Search

Abstract: The structure of the hardening η′-phase precipitates in Al–Zn–Mg alloys has been investigated by using precession electron diffraction and X-ray synchrotron radiation diffraction. The latter was recorded as a three-dimensional, continuous intensity distribution from a single alloy grain, from which patterns of remarkable sharpness from the precipitate particles could be extracted. High resolution electron microscopy revealed extensive structural variations with prolific faults in the η′ precipitates. The η′-structures are described in terms of two structure models based on two icosahedral elements that are inherent in the equilibrium η-MgZn2 structure. The role of these icosahedra in the transformations of the alloy system is discussed. [Copyright &y& Elsevier]

A phase transformation in diamond into an intermediate carbon phase (ICP) was revealed in regions of maximal shear stress of diamond anvils. The transition was stimulated by additional stresses supplied to the compressed anvils with torque by a rotation of the anvil around the anvil's axis; maximal shear stress approached 55 GPa during the rotation. Creation of an ICP is considered as a mechanism of the stress-induced stability loss of the diamond structure. The characteristic Raman bands of ICP near 250, 500, 650-850 and 1050-1390 cm-1 were observed in the failure regions. [ABSTRACT FROM AUTHOR]

Metastable solid-solution Ti1− x Al x N thin films synthesized by plasma-assisted vapour deposition crystallize in the cubic NaCl structure with AlN mole fractions x ⩽0.7. Based on X-ray diffraction and ab initio calculations, we reveal that this critical value only slightly decreases to 0.69 with the addition of up to n =0.125mol fraction NbN to form cubic Ti1− x − n Al x Nb n N. During annealing in vacuum to 1450°C, the as-deposited single-phase cubic coatings decompose to form cubic Ti1− n Nb n N and wurtzite AlN. [ABSTRACT FROM AUTHOR]

The equilibrium viscosities of the Zr57Cu15.4Ni12.6Al10Nb5 and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 bulk metallic glasses are determined in three-point beam-bending experiments. The experimental data are described by the Vogel–Fulcher–Tammann equation. The fragility parameters are found to be 35.2 and 21.0, respectively. Viscosity measurements close to the glass transition show an initial relaxation into the supercooled liquid region, followed by partial crystallization of the amorphous matrix. This is evidenced by a dramatic increase in the viscosity into a new, metastable composition for longer annealing times. [Copyright &y& Elsevier]

Abstract: CoNiGa alloys have received considerable interest due to their high-temperature shape memory properties. Although there have been many investigations on the mechanical and magnetic behavior of these materials, little is known about the microscopic basis for the observed macroscopic behavior. In this work, we discuss the stability of Co2NiGa-based structures. The austenite phase is modeled as fully ordered L21 and as partially ordered B2. The stability of the austenite phase with respect to tetragonal distortions is examined. Lattice dynamics calculations suggest that the mechanism for the transformation is different from that of the much more studied and chemically similar Ni2MnGa shape memory alloy (SMA). The electronic basis for the observed metastability of the cubic Co2NiGa austenite is found to be qualitatively different from that observed in other ferromagnetic SMAs, especially Ni2MnGa. [ABSTRACT FROM AUTHOR]

Abstract: The goal of this study is to clarify the effect of the addition of Al2O3 on the grain boundaries of yttria stabilized zirconia using high resolution transmission electron microscopy. Basically excessive concentration of alumina, which is not solved in YSZ, segregates within YSZ matrix. Alumina segregates as grains between YSZ grains and as particles within YSZ grain boundaries. t′ metastable phase was detected within the grains of the sintered YSZ powders. By adding alumina into the primary YSZ powders and sintering it all together, metastable tetragonal phases appear in the grain boundaries between YSZ and segregated alumina grains. Similar phenomenon was detected in the boundaries of the two neighboring grains of YSZ doped with Alumina. Appearance of these phases might be due to the accumulated strain energies which are generated because of the alumina segregation into grain boundaries and matrix of YSZ. Hence, by controlling the dopant concentration, it could be possible to form YSZ structured by t′ metastable phase. Fabrication of this material is in the great attention of the high temperature applications due to the high resistive properties of the t′ metastable phase against high temperature degradation of the YSZ. [ABSTRACT FROM AUTHOR]

Abstract: First-principles pseudopotential calculations have been performed to investigate the structural phase transition, electronic and elastic properties of SrSe considering several possible structural phases. Our calculations show that SrSe crystalizes in NaCl-type (B1) structure at ambient pressure and undergoes first-order phase transition to CsCl-type (B2) structure at 13.7GPa with a relative volume collapse of 10.37%, and no further transition is found up to 40GPa, the highest pressure attempted in the calculations. For metastable phase, SrSe prefer h-MgO instead of wurtzite (B4) structure, which is consistent with the fact that the ionic compound prefers a high coordination. The influence of the crystallographic structure and the hydrostatic pressure on elastic constants and energy band structures of SrSe have also been investigated. Our calculated results are discussed and compared with available experimental and theoretical data. [Copyright &y& Elsevier]

