Investigation on the phase separation in undercooled Cu–Fe melts

On the basis of the gravity difference and the temperature dependence of the interfacial energy of the separated phases, the amalgamation of the droplets of minor phase was affected by Stokes sedimentation and Marangoni motion during the liquid-phase separation. Moreover, the velocity of Stokes motion increased distinctly with the undercooling, while the velocity of Marangoni motion was slightly impacted. At the beginning of the liquid-phase separation, the droplets of minor phase were dominated by Marangoni motion when the droplets radius was small. As the droplets radius increased by combination, the effect of Stokes sedimentation strengthened gradually. Additionally, the coagulation process was mainly controlled by Stokes sedimentation when a critical radius r_d was far exceeded.     

Liquid–liquid transitions,crystallization and long range fluctuations in supercooled yttrium oxide–aluminium oxide melts

Employing small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) combined with laser-heated aerodynamic levitation has enabled different transitions in supercooled yttrium oxide–aluminium oxide to be distinguished. These include liquid–liquid phase transitions as well as high temperature crystallization for different compositions. Prerequisites for avoiding crystallization in order to reveal polyamorphic phase separation in the supercooled state are established. We also show how the rise in SAXS intensity at low wavevectors can be used to identify correlation distances in long range fluctuations in high temperature melts. These distances appear to scale with melt viscosity and to extend temporarily during liquid–liquid transitions.     

Thermal expansion and density of glassy PdNiP and PtNiP alloys

Thermal expansion and density of (Pd_1?xNi_x)_0.80P_0.20 and (Pt_1?yNi_y)_0.75P_0.25 alloys in their various states have been measured from room temperature to the glass transition temperature T_g. The thermal expansion of the glassy alloys at room temperature varies linearly with x and y and is 10 to 20% higher than that of corresponding pure metals. The thermal expansion of the undercooled alloy liquids near T_g as well as the molar volume $\text{v}\text{?}$ deduced from the density of glasses in contrast exhibits a negative deviation with composition x and y.This behavior is in line with the previously reported negative deviation of the glass transition temperature of these glassy alloys with metal content and may be explained in terms of excess volume associated with a mixture of hard spheres.     

Composition dependence of the glass transition temperatures of PdNiP and PtNiP glasses

Thermal properties of glassy PdNiP and PtNiP alloys have been measured as a function of the concentration of transition metals. The glass transiion temperature, T_g, of these alloys glasses exhibits a negative linear deviation with transition metal content - which is in contrast to the increasing T_g of binary glassy alloys with increasing metalloids.It is suggested that the suppression of the glass transition temperature of these glassy alloys may be attributed to the excess configurational entropy of disorder associated with a mixture of hard spheres differing in radius. In contrast, the increasing T_g of binary glassy alloys with the metalloid content may be associated with the short-range order resulting from strong interactions between metal and metalloid atoms.     

Experimental determination of the solid–liquid equilibrium,metastable zone,and nucleation parameters of the flunixin meglumine–ethanol system

Measurements of the metastable zone and solubility for flunixin meglumine–ethanol system were obtained. The solubility was measured within the temperature range from 288.15 to 328.15 K. The mole fraction solubility was correlated satisfactorily with the temperature by the equation: x_eq=2.35×10^?12e^0.07121T. The value of enthalpy of dissolution, enthalpy of fusion and enthalpy of mixing were determined to be 49.04, 64.03 and ?14.99 kJ mol^?1 respectively. The metastable zone width of flunixin meglumine was measured by an electric conductivity method. A comparison of the nucleation temperatures from electric conductivity measurement and from focused beam reflectance measurement (FBRM) shows that both detection techniques give almost the same results for flunixin meglumine. The nucleation parameters of flunixin meglumine in ethanol were determined from the metastable zone data. Over the equilibrium temperature range from 312.28 to 325.55 K, the nucleation rate constant was varied from 0.00001 to 0.00120 #/m² min, whereas the nucleation order was varied from 2.23022 to 3.39299. The obtained high values of nucleation order indicated a high rate of nucleation.     

The internal friction and elastic modulus of amorphous Pd–Si and Fe–P–C alloys

The internal friction and the shear modulus of the amorphous Pd₈₀–Si₂₀–, Fe₈₀–P₁₃–C₇ and Fe₅₀–Ni₃₃–P₁₂–C₅ alloys have been measured at about 0.5 Hz over a temperature range from room temperature to about 550°C. The internal friction rises steeply with temperature and shows maxima around the crystallization temperature. The activation energy for the steeply rising internal friction has been estimated by the two different procedures; from the shift of the curve by the frequency change and from the slope of the In Q^?1 versus 1/T plot. The two values are very different, which indicates the existence of a wide distribution of activation energies. Crystallization of the amorphous alloys resulted in an increase of about 30% in the shear modulus.     

