Nucleation Of New Phase Research Articles

Damage-failure transition in titanium alloy Ti-6Al-4V under dwell fatigue loads

The role of structural mechanisms responsible for the consequent staging of damage-failure transition as the combination and continuity of ductile and creep kinetics of the structure evolution and the modeling in dwell fatigue regime. Damage-failure transition is considered as critical phenomena, the structural-scaling transition, when the damage develops as specific phase with characteristic stages: nucleation of new phase and the phase growth kinetics. In the case of dwell fatigue, the nucleation stage is associated with slip localization, faceting, voids and microcrack initiation; the phase growth kinetics has the relation to specific non-linearity of the free energy release responsible for the staging of damage-failure transition. Statistically based phenomenological model of damage-failure transition specified the links of macroscopic material parameters with structural parameters responsible for the influence of microstructure on the structure sensitive mechanical properties. The developed conception of modeling of Ti alloys based on the duality of damage kinetics in dwell fatigue loads allowed us to propose the strategy of structural study to provide in perspective the links of structural parameters of /phases with phenomenological parameters responsible for different mechanisms of damage accumulation at LCF and stress hold regimes.

Direct Observation of Vacancy-Cluster-Mediated Hydride Nucleation and the Anomalous Precipitation Memory Effect in Zirconium.

Controlling the heterogeneous nucleation of new phases is of importance in tuning the microstructures and properties of materials. However, the role of vacancy-a popular defect in materials that is hard to be resolved under conventional electron microscopy-in the heterogeneous phase nucleation remains intriguing. Here, this work captures direct in situ experimental evidences that vacancy clusters promote the heterogeneous hydride nucleation and cause the anomalous precipitation memory effect in zirconium. Both interstitial and vacancy dislocation loops form after hydride dissolution. Interestingly, hydride reprecipitation only occurs on those vacancy loop decorated sites during cooling. Atomistic simulations reveal that hydrogen atoms are preferentially segregated at individual vacancy and vacancy clusters, which assist hydride nucleation, and stimulate the unusual memory effect during hydride reprecipitation. The finding breaks the traditional view on the sequence of heterogeneous nucleation sites and sheds light on the solid phase transformation related to vacancy-sensitive alloying elements.

Short review on mechanical activation in non-metallurgical alumina production

The terms mechano-chemistry and mechanical activation of solid materials were introduced in chemical literature by Ostwald at the beginning of the XX century. Both terms cover a whole range of interconnected phenomena taking place during the mechanical action on solids or their separate parts participating in chemical reactions, phase transitions, mixing and creating composite materials, alloying and crystal growth in the solid state, deformation and changing physical and thermal properties, all of them at low temperature. The common effects of the mechanical activation on solid material are fracturing and reduction of particle sizes, generation of new reactive surfaces, diffusion of atoms of the reactant phase through the product phase, and quite significantly, accumulating energy in crystalline or amorphous structure (enough twists in atomic and molecular networks, tensions in atomic bond and active sites to trigger the nucleation of new phases). Mechanical activation is very used to produce all clean alumina mineralogical phases with uniform particle size dimensions from nano to macro size. Also, mechanical activation may extend the specific surface of some minerals, enhancing the yields in the solid-liquid extraction process. With adequate precursors, all phase transitions from amorphous to alfa α-Al2O3 can be carried out on the same route as in thermally activated alumina, but some other routes, impossible by thermal activation, might be followed. The difference between the two activation ways is that mechanical activation is made at room temperature.

Nucleation of New Phases in Alloy: A Long Way to True

The article presents our generalization of electron microscopy results that got for binary and some ternary alloys based on Ni. These results are considered as the basis for the conclusion that chemical bonds between atoms are realized in binary alloys according to the principle of pair-wise chemical interaction. In ternary alloys, such a process begins with the separation of the liquid alloy into diffusion micro-pairs, inside which particles of a new phase are subsequently formed. The latter circumstance allows us to consider the liquid state of the alloy as the initial stage of the formation of a new phase. That formation of diffusion micro-pairs (and particles of a new phase inside them) occurs because of the presence of alloys, along with a metallic bond, of the ionic and covalent components of a strong chemical bond, which exist at all temperatures of the condensed state. The article shows what exactly needs to be done so that such a branch of science as the science of alloys can get rid of the empirical approach when creating new alloys.

