Effects of Crucible Wetting During Solidification of Immiscible Pb-Zn

TITLE AND SUBTITLE:
Effects of Crucible Wetting During Solidification of Immiscible Pb-Zn

AUTHOR(S):
Henry C. de Groh III and Hubert B. Probst

REPORT DATE:
December 1988

FUNDING NUMBERS:
WU-674-25-05-00

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191

PERFORMING ORGANIZATION REPORT NUMBER:
E-4419

SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Washington, DC 20546-0001

REPORT TYPE AND DATES COVERED:
Technical Memorandum

SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA TM-101372

SUPPLEMENTARY NOTES:
Material similar to that presented at the 27th Aerospace Sciences Meeting sponsored by the American Institute of Aeronautics and Astronautics, Reno, Nevada, January 9-12, 1989.

ABSTRACT:
Many industrial uses for liquid phase miscibility gap alloys have been proposed. However, the commercial production of these alloys into useful ingots with a reasonable amount of homogeneity is arduous because of their immiscibility in the liquid state. In the lowg environment of space gravitational settling forces are abated, thus solidification of an immiscible alloy with a uniform distribution of phases becomes feasible. Elimination of gravitational settling and coalescence processes in lowg also makes possible the study of other separation and coarsening mechanisms. Even with gravitational separation forces reduced, many lowg experiments have resulted in severely segregated structures. The segregation in many of these cases was due to preferential wetting of the crucible by one of the immiscible liquids. Our objective was to analyze the wetting behavior of PbZn alloys on various crucible materials in an effort to identify a crucible in which the fluid flow induced by preferential wetting is minimized. It is proposed that by choosing the crucible for a particular alloy so that the difference in surface energy between the solid and two liquid phases is minimized, the effects of preferential wetting can be diminished and possibly avoided. Qualitative experiments were conducted and have shown the competitive wetting behavior of the immiscible PbZn system and 13 different crucible materials. The three crucibles preferentially wet by Zn were attacked by the molten Zn and partially or completely dissolved. Of these Nb reacted the least. Of the crucible materials preferentially wet by Pb, carbon and tungsten had the largest dihedral angles, thus C and W are believed to have the smallest surface energy difference and therefore minimize the possibility of complete wetting and associated fluid flows. It is expected that this procedure will assist in the choice of crucibles, for other alloys as well as PbZn, which will reduce the fluid flow and segregation normally caused by competitive wetting in lowg.

SUBJECT TERMS:
Immiscible alloys; Crucible wetting; Pb-Zn; Segregation; Critical point wetting

NUMBER OF PAGES:
8

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