Phase field calculation of interface mobility in a ternary alloy

A novel approach based on the quantitative phase field model was proposed to calculate the interface mobility and applied to the α/β interface of a ternary Ti-6Al-4V alloy.Phase field simulations indicate that the higher interface mobility leads to the faster transformation rate,but only a unique value of interface mobility matches the diffusion equation under the diffusion-controlled condition.By comparing the transformation kinetics from phase field simulations with that from classical diffusion equation,the interface mobility at different temperatures can be obtained.The results show that the calculated interface mobility increases with increasing temperature and accords with Arrhenius equation very well.

Effect of microalloying on wettability and interface characteristics of Zr-based bulk metallic glasses with W substrate

The infiltration casting method is widely employed for the preparation of ex-situ composite materials.However,the production of composite materials using this method must necessitates a comprehensive understanding of the wettability and interface characteristics between the reinforcing phase and the bulk metallic glasses(BMGs).This work optimized the composition of Zr-based BMGs through microalloying methods,resulting in a new set of Zr-based BMGs with excellent glass-forming ability.Wetting experiments between the Zr-based BMGs melts and W substrates were conducted using the traditional sessile drop method,and the interfaces were characterized utilizing a scanning electron microscope(SEM)equipped with energy dispersive X-ray spectroscopy(EDS).The work demonstrates that the microalloying method substantially enhances the wettability of the Zr-based BMGs melt.Additionally,the incorporation of Nb element impedes the formation of W-Zr phases,but the introduction of Nb element does not alter the extent of interdiffusion between the constituent elements of the amorphous matrix and W element,indicating that the influence of Nb element on the diffusion of individual elements is minute.

Effects of grinding-induced grain boundary and interfaces on electrical transportation and structure phase transition in ZnSe under high pressure

Interface and scale effects are the two most important factors which strongly affect the structure and the properties of nano-/micro-crystals under pressure.We conduct an experiment under high pressure in situ alternating current impedance to elucidate the effects of interface on the structure and electrical transport behavior of two Zn Se samples with different sizes obtained by physical grinding.The results show that（i） two different-sized Zn Se samples undergo the same phase transitions from zinc blend to cinnabar-type phase and then to rock salt phase;（ii） the structural transition pressure of the859-nm Zn Se sample is higher than that of the sample of 478 nm,which indicates the strong scale effect.The pressure induced boundary resistance change is obtained by fitting the impedance spectrum,which shows that the boundary conduction dominates the electrical transport behavior of Zn Se in the whole experimental pressure range.By comparing the impedance spectra of two different-sized Zn Se samples at high pressure,we find that the resistance of the 478-nm Zn Se sample is lower than that of the 859-nm sample,which illustrates that the sample with smaller particle size has more defects which are due to physical grinding.

Emerging low-density polyethylene/paraffin wax/aluminum composite as a form-stable phase change thermal interface material

Thermal interface materials(TIMs) play a vital role in the thermal management of electronic devices and can significantly reduce thermal contact resistance(TCR). The TCR between the solid–liquid contact surface is much smaller than that of the solid–solid contact surface, but conventional solid–liquid phase change materials are likely to cause serious leakage. Therefore, this work has prepared a new formstable phase change thermal interface material. Through the melt blending of paraffin wax(PW) and low-density polyethylene(LDPE), the stability is improved and it has an excellent coating effect on PW. The addition of aluminum(Al) powder improves the low thermal conductivity of PW/LDPE, and the addition of 15wt% Al powder improves the thermal conductivity of the internal structure of the matrix by 67%. In addition, the influence of the addition of Al powder on the internal structure, thermal properties, and phase change behavior of the PW/LDPE matrix was systematically studied. The results confirmed that the addition of Al powder improved the thermal conductivity of the material without a significant impact on other properties, and the thermal conductivity increased with the increase of Al addition. Therefore, morphologically stable PW/LDPE/Al is an important development direction for TIMs.

