Effect Of Undercooling Research Articles

Crystal multiplication in undercooled Cu + 2 Pct Sn alloy

The effects of undercooling (AT) from 10 to 175° on grain structure were observed in a Cu + 2 wt pct Sn alloy, in which grain refinement does not occur at large degrees of under-cooling. Quenching soon after recalescence retained transient grain structures not previ-ously reported in the literature. Crystal multiplication by dendrite fragmentation occur-red when undercooling below the liquidus lay in the range △T = 10 to 70°, and resulted in complete grain refinement in the range △T = 50 to 70°. Fragmentation affected primary, secondary and tertiary dendrite arms during and after recalescence. At △T = 70° a sharp transition occurred to a radiating fan-shaped structure of twin-related grains ori-ginating from a single point of nucleation, with no evidence of fragmentation. It is pro-posed that the transition results from a change in the free dendritic growth mode, the new shape being a wholly primary form without side-arms. The absence of fragmentation in this range (△T > 70°) suggests that self-buckling contributes to fragmentation in the other range (△T < 70°) and could be at least equal in importance to remelting.

Metallography of aluminum and it's alloys solidified under high hydrostatic pressure

This paper reports macroscopic and microscopic metallography of aluminum and its alloys solidified in a cylindrical die under high hydrostatic pressure of 1000-6000kg/cm2.When the pressure was applied at 50-60°C higher than the melting temperature, columnar crystals, which had originated on the surface of die, easily developed towards the center of die, although other conditions were selected to allow the formation of equi-axed crystals under normal pressure. Less superheating, on the other hand, often generated a center zone of equi-axed crystals, and the zone was wider with the increase of pressure. Preferential linear growth of dendrite stems in columnar zone remarkably occurred under high pressure, and exclusion of solute to liquid side of solid/liquid interface was facilitated by the application of high pressure. It resulted in normal segregation in aluminum-silicon and aluminum-copper alloys. When the pressure was constant and the temperature at which pressure was applied was lower, the equiaxed zone was wider, and the crystals were finer by the effects of undercooling (accompanied by the rise of the melting temperature) and rapid cooling. It was found that pure aluminum solidified at 11°C higher than normal melting temperature under applied pressure of 1500kg/cm2.

The setting temperature of pectin jellies

AbstractThe setting temperature of a pectin jelly is shown to be a determinate physical property, whereas the setting time is a secondary property dependent on temperature conditions. A technique for measuring setting temperature is described. As ordinarily manifested the setting temperature is subject to undercooling effects. It is shown that, as with jelly strength, PH conditions are a primary factor in regard to setting temperature, increase of PH causing a rapid fall of the latter; and that soluble solids concentration, pectin concentration, nature of buffer cations and heating have subsidiary effects. The setting temperature does not appear to be related to the jelly strength in any direct way, as judged by a comparison of the effects of the factors studied on the two properties.

The Undercooling of some Aluminium Alloys

ALTHOUGH the undercooling of pure metals was observed by Roberts-Austen so long ago as 1898, no experiment have so far been published regarding the super of although explanations of certain structte have been based on their existence particularly regard to eutectics. The recent May Lecture of Sir Henry to the Institute of Metals o.n The Growth of Crystals in Supersaturated Liquids is now followed by a paper by Dr. Marie L. V. Gayler, delivered before the Institute of Metals on Sept. 7, on the effects of undercooling in some alloys of aluminium, in par-ticular with silicon. The work was carried out for the Engineering Research Board at the National Physical Laboratory under the supervision of Dr. W. Rosenhain and breaks entirely new ground. For the first time the supersolubility curves for an alloy system are available, and with their aid an explanation of the structures of the aluminium-silicon alloys can be offered with a considerable degree of certainty.