SOLIDIFICATION PARAMETERS AND STRUCTURES IN THE COLUMNAR TO EQUIAXED TRANSITION IN LEAD TIN ALLOYS

A. E. ARES; C. E. SCHVEZOV

, San Diego, California. USA

Conferencia; SOLIDIFICATION 1999; 1999

The Minerals, Metals and Materials Society

Lead Tin alloys were solidified directionally upwards under different thermal conditions and alloy compositions in order to study the conditions for the columnar to equiaxed transition as well as the solidification parameters during both the columnar and equiaxed growth. The alloy compositions employed were Lead-containing Tin from 2% to 40%. A number of relevant solidification parameters were determined from the measured temperatures such as temperature gradients, position of the liquid and solid fronts, solidification velocity, amounts of heat extraction. In addition, the sizes of the columnar and equiaxed grains were determined. The results show that there are critical low values of gradients, heat flow and solidification speed associated with the transition. These values are independent of the columnar size and alloy composition. There is recalescence observed and associated with the transition whose magnitude is measured. The speed of liquidus front determined from the temperature measurements show a sudden acceleration. These results are presented, analyzed and compared with theory.