Strain-driven structural selection and amorphization during first-order phase transitions in nanocrystalline Ho2O3 under pressure

Pressure-induced first-order phase transition often involves spatial disruption around the nucleus of a new phase, due to the inherent volume change. Atomic relaxations during this process produce lattice strain that in turn affects the nucleation kinetics and dynamics of transition, especially in nanoparticles. However, it is difficult to experimentally measure the lattice strain of materials, leading to many unsettled questions regarding size-dependent phenomena in nanomaterials at pressure. Here we present a method to determine the lattice strain of nanoparticles during first-order phase transitions using the pressure-volume data. A case study of nano-${\mathrm{Ho}}_{2}{\mathrm{O}}_{3}$ with multiple pressure-induced phase transitions is systematically performed to reveal the critical role of lattice strain in the size-dependent phase selection and amorphization. A phenomenological model is also given to describe the metastability of intermediate phases and size-tunable phase evolution during the nucleation of new phases at pressure.

Relationship between microstructures and resistance in mafic assemblages that deform and transform

Abstract. Syn-kinematic mineral reactions play an important role for the mechanical properties of polymineralic rocks. Mineral reactions (i.e., nucleation of new phases) may lead to grain size reduction, producing fine-grained polymineralic mixtures, which have a strongly reduced viscosity because of the activation of grain-size-sensitive deformation processes. In order to study the effect of deformation–reaction feedback(s) on sample strength, we performed rock deformation experiments on “wet” assemblages of mafic compositions in a Griggs-type solid-medium deformation apparatus. Shear strain was applied at constant strain rate (10−5 s−1) and constant confining pressure (1 GPa) with temperatures ranging from 800 to 900 ∘C. At low shear strain, the assemblages that react faster are significantly weaker than the ones that react more slowly, demonstrating that reaction progress has a first-order control on rock strength. With increasing strain, we document two contrasting microstructural scenarios: (1) the development of a single throughgoing high-strain zone of well-mixed, fine-grained aggregates, associated with a significant weakening after peak stress, and (2) the development of partially connected, nearly monomineralic shear bands without major weakening. The lack of weakening is caused by the absence of interconnected well-mixed aggregates of fine-grained reaction products. The nature of the reaction products, and hence the intensity of the mechanical weakening, is controlled by the microstructures of the reaction products to a large extent, e.g., the amount of amphibole and the phase distribution of reaction products. The samples with the largest amount of amphibole exhibit a larger grain size and show less weakening. In addition to their implications for the deformation of natural shear zones, our findings demonstrate that the feedback between deformation and mineral reactions can lead to large differences in mechanical strength, even at relatively small initial differences in mineral composition.

Effect of Cooling Rate on the Controlled Solidification of “Fe<sub>2</sub>O<sub>3</sub>”–CaO–SiO<sub>2</sub> Liquids in Air in Synthetic Iron Ore Sinter