We report the nonlinear elastic deformation behaviour of Ti–30Nb–12Zr alloys containing varying amounts of oxygen and/or nitrogen. These alloys feature an electron/atom (e/a) ratio of ∼4.19, in between the e/a values of two groups of multifunctional titanium alloys reported previously (Gum Metal ∼4.24 and Ti2448 ∼4.15), and thus demonstrate an independence of the nonlinear elasticity on the e/a ratio. This study also found that the nonlinear elasticity persists in this type metastable β titanium alloys regardless of the presence of a small amount of other phases such as α, α′′ and ω. [Copyright &y& Elsevier]

Abstract: In this study, the metastable beta Ti–12Mo (wt.%) alloy was synthesized by the cold crucible levitation melting (CCLM) method and then quenched in water from the beta domain. The tensile test carried out on the as-quenched alloy showed an important ductility reaching 45% of elongation before fracture. From the as-quenched metastable beta state, non-isothermal electrical resistivity and dilatometry measurements were carried out to detect the phase transition in order to control the nanophase precipitation sequence. After heating, XRD analysis and TEM observations revealed a very fine nano-scale omega and alpha precipitation in the beta matrix. Tensile test results indicated a very high strengthening effect after appropriate thermo-mechanical treatments, which was observed particularly huge after a two-step annealing process where a tensile strength as high as around 1600MPa was obtained. This highly enhanced tensile strength was attributed to the complex intragranular nanostructure observed by TEM consisting of two-scale alpha nanoprecipitates inside sub-micrometer beta grains. [Copyright &y& Elsevier]

Abstract: Eutectic composition Cu–Ag alloy thin films were prepared by co-deposition at room temperature onto oxidized Si substrates by thermal evaporation. Morphological development, structure and phase state of the films were investigated by transmission electron microscopy. The films possess fibre morphology 10–30nm in diameter and strong <111> texture is present. The fibres are nanocrystalline composed of 2–3nm size zones of Cu and Ag rich solid solution phases and a model for morphological development and phase separation is described. In the early stages of growth phase separation occurs by nucleation in melted islands and a eutectic of randomly oriented crystallites forms. In later stages of growth the phase separation takes place by spinodal decomposition. It results in a strain stabilized unique morphology corresponding to an intermediate stage of phase separation. [Copyright &y& Elsevier]

Solution nitriding was applied to type 304 stainless steel plate to make the austenite phase in the surface layer stable against cold rolling. Through this treatment, we could produce a structure-gradient stainless steel plate where an austenitic structure exists in the surface layer while a large fraction of deformation-induced martensitic structure is dispersed inside the plate. This surface-layer microstructure control significantly suppressed the permeation of hydrogen from the atomosphere owing to the low diffusivity of hydrogen in the stable austenitic surface layer. [Copyright &y& Elsevier]

In this paper, a low dimensional model is constructed to approximate the nonlinear ferroelastic dynamics involving mechanically and thermally-induced martensite transformations. The dynamics of the first order martensite transformation is first modeled by a set of nonlinear coupled partial differential equations (PDEs), which is obtained by using the modified Ginzburg-Landau theory. The Chebyshev collocation method is employed for the numerical analysis of the PDE model. An extended proper orthogonal decomposition is then carried out to construct a set of empirical orthogonal eigenmodes of the dynamics, with which system characteristics can be optimally approximated (in a specified sense) within a range of different temperatures and under various mechanical and thermal loadings. The performance of the low dimensional model is analyzed numerically. Results on the dynamics involving mechanically and thermally-induced phase transformations and the hysteresis effects induced by such transformations are presented. [ABSTRACT FROM AUTHOR]

Ab initio calculations are employed to demonstrate a strong pressure dependence of the maximum AlN mole fraction preserving the cubic phase in Ti1− x Al x N and Cr1− x Al x N hard coatings before transforming to the wurtzite structure. Under a compression of 4GPa an increase by ∼0.1 AlN mole fraction is obtained for both systems. Consequently, stress-related effects cannot be neglected in the discussion of the wide spread of experimentally obtained stability ranges. [Copyright &y& Elsevier]