Microscopic phase-field simulation of ordered domain interfaces formed between DO_(22) phases along [100] direction

Ordered domain interfaces formed between DO22 (Ni3V) phases along [100] direction during the precipitation process of Ni75AlxV25-x alloys were simulated by using the microscopic phase-field model. The atomic structure, migration process, and compositions of interfaces were investigated. It is found that there are four kinds of stable ordered domain interfaces formed between DO22 phases along [100] direction and all of them can migrate. During the migration of interfaces, the jump of atoms shows site selectivity behaviors and each stable interface forms a distinctive transition interface. The atom jump selects the optimist way to induce the migration of interface, and the atomic structures of interfaces retain the same before and after the migration. The alloy elements have different preferences of segregation or depletion at different interfaces. At all the four kinds of interfaces, Ni and Al segregate but V depletes. The degrees of segregation and depletion are also different at different interfaces.

PHASE INTERFACE SEGREGATION OF Mg IN A Ni-BASE SUPERALLOY IN100

The segregation of Mg to phase interfaces in a nickel base superalloy IN 100 has been investi- gated using EPT(Electron Microprobe Technique).AES(Auger Electron Spectroscopy) and EDS analyses on thin TEM film.The results show that Mg segregates to the phase inter- faces of MC/γ and γ′/γ.The segregation concentration and layer thickness of Mg on MC/γ phase interface are larger than that on γ′/γ phase interface.Mg is not only a grain boundary segregation element,but also a phase interface segregation one.

Interface evolution of TiAl/Ti6242 transient liquid phase joint using Ti, Cu foils as insert metals

The interface evolution of TiAl/Ti6242 joint produced by transient liquid phase(TLP) bonding with Ti, Cu foils as insert metals was investigated. The results show that the surface oxide layer on TiAl plays a very important role in the formation process of the joint. A ‘bridge’ effect is observed because of the presence of the oxide layer on the surface of TiAl. The diffusion behavior of Cu atoms in TiAl is strongly controlled by the vacancies beneath the surface of TiAl. Based on the interface diffusion and interface wettability, a mechanism for the effect of bonding pressure, bonding temperature, holding time and stacking sequence of the insert foils on the joint formation process were proposed.

INVESTIGATION ON THE INTERFACE PHASE BY TEM IN A NEWLY DEVELOPED NEAR α TITANIUM ALLOY

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Investigation on the Interface between Exons and Introns in the Genomic DNA of Arabidopsis thaliana in the Phase Space

In this study,three weight vectors L1,L2 and L3 were set.After calculating the probability of three bases in the exons or introns in the genomic DNA of Arabidopsis thaliana,64-dimensional vector P was obtained.Dot products of P vector and three weight vectors were the feature coordinates for the exons and introns in 3-dimensional phase space.The expression for the interface between the exons and the introns in the genomic DNA of Arabidopsis thaliana in 3-dimensional phase space was established,which could be used to distinguish the exons and the introns in the genomic DNA of Arabidopsis thaliana with an accuracy higher than85%in 3-dimensional phase space.

Effect of the formation process of transient liquid phase (TLP) on the interface structure of TiAl joints

TiAl has been joined employing the transient liquid phase （TLP） bonding with Ti combined with Cu, Ni or Fe foils. Experimental results showed that though the interface structures of the joints are quite different, all the joined zones are composed of five sublayers, i.e. two diffusion zones, two interfacial zones and an interlayer. It has been convinced that the formation process of the transient liquid phase controls the diffusion behavior of melting point depressant （MPD） Cu, Ni, and Fe atoms, which leads to form different interface structures of the joints.

Interface-induced topological phase and doping-modulated bandgap of two-dimensioanl graphene-like networks

Biphenylene is a new topological material that has attracted much attention recently.By amplifying its size of unit cell,we construct a series of planar structures as homogeneous carbon allotropes in the form of polyphenylene networks.We first use the low-energy effective model to prove the topological three periodicity for these allotropes.Then,through first-principles calculations,we show that the topological phase has the Dirac point.As the size of per unit cell increases,the influence of the quaternary rings decreases,leading to a reduction in the anisotropy of the system,and the Dirac cone undergoes a transition from type II to type I.We confirm that there are two kinds of non-trivial topological phases with gapless and gapped bulk dispersion.Furthermore,we add a built-in electric field to the gapless system by doping with B and N atoms,which opens a gap for the bulk dispersion.Finally,by manipulating the built-in electric field,the dispersion relations of the edge modes will be transformed into a linear type.These findings provide a hopeful approach for designing the topological carbon-based materials with controllable properties of edge states.