The cooling rate of the liquid oxide can be controlled in industrial sintering processes through the draft pressure and has the potential to influence microstructure formation. The solidification of a liquid within the hematite primary phase field in the ternary FeO-CaO-SiO system in air was undertaken at different cooling rates to determine the impact of cooling rate on the formation of product microstructures. Samples with a bulk composition of 72.7 wt% FeO and a CaO/SiO ratio of 3.46, were cooled from 1623 K (1350°C) at 2 K/s, 0.5 K/s, 0.1 K/s and 0.01 K/s and quenched at 5 K temperature intervals from 1533 K (1260°C) to 1453 K (1180°C). During cooling, four stages of phase assemblage formation were consistently observed at all cooling rates; in order of formation these are, Liquid +hematite (I), Liquid+hematite+dicalcium silicate(CS)(II), Liquid+CS+calcium diferrite (CF)(III) and CS+CF+calcium ferrite (CF)(IV). An intergrowth of silico-ferrite of calcium and aluminium-I (SFCA-I) and CaFeFeO was observed to form in some conditions in regions free of hematite, present in liquids solidifying at 0.5 K/s and 0.1 K/s. The sizes and shapes of microstructures were observed to systematically change with cooling rate, with a slower cooling rate typically resulting in coarser coupled microstructures and larger individual crystals. A larger proportion of coupled microstructures are observed at slower cooling rates, this appears to be related to the degree of undercooling prior to the nucleation of new phases. The equilibrium silico-ferrite of calcium (SFC) phase was not observed at any of the cooling rates investigated.

Evaluation of the critical nucleus size without using interface free energy

Abstract The size of the critical nucleus serves as a benchmark in the nucleation theories. But its thermodynamic calculation requires knowledge of the interface free energy, which is size-dependent. A theoretical approach avoiding the need of interfacial energy data for evaluating the size of the critical nucleus is described in this paper. The point at which the volume term of the free energy change during new-phase nucleation balances the surface term is used. The size of the new-born crystals that survive up to this point (denominated ‘stable nuclei’) enables evaluation of the critical nucleus size.

Effect of C and N and their absence on the kinetics of austenite-ferrite phase transformations in Fe-0.5Mn alloy

Investigating the partitioning effect of substitutional and interstitial elements on the migration of transformation interfaces during austenite-ferrite phase transformation in steels with the conventional experimental method is extremely challenging due to interaction between the solute atoms and the transformation interfaces. Additionally, the simultaneous nucleation of new phases during phase transformations limits the accuracy of extracted growth rates from experimental kinetics measurements of phase fractions. In a novel experimental approach, the cyclic partial phase transformation concept is used to avoid the effect of nucleation on total kinetics of phase transformations. In this study, a Fe-0.5Mn alloy in the presence and absence of interstitial C and N additions is subjected to different cyclic transformation routes to examine the possible interaction between solute atoms and migrating interfaces. The experimental results are in semi-quantitative agreement with modelling predictions made by the local equilibrium approach and provide indirect evidence of Mn partitioning at austenite/ferrite interface in absence of any interstitial elements. It is also confirmed that the presence of interstitial elements promotes Mn interaction with the interface, whereas N promotes more Mn partitioning at transformation interface compared to C.

Control over phase separation and nucleation using a laser-tweezing potential.

Control over the nucleation of new phases is highly desirable but elusive. Even though there is a long history of crystallization engineering by varying physicochemical parameters, controlling which polymorph crystallizes or whether a molecule crystallizes or forms an amorphous precipitate is stilla poorly understood practice. Although there are now numerous examples of control using laser-induced nucleation, the absence of physical understanding is preventing progress. Here we show that the proximity of a liquid-liquid critical point or the corresponding binodal line can be used by a laser-tweezing potential to induce concentration gradients. A simple theoretical model shows that the stored electromagnetic energy of the laser beam produces a free-energy potential that forces phase separation or triggers the nucleation of a new phase. Experiments in a liquid mixture using a low-power laser diode confirm the effect. Phase separation and nucleation using a laser-tweezing potential explains the physics behind non-photochemical laser-induced nucleation and suggests new ways of manipulating matter.

