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The migration of grain boundary (GB), which plays a key role in the microstructural evolution of polycrystalline materials, remains mysterious due to the unknown relationship between GB mobility associated with specific geometry and external conditions (e.g. temperature, stress, etc., hence the thermodynamic driving force). Combining the rate equation of GB migration with molecular dynamics simulations, an intrinsic correlation between driving force and energy barrier for the migration of various types of GBs (i.e. twist, symmetric tilt, asymmetric tilt, and mixed twist-tilt) is herein explored, showing the decrease of energy barrier with increasing thermodynamic driving force.

Effects of a preexisting disconnection dipole on the migration of a Σ 5 ( 3 ¯ 1 0 ) / [ 0 0 1 ] grain boundary (GB) at low shear rates have been investigated by using the minimized bulk dissipation phase field crystal model. Simulation results show that the two disconnections play different roles during the process of shear-coupled GB migration via different behaviors regarding heterogeneous nucleation and propagation of disconnections. Specifically, the different roles can be attributed to their structural deviation from the equilibrated crystallographic structure caused by shear loading: one disconnection contributes to the onset of GB migration by heterogeneous nucleation of disconnections, while the other one slows down the corresponding GB migration dynamics through the impediment of homogeneous nucleation in the flat GB plane.

Anomalous eutectics are argued to form due to the remelting of the primary solid during solidification of deeply undercooled eutectic alloy melts. As an indicator of the tendency for anomalous eutectic formation, the remelted fraction of the primary eutectic was analyzed systematically based on the eutectic dendrite growth theory. For eutectic alloys with either larger equilibrium solute distribution coefficients or gentle liquidus slopes, the primary eutectic is highly supersaturated with solute and more prone to remelting. When the eutectic composition is set to different values, (e.g. the eutectic point is closer to one phase of the eutectic), the two eutectic phases under rapid growth change their compositions simultaneously, but their remelted fractions during temperature recalescence do not vary significantly. Three representative binary eutectic alloys Ag–39.9 at.%Cu, Ni–19.6 at.%P and Pd–16.0 at.%P – their eutectic products are solid solution–solid solution, solid solution–stoichiometric intermetallic compound and stoichiometric intermetallic compound–stoichiometric intermetallic compound, respectively, were solidified at large undercooling. Anomalous eutectics were observed in the first two eutectic alloys whose eutectic structure consists of at least one solid solution phase, whereby the stoichiometric intermetallic compound phase remained highly oriented whereas the solid solution phase had a near random distribution of orientations. For the Pd–16.0 at.%P alloy, however, the primary eutectic retained its original morphology as the final solidification structure regardless of the degree of undercooling. All these experimental results validate the argument that anomalous eutectics result from the remelting of the primary solid.

We proposed a quantitative method to detect atomic position in atomic intensity images from experiments such as high-resolution transmission electron microscopy, atomic force microscopy, and simulation such as phase field crystal modeling. The evaluation of detection accuracy proves the excellent performance of the method. This method provides a chance to precisely determine atomic interactions based on the detected atomic positions from the atomic intensity image, and hence to investigate the related physical, chemical and electrical properties.

In recent years, the phase field crystal (PFC) model has been confirmed as a good candidate to describe grain boundary (GB) structures and their nearby atomic arrangement. To further understand the mechanical behaviours of nanocrystalline materials, strain fields near GBs need to be quantitatively characterized. Using the strain mapping technique of geometric phase approach (GPA), we have conducted strain mapping across the GBs in nanocrystalline grains simulated by the PFC model. The results demonstrate that the application of GPA in strain mapping of low and high angles GBs as well as polycrystalline grains simulated by the PFC model is very successful. The results also show that the strain field around the dislocation in a very low angle GB is quantitatively consistent with the anisotropic elastic theory of dislocations. Moreover, the difference between low angle GBs and high angle GBs is revealed by the strain analysis in terms of the strain contour shape and the structural GB width.

