial voids during oxidation.
 
(a) and (b) Vickers microhardness vs. aging time at 300 °C for Al-0.06 Sc-0.02 RE, Al-0.06 Sc, and Al-0.06 Sc [31,32]. Error bars are 1 standard deviation from the mean. 
Article
The microhardness of Al-0.06 Sc-0.02 RE alloys (at.%, with RE (rare-earth) = Dy, Er, Gd, Sm, Y, or Yb) is measured as a function of aging time at 300 degrees C. As compared to Al-0.08 Sc, the ternary alloys exhibit: (i) the same incubation time, except for Al-0.06 Sc-0.02 Yb which hardens much faster; (ii) the same or reduced peak microhardnesses (which are higher than for Al-0.06 Sc); and (iii) the same over-aging behavior. All REs segregate to the core of Al-3(Sc1-xREx) precipitates. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
 
Article
Grain growth in an Al–0.1% Mn sample has been measured non-destructively using a three-dimensional X-ray diffraction (3DXRD) microscope. The 3-D grain morphology as well as the crystallographic orientation was determined for 483 grains in the illuminated volume prior to annealing. After annealing, a second map revealed that significant grain growth had taken place, with only 27 remaining grains in the same volume. The correlation between grain orientation, growth of grains and neighbouring relationships is explored.
 
Schematic drawing of the heat treatment process in this study. 
Optical micrographs of the (a) ECO-6, (b) ECO-7, (c) ECO-8 and (d) ECO-9 isothermally heated at 430 °C for 5 min and etched with sodium metabisulphite solution. 
Tensile stress-strain curves of the samples isothermally heated at 430 °C for 5 min. 
Mechanical properties of the samples isothermally heated at 430 °C as a function of holding time. 
Retained austenite volume fraction changes of the samples isothermally heated at 430 °C as a function of holding time. 
Article
Cold-rolled steels based on 0.15C-1.5Mn-1.5Si-0.5Cu containing Cr or/and Ni were prepared, and intercritical annealing and isothermal treatment, were carried out. The addition of Cu or Cu+Ni resulted in a large increase of the retained austenite volume fraction as well as an improvement of elongation and the strength-ductility balance. However, the addition of Cr or Cu+Ni showed a dual-phase deformation behavior having higher tensile strength and lower elongation. © 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.
 
Article
An Mg-2.4Zn-0.1Ag-0.1Ca-0.1Zr alloy sheet, with a tensile yield strength of 316 MPa, an ultimate tensile strength of 342 MPa and an elongation of 17%, has been processed by twin roll casting (TRC), hot rolling and heat treatment. The high yield strength has been attributed to a uniform distribution of fine rod-like precipitates of MgZn(2) phase. The TRC and hot-rolled sheet also showed an exceptionally high stretch formability with a limiting dome height much larger than those of other Mg alloys.
 
Article
The Sn–8.5Zn–0.5Ag–0.1Al–xGa solders were investigated. The results showed that the microstructure of the solders were eutectic. The addition of Ga dramatically decreased the melting point of solders. Notably, the increase in Ga content of the solder improved the solderability, the tensile strength and reduced the ductility.
 
Article
Cast and aged Al–0.1Zr and Al–0.1Zr–0.1Ti (at.%) alloys, upon compressive creep deformation at 300–400 °C, exhibit threshold stresses attributable to climb-controlled bypass of coherent Al3Zr and Al3(Zr1−xTix) precipitates. Al–0.1Zr–0.1Ti exhibits a smaller threshold stress than Al–0.1Zr, which is attributed principally to a reduced lattice parameter mismatch between the Al3(Zr1−xTix) precipitates and the matrix. The present alloys are less creep resistant than Al–Sc and Al–Sc–Zr/Ti alloys with similar precipitate radii and volume fractions.
 
Article
The solidification of the alloy ASTM F-75 ends with sigma phase formation instead of M7C3 carbide as presumed from literature. The M23C6 carbide observed in cast specimens precipitates from the sigma phase (σ) according to the global reaction σ+C→M23C6 over the range 1403–1303 K. Additionally, lamellar carbides appear below 1262 K for cooling rates lower than 35 K/min.
 
Article
Thermal desorption spectrometry study of the hydrogen trapping capability of a tempered Fe–0.2C martensite indicated that dislocations in the martensitic substructure are the primary traps and new grain boundaries resulting from recovery and recrystallization of the ferrite matrix are the secondary traps for hydrogen. Cementite has a negligible effect on hydrogen trapping.
 
Article
Nanocrystalline powders synthesized by mechanochemical activation were successfully used to process high-density submicron- and nanostructured 0.8Pb(Mg1/3Nb2/3)O3–0.2PbTiO3 perovskite phase ceramics by hot pressing, with average grain size ranging from 0.36 μm down to 88 nm. These materials are very suitable for studying the size dependence of the properties across the submicron range approaching the nanoscale. This is the first report of such a series of ceramic materials of a relaxor-based morphotropic phase boundary composition, and of its properties as a function of the grain size.
 