Solid–liquid interfacial energy of neopentylglycol solid solution in equilibrium with neopentylglycol–(D) camphor eutectic liquid

The grain boundary groove shapes for equilibrated solid neopentylglycol (NPG) solution (NPG–3 mol% D-camphor) in equilibrium with the NPG–DC eutectic liquid (NPG–36.1 mol% D-camphor) have been directly observed using a horizontal linear temperature gradient apparatus. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficient (Г), solid–liquid interfacial energy (σ_SL) of NPG solid solution have been determined to be (7.5±0.7)×10^?8 K m and (8.1±1.2)×10^?3 J m^?2, respectively. The Gibbs–Thomson coefficient versus T_mΩ^1/3, where Ω is the volume per atom was also plotted by linear regression for some organic transparent materials and the average value of coefficient (τ) for nonmetallic materials was obtained to be 0.32 from graph of the Gibbs–Thomson coefficient versus T_mΩ^1/3. The grain boundary energy of solid NPG solution phase has been determined to be (14.6±2.3)×10^?3 J m^?2 from the observed grain boundary groove shapes. The ratio of thermal conductivity of equilibrated eutectic liquid to thermal conductivity of solid NPG solution was also measured to be 0.80.     

Investigation of glass forming ability in Ce–Al–Ni alloys

The compositional dependence of the glass forming ability (GFA), the correlation between their GFA and the GFA related parameters, and the thermal stability of the Ce–Al–Ni alloys were investigated. Rapidly quenched Ce₆₅Al_xNi_35 ? x (x = 2, 5, 10, 17, 20) and Ce₇₀Al_xNi_30 ? x (x = 2, 5, 10, 15, 20) ribbons were prepared by melt spinning, and their phase transformations were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The experimental results indicated that the GFA of Ce₆₅Al_xNi_35 ? x (x = 2, 5, 10, 17, 20) and Ce₇₀Al_xNi_30 ? x (x = 2, 5, 10, 15, 20) alloys increased firstly and then decreased with the increasing of the Al content up to 20 at.%, respectively. It was found that only one parameter, F₁, in evaluated currently available empirical GFA parameters searching for metallic glasses with a good GFA, can reflect the GFA of the Ce–Al–Ni alloys. It was indicated that the thermal stability of alloy with fully amorphous maybe lower than that of alloy with partial amorphous.     

Solid–liquid interface energies in the succinonitrile and succinonitrile–carbon tetrabromide eutectic system

The equilibrated grain boundary groove shapes for the commercial purity succinonitrile (SCN) and succinonitrile–carbon tetrabromide (CTB) eutectic system were directly observed. From the observed grain boundary groove shapes, the Gibbs–Thomson coefficients for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been determined to be (5.43±0.27)×10⁻⁸ Km and (5.56±0.28)×10⁻⁸ Km, respectively, with numerical method. The solid–liquid interface energies for the solid SCN–liquid SCN and solid SCN–liquid SCN CTB have been obtained to be (7.86±0.79)×10⁻³ J m⁻² and (8.80±0.88)×10⁻³ J m⁻², respectively from the Gibbs–Thomson equation. The grain boundary energies in the SCN and SCN rich phase of the SCN–CTB system have been calculated to be (15.03±1.95)×10⁻³ J m⁻² and (16.51±2.15)×10⁻³ J m⁻², respectively, from the observed grain boundary groove shapes. The thermal conductivity ratios of the liquid phase to the solid phase for SCN and SCN–4 mol% CTB alloy have also been measured.     

Formation of a blocky ferrite in Fe–Cr–Ni alloy during directional solidification

Formation and evolution details of a blocky microstructure in AISI 304 stainless steel are studied by quenching method during directional solidification. Results show that a coupled growth microstructure, consisting of lathy ferrite and austenite, forms first from the melt. At solid-state transformation stage, most lathy ferrite disappears due to the phase transformation from ferrite to austenite. With further decreasing of the temperature, plenty of fine ferrite colonies occur in the original austenite region. The formation of the blocky ferrite indicates that reverse solid-state transformation from austenite to ferrite takes place. This transformation is due to the segregation and the instability of austenite during the growth of austenite under low cooling rate. The fine ferrite colonies transform into blocky ferrite at room temperature. TEM and EDS analyses were carried out to identify the phases and determine the phase composition, respectively.     

Specific Features of Microstructure Formation in Co–Cr–Ni–W–Ta Alloys and Their Mechanical Properties

Crystallography Reports - The microstructure and mechanical properties of three experimental compositions of a new heat- and corrosion-resistant cast cobalt-based alloy have been investigated. It...     