Abstract: Using first-principles total energies and frozen phonon calculations, we predict the thermodynamic properties (enthalpies of formation and vibrational entropies) for three phases in the Al–Mg–Si system: the stable phase (β-Mg2Si), and two metastable precipitate phases ( and ). The stable and the metastable and phase boundaries are obtained from a combination of the Gibbs energy of the compounds determined from first-principles and the free energy of the Al-rich solid solution (fcc phase) taken from the literature. Predicted phase boundaries show good agreement with available phase stability measurements. The present work demonstrates the capability of first-principles calculations in predicting Gibbs energies of stable and metastable phases. [Copyright &y& Elsevier]

Through the systematic replacement of Co for Cu as a β-Ti phase stabilizer in the γ-TiCu alloy, a wide range of (β + γ) two-phase microstructures can be prepared in the Ti50Cu50-xCox alloys. Enhanced yield strength (>850 MPa) combined with high ductility (>22%) of the Ti50Cu40Co10 alloy is attributed to the formation of micron-scaled β dendrites embedded in the γ matrix. By controlling the volume fraction of the β dendrites, simultaneous increases in strength and ductility can be effectively achieved. [ABSTRACT FROM AUTHOR]

Abstract: X-ray photoelectron spectroscopy (XPS) is a standard method of determining chemical bonding in e.g. nanocomposites. We demonstrate that sputter-cleaning of the sample prior to analysis can substantially alter the attained information. We present an in-depth analysis of sputter damage on binary and ternary TiC-based coatings in the Ti–Ni–C system. XPS was performed after sputter etching with different ion energies (0.15–4keV). Results are compared to data from the bulk of undamaged samples attained using high kinetic energy XPS. We observe substantial sputter damage, strongly dependent on sputter energies and coating stability. Metastable samples exhibit severe sputter damage after etching with 4keV. Additional samples from other Ti–Me–C (Me=Al, Fe, Cu or Pt) systems were also examined, and notable sputter damage was observed. This suggests that accurate analysis of any metastable nanocomposite requires careful consideration of sputter damages. [Copyright &y& Elsevier]

We report interesting microscopic features that evolve as a function of electron dose from the starting aluminum trihydroxide to the resulting transition aluminas with layered mesoporous structures. Remarkably, the sizes of pores and crystals in the porous structure were reduced as the electron dose was increased. The properties of the layered structure from the aluminum trihydroxide were maintained through the transition process, and hence the final mesoporous structures (mainly γ-alumina) were of lamella-type microstructure. [Copyright &y& Elsevier]

The self-consistent electronic structure calculations were carried out with the accurate frozen-core full-potential projector augmented-wave method on 13 Ni-Pt intermetallic compounds of simple crystalline structures, i.e. A15, D019, D03 and L12 Ni3Pt and NiPt3, and α-NiAs, B1, B2, L2 a , and L10 NiPt. The calculations reveal that the L12 Ni3Pt, L10 NiPt and L12 NiPt3 are energetically more stable than their respective competitive structures, indicating that the three structures may be formed in some appropriate conditions. The obtained results match well with the experimental observation or other theory predictions. It is found that there is hybridization between Ni 3 d and Pt 5 d states, which may significantly affect the structural stability and magnetism of metastable Ni-Pt intermetallic compounds. [ABSTRACT FROM AUTHOR]

Abstract: Co,Ti-substituted Ba-hexaferrite (BaCoTiFe10O19) coatings for applications as microwave absorbers were deposited by the APS and HVOF techniques, using BaCoTiFe10O19 powders manufactured by solid-state reaction followed by spray-drying. The SEM+EDX, XRD and micro-Raman analyses indicated that impact quenching of molten agglomerates on the substrate hindered the crystallisation of the hexaferrite structure, resulting in poor magnetic properties of the coatings. Adjusted processing conditions enabled the deposition of a coating retaining enough hexaferrite phase, whose magnetic properties, close to bulk BaCoTiFe10O19, are very promising for electromagnetic wave absorption. [Copyright &y& Elsevier]

Within the framework of the medium-field approximation, it has been shown that lattice relaxation can stabilize a solid solution relative to small fluctuations of the composition, causing the kinetics of spinodal decomposition of the alloy to substantially change. The metastable state diagram has been constructed and the kinetics of transformations with allowance for the lattice relaxation has been investigated. It has been found that the decomposition develops by the mechanism of growth of eutectoid-type colonies or twin lamellas from the region with a disturbed homogeneity. [ABSTRACT FROM AUTHOR]

