Showing papers on "Directional solidification published in 1973"

Eutectic Solidification of MgO-MgAl2O4

Abstract: Directional solidification of the MgO-MgAl2O4 eutectic yields MgO whiskers in a spinel matrix. Microstructures produced at solidification rates of 0.4 to 30.0 cm/h were studied. The interlamellar spacing agrees with the inverse-square-root dependence on solidification rate. Colony-free microstructures formed in all ingots solidified at rates of <2.0 cm/h. For ingots solidified with planar growth, the orientation relation of the phases is:

The ZnP 2 -Ge system and growth of single crystals of ZnGeP 2

Abstract: The phase relations in the ZnP2-Ge join in the Zn-Ge-P system were determined. ZnGeP2 melts congruently at 1027 ± 3°C and undergoes a solid state transformation at 950 ± 5°C, in agreement with previous work. The low temperature phase, designated as αZnGeP2, has the tetragonal chalcopyrite structure, while the structure of the high temperature phase, designated as βZnGeP2, is unknown. Two eutectics are present: one between αZnGeP2 and Ge at 865 ± 4°C and 95 mol % Ge, and the other, between βZnGeP2 and ZnP2 at 970°C ± 4°C and 15 mol % Ge. Large crack- and bubble-free single crystals of ZnGeP2 can be grown by directional solidification without seeding, and the phase transition appears to be no impediment to the growth of large crystals. The extra absorption of a few cm-1 which exists between the band edge and 2μ has been shown to depend on crystal growth conditions. The source of the absorption, however, has not been identified. The absorption spectrum of a crystal grown from a liquid Bi-Pb alloy is compared with the spectra of crystals grown directly from ZnGeP2 melts.

Method for directional solidification

Abstract: Method and apparatus for improving the prodution rate of directionally solidified castings employing an annular mold having one or more molding cavities therein and a pair of heat radiating elements disposed concentrically with the mold, one being located inside and the other being located outside the mold, the heat radiating elements being arranged so that no temperature gradient exists across the mold. A pair of heat sinks is provided, the heat sinks being coaxial with the two heat radiating elements. Means are provided for causing relative movement between the annular mold and the heat radiating elements and the coaxially aligned heat sinks. The annular mold is positioned on a highly heat conductive pedestal or chill. The mold is preheated by the heat radiating elements to a temperature above the solidification temperature of the metal to be cast. After casting, the solidification of the metal progresses upwardly from the chill and the relative movement between the annular mold and the heat radiator-heat sink combination causes the solidification innerface to occur at or near the boundary between the heat radiators and the heat sinks. A baffle is advantageously positioned at this boundary to prevent heat being radiated from the heat radiators to the heat sinks. The solidified metal in passing through the heat sinks radiates heat uniformly to the heat sinks so as to prevent a lateral or radial thermal gradient across the mold during solidification of the metal therein.

The melt growth and doping of CdGeP2

Abstract: Crystals of the ternary chalcopyrite CdGeP2 have been grown from doped and undoped melts by directional solidification. We find that the stoichiometry and temperature gradient in the melt are critical factors in determining crystal quality. The effect of excess phosphorous is particularly dramatic, causing a rapid deterioration of crystal quality when the excess is greater than 3 at.% in the charge. This empirical observation led us to perform measurements of the total vapor pressure over CdGeP2 as a function of temperature. The vapor species was found to consist almost entirely of phosphorous and the measured pressure at 790°C was 1.92±.15 atm. An extensive search for dopants suitable for the production of low-resistivity CdGeP2 was unsuccessful. It was found that doping heavily with In and Ga produced high-resistivity n- and p-type crystals, respectively, but no shallow donors or acceptors were found.

The effect of an electric field on the solidification of off-eutectic tin-lead composite alloys

Abstract: The influence of an electric field upon the directional solidification of hypoeutectic and hypereutectic Sn-Pb composite alloys was studied. Equations were derived to account for the effect of electrotransport of solute in the liquid upon the solid composite composition. Experimental results support the theoretical predictions. Mixing in the liquid is more strongly influenced by unstable solute gradients than by current induced convection. Electrotransport shows limited promise as a method for control of the volume fraction fibre phase in the preparation of aligned composites by directional solidification.

Nonmetallic inclusions in magnetic alloys of the YuNDK35T5 type

Abstract: 1. The results obtained only partially confirm the assumption that titanium nitrides and oxides impair the columnar solidification of YuNDKT alloys [4–6], since titanium oxides are not observed in the presence of aluminum, and titanium carbonitrides (nitrides) exist in the alloys without additions of sulfur and carbon, which along with the aluminum oxides may affect the solidification of the alloy. 2. The addition of sulfur and carbon results in the fact that some of the aluminum oxides and titanium carbonitrides are isolated from the heat by titanium sulfides and carbosulfides, which is full agreement with the assumptions made in [2, 11]. Other mechanism may also operate, as the result of which sulfur and carbon evidently form gaseous oxides that carry along solid particles of carbonitrides and aluminum oxides. This is confirmed by the formation of substantial clusters of corundum and carbonitrides in the head of castings with directional solidification when sulfur and carbon are added.

Formation of CO and Macrosegregation during Uni-directional Solidification of Iron

Abstract: Synopsis: Experimental studies have been made of the uni-directional solidification of iron with a view of studying the mechanism of solidification with the formation of CO. From the experiments at the solidification velocity of 5mm/min and [%C]L•¬0.1, it is shown that oxygen contents of 0.003 to 0.006% correspond to the transitional concentrations for the formation of CO bubbles and macrosegregation. In this concentration range elongated blowholes are formed, resulting in lowering kc* and kp*. At oxygen contents higher than 0.006%, kp* is unaffected by the increase of oxygen concentration of the melt, whereas kc* tends to decrease at high oxygen contents. An expression has been derived to predict the onset of constitutional supercooling for the case of solidification without the formation of CO. From the calculation, it is suggested that the solidification morphology at oxygen contents below 0.003% is dendritic structure. The solute distribution at solid-liquid fronts growing with bubble formation is explained on the bases of the model that the enriched liquid is being pushed to the liquid ahead of the growth front. Due to the consumption of carbon in the reaction with oxygen kc* is lowered more than kp*. It is shown that the present data give a satisfactory explanation to the phenomena occurring during solidification of a rimming steel.