Article
Tensile properties of Ti-47Al-2Cr-0.2Si sheet materials with different microstructures were investigated in the temperature range 20–800 °C. Deformation and fracture at ambient temperatures seem to be determined by microstructural features such as phase distribution and grain size. At elevated temperatures dislocation climb processes seem to be involved in the deformation, which results in rate dependent strength properties.
 
Article
In Mg alloys, prismatic plates are predicted to be more effective for age hardening compared with the basal plates that are commonly observed in Mg–rare earth (RE) or Mg–Ca alloys with Zn. This study reports that a high number density of thin prismatic plates can be precipitated in Mg–0.3Ca alloy by microalloying with In, resulting in an enhanced age-hardening response three times higher than that for the binary alloy. The precipitates are composed of three {1 0 0} prismatic planes enriched with Ca and In.
 
Article
The direct laser sintering of Al–7Si–0.3Mg/SiC composites was studied. It is shown that the densification rate obeys first-order kinetics. The rate constant is found to increase at low SiC fractions but abruptly decreases at >∼5 vol.%. In the presence of ceramic particles, the melt track becomes more stable and a more continuous sintered surface is obtained. Meanwhile, significant reaction occurs between the aluminum melt and the reinforcement particles, leading to formation of Al4SiC4 and silicon particles. The solidification microstructure is also altered.
 
Article
Friction stir processing (FSP) was applied to extruded Al–4Mg–1Zr to produce fine-grained microstructure with grains sized 0.7–1.6 μm. Low temperature deformation behavior was investigated at 175 °C and initial strain rates of 5 × 10−5–3 × 10−3 s−1. Low temperature superplasticity was observed in ultrafine-grained material. A maximum superplastic elongation of 240% was obtained in ultrafine-grained (0.7 μm) FSP sample at an initial strain rate of 1 × 10−4 s−1 where a maximum strain rate sensitivity of 0.34 was observed.
 
Article
The hydrogen induced delayed fracture of ultrafine grained 0.6% O steel with dispersed oxide particles was discussed. The MM of 0.6% O steel powder followed by consolidation at 700 °C resulted in the ultrafine grained steel having an average ferrite grain size of 0.3 μm and the dispersion of Cr 2O3 particles of 10 nm. It was found that the grained steel exhibit high resistance to hydrogen embrittlement at the tensile strength of 1300 MPa by hydrogen trapping effect related to the nanosize oxide particles.
 
Article
Manganites are one of only a small number of material families currently being trialled as room-temperature magnetic refrigerants. Here we examine the dependence of the thermal conductivity, κ, of La0.67Ca 0.33MnO3±δ as a function of density, grain size and silver impregnation around room temperature. We use a simple effective medium model to extract relevant trends in the data and demonstrate a 3-fold increase in thermal conductivity by silver impregnation. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
 
Article
The creep behavior of a cast TiAl-based alloy was investigated in the temperature range 700–800 °C and at applied tensile stresses ranging from 200 to 390 MPa. The power law stress exponent is determined to be five and apparent activation energy for creep is calculated to be 355 kJ/mol. The kinetics of creep deformation is proposed to be controlled by dislocation climb.
 
Article
The site exchange between Ge and surfactant atoms in the growth of Ge on the group V element-covered Si(0 0 1) has been studied using first-principles total energy calculations. On the Bi-covered Si(0 0 1) and the As-covered Si(0 0 1), a single adatom site exchange process can occur energetically, but with different pathways. The energy barriers for the single adatom site exchange are very small. The site exchange can therefore occur very easily. This will suppress the Ge diffusion, and favors the layer-by-layer growth mode.
 
Article
The texture evolution of polycrystalline AA 5182 aluminium alloy with an initial {001} '110' texture during rolling was discussed. The lattice rotation paths of the {001} '110' orientation and the lattice rotation with true strain were determined and compared with experimental results for single crystals. The grain boundaries showed no effect on the lattice rotation of the {001} '110' orientation during rolling. The texture evolution of polycrystalline aluminium alloy was investigated using X-ray diffraction.
 
Article
Ni and Ni base alloys are good candidate substrate materials in the development of coated conductors. The present paper reports the development of a high strength (Ni–3%W/Ni–10%Cr–1.5%Al) composite tape of 80 μm thickness with strong cube texture.
 
