| Abstrakt: |
For the volume changes accompanying solidification, distinctions are made between the volume change β for the whole freezing process, the volume change β for liquid entrapped within the freezing zone, and the localized volume change β accompanying the liquid-solid phase transformation at a given temperature. The first volume change is important in mold design, while the latter two are important factors in the formation of casting defects such as shrinkage pores, solidification cracks, and inverse segregation. Values of β , β, and β are deduced for equilibrium conditions in the representative alloy systems Al-Cu, Bi-Sb, Fe-C and Pb-Sn. While the volume change β may vary only moderately with alloy composition, β is a strong function of composition and of the temperature of enclosure. The isothermal volume change, β , equal to the relative density difference between solid and liquid, varies during the freezing process and is strongly dependent upon composition. Isothermal volume changes and hence density differences as large as 20 pct are deduced for some Bi-Sb and Pb-Sn alloys. [ABSTRACT FROM AUTHOR] |