Abstract: A plate-like Zr-based bulk metallic glass (BMG) was prepared by using a copper mold suction casting and an X-ray diffractometer (XRD) was utilized to determine its structure. Co ion implantation was carried out in a MEVVA source system. The influences of Co ion implantation on thermal stabilities and non-isothermal crystallization behaviors of the BMG were studied via a differential scanning calorimeter (DSC). The results show that Co ion implantation lowered the BMG''s glass transition and crystallization onset temperatures, meanwhile, enhanced its super-cooled liquid regions. After Co ion implantation, crystallization behavior of the BMG changed from a single-stage precipitation process to a two-stage crystallization precipitation process. The apparent activation energies for glass transition and crystallization were enhanced. The crystallization process of the as-implanted specimen was relatively laggard compared to that of the as-cast one. The crystallization of the latter was typical nucleation and growth mechanism, while that of the former was interaction of annihilation of the free volumes, reduction of voids, short-range rearrangement caused by high energy implanted Co ions, various unknown complicated energy deliveries as well as nucleation and growth of crystalline grains. [Copyright &y& Elsevier]

Abstract: Precipitate evolution in friction stir welding of 2219-T6 aluminum alloys was characterized by transmission electron microscopy. In the weld nugget zone and the thermo-mechanically affected zone some metastable precipitates overaged to equilibrium phase while others solutionized into the aluminum solid solution. In the heat-affected zone the precipitates coarsened. [Copyright &y& Elsevier]

Significant benefits of either heterogeneous microstructures or deformation-induced martensitic transformation (DIMT) in metallic materials stem from their superior strain hardening and tensile properties. Herein, we present an unprecedented strain hardening behavior at 77 K in a ferrous medium-entropy alloy comprising a metastable face-centered cubic (FCC) bimodal microstructure with different grain sizes. Pre-straining yields fine body-centered cubic (BCC) martensites, and subsequent heat treatment causes reverse martensitic transformation from BCC to FCC, affording the bimodal FCC microstructure. Furthermore, the yield strength is enhanced due to the presence of submicron FCC grains and geometrically necessary dislocations (GNDs) that are generated during the pre-straining. Profuse GNDs in reversely transformed FCC promote DIMT. Moreover, when true strain exceeds 0.2, widespread DIMT in the interior of the remaining FCC drastically increases the strain hardening rate and consequently delays necking. The outstanding tensile properties derived from this thermomechanical process are because of the DIMT and hetero-deformation-induced strengthening. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses the structural and compositional changes at the nanometer scale associated with the nucleation and growth of α precipitates in the β titanium alloy Ti-5553 (Ti–5Al–5Mo–5V–3Cr–0.5Fe) with ω precipitates acting as heterogeneous nucleation sites. The microstructural evolution in this alloy, during β-solutionizing, quenching and aging type heat-treatments, has been investigated by combining results from scanning electron microscopy, orientation imaging microscopy, transmission electron microscopy, high-resolution TEM and three-dimensional atom probe (3DAP) tomography. Athermal ω precipitates form in this alloy on quenching from above the β transus temperature. On isothermal annealing at low temperatures, these ω precipitates coarsen to form chemically ordered ω precipitates, accompanied by the nucleation of the stable α phase. Annealing at higher temperatures leads to dissolution of ω and further growth of α precipitates accompanied by clustering of different α variants in self-accommodating morphologies. 3DAP results indicate that annealing at lower temperatures (∼350°C) leads to initial nucleation of α precipitates with a non-equilibrium composition, nearly identical to that of the β matrix. Subsequent aging at higher temperatures (∼600°C) leads to more pronounced partitioning of alloying elements between the two phases. These results indicate that the structural body-centered cubic to hexagonal close-packed transformation and the compositional partitioning of alloying elements occur in sequential steps, resulting in a mixed-mode displacive-diffusional transformation, similar to the bainite transformation in steels. [Copyright &y& Elsevier]

Abstract: Yttria-doped zirconia (YDZ) thin films with nanometric sized grains were prepared by reactive RF sputtering and their oxygen ion conductivities were systematically measured as a function of yttria doping with levels in the range 0.5–9.1mol.% Y2O3. Enhanced oxygen ion conductivities, as derived from impedance spectra, were observed when compared with values reported for bulk YSZ. Furthermore, the peak conductivity for the YDZ films was observed to occur at considerably reduced yttria levels, i.e., at 6.5mol.% Y2O3 (for T >∼400°C) and at 3.2mol.% Y2O3 (for T <∼300°C) vs. 9mol.% Y2O3 in bulk YSZ. Based on an analysis of the Raman spectra, these results are believed to result from the extended meta-stability of the cubic phase to reduced yttria levels at nanometric grain sizes. [Copyright &y& Elsevier]

Transmission electron microscopy has been used to study the precipitates that develop in the A2 phase of an Nb–Mo–Cr–Al–Si alloy upon heat treatment. The precipitates include a Laves-phase that adopts the cubic C15 structure initially and the hexagonal C14 structure in the later stages of precipitation. The morphologies, orientation relationships and defect microstructures indicate that the metastable C15 phase arises due to tensile coherency stresses and that a synchroshear polymorphic transformation to the equilibrium C14 phase occurs as these relax. [Copyright &y& Elsevier]