Through phase-field-crystal (PFC) simulations, we investigated, on the atomic scale, the crucial role played by interface energy anisotropy and growth driving force during the morphological evolution of a dendrite tip at low growth driving force. In the layer-by-layer growth manner, the interface energy anisotropy drives the forefront of the dendrite tip to evolve to be highly similar to the corner of the corresponding equilibrium crystal from the aspects of atom configuration and morphology, and thus affects greatly the formation and growth of a steady-state dendrite tip. Meanwhile, the driving force substantially influences the part behind the forefront of the dendrite tip, rather than the forefront itself. However, as the driving force increases enough to change the layer-by-layer growth to the multilayer growth, the morphology of the dendrite tip's forefront is completely altered. Parabolic fitting of the dendrite tip reveals that an increase in the influence of interface energy anisotropy makes dendrite tips deviate increasingly from a parabolic shape. By quantifying the deviations under various interface energy anisotropies and growth driving forces, it is suggested that a perfect parabola is an asymptotic limit for the shape of the dendrite tips. Furthermore, the atomic scale description of the dendrite tip obtained in the PFC simulation is compatible with the mesoscopic results obtained in the phase-field simulation in terms of the dendrite tip's morphology and the stability criterion constant.

The process of grain rotation with small initial misorientation angles in nanocrystalline materials is investigated by using the phase field crystal (PFC) method. Simulation results reproduce the grain rotation process of nanocrystalline grains and are consistent with the classical coupled motion theory excellently. The grain rotation with very small initial misorientations, which cannot be illustrated via the Frank formula because of the large elastic distortion in the grain, is reasonably described by the strain field analysis. It is also revealed that the significant elastic distortion induced by grain boundaries (GBs) determines the rotational dynamics; moreover, the movement of grain boundary dislocations (GBDs) plays a dominant role in the evolution of elastic distortions which results in the grain rotation.

Solid/liquid interface is very essential for nucleation and the crystal growth process. In the present paper, we present a new method to prepare the crystal–fluid interface of colloidal hard spheres by evaporation in microchannel, which is a good candidate as a model system for the investigation of solid/liquid interface. In the system, the quasi-equilibrium colloidal solid/liquid interface is obtained at low osmotic pressure controllable by evaporation. The results show a dynamical broadening amorphous region near the solid/liquid interface. The crystal growth process in the dynamical broadening region depends on the competition between the attaching kinetics and the supersaturation related to the volume fraction. The results agree with previous investigations.

Using the phase-field crystal method, we investigated the bcc {1 0 1} vicinal surface growth from melts at the atomic scale with emphasis on the growth kinetics of two growth modes: step flow growth and island growth on terrace. Simulation results show that, for step flow growth, with the decrease of terrace width, the competition for feeding atoms between neighboring steps causes growth rate vs. step density to deviate from a linear relationship, and finally converge to a finite value. The step crystal direction also strongly influences the growth kinetics: vicinal surface with steps along the closest packed direction-[1 1 1] grows slower than that with [0 0 1] step. For island growth on terrace, the growth exponent of each layer in multi-layer island gradually transits from 1/2 for the top layer to 1/3 for the bottom layer, which demonstrates the transition from global diffusion controlled growth for top layer to surface diffusion controlled growth for bottom layer. The growth mechanism selection map with respect to terrace width and supersaturation is summarized and atom attaching rates of different growth mechanisms are also compared. (c) 2013 Elsevier B.V. All rights reserved.

Due to the large grain boundary (GB) volume fraction in nanocrystalline materials, interactions between GB and compositional domain boundary (CDB) play an important role in determining the nanoscale-modulated domain structures during spinodal decomposition. In the present paper, the phase field crystal model is employed to investigate the interactions between GB and CDB. Simulation results show that CDB coarsening can drive the GB migration and bring the impingement of particles with different orientations; the large volume fraction of GB can increase the dislocation volume fraction in CDBs but does not change its proportion in the whole defects number; the crossover point of the coarsening dynamic comes from the block effect of GB with large volume fraction.