Article
Cu-Zr-based bulk glassy alloys are synthesized with high glass-forming ability in a Cu42-xZr42+xAg8Al8 system by copper mold casting. Bulk glassy alloys with a diameter of 10 mm can be easily obtained in this alloy system. Also, 15-mm glassy alloy rods are formed for the Cu40Zr44Ag8Al8, Cu38Zr46Ag8Al8 and Cu36Zr48Ag8Al8 alloys by copper mold casting. These glassy alloys exhibit high fracture strengths of over 1850 MPa with Young's moduli of about 115 GPa. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
 
Article
Laser deposition of Inconel 738 on directionally solidified (DS) Ni-based superalloy demonstrates a strong susceptibility to cracking. Cracks originate from the liquation of low melting point eutectic on the DS grain boundary. Five boundary liquation and interface cracking styles were identified. Sound Inconel 738 deposition layers were achieved free of cracks.
 
Article
High-entropy nitride films were deposited by reactive sputtering from an AlCrNbSiTiV equimolar alloy target. The films persisted in single solution phase with an NaCl structure and retained their nanograin size, even after annealing at 1000 °C for 5 h. The films were superhard (>40 GPa), and have a high entropy effect that stabilizes the solution phase, and a severe-lattice-distortion effect that inhibits nanograin coarsening. The proposed inhibition mechanism for such high-entropy nitride coatings is based on thermodynamics.
 
Article
This paper is written as a reaction to the discussion by Aaronson et al. on our conclusion that the activation energy for ferrite nucleation during the austenite decomposition in medium carbon steel is two orders of magnitude smaller than predicted from the pillbox model of Lange et al. [Metall. Trans. A 19A (1988) 427].
 
Article
The kinetics of ferrite to austenite phase transformation in 1005 steel during welding was quantitatively determined by a combination of phase mapping using X-ray diffraction and transport phenomena based numerical modeling. The results can be used to calculate the phase transformation rates under various thermal cycles for this steel.
 
Article
We have investigated the effects of He-ion irradiation on structures of FePt nanoparticles dispersed in thin films with amorphous Al2O3 matrix. The coarsening of FePt nanoparticles is suppressed under irradiation with 100 keV He+ ions at an elevated temperature, such as 923 K. The delay of particle growth is also recognized in the post-irradiation annealing. On the other hand, He-irradiation is of little assistance in promoting L10 ordering in the nanogranular films at a temperature as low as 573 K.
 
Article
The growth process of of (-1012) twins is studied in Magnesium using atomistic simulations. Two twin seeds are considered and both cases, a specific interface, which places face-to-face prismatic and basal planes, plays an important role. This interface has a low energy corresponding to a cusp in the orientation-dependent interface energy of a twinned bicrystal. This interface appears in several published twin structures and for instance accommodates the large deviations of twin interfaces from (-1012) planes reported recently [Zhang et al., Scr. Mater. 67 (2012) 862].
 
Article
An unusual fatigue behavior, observed in the α+β microstructures of the β-titanium alloy, Ti–10V–2Fe–3Al, is reported. It is the duality of the S–N fatigue curve where the fatigue data of specimens failing from cracks nucleated at the surface and subsurface regions grouped in to two separate S–N curves. The microstructural factors causing this effect are analyzed.
 
Article
Grain size in beta-solution treated Ti-10V-2Ye-3Al alloy has been shown to have a profound effect on the triggering stress of the stress induced martensitic (SIM) transformation. The triggering stress is shown to increase with increasing beta grain size up to a grain size of 300 mu m, after which it was found to become constant. Dependence of the triggering stress on beta grain size has been explained in terms of the free energy change during such a transformation. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
 
Article
Susceptibility to intergranular corrosion of asymmetric grain boundaries in pure copper was well correlated with a geometric criteria, i.e. the effective interplanar spacing of grain boundaries rather than coincidence site lattice (CSL) scheme if we rationally assume that the grain boundary structure relaxes to be formed by low-index planes, therefore resulting in high interplanar spacing.
 
Article
Friction stir-processing (FSP) was utilized to successfully disperse and embed nitinol particles in Al 1100 matrix. Directional residual stresses were introduced in the prepared material that consequently showed improved mechanical properties as found experimentally and through modeled results. No harmful interfacial products could be found in the material as a consequence of processing. The current work highlights the preparation and properties of this composite. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
 
Article
Friction stir welding (FSW) was applied to an accumulative roll-bonded (ARBed) Al alloy 1100. FSW resulted in reproduction of fine grains in the stir zone and small growth of the ultrafine grains of the ARBed material just outside the stir zone. Consequently, FSW effectively prevented the softening in the ARBed alloy.
 
Article
Cold-spraying of 1100 Al powder particles onto 1100 Al substrate was accomplished using carrier gases 100 vol.% He and a mixture of He–20 vol.% N2. TEM characterization correlates very well the occurrence of dislocations, presence of oxide, and surface instability phenomenon with observed mechanical and corrosion properties of the cold-sprayed coating.
 
