Cooling Rate Of Melt Research Articles

Effect of the Melt Cooling Rate on the Structural-Phase State of the Al–Si Alloy Doped with Metals

Effect of the Melt Cooling Rate on the Structural-Phase State of the Al–Si Alloy Doped with Metals

On the Effect of the Melt Cooling Rate upon Spinning on the Structure of the Surface Layers of Fe77Ni1Si9B13 Alloy Ribbons

On the Effect of the Melt Cooling Rate upon Spinning on the Structure of the Surface Layers of Fe77Ni1Si9B13 Alloy Ribbons

Structural rearrangements during sub-Tg relaxation and nucleation in lithium disilicate glass revealed by a solid-state NMR and MD strategy

Structural rearrangements taking place during relaxation and crystal nucleation in lithium-disilicate (LS2) glass have been investigated by a comprehensive set of solid-state nuclear magnetic resonance (NMR) experiments, supported by molecular dynamics (MD) simulations. Samples were subjected to heat treatments at 435 °C, i.e., 20 K below the laboratory glass transition temperature (Tg). Raman and NMR data indicate that under these conditions both relaxation and nucleation occur without detectable changes in the network former unit distribution of the glassy silicon-oxide network. Instead, relaxation of the frozen supercooled melt and nucleation of LS2 crystals occur principally in terms of a changing lithium local environment: 7Li spin-echo decay NMR indicates average Li-Li distances, characterized by homonuclear dipolar second-moment measurements, are reduced after very short heat treatments and approach those found in the isochemical crystal. This finding is supported by molecular dynamics (MD) simulations predicting a dependence of the Li+ ion distribution on the melt-cooling rate. In addition, the structural reorganization also impacts the distribution of electric field gradients as detected by 7Li satellite transition NMR spectroscopy. Finally, crystal nucleation becomes most evident by the appearance of minor amounts of sharp 29Si MAS resonances and a significant change in the 7Li NMR satellite transitions, as visualized by difference spectroscopy. This study defines a new NMR strategy, generally applicable for investigating the structural relaxation process accompanying the internal crystallization of ion-conducting frozen supercooled melts containing suitable NMR active nuclear probes (7Li, 23Na, 133Cs, etc.).

Melt Cooling Rate Effect on the Microstrucutre of Al–Si Alloy Doped with Mg, Mn, Fe, Ni, and Cu

Melt Cooling Rate Effect on the Microstrucutre of Al–Si Alloy Doped with Mg, Mn, Fe, Ni, and Cu

Investigation of Two-Phase State of Fe–Cu Melts during Cooling in a Viscometer

Fe–Cu alloys can be characterized as a system with immiscible components (IC). This statement is based on a weak mutual solubility in the solid state. In addition, Fe–Cu system stratifies in the liquid state at low carbon content. Alloys with ICs have a simple phase composition of almost pure components, which determines a significant practical interest in these alloys. Manufacturers have technologically succeeded in achieving damping alloys of Fe–Cu–Pb system. With proper technological preparation, the final product can be obtained by combining the properties of pure alloy components in the fraction required for practical application. For example, diamagnetic copper has high electrical conductivity and thermal conductivity in Fe–Cu alloys, while ferromagnetic iron has enhanced strength characteristics compared to copper. When the alloy structure is organized in a certain way, a final product can be obtained with high electrical conductivity and thermal conductivity of copper, enhanced strength properties of iron, or a hard magnetic material with copper ductility. The studies of iron-copper alloys focused on the structural studies and measurements of service properties. At the same time, the dynamics of macro- and microstructure alloy formation were not analyzed. In the present studies, the macrostructure formation dynamics of the solid phase enriched with iron at the crystallization melt process during cooling was studied using high-temperature viscometry. Due to the effect of the melt-cooling rate on the size and morphology of crystallizing inclusions, as well as a significant amount of the two-phase area, special attention was paid to the thermophysical analysis of the measurement mode. Analysis of the reliability of the results obtained was made by the viscosity measurement method. The phase state of Fe–Cu system melts was investigated during cooling by changing the damping factor. The analysis of thermophysical processes occurring during measuring the damping factor was carried out. The measuring process of damping decrement takes place under quasi-equilibrium conditions and the cooling rate is close to zero. There are no temperature gradients, both in radius and in height. For compositions Fe50Cu50, Fe40Cu60, and Fe30Cu70, the precipitation dynamics of the solid phase was determined.

Effect of Melt Cooling Rate on Microstructure of Sn - Bi and Sn - Pb Eutectic Alloys

The results of microstructure investigation of eutectic alloys Sn Bi and Sn Pb, obtained at cooling rates of the melt 10-2 K/s, 1 K/s and 105 K/s are represented. Various cooling rates are achieved by graphite mold casting and by ultra fast quenching from the melt. Microstructure and grain structure are investigated by scanning electron microscopy and the electron backscatter diffraction technique. It has found that the melt cooling rate increasing at rapid quenching leads to microcrystalline structure and to a change of the solidification mechanism. The reasons for the transition from lamellar to the microcrystalline structure are discussed.

Preparation and characterization of lead and zinc tellurite glasses

Glasses of two systems: xPbO–(100 − x)TeO 2 ( x = 13, 15, 17, 19 and 21 mol%) and yZnO–(100 − y)TeO 2 ( y = 18, 20, 22, 25, 30, 33 and 35 mol%) were prepared at two melt-cooling rates and characterized by density, UV–visible and Raman spectroscopy, DSC and XRD measurements. ZnO produces a larger compaction in the tellurite network than PbO. Density decreases with melt-cooling rate in both glass series. DSC studies found that the glass transition temperature decreases with increase in PbO concentration in lead tellurite glasses, but increases with increase in ZnO concentration in zinc tellurite glasses. Lead tellurites prepared at higher cooling rates were mostly amorphous while samples containing 19 and 21 mol% of PbO, prepared at slower cooling rates were translucent glass–ceramics containing crystals of PbTeO 3, Pb 2Te 3O 8 and TeO 2. These slowly cooled samples exhibit an absorption shoulder in the UV–visible absorption spectra, just below the absorption edge. This is attributed to excitonic transitions in nanocrystals that coexist with glassy phase in slowly cooled samples. Raman scattering studies found that the addition of PbO and ZnO produces an increase in the intensity of the absorption band between 720 and 745 cm −1 relative to the intensity of band between 645 and 670 cm −1. This is due to the continuous distortion of symmetry of TeO 4 units, leading to the creation of TeO 3+1 polyhedron and/or TeO 3 trigonal units. Raman studies found a very sharp peak at 76 cm −1 in both lead and zinc tellurite glasses. The position of this peak was independent of the glass composition.

Determination of the supercooling dependence of the (211) facet of BGO crystal on growth rate from the temporal dependence of supercooling at a prescribed melt-cooling rate

The results of determination of the supercooling dependence at the interphase boundary on the rate of growth from melt of the monocrystal Bi4Ge3O12 in the [211] direction are presented. Determination of supercooling was based on optical pyrometer measurements of the intensity of heat emission from the interphase boundary through the growing crystal. The crystal was grown by the AHF method (axial heat flux near the front of crystallization) by cooling the AHF heater at a specified rate. The growth rate corresponding to the measured supercooling value was determined by calculations. The study has shown that the supercooling is high and varies nonlinearly with the growth rate.