Exploring the Spatial Control of Topotactic Phase Transitions Using Vertically Oriented Epitaxial Interfaces

Engineering oxygen vacancy formation and distribution is a powerful route for controlling the oxygen sublattice evolution that affects diverse functional behavior.The controlling of the oxygen vacancy formation process is particularly important for inducing topotactic phase transitions that occur by transformation of the oxygen sublattice.Here we demonstrate an epitaxial nanocomposite approach for exploring the spatial control of topotactic phase transition from a pristine perovskite phase to an oxygen vacancy-ordered brownmillerite(BM)phase in a model oxide La_(0.7)Sr_(0.3)MnO_(3)(LSMO).Incorporating a minority phase NiO in LSMO films creates ultrahigh density of vertically aligned epitaxial interfaces that strongly influence the oxygen vacancy formation and distribution in LSMO.Combined structural characterizations reveal strong interactions between NiO and LSMO across the epitaxial interfaces leading to a topotactic phase transition in LSMO accompanied by significant morphology evolution in NiO.Using the NiO nominal ratio as a single control parameter,we obtain intermediate topotactic nanostructures with distinct distribution of the transformed LSMO-BM phase,which enables systematic tuning of magnetic and electrical transport properties.The use of self-assembled heterostructure interfaces by the epitaxial nanocomposite platform enables more versatile design of topotactic phase structures and correlated functionalities that are sensitive to oxygen vacancies.

Qualititative Analysis of Interface Behavior under First Phase Transition

At present there is no explanation of the nature of interface instability upon first order phase transitions. The well-known theory of concentration overcooling under directed crystallization of solutions and Mullins-Sekerka instability cannot account for the diversified liquid component redistribution during solid state transition. In [1-3], within the framework of the nonequilibrium mass transfer problem, it has been shown that there are regimes of the interface instability, which differ from the known ones [4-6]. Moreover, the instability theory of works [1-3] demonstrates a complete experimental agreement of the dependence of eutectic pattern period on interface velocity. However, it is difficult to explain interface instability within the framework of a general setting of the mass-transfer problem. This paper is de-voted to qualitative analysis of the phenomena that are responsible for interface instability. The phenomena are connected by a single equation. Qualitative analysis revealed a variety of different conditions responsible for instability of flat interface stationary movement upon phase transition. The type of instability depends on system parameters. It is important that interface instability in the asymptotic case of quasi-equilibrium problem setting is qualitatively different from interface instability in the case of nonequilibrium problem setting.

Deformation Nano-Mechanisms Occurring on the Interface of Dissimilar Materials Joined in Solid Phase by Means of High Temperature Rolling

Nano-mechanisms of crystal lattice deformation on the interface of dissimilar materials (Cu-Nb), joined by vacuum rolling in solid phase under high temperature (950℃) were studied by means of high resolution electron microscopy. Input of carriers of rotation modes—nano-dipoles of partial disclinations and nano-twist disclinations in the form of double spirals in deformation mechanisms were analyzed. The role of these mechanisms in decrease of shear stability of the interface areas and in production of high-quality rolled metal is discussed.

Characterization and evaluation of interface in SiC_p/2024 Al composite

35% SiCp/2024 Al（volume fraction） composite was prepared by powder metallurgy method. The microstructures of Si Cp/Al interfaces and precipitate phase/Al interfaces were characterized by HRTEM, and the interface conditions were evaluated by tensile modules of elasticity and Brinell hardness measurement. The results show that the overall Si Cp/Al interface condition in this experiment is good and three kinds of Si Cp/Al interfaces are present in the composites, which include vast majority of clean planer interfaces, few slight reaction interfaces and tiny amorphous interfaces. The combination mechanism of Si C and Al in the clean planer interface is the formation of a semi-coherent interface by closely matching of atoms and there are no fixed or preferential crystallographic orientation relationships between Si C and Al. MgAl2O4 spinel particles act as an intermediate to form semi-coherent interface with SiC and Al respectively at the slight reaction interfaces. When the composite is aged at 190 °C for 9 h after being solution-treated at 510 °C for 2 h, numerous discoid-shaped and needle-shaped nanosized precipitates dispersively exist in the composite and are semi-coherent of low mismatch with Al matrix. The Brinell hardness of composites arrives peak value at this time.