(Cu46Zr46Al8)100¹xCox (x = 0, 1, 2, 3 and 4) bulk metallic glasses (BMGs) were synthesized by copper mold casting, and the effect of Co addition on the microstructure and mechanical properties of Cu46Zr46Al8 BMG was investigated. The existence of immiscibility gap between Co and the main component Cu is responsible for liquid separation to form droplet-type structure during solidification. The size scale for the droplettype structure trends to increase with the Co concentration. Depending on the glass-forming ability of the separated liquid phase, amorphous/ amorphous or amorphous/crystalline composite structure can be obtained. The results of compression test reveal that the plasticity and the fracture strength can be simultaneously enhanced with an appropriate amount of Co addition owing to nanoscale phase separation with the formation of Cu-rich and Co-rich glassy phases. [doi:10.2320/matertrans.M2012375]

A series of Co–Sn alloys with Sn content ranging from 12% to 32% (mole fraction) were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification microstructures. A boundary clearly exists, which separates the coupled growth zone from the decoupled growth zone of eutectic phases for the alloys with Sn content ranging from 14% to 31% (mole fraction). The other Co–Sn alloys out of this content range are hard to be undercooled into the coupled growth zone in the experiment. It is found that the so-called non-reciprocal nucleation phenomenon does not happen in the solidification of undercooled Co–Sn off-eutectic alloys.

Using the phase-field crystal model, we investigate the orientation selection of the cubic dendrite growth at the atomic scale. Our simulation results reproduce how a face-centered cubic (fcc) octahedral nucleus and a body-centered cubic (bcc) truncated-rhombic dodecahedral nucleus choose the preferred growth direction and then evolve into the dendrite pattern. The interface energy anisotropy inherent in the fcc crystal structure leads to the fastest growth velocity in the directions. New {111} atomic layers prefer to nucleate at positions near the tips of the fcc octahedron, which leads to the directed growth of the fcc dendrite tips in the directions. A similar orientation selection process is also found during the early stage of bcc dendrite growth. The orientation selection regime obtained by phase-field crystal simulation is helpful for understanding the orientation selection processes of real dendrite growth. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The homogeneous liquid was separated into two phases, (Fe, Co)-rich L1 and Cu-rich L2, once the melt was undercooled below a liquid-phase separation temperature T sep . If the duration from T sep to T s1 (solidification temperature of L1 phase), termed the liquid-phase separation interval Δ t , exceeded a critical value, an eggtype structure was observed. By utilizing differential thermal analyses (DTA), the solidification process of the undercooled Fe-Co-Cu alloys was studied. Additionally, an immiscible boundary was obtained, which was a convex parabola with a symmetrical axis of x Cu =0.52. Depending on the relative amounts of L1 and L2, the minor phase was nucleated firstly to form liquid droplets and separated from the original liquids at the beginning of liquid-phase separation.

It is known that heat treatment causes the spheroidization of eutectic silicon. This paper presents the influence of T6 heat treatment on the microstructures, tensile properties, and fracture behavior of the A356 alloys modified by mischmetal containing La and Ce elements. Microstructural analysis showed that the size of eutectic silicon particles was greatly reduced and the extent of speroidisation of Si particles was remarkably improved for the modified A356 alloys. Comparison between the unmodified and modified alloys suggested that the values of mean diameter, roundness, and aspect ration of eutectic silicon particles were decreased by 48.10–56.85%, 49.55–54.52%, and 13.36–30.17%, respectively. The tensile properties of the modified A356 alloys can be enhanced, especially the ductility. These could be associated with the decrease of secondary dendrite arm spacing, spheroidization of fine eutectic silicon and precipitation hardening. Scanning electron microscopy (SEM) examination indicated that the ductile fracture mechanism was responsible for the modified alloys due to the existence of a couple of fine and uniformly distributed dimples. And the eutectic silicon particles and RE-containing intermetallic compounds provide the weak locations during the fracture process.