Abstract: We have performed in situ synchrotron X-ray diffraction experiments to assess the influence of aluminium and phosphorus on the austenite stability in low-alloyed transformation-induced plasticity steels during the high-temperature bainitic holding and the subsequent martensitic transformation during cooling to temperatures between room temperature and 100K. Although the addition of aluminium increases the chemical driving force for the formation of bainitic ferrite plates significantly, the phosphorus exerts a larger influence on the bainitic transformation kinetics. Consequently, the addition of phosphorus leads to a higher degree of carbon enrichment and a narrower grain volume distribution of the metastable austenite. The stability of the individual austenite grains with respect to their martensitic transformation depends on both the local carbon content and the grain volume for austenite grains smaller than 20μm3. The presence of aluminium and phosphorus further stabilizes the austenite grains. [Copyright &y& Elsevier]

Abstract: The effects of surface confinement on the kinetics of ordering in fcc alloy films are studied by the Monte Carlo method. Under weak surface confinement, there are two kinds of kinetic path for alloy films with even layer. One is the films directly relaxing to the equilibrium state, the other is the films relaxing to a metastable state first. Even for the same initial atomic configuration, the kinetic path of ordering is randomized, and the possibility that the films relax to a metastable state is independent with the initial atomic configurations. We attribute this randomicity to the competition between surface confinement and chemical ordering. The evolution of the metastable state to the equilibrium state is also simulated. The results indicate that an alloy film with weak surface segregation can easily be trapped into metastable state. [Copyright &y& Elsevier]

Structural transformations in extended solids result from local atomic rearrangements and phase growth mechanisms. A broad class of technologically relevant properties critically depends on local structural issues connected with domain sizes, domain boundary geometries, and defects. However, a precise understanding of structural transformation mechanisms and domain formation is still an open question. Here, we demonstrate the feasibility of very detailed mechanistic investigations in real materials as a prerequisite for intelligent property control. We address the problem of domain fragmentation in bulk CdSe under pressure, jointly by molecular dynamics simulations, high-pressure experiments, and HR-TEM imaging. We show that domain fragmentation is taking place in the high-pressure regime, where nucleation events generate both zinc blende (B3) and wurtzite (B4) structural motifs and, in turn, cause the final lamellar appearance observable by highresolution TEM. A changed nucleation pattern and a modified B3/B4 ratio represents the system's response to modified external stress conditions. [ABSTRACT FROM AUTHOR]

Transition aluminas induced by electron-beam irradiation from an aluminum trihydroxide were quantitatively investigated. After the transition of an aluminum trihydroxide initiated at a threshold value of an electron dose, the advent of the major phase in each transition step depended on the total electron dose. The transition process can be categorized into a three-stage transition: (A) rapid dehydration (χ-alumina) →(B) gradual dehydration (γ-alumina)→(C) nanocrystallization (γ- and σ-alumina). [Copyright &y& Elsevier]

Abstract: Using in situ digital image correlation to obtain full-field measurements, we study the intermartensitic transformations in single-crystal NiFeGa. Full-field strain measurements identify the coexistence of modulated martensite phases during the first plateau of the multistage stress–strain curve at room temperature. At a higher temperature, the measurements indicate the bypassing of one of the modulated phases. Strain as high as 13% is measured as a result of the transformation to the intermediate monoclinic modulated and final tetragonal phase. Based on the full-field strain measurements, the phase fractions during the nucleation and the progression of the transformation are obtained. The evolution of the local strain and the phase fractions prove critical in explaining strain softening, hysteresis and other phenomena observed in the stress–strain curves. [Copyright &y& Elsevier]

Abstract: The effect of composition and metal sublattice population on the phase stability, structure and elastic properties of cubic (c), hexagonal (h) and orthorhombic spin-polarized Cr1– x Al x N was studied using ab initio calculations. Excellent correlation between ab initio and experimentally obtained lattice parameters and elastic constants was obtained. The energy of formation suggests that the cubic phase can be stabilized for x in the range 0.48–0.75, depending on the metal sublattice population. The broad range of x, which is also observed in experiments, can be understood by considering the Al distribution induced changes in the configurational contribution to the total energy. [Copyright &y& Elsevier]

The effects of plastic strain on deformation-induced martensitic transformations have been investigated experimentally. Austenitic metastable stainless steel samples were heated to a temperature at which the transformation is suppressed and were plastically strained to different amounts. The resulting pre-strained material was cooled to room temperature and a tensile test was conducted during which transformation was monitored via a magnetic sensor. Results of these tests are discussed concerning the existing theories that describe the mechanically induced martensitic transformation phenomenon. [Copyright &y& Elsevier]