Air-stable MgH2 − CeO2 composite with facilitated de/hydrogenation kinetics synthesized by high energy ball milling

The oxidation of Mg seriously limits its long-life applications as a hydrogen storage material. Considering the catalytic effects and unique redox instincts of rare earth oxides, MgH2 with CeO2 on the surface has been prepared by high energy ball milling MgH2 with CeO2 (20wt%) in Ar and air atmosphere, respectively. It is expected to improve the oxidation resistance of Mg and elucidate the underlying mechanism by detailed microstructure observation and de-/hydrogenation kinetics analysis. CeO2 with particle size in the range of ~20–100nm are uniformly distributed on the surface of MgH2 matrix after milling. For pure MgH2 milled in air, both hydrogen capacity and de-/absorption kinetics deteriorate evidently comparing with those of pure MgH2 milled in Ar. However, both MgH2+CeO2 milled in Ar and air can rapidly absorb and desorb hydrogen. MgH2+CeO2 milled in air can absorb ~4wt% hydrogen within 4min at 300°C. For pure MgH2 milled in Ar after air exposure, a long incubation period is necessary before fast dehydrogenation, while fast desorption is still observed for air-exposed MgH2+CeO2. It is believed that the uniformly distributed cerium oxides, which serve as catalysts promoting recombination of hydrogen and nucleation of new phase, can effectively prevent forming a dense and continuous MgO layer on the MgH2 surface during air exposure due to the unique instincts of CeO2. The obtains in this work can be expected to provide guidelines to ameliorate the oxygen-free conditions of Mg-based hydrogen storage alloys by selecting proper catalyst and reasonable processing.

A continuum theoretical model and finite elements simulation of bacterial flagellar filament phase transition.

The Bacterial flagellar filament can undergo a polymorphic phase transition in response to both mechanical and chemical variations in vitro and in vivo environments. Under mechanical stimuli, such as viscous flow or forces induced by motor rotation, the filament changes its phase from left-handed normal (N) to right-handed semi-coiled (SC) via phase nucleation and growth. Our detailed mechanical analysis of existing experiments shows that both torque and bending moment contribute to the filament phase transition. In this paper, we establish a non-convex and non-local continuum model based on the Ginzburg-Landau theory to describe main characteristics of the filament phase transition such as new-phase nucleation, growth, propagation and the merging of neighboring interfaces. The finite element method (FEM) is adopted to simulate the phase transition under a displacement-controlled loading condition (rotation angle and bending deflection). We show that new-phase nucleation corresponds to the maximum torque and bending moment at the stuck end of the filament. The hysteresis loop in the loading and unloading curves indicates energy dissipation. When the new phase grows and propagates, torque and bending moment remain static. We also find that there is a drop in load when the two interfaces merge, indicating a concomitant reduction in the interfacial energy. Finally, the interface thickness is governed by the coefficients of the gradient of order parameters in the non-local interface energy. Our continuum theory and the finite element method provide a method to study the mechanical behavior of such biomaterials.

The OpenCalphad thermodynamic software interface

Thermodynamic data are needed for all kinds of simulations of materials processes. Thermodynamics determines the set of stable phases and also provides chemical potentials, compositions and driving forces for nucleation of new phases and phase transformations. Software to simulate materials properties needs accurate and consistent thermodynamic data to predict metastable states that occur during phase transformations. Due to long calculation times thermodynamic data are frequently pre-calculated into “lookup tables” to speed up calculations. This creates additional uncertainties as data must be interpolated or extrapolated and conditions may differ from those assumed for creating the lookup table. Speed and accuracy requires that thermodynamic software is fully parallelized and the OpenCalphad (OC) software is the first thermodynamic software supporting this feature.This paper gives a brief introduction to computational thermodynamics and introduces the basic features of the OC software and presents four different application examples to demonstrate its versatility.

Microstructural evolution of ASTM grade 91 after long-term creep testing

Modified 9Cr–1Mo steel (ASTM grade P/T91) is conventionally applied in the construction of high efficiency supercritical and ultra-supercritical boilers, reaching metal temperatures up to 600–610 °C. As a part of the characterisation process of commercial pipes, Tenaris has performed over the years several long-term creep tests, with duration up to over 100,000 h, for temperatures between 550 and 650 °C. Microstructural characterisation has been performed on broken specimens, including analysis of the state of precipitation after TEM imaging of extraction replicas. The evolution of M23C6 coarse carbides, and MX carbo-nitrides, as well as the nucleation of new phases, such as Laves and Z are described in this paper. Observations reveal Laves phase nucleation and growth peak at 600 °C, whereas almost no particles were observed after ageing at higher temperature; moreover, transformation of MX carbo-nitrides into Z-phase is also faster at 600 °C, and slows at higher temperature.