Selection mechanisms of primary dendritic spacing in directional solidification are investigated by the phase field method. Results show that the lower and upper limits of primary spacing are determined by the interdendritic solutal interactions and the interdendritic undercooling respectively. The upper limit of primary spacing resulting from overgrowth of the tertiary arm could be about four times as large as the lower limit. The microstructural evolution from the onset of planar instability during directional solidification with a constant pulling velocity can be divided into three stages: an initial competition stage, a submerging stage and a lateral adjustment stage. Simulation results also demonstrate that the final primary spacing with a constant pulling velocity is very close to the lower limit due to the dendrite submerging mechanism.

The microstructures and free-volume evolutions of as-cast and pre-annealed Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glasses during rolling deformation have been investigated. No phase transformation is detected in the as-cast/rolled specimen. However, the structural stability of the glass against plastic deformation is worse after pre-annealing, indicated by nanocrystallization in pre-annealed/rolled specimens with large deformation degrees. Moreover, with increasing deformation degree, the free-volume content in a pre-annealed/rolled specimen increases at a lower average rate than that in an as-cast/rolled specimen.

We investigate surface-enhanced Raman scattering(SERS) spectra of pyridine-A(n) (n = 2-8) complexes by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. In simulated normal Raman scattering (NRS) spectra, profiles of pyridine-Ag-n (n = 2-8) complexes are analogical with that of isolated pyridine. Nevertheless, calculated pre-SERS spectra are strongly dependent on electronic transition states of new complexes. Wavelengths at 335 nm, 394.8 nm, 316.9 nm and 342.6 nm, which are nearly resonant with pure charge transfer excitation states, are adopted as incident light when simulating pre-SERS spectra for pyridine-Ag-n (n = 2-8) complexes, respectively. We obtain enhancement factors from 103 to 105 in pre-SERS spectra compared with corresponding NRS spectra. The obvious increase in Raman intensities mainly result from charge transfer resonance Raman enhancement. A charge difference densities (CDDs) methodology is adopted in describing chemical enhancement mechanism. This methodology aims at visualizing charge transfer from Ag-n (n = 2-8) clusters to pyridine on resonant electronic transition, which is one of the most direct evidences for chemical enhancement mechanism. (C) 2011 Elsevier B.V. All rights reserved.

Applying glass fluxing and cyclic superheating, high undercooling up to ∼350 K was achieved for Ni–Si hypoeutectic alloy melt. By isothermally annealing the as-solidified alloy subjected to different undercoolings, precipitation behavior of Ni3Si particle, at 973 K, was systematically studied. It was found that, the nucleation density and the real-time particle size, as well as the precipitation rate, were all increased, provided the sample was solidified subjected to higher undercooling. This was ascribed mainly to the increased solid solubility of Si atom in α-Ni matrix upon non-equilibrium solidification. On this basis, the non-equilibrium dendrite growth upon solidification and the soft impingement prevailing upon solid-state precipitation have been quantitatively connected. As such, the effect of liquid/solid transformation on subsequent precipitation was described.

A series of Zr–Cu glassy ribbons were fabricated, and the compositional dependence of microhardness in the as-quenched and annealed state was systematically investigated. The as-quenched microhardness exhibits a positive deviation from linearity at the compositions which correspond to local maximum in glass forming ability (GFA). Upon annealing, the microhardness change is relatively smaller for the high GFA compositions. High atomic packing density at the special compositions should be responsible for the microhardness behavior.