Abstract: Stress-induced martensitic transformations are clarified in classes of NiMnGa alloys which undergo the stress-free, thermal-induced inter-martensite transformation austenite (A)⇌pre-martensite (PM)⇌martensite. This study implements a comprehensive experimental approach, including analysis of the strain–temperature and stress–strain response, which discloses stress-induced inter-martensite transitions. The evolution of the transitions is elucidated using in situ digital image correlation (DIC) measurements of meso-scale strain fields. Under stress, this body of work unequivocally demonstrates that the transformation path becomes A⇌PM⇌I⇌10M. The I-phase is an intermediate stress-induced martensite with a modulation period between three and five-layers. Owing to the intermediate transition, the thermal hysteresis in the strain–temperature response is tiny (<10°C) compared with the hysteresis (32°C) for A⇌10M. The differential hysteresis levels are rationalized based on a thermo-mechanical formulation. Meso-scale DIC measurements quantify inter-martensite strain levels, which are indistinguishable from macro-scale stress–strain and strain–temperature responses. [Copyright &y& Elsevier]

The Clausius-Clapeyron coefficient (CCC or αCC) or relation of the stress to transform a thermoelastic SMA sample and temperature, is revisited for 1-dimensional stressed SMA when polycrystalline materials are used. The experimental method is discussed in the frame of equilibrium thermodynamics for polycrystalline materials. Suggestions for evaluation of the experimental value in polycrystalline NiTi and CuAlBe specimens are proposed. The analysis for NiTi wire gives a CCC of αCC=6.3±0.3 MPa K−1. On the other hand CuAlBe provides a value of αCC=2.2±0.4 MPa K−1 for tensile stress. [ABSTRACT FROM AUTHOR]

Abstract: Although, bulk metallic glasses exhibit remarkable mechanical, physical and chemical properties, their critical size (the largest size of fully glassy sample produced by casting) is limited. The utilization of a welding technique enables producing larger glassy samples. Ni53Nb20Ti10Zr8Co6Cu3 glassy alloy ribbon samples prepared by melt spinning of the pre-alloyed arc-melted ingots were welded by the electron-beam and fiber laser-beam welding techniques. The detailed structural investigations of the welded bead and thermally affected zone were performed by micro-area X-ray diffractometry, scanning and transmission electron microscopy. At certain optimized welding conditions the amorphous structure can be retained after melting. The obtained data are promising for future applications of the laser and electron-beam welding techniques to glassy alloys. [Copyright &y& Elsevier]

Abstract: The method of molecular dynamics has been used to calculate the pressure, internal energy and isochoric heat capacity of the Lennard–Jones fluid for 208 states in the range of temperatures 0.35≤ k B T/ɛ≤2.0 and densities 0.001≤ ρσ 3 ≤1.2. The array of data obtained, along with stable states, includes homogeneous metastable states (supersaturated vapor, superheated and supercooled liquid). Spinodals of supersaturated vapor and superheated liquid have been approximated. In a stable region the data obtained are compared with the results of previous papers. The behavior of thermodynamic properties of the fluid in the event of homogeneity disturbance and formation of micro-heterogeneous (“two-phase”) states has been considered. [Copyright &y& Elsevier]

Abstract: In situ three-dimensional (3-D) X-ray diffraction experiments have been performed at a synchrotron source on low-alloyed multiphase TRIP steels containing 0.25 wt.% Si and 0.44 wt.% Al and produced with different bainitic holding times, in order to assess the influence of the bainitic transformation on the thermal stability of individual austenite grains with respect to their martensitic transformation. A detailed characterization of the austenite grain volume distribution at room temperature was performed as a function of the prior bainitic holding time. In addition, the martensitic transformation behaviour of individual metastable grains was studied in situ during cooling to a temperature of 100K. Both the carbon content and the grain volume play a key role in the stability of the austenite grains below 15 μm3, while the carbon content exerts the dominant effect in the stability of the bigger grains. Measurements also suggest that the tetragonality of the thermally formed martensite is suppressed. [Copyright &y& Elsevier]