Usual stress relaxation in an ‘unusual’ Pd40Cu40P20 metallic glass

This work presents isochronal and isothermal shear stress relaxation measurements in glassy Pd₄₀Cu₄₀P₂₀, which is uniquely denser as compared with the reference tetragonal Pd₂Cu₂P crystal. However, the relaxation kinetics of this glass in different structural states is quite similar to that in ‘usual’ metallic glasses confirming a minor role of the free volume in the flow behavior below T_g.     

Phase transformation regularities of Zn in the solution systems by solid–liquid reaction milling

Zn powders were milled by stainless steel balls in the aqueous solution whose PH value were adjusted to 3, 7, and 11, respectively. Zn(OH)₂ and ZnO powders could be synthesized via this novel solid–liquid ball milling method. The compositions and the microstructures of the as-milled products were characterized by X-ray diffraction and SEM, respectively. The experimental results showed that the higher PH value is helpful to accelerate the reaction between Zn and H₂O. ZnO is the preferential product in the neutral and alkaline solutions. As a preferential product, a large number of ZnO could be obtained in the neutral and alkaline solutions after reaction. Finally, the phase transformation regularities of the as-milled products were also discussed.     

Direct density determination of low- and high-density glassy polyamorphs following a liquid–liquid phase transition in Y2O3–Al2O3 supercooled liquids

Evidence has been presented for a density-driven phase transition occurring between supercooled liquids in the system Y₂O₃–Al₂O₃. The high- and low-density liquids were quenched to metastably coexisting glasses. Chemical analysis showed the compositions of the two glasses to be identical, and it was inferred that they differed in their densities and entropies. The entropy difference has been verified by calorimetry. Here, we confirm that the chemical compositions of the glassy materials derived from the high- and low-temperature liquids are identical. We present a direct density determination of the two glasses using sink-float techniques. The measured densities are 3.72(3) g/cm³ for the glass derived from the high-temperature liquid (i.e., the high-density amorphous or HDA polyamorph), and 3.58(1) g/cm³ for the low-temperature (low-density, LDA) polyamorph.     

Short-range structure and in vitro behavior of ZnO–CaO–P2O5 bioglasses

Ternary zinc–calcium-phosphate glasses prepared by classical melting method were characterized through X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) along with energy dispersive X-ray analysis (EDAX), Fourier Transform InfraRed (FTIR) and Raman spectroscopy. The study of these glasses was done in order to supply information regarding their structural particularities since the zinc role in biological environment, especially in the bone, is still under debate.XRD analysis confirmed the vitreous character of the as-prepared samples, while SEM and EDAX measurements indicated the presence of some non-homogeneous domains on their surfaces with approximately similar elemental composition. According to FTIR and Raman spectroscopy, the local structure of glasses up to 10 mol% ZnO is mainly built by Q² tetrahedrons connected by P–O–P linkages. For 50 mol% ZnO, the modifier role of zinc ions is strongly reflected on the local structure dominated in this case by Q¹ pyrophosphate units.The surface reactivity of the samples has been analyzed in vitro by immersion in simulated body fluid (SBF) at 37 °C. XRD, SEM–EDAX, FTIR and Raman methods were employed to characterize the structural changes that occurred on the surface of ZnO–CaO–P₂O₅ samples reacting with SBF. The X-ray diffraction patterns demonstrated the formation of a hydroxyapatite layer on the samples surface while the other used methods didn't reveal concisely that phenomenon. Based on X-ray measurements, the influence of zinc concentration on the hydroxyapatite layer development was followed.     

Emission Mössbauer Spectroscopy of Grain Boundaries in Ni–34%Cu Alloy

Crystallography Reports - The grain boundaries in Ni–34%Cu alloy have been analyzed by emission Mössbauer spectroscopy. The mechanism of grain-boundary Co diffusion in the alloy and the...     

Composition analysis of glasses in the PbBr2–PbCl2–PbF2–PbO–P2O5 system

Composition change during the melting process of some glasses in the PbBr₂–PbCl₂–PbF₂–PbO–P₂O₅ system melted at 450–470°C for 15 min was studied. Results show that there was a remarkable difference between the batch composition and the analyzed composition. Large amount of P, Br, Pb, and Cl were lost mainly in the form of PbBr₂, PbCl₂ and P₂O₅. The content of O is influenced by two factors. The incomplete decomposition of NH₄H₂PO₄ or the reaction between P₂O₅ and H₂O in the atmosphere increases the content of O, while the volatilization of P₂O₅ decreases the content of O.