The growth behavior of Ni 3 Al phase layer in the β/γ diffusion couple of Ni–Al binary system, including the shape evolution and growth kinetics, have been simulated by using the KKS multiphase field model. Simulation results indicate that, when Ni 3 Al layer growth is controlled completely by volume diffusion, it could be regarded as parabolic growth. However, if the fast grain boundary diffusion is taken into account, the growth rate of Ni 3 Al phase is accelerated, and the growth kinetics deviates from parabolic growth, which is consistent with experiments and other simulation results. Simulation results also demonstrate some details of shape evolution of grains, such as the uneven Ni 3 Al/γ and Ni 3 Al/β interfaces and the grain boundary migration of Ni 3 Al grains caused by fast grain boundary diffusion.

The influence of 0.1–1.0 wt% mischmetal (MM) additives on the microstructures, tensile properties, and fracture behavior of A356 alloys were investigated in detail under the as-cast condition. Experimental results show that, after introducing a small amount of MM, grain coarsening occurred, the eutectic silicon was well modified, and RE-containing intermetallic compounds containing Al, Si, Mg, La, and Ce elements were formed. The size, shape, and distribution of RE-containing compounds are also studied. Tensile tests revealed that MM addition decreases the tensile strength and ductility of the materials. The fracture path goes through the interdendritic regions containing eutectic silicon and RE-containing compounds.

Departing from the volume-averaging method, the equiaxed solidification model was extended to describe the overall solidification kinetics of undercooled single-phase solid-solution alloys. In this model, a single grain, whose size is given assuming site saturation, is divided into three phases, i.e. the solid dendrite, the inter-dendritic liquid and the extra-dendritic liquid. The non-equilibrium solute diffusion in the inter-dendritic liquid and the extra-dendritic liquid, as well as the heat diffusion in the extra-dendritic liquid, is considered. The growth kinetics of the solid/liquid interface is given by the solute or heat balance, where a maximal growth velocity criterion is applied to determine the transition from thermal-controlled growth to solutal-controlled growth. A dendrite growth model, in which the nonlinear liquidus and solidus, the non-equilibrium interface kinetics, and the non-equilibrium solute diffusion in liquid are considered, is applied to describe the growth kinetics of the grain envelope. On this basis, the solidification path is described.

The microstructures and mechanical properties of Al matrix composites reinforced by different volume fractions of Al-Ni-Co intermetallic particles were investigated. Three different volume fractions of Al-Ni-Co particles were added to pure Al matrix using a stir-casting method. Microstructural analysis shows that with the increasing of the reinforcement volume fraction, the matrix grain size decreases and the porosity increases. The mechanical properties of the composites are improved over the matrix materials, except for the decreasing of the ductility. Fracture surface examination indicates that there is a good interfacial bonding between the Al matrix and the Al-Ni-Co particles and the fracture initiation does not occur at the particle-matrix interface.

In the present study, the A356Al-base composite materials were fabricated by introducing 2.5, 5, 7.5, 10 mass% of Al–Ni–Co decagonal quasicrystalline particles using the mechanical stirring method. The microstructures, mechanical properties, and Brinell hardness of these composites were investigated in detail by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that serious compositional diffusion occurs between the Al72Ni12Co16 quasicrystalline particles and the Al melt. Microstructural analysis of all as-cast composites shows that the structure of the quasicrystal disappears and is replaced by the formation of two crystalline phases, Co-rich θ-phase and Ni-rich γ-phase which all contain Al, Si, Ni, and Co. The particle sizes of the two crystalline phases are much smaller than that of the original decagonal quasicrystalline phase. The composites exhibit improvement of 10.5–24% and 20–25% in yield strength and Brinell hardness, respectively, while the percent elongation decreases obviously. Examination of the fracture surface of the as-cast A356Al-base composites shows that they exhibit typical brittle fracture mode.

Zr55Al10Cu30Ni5 bulk metallic glass was rolled up to 95% in thickness reduction at room temperature, and the dependences of microstructure and thermal stability on the strain were investigated. It is revealed that phase transformations do not occur during the rolling, but the split of the crystallization peaks becomes more and more obvious with increasing thickness reduction. Analyses of the radial distribution functions and the pair correlation functions indicate that the rolling has enhanced the short-range order, which should be responsible for the enlarging split of the crystallization peaks.