Abstract: The SAFE ICE project, supported by the European Commission, addresses and overcomes specific scientific and technological hurdles to make an informed judgment on the relevance of food related effects of High-Pressure in the Low-Temperature (HPLT) domain as well as to realize and to deliver their full benefits to the end users. Such hurdles include the lack of systematic data, and a limited understanding related to the mechanisms involved in phase transitions under pressure at subzero temperatures. The project involves seven partners, bringing together academic and research centres with food industry and equipment manufacturing parties. The main findings of the research carried out in the frame of the project are: the systematic compilation of thermophysical properties of water, aqueous model solutions and model foods to be applied in mathematical models able to reproduce and predict freezing and thawing time profiles at high pressure; the comprehension of the kinetics of phase transition phenomena at HP, including the definition of metastable phases; a key to define critical processing parameters to obtain optimized freezing and thawing paths; the study of the effect of HPLT on key food spoilage enzymes and on microorganisms; the study of consumer acceptance of the technology; the evaluation of the impact of SAFE ICE processes on food quality related parameters and the development of prototypes (HPLT microscopic cell and HPLT differential thermal analysis cell) and process and products concepts for industrial development of SAFE ICE processes. [Copyright &y& Elsevier]

Abstract: Formation of shear bands and strain-induced ε- and α′-martensite phases during tensile deformation of austenitic stainless steels was studied. Stacking fault energies (SFE) of the studied steels were measured by X-ray diffraction. Effects of external stress and SFE on the width of the stacking faults were analysed. An excellent correlation between the calculations and actual microstructures examined by scanning electron microscopy was found. Effect of overlapping of stacking faults on the fault width was discussed. Based on the discussions and experimental results, compositional, temperature and strain rate dependencies of the strain-induced α′-martensite transformation are believed to be governed mainly by the variation in the SFE. [Copyright &y& Elsevier]

Abstract: Using a model amorphous alloy series, Zr2Cu1− x Pd x (x =0, 0.25, 0.5, 0.75 and 1), we demonstrate that ab initio calculations can predict likely metastable phase formation during devitrification by comparing these with time-resolved X-ray scattering studies. All compositions share the same equilibrium C11b phase, yet they follow different devitrification pathways. Only x =0.5 leads to a metastable C16 phase formation. This corresponds precisely to calculations showing the C16 phase is closest in energy to the stable C11b phase. The competition is shown to be dominated by electronic structure rather than size effects, with the favored composition for the C16 phase forming a pseudo-gap at the Fermi energy. All Pd-containing compounds devitrify first into a quasicrystalline phase. Zr2Cu1− x Pd x compounds based on the NiTi2 structure are higher in energy relative to the C16 and C11b structures for all compositions, and the calculations show no increase in stability with Pd concentration. [Copyright &y& Elsevier]

It was found that Sm–Fe alloys with the Sm5Fe17 phase can be obtained by annealing of the amorphous melt-spun ribbon. Unlike the Nd5Fe17 phase, the hard magnetic Sm5Fe17 phase was found to be the metastable phase. Thermomagnetic studies revealed the Curie temperature of the Sm5Fe17 phase to be 550K. The resultant annealed melt-spun ribbon exhibited a large coercivity value of 2.9MAm−1 at room temperature and 5.0MAm−1 at 4K. [Copyright &y& Elsevier]

This short review covers some particular aspects of the production of new materials under high pressures. Despite the fact that there is an extremely wide range of new high-pressure synthesized substances with unique properties, a commercial synthesis has been used up to date only for producing superhard materials - these are real treasures of today's industry. At the same time, as should be underlined here, high-pressure experiments often give scientists material with helpful hints of what new intriguing substances can exist in principle. This is true both for new superhard, semiconducting, magnetic, superconducting, optical materials already synthesized under pressure and a large number of hypothetic new polymers from low-Z elements. [ABSTRACT FROM AUTHOR]

A determination of the enthalpy increments for single phases of polymorphs through exact calorimetric measurements of respective heat capacities in stable and metastable regions, determination of the enthalpy increments for the liquid phase through dynamic measurements in the glassy state and separate measurements of the heat of fusion of polymorphs created precise data base which permitted to use the heat-of-fusion rule in a rigorous way and to verify univocally that the polymorphs III and I in carbamazepine form an enantiotropic system. The approach elaborated in the present study can be used in identification of all difficult polymorphic systems, where the solid-solid transitions have a complicated nature, are kinetically driven or hindered by other constraints. [ABSTRACT FROM AUTHOR]

Metastable Ti1−x Al x N thin films synthesized by plasma-assisted vapour deposition crystallize in the industrially preferred cubic NaCl (c) structure with AlN mole fractions (x)⩽0.7. We reveal, via X-ray diffraction and transmission electron microscopy, that the addition of yttrium to c-Ti1−x Al x N shifts the solubility limit to lower AlN contents, resulting in mixed c- and hexagonal ZnS–wurtzite (w) phase (Ti1−x Al x )1−y Y y N coatings. Ab initio calculations yield a ∼23% decrease in the solubility limit in c-Ti1−x Al x N, from x ∼0.69 to 0.56 with the addition of y =12.5at.% Y. [Copyright &y& Elsevier]