Synthesis of multicomponent metallic layers during impulse plasma deposition

AbstractPulsed plasma in the impulse plasma deposition (IPD) synthesis is generated in a coaxial accelerator by strong periodic electrical pulses, and it is distributed in a form of energetic plasma packets. A nearly complete ionization of gas, in these conditions of plasma generation, favors the nucleation of new phase of ions and synthesis of metastable materials in a form of coatings which are characterized by amorphous and/or nanocrystalline structure. In this work, the Fe–Cu alloy, which is immiscible in the state of equilibrium, was selected as a model system to study the possibility of formation of a non-equilibrium phase during the IPD synthesis. Structural characterization of the layers was done by means of X-ray diffraction and conversion-electron Mössbauer spectroscopy. It was found that supersaturated solid solutions were created as a result of mixing and/or alloying effects between the layer components delivered to the substrate independently and separately in time. Therefore, the solubility in the Fe–Cu system was largely extended in relation to the equilibrium conditions, as described by the equilibrium phase diagram in the solid state.

Boron Grain Boundary Segregation in a Heat Treatable Steel

By applying a heat treatment, such as hardening and tempering, the properties of a heat treatable steel, like 42CrMo4, can be adjusted over a wide range. In addition to the heat treatment, an appropriate alloying concept is crucial to be able to guarantee an outstanding performance over a large variety of applications. In the present study, the effects of boron as a microalloying element on a heat treatable steel were examined. It is well known that boron, if added in a proper amount, can significantly retard the transformation of austenite to bainite or ferrite/pearlite in low alloyed steels. During the heat treatment, it diffuses to the austenite grain boundaries, where it reduces the driving force for the nucleation of new phases. In order to prove this theory in a heat treatable steel, a prior austenite grain boundary was prepared for atom probe tomography (APT). The specimen preparation was carried out by electro-polishing, etching, and sharpening by focused ion beam (FIB) in combination with transmission Kikuchi diffraction (TKD). In the reconstruction of the corresponding APT measurement, boron could be found at the same prior austenite grain boundary.

Creep cavitation bands control porosity and fluid flow in lower crustal shear zones