Bonding properties of interface in Fe/Al clad tube prepared by explosive welding

A Fe/Al clad tube was prepared by explosive welding.Then the bonding characteristic of the interface was investigated by compression,flattening and compression-shear test.The test results exhibit that the clad tubes possessing good bonding interface have higher shear strength than that of pure aluminum and can bear both axial and radial deformation.The original interface between aluminum layer and ferrite layer was observed by scanning electron microscopy（SEM）.The results show that the clad tubes with good bonding properties possess the interface in wave and straight shape.The Fe/Al clad tube was used to manufacture the T-shape by hydro-bulging.It is found that the good-bonding interface of the Fe/Al clad tube plays a dominant role in the formation of the T-shape.

Effect of immersion Ni plating on interface microstructure and mechanical properties of Al/Cu bimetal

A nickel-based coating was deposited on the pure Al substrate by immersion plating,and the Al/Cu bimetals were prepared by diffusion bonding in the temperature range of 450-550 ℃.The interce microstructure and fracture surface of Al/Cu joints were studied by scanning electron microscopy（SEM） and X-ray diffraction（XRD）.The mechanical properties of the Al/Cu bimetals were measured by tensile shear and microhardness tests.The results show that the Ni interiayer can effectively eliminate the formation of Al-Cu intermetallic compounds.The Al/Ni interface consists of the Al3Ni and Al3Ni2 phases,while it is Ni-Cu solid solution at the Ni/Cu interce.The tensile shear strength of the joints is improved by the addition of Ni interiayer.The joint with Ni interiayer annealed at 500 ℃ exhibits a maximum value of tensile shear strength of 34.7 MPa.

First-principles thermodynamics of metal-oxide surfaces andinterfaces:A case study review

An important step for achieving the knowledge-based design freedom on nano-and interfacial materials is attained by elucidating the related surface and interface thermodynamics from the first principles so as to allow engineering the microstructures for desired properties through smartly designing fabrication processing parameters.This is demonstrated for SnO2 nano-particle surfaces and also a technologically important Ag-SnO2 interface fabricated by in-situ internal oxidation.Based on defect thermodynamics,we first modeled and calculated the equilibrium surface and interface structures,and as well corresponding properties,as a function of the ambient temperature and oxygen partial pressure.A series of first principles energetics calculations were then performed to construct the equilibrium surface and interface phase diagrams,to describe the environment dependence of the microstructures and properties of the surfaces and interfaces during fabrication and service conditions.The use and potential application of these phase diagrams as a process design tool were suggested and discussed.

Revealing the atomic mechanism of diamond–iron interfacial reaction

Diamond,with ultrahigh hardness,high wear resistance,high thermal conductivity,and so forth,has attracted worldwide attention.However,researchers found emergent reactions at the interfaces between diamond and ferrous materials,which significantly affects the performance of diamond-based devices.Herein,combing experiments and theoretical calculations,taking diamond–iron(Fe)interface as a prototype,the counter-diffusion mechanism of Fe/carbon atoms has been established.Surprisingly,it is identified that Fe and diamond first form a coherent interface,and then Fe atoms diffuse into diamond and prefer the carbon vacancies sites.Meanwhile,the relaxed carbon atoms diffuse into the Fe lattice,forming Fe_(3)C.Moreover,graphite is observed at the Fe_(3)C surface when Fe_(3)C is over-saturated by carbon atoms.The present findings are expected to offer new insights into the atomic mechanism for diamondferrous material's interfacial reactions,benefiting diamond-based device applications.

Improvement of the matrix and the interface quality of a Cu/Al composite by the MARB process

The matrix accumulative roll bonding technology （MARB） can improve the matrix performance of metal composite and strengthen the bonding quality of the interface./n this research, for the fwst time, the technology of MARB was proposed. A sound Cu/AI bonding composite was obtained using the MARB process and the bonding characteristic of the interface was studied using scanning electricity microscope （SEM） and energy-dispersive spectroscopy （EDS）. The result indicated that accumulation cycles and diffusion annealing temperature were the most important factors for fabricating a Cu/AI composite material. The substrate aluminum was strengthened by MARB, and a high quality Cu/AI composite with sound interface was obtained as well.