Abstract: The strain–temperature response of Ni–Fe–Ga single crystals underscores the role of the inter-martensitic transformation in creating intersecting heating and cooling segments; the separation of these segments occurs due to irreversibilities at high stresses and at high temperatures. An ultra-narrow tensile (1°C) and compressive (<10°C) thermal hysteresis are observed for the A ⇌10M ⇌14M case, accompanied by a small stress hysteresis (<30MPa) in compressive and tensile stress–strain responses. The hysteresis levels increase and the intersecting segments disappear at high stresses and at high temperatures. This paper reports the use of a thermo-mechanical formulation to rationalize the role of inter-martensitic transformations. Plotting the transformation stress as a function of temperature indicates that inter-martensitic transformations enable a very wide pseudoelastic temperature range, as high as 425°C. The measured Clausius–Clapeyron curve slope in compression (2.75MPa°C−1) is eight times the tensile slope (0.36MPa°C−1); the higher slope is attributed to the predominance of A ⇌ L10 at high temperatures. [Copyright &y& Elsevier]

Abstract: Co metastable structures are formed in Co–Ag alloy films with the aid of glancing incident ions during deposition. The structures of Co are characterized by X-ray absorption near-edge structure (XANES) spectroscopy at the Co K-edge. The results indicate that two kinds of Co phases coexist in every film. One is α-Co or β-Co and the other is named fcc-II with a =4.06Å. It is thought that the stress between Co and Ag clusters induces the formation of β-Co and the fcc-II phase. The role of glancing incident ions is to trigger a collision cascade on the surface and to facilitate both thermodynamics and kinetics aspects of cluster mixing. [Copyright &y& Elsevier]

Nematogenic trans 4'-n-hexyl-4-cyclohexyl-1-thiocyanophenyle was studied using differential scanning calorimetry (DSC) and polarizing microscopy. Melting was observed in DSC at two peaks with various intensities depending upon the thermal history of the sample. After cooling to temperatures lower than 262 K double melting at 283.4 K (more intense) and 285.4 K (weaker) was noticed. The cooling to temperatures slightly higher than 262 K resulted in two peaks of equal intensity, further increasing of this temperature showed the domination of melting at the higher peak. Observations of melting starting from 269 to 276 K were leading to a single peak at 286 K. DSC results were confirmed by polarizing microscopy observations: three different textures were observed for the crystal, intermediate (also crystalline) and nematic phases. Moreover at lower temperatures on heating one could observe two extra coupled transitions (endothermic and exothermic ones). [ABSTRACT FROM AUTHOR]

Abstract: The solidification of concentrated alloys containing ordered compounds is less well understood. These alloys often exhibit complex phase change like peritectic reaction during liquid to solid transformation. The Fe-rich part of Fe–Ge binary alloy system consists of several critical points and ordered–disorder transitions and can be used as a model system to study the effect of departure from equilibrium on the solidification microstructure. In order to understand the phase selection and morphological transitions, undercooling and recalescence behaviour; growth rate of the solidifying phases and microstructure need to be explored. In the present paper, we summarise the results obtained in several iron rich alloy compositions (Fe–(14–25)at.% Ge) using techniques of melt quenching, levitation and laser resolidification. These results provide insight to the current theories of dendritic growth and reveals possibility of a new pathway for phase evolution in peritectic alloys at high undercooling involving a massive transformation. [Copyright &y& Elsevier]

Abstract: The total energies and lattice constants of binary hcp- and fcc-TiN, AlN and ternary Ti0.5Al0.5N phases are calculated by ab initio method using the Vienna ab initio simulation package (VASP). The values of total energies are then used to calculate the lattice stabilities of binary hcp- and fcc-TiN, AlN and the interaction parameter of ternary Ti1−x Al x N phases on the basis of the semiempirical, thermodynamic sub-lattice model. Based on these data, the Gibbs free energy diagram of the immiscible quasi-binary TiN–AlN system are constructed in order to discuss the relative phase stability of the metastable ternary hcp- and fcc-Ti1−x Al x N phases over the entire range of compositions. The prediction is compared with the published results from PVD and CVD experiments. The calculated lattice energy and the constructed Gibbs free energy diagram show, in agreement with the experiments, that metastable fcc-Ti1−x Al x N coatings can easily undergo spinodal decomposition into coherent fcc-TiN and fcc-AlN, but there is a relatively large barrier for the formation of the stable hcp-AlN. A comparison with the TiN–Si3N4 system shows that, due to the much higher de-mixing energy of this system as compared to the TiN–AlN one, spinodal decomposition may occur in that system also for semicoherent TiN and Si3N4 phases. [Copyright &y& Elsevier]