The interfacial reaction between Al72Ni12Co16 quasicrystalline particles and pure Al melt at 670 °C was investigated. For all the studied samples, only one interfacial reaction product was detected at the interface by scanning electron microscopy. The product was identified to be the Al9(Co, Ni)2 crystalline phase, which show an rod-like morphology. The growth rate of the Al9(Co, Ni)2 phase layer is very fast. Based on the microstructure analysis results, it is proposed that the layer growth is initially towards the liquid phase, but changes direction towards the quasicrystalline phase by the solid state reaction of diffusional Al with the quasicrystalline phase at the Al72Ni12Co16/Al9(Co, Ni)2 interface. A grain boundary grooving effect is deduced to have been involved during the reaction process.

Zr55Al10Ni5Cu30 bulk metallic glass was prepared through water-cooled copper mold suction casting, and was rolled up to 95% in thickness reduction. The structures and thermal stabilities of the as-cast and as-rolled specimens were examined by X-ray diffractometer and differential scanning calorimeter. As the thickness reduction increases, the crystallization onset temperature, peak temperature and the apparent activation energy of crystallization almost keep constant, while the glass transition temperature decreases from 681 to 671 K and the apparent activation energy of glass transition increases from (404±26) to (471±29) kJ/mol. The glass transition process is markedly affected by the rolling induced changes of microstructure and structural relaxation.

The effect of repeated melting of master alloy ingots on the bending properties of Zr55Al10Ni5Cu30 bulk metallic glass (BMG) was investigated. The bending plasticity of Zr55Al10Ni5Cu30 BMG was found to be improved with the increased remelting times. When remelted 10 times, the BMG sample cast from the master alloy ingot undergoes bending, but it does not fracture even though the bending angle increases to 100°; the maximum bending stress and elastic strain remain almost constant. The bending plasticity improvement may be attributed to the fact that the increased remelting times result in more free volume and more disorder and homogeneous microstructure in the BMG, which favors the initial nucleation of profuse shear bands and reduces the probability of catastrophic fracture.

The effects of soft impingement on precipitation are considered. A physically realistic analytical treatment of soft impingement has been developed for solid-state precipitation in a nonisothermal heating/cooling process following the basic assumptions (i.e., a two-stage transformation including site saturation of nucleation, isotropic growth and linear approximation for a concentration gradient in front of the precipitate/matrix interface). Furthermore, both one- and three-dimensional precipitations have been described using a compact expression which is analogous to Zener’s model but with a temperature-dependent growth coefficient. A detailed description for the model parameters has been given for the model application. Good agreement with published experimental data, for example, the decomposition of austenite in a 0.038–0.30wt%Mn plain carbon steel, has been achieved.

High undercooling (about 392 K) was achieved in the bulk eutectic Ni70.2Si29.8 alloy melt through glass fluxing combined with cyclic superheating. It is found that the metastable phases Ni3Si2 and NiSi are obtained through slow post-solidification when undercooling exceeds 240 K. The metastable phases are confirmed by using the method of X-ray diffraction and differential scanning calorimetry (DSC). Based on the principle of the free energy minimum and the transient nucleation theory, the phase selection of melt is investigated with regard to the metastable phases formation in the bulk undercooled eutectic Ni70.2Si29.8 melts. The formation of metastable phases from undercooled Ni70.2Si29.8 melts is ascribed to competitive nucleation with the undercooling, i.e. high undercooling facilitates the preferential nucleation of metastable phases.