Article
A detailed analysis of dislocations in a RuAl alloy following room temperature deformation indicates the presence of a significant density of 〈111〉 dislocations. The deformation behavior of this alloy with 2 at.% Pt is compared to other RuAl alloys and reasons for the presence of 〈111〉 dislocations, which are not preferred in high melting point B2 compounds, are explored.
 
Article
Oxidation of a Cu–2.2 at.%Al alloy (Cu–2Al) produces external scales containing Cu-oxides plus some alumina with almost no internal oxidation of aluminum. The addition of 3.9 at.%Cr to Cu–2Al has little effect on the oxidation behavior, while addition of 8.1 at.%Cr promotes a fast formation of an alumina layer in contact with the alloy with a simultaneous large reduction in the oxidation rate. This form of third-element effect, not related to the transition from internal to external oxidation of aluminum but to the inhibition of the copper oxidation, is attributed to the complete solubility between alumina and chromia.
 
The von Mises accumulated strain in one pass as a function of the n exponent of the flow line function.
Simulated textures obtained with discontinuous shear model and self consistent in Copper for Route A. (isovalues: 2, 3, 4, 6, 8, 10, 12, 16, 20, 24.)
Simulated textures obtained with flow line and self consistent in Copper for Route A with n=12,4,4. (isovalues: 2, 3, 4, 6, 8, 10, 12, 16, 20, 24.)
Article
A flow line function is proposed to describe the material deformation in ECAE for a 120\degree die. This new analytical approach is incorporated into a viscoplastic self-consistent polycrystal code to simulate the texture evolution in Route A of copper and compared to experimental textures as well as to those corresponding to simple shear.
 
Article
The industrial manufacturing of the long-length iron-pnictide wires and tapes requires simple and low-cost technology. Although the transport critical current density of the FeAs-122 tapes has already achieved the practical application level, their fabrication procedures are relatively complicated or required specialized instruments. Ag-sheathed Ba0.6K0.4Fe2As2 superconducting tapes were fabricated by the scalable rolling process. At 4.2 K and 10 T, the critical current density Jc has achieved 5.4x10^4 A/cm2. We ascribe the excellent performance to the high purity and homogeneity of the superconducting phase, high density and high c-axis texture of the superconducting core. Our method provides a simple way to scale up the production of the long-length iron-based superconducting tapes with high Jc.
 
Article
The effects of temperature on pressure infiltration of packed SiC particles by liquid Al and the eutectic Al–12wt.%Si alloy have been investigated over the temperature range 923–1273 K. Below 1173 K, the threshold pressure P0 for infiltration of pure Al slightly (and linearly) decreases with temperature. At that temperature a sharp drop occurs, followed by a faster decrease of P0. The contact angle θ derived from the threshold pressure data shows a similar behavior. Results for the Al–Si eutectic alloy are very similar for temperatures below 1173 K, but, above this temperature, the threshold pressure decreases faster than for pure Al. These results are consistent with contact angle data derived from sessile drop experiments. In addition compact permeability is significantly reduced for T > 1173 K, a result likely related to the reaction between aluminum and SiC.
 
Article
The γ/γ′ interfacial dislocation networks in a third generation and a fourth generation superalloy have been characterized after creep rupture at 137 MPa and 1100°C. The γ/γ′ interface in the fourth generation superalloy has dense interfacial dislocations acting as barrier for matrix slip dislocations. Meanwhile these interfacial dislocations are distributed homogeneously. The interfacial dislocation networks are morphologically different in the third and the fourth generation superalloys. In the third generation, the network is in a distortion state caused by dislocation reaction and climb. In the fourth generation, the network is in regular square shape. These factors are considered to contribute to the superior creep properties of the fourth generation superalloy.
 
Article
Microcompression specimens, 10–15 μm in diameter by 20–30 μm in height, were produced from individual parent grains in a polycrystalline U–13 at.%Nb shape-memory alloy using the focused ion beam technique. The specimens were tested in a nanoindentation instrument with a flat diamond tip to investigate stress–strain behavior as a function of crystallographic orientation. The results are in qualitative agreement with a single-crystal accommodation strain (Bain strain) model of the shape-memory effect for this alloy.
 
Article
Heat treatment produces the coherent precipitation of a 14H-type long period ordered (LPO) structure from a supersaturated α′-Mg matrix in Mg–Zn–Gd. Warm-extruded Mg96.5Zn1Gd2.5 (at.%) alloys with an LPO structure exhibited high tensile yield strength (345 MPa) and large elongation (6.9%), due to the refinement of α-Mg grains and the high dispersion of a hard LPO structure phase.
 
Top-cited authors
Kazuhiro Hono
  • National Institute for Materials Science
Nobuhiro Tsuji
  • Kyoto University
Isao Tanaka
  • University of Yamanashi
Ruslan Z Valiev
  • Ufa State Aviation Technical University
J.F. Nie
  • Monash University (Australia)