Research Article| March 01, 2015 Creep cavitation bands control porosity and fluid flow in lower crustal shear zones Luca Menegon; Luca Menegon 1School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth PL4 8AA, UK Search for other works by this author on: GSW Google Scholar Florian Fusseis; Florian Fusseis 2School of Geosciences, University of Edinburgh, Edinburgh EH9 3FE, UK Search for other works by this author on: GSW Google Scholar Holger Stünitz; Holger Stünitz 3Department of Geology, University of Tromsø, 9037 Tromsø, Norway Search for other works by this author on: GSW Google Scholar Xianghui Xiao Xianghui Xiao 4Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Luca Menegon 1School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth PL4 8AA, UK Florian Fusseis 2School of Geosciences, University of Edinburgh, Edinburgh EH9 3FE, UK Holger Stünitz 3Department of Geology, University of Tromsø, 9037 Tromsø, Norway Xianghui Xiao 4Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA Publisher: Geological Society of America Received: 25 Sep 2014 Revision Received: 15 Dec 2014 Accepted: 17 Dec 2014 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2015 Geological Society of America Geology (2015) 43 (3): 227–230. https://doi.org/10.1130/G36307.1 Article history Received: 25 Sep 2014 Revision Received: 15 Dec 2014 Accepted: 17 Dec 2014 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Luca Menegon, Florian Fusseis, Holger Stünitz, Xianghui Xiao; Creep cavitation bands control porosity and fluid flow in lower crustal shear zones. Geology 2015;; 43 (3): 227–230. doi: https://doi.org/10.1130/G36307.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Shear zones channelize fluid flow in Earth’s crust. However, little is known about deep crustal fluid migration and how fluids are channelized and distributed in a deforming lower crustal shear zone. This study investigates the deformation mechanisms, fluid-rock interaction, and development of porosity in a monzonite ultramylonite from Lofoten, northern Norway. The rock was deformed and transformed into an ultramylonite under lower crustal conditions (temperature = 700–730 °C, pressure = 0.65–0.8 GPa). The ultramylonite consists of feldspathic layers and domains of amphibole + quartz + calcite, which result from hydration reactions of magmatic clinopyroxene. The average grain size in both domains is <25 μm. Microstructural observations and electron backscatter diffraction analysis are consistent with diffusion creep as the dominant deformation mechanism in both domains. Festoons of isolated quartz grains define C′-type bands in feldspathic layers. These quartz grains do not show a crystallographic preferred orientation. The alignment of quartz grains is parallel to the preferred elongation of pores in the ultramylonites, as evidenced from synchrotron X-ray microtomography. Such C′-type bands are interpreted as creep cavitation bands resulting from diffusion creep deformation associated with grain boundary sliding. Mass-balance calculation indicates a 2% volume increase during the protolith-ultramylonite transformation, which is consistent with synkinematic formation of creep cavities producing dilatancy. Thus, this study presents evidence that creep cavitation bands may control deep crustal porosity and fluid flow. Nucleation of new phases in creep cavitation bands inhibits grain growth and enhances the activity of grain size–sensitive creep, thereby stabilizing strain localization in the polymineralic ultramylonites. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

New-phase nucleation due to the collision of two nonstationary waves

New-phase nucleation due to the collision of two nonstationary waves

Impulse Plasma In Surface Engineering - a review

The article describes the view of the plasma surface engineering, assuming the role of non-thermal energy effects in the synthesis of materials and coatings deposition. In the following study it was underlined that the vapor excitation through the application of an electric field during coatings deposition gives new possibilities for coatings formation. As an example the IPD method was chosen. During the IPD (Impulse Plasma Deposition) the impulse plasma is generated in the coaxial accelerator by strong periodic electrical pulses. The impulse plasma is distributed in the form of energetic plasma pockets. Due to the almost completely ionization of gas, the nucleation of new phases takes place on ions directly in the plasma itself. As a result the coatings of metastable materials with nano-amorphous structure and excellent adhesion to the non-heated intentionally substrates could be deposited. Recently the novel way of impulse plasma generation during the coatings deposition was proposed and developed by our group. An efficient tool for plasma process control, the plasma forming gas injection to the interelectrode space was used. Periodic changing the gas pressure results in increasing both the degree of dispersion and the dynamics of the plasma pulses. The advantage of the new technique in deposition of coatings with exceptionally good properties has been demonstrated in the industrial scale not only in the case of the IPD method but also in the case of very well known magnetron sputtering method.

Evaluation of metastable region boundaries for liquid and solid states in MD simulations

An automatic method based on MD simulations was developed for detecting and tracing the boundaries of metastable states of superheated crystal and supercooled liquid. The main criterion of the detection of early nucleation of new phase is the self-diffusion coefficient temperature dependence. The scanning for nucleation events is performed at continuous temperature change. The set of independent nucleation events at a given pressure allows evaluation of temperature dependence of specific nucleation frequency. The collection of a large number of these calculations allows accurate approximation of pressure and temperature dependence of the specific nucleation frequency in both directions between phases. This dependence allows estimating the behavior of the free energy in the region between superheating and supercooling curves. In addition, dependence of nucleation frequency on pressure and temperature provides an opportunity to integrate the probability of nucleation under dynamic loading and subsequent release and thus to determine the likelihood of the crystallization and melting. The technique was applied to tin. MD simulation was carried out with the help of the EAM interatomic potential, well reproducing the properties of BCC phase.