In the present investigation, the microstructures and growth morphology of Mg32(Al,Zn)49 Frank-Kasper phase in rapidly solidified Mg32Al17Zn32 ternary alloys were studied in detail. The samples were characterised by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM) and energy dispersive spectrum (EDS). The results show that the microstructures mainly consist of Mg32(Al,Zn)49 Frank-Kasper phase and interdendritic Mg-rich Φ-phase. Under rapid solidification condition, Mg32(Al,Zn)49 Frank-Kasper phase reveals a perfect faceted dendritic characteristic in the shape of a three-fold symmetric microstructure with doublet tips in the axes direction. Observations for fracture surfaces show that the growth morphology of Mg32(Al,Zn)49 grains was truncated cubic, and its growth mechanism was also discussed.

A new intermetallic particle reinforced metal matrix composite was produced from pure Al and 15 wt% Al72Ni12Co16 quasicrystalline particles by stir-casting method, followed by hot-extrusion. Microstructural analysis of the as-cast composite shows that the Al72Ni12Co16 quasicrystalline phase has transformed to the crystalline phase Al9(Co, Ni)2 and an eutectic structure has formed in the Al matrix during the casting process. The particle size of the Al9(Co, Ni)2 phase is much smaller than that of the original quasicrystalline particles. After extrusion, the composite has a more uniform distribution of the reinforcement particles and eutectic structure as well as a reduced porosity. Tensile tests indicate that the mechanical properties of the as-cast composite are improved over the matrix properties remarkably, except for the ductility. The strength and ductility of the composite can be improved by the hot-extrusion, while the elastic modulus can be slightly decreased.

The Ag–28.1 wt.%Cu alloy without or with a minor addition (0.5 or 1 wt.%) of Sb was undercooled and spontaneously solidified in the encasement of a glass flux. A non-steady-state radial growth from the nucleation site on the sample surface results in two types of structures, anomalous eutectics near the nucleation site and lamellar eutectics in the other part. The large thermal diffusion coefficient of the Ag–Cu eutectic alloy melt and the relatively slow growth velocity should be responsible for the non-steady-state growth. After a little Sb is added, the solidification interface changes from a cellular morphology into a cellular dendrite and then an undeveloped dendrite, and the tip radius decreases. Correspondingly, the recalescence degree and the recalescence rate increase and the granular particles in the anomalous eutectics become larger because the solidification deviates significantly from the equilibrium state.

An analytical model has been developed to describe the overall kinetics of diffusion-controlled transformations assuming site saturation or continuous nucleation, in combination with one-dimensional growth. On the basis of linear approximation of the concentration gradient, the method of probability calculation is adopted to model the transformed fraction. First, the so-called geometrical model was re-derived, assuming that the diffusion-controlled growth, according to the parabolic growth law, stops due to geometrical impingement of grains plus their diffusion fields. Then, the transformation kinetics subjected to soft impingement was described, following an analogous approach. The effect of soft impingement, depending on the degree of supersaturation, has been interpreted by evolution of the transformed fraction and the growth exponent. The model was applied to describe the isothermal austenite–ferrite transformation of 0.37C–1.45Mn–0.11 V microalloyed steel, and a good agreement between model predictions and experimental results has been obtained.

Combining the empirical relation for grain boundary (GB) segregation upon isothermal grain growth and the generalized parabolic growth law, the influence of GB energy on the grain size evolution in nanocrystalline (NC) materials is studied, while the grain-size-dependent solute excess is given using Mclean’s equation. Satisfactory agreement between model prediction and experimental data from NC growth of dense NC gadolinia-doped ceria [J.L.M. Rupp, A. Infortuna, L.J. Gauckler, Acta Mater. 54 (2006) 1721–1730] has been achieved. Solute excess in GBs increases with grain growth and then tends to its saturated value, therefore, the inhibition of grain growth can be attributed to the reduction of GB energy through solute segregation, whereas, the consumed annealing time before the stop of grain growth is mainly affected by GB mobility.

In order to develop the ignition-proof magnesium alloy, the effect of alloying elements, Ca and Y, on the oxidation behavior of AZ91 magnesium alloy at elevated temperatures was investigated. The ignition-proof performance, oxide products and oxidation kinetics of Ca- and Y-containing AZ91 alloys were studied. The results indicate that the proper addition of Ca can increase the ignition point of AZ91 alloy greatly. However, the oxide film of Ca-bearing AZ91 alloy formed at elevated temperature is thick and brittle, which is prone to crack in melting and cooling process. In addition, the oxide film of AZ91-xCa alloy is incompact and cannot inhibit the diffusion of reaction particles. The oxide film of AZ91-xCa alloy turns to thin and plastic one after Y is added, and the density of the oxide film increases greatly due to the formation of composite oxide film composed of MgO, CaO and Y2O3.

The mechanical properties (σb, σ0.2, and δ) and fracture behavior of tensile specimens of the refined A356 alloys were investigated as a function of the addition level of Al-Ti-B master alloy under both as-cast and T6 heat-treated conditions. The results show that as the addition level of Al-5Ti-1B master alloy increases from 0.1 wt.% to 5.0 wt.%, the mechanical properties of refined A356 alloys improve steadily and then decrease slightly under both as-cast and T6 heat-treated conditions. Also, they display excellent mechanical properties with σb = 231.30–258.30 MPa, σ0.2 =134.00–155.50 MPa, and δ = 8.5%–11.75% at T6 heat-treated state. The excellent mechanical properties of refined A356 alloys are ascribed to the formation of α-Al equiaxed dendrites, the improvement of eutectic structure from needle/plate-like to short-lathy/block-shaped, and the Mg2Si aging precipitation phase after T6 heat treatment. The fracture surface examined by SEM exhibits a mixed fracture mode of refined A356 alloys at as-cast state, while it reveals a ductile fracture mode after T6 heat treatment.

A theoretical model for lamellar eutectic growth in undercooled eutectic alloy melts with a third element has been developed; it was assumed that no other phase forms. It is found that the tip radius of eutectic dendrite decreases with increasing content of the third element so as to diffuse away its enriched atoms ahead of the solidifying interface easily. A critical content exists below which the eutectic growth is accelerated within a certain undercooling range due to the third element addition, but slowed down otherwise. When more of the third element is contained, the growth velocity is always reduced. However, the eutectic lamellar spacing varies with the content in an opposite way. The influence of the third element addition is enhanced when the difference in distribution coefficients of the third element in two eutectic phases becomes greater.

The kinetics and thermodynamics of normal grain growth can be linked by two open questions. Is it physically practicable to incorporate the grain boundary (GB) energy decrease with GB segregation into the parabolic kinetics of grain growth? Subsequently, how can a model for grain growth that considers the mixed effect of kinetics and thermodynamics be derived? Departing from Borisov’s equation, a qualitative description is provided to validate the incorporation of GB energy into the grain growth kinetics. Then, a thermokinetic model considering the mixed effect of solute drag and reduced GB energy is developed. Subjected to specific limitations, the thermokinetic model reduces to a purely kinetic model, a purely thermodynamic model and a model considering only grain-size-dependent solute drag. By application of the model to experimental results obtained from nanocrystalline Ni–P and oxygen-doped nickel, it has been shown that the effect of solute drag could retard but not stop the grain growth, and that the main cause of a stabilized nanocrystalline structure is not the solute drag but the reduction in GB energy.

A solution entropy model was developed for the undercooled binary eutectic alloy systems. As an extension of Taylor and Fidler et al.’s model, the present model considered the change of phase composition with the increase of undercooling. Furthermore, the sub-regular solution model and the interaction parameter (I AB ) were also introduced. In this paper, the extended model is used to calculate the solution entropy for binary eutectic phases under the undercooled condition, and the application scope of the model is also extended. Not only the growth manner of eutectic phases, but also the transition of morphologies may be predicted and explained by calculating the solution entropy of eutectic phases under the non-equilibrium condition with the developed model. Experimental results show that the developed model is valid for the undercooled Ni-Si and Ni-Sn eutectic alloy systems.