Microgravity experiments to enhance development of ferrous castings: a literature review

摘要

A research program was initiated to determine the effects of microgravity on the solidification processes, microstructures and properties of cast irons and steels. The purpose was to identify those phenomena that are influenced by a gravity force vector, and to use the information obtained to find ways to improve the quality of iron and steel castings that are produced under normal gravity conditions. A literature search was completed to evaluate the current state of the art of the effects of micro gravity on the solidification of metals and alloys, and the results are summarized in this paper. Data from nonferrous alloy systems will show the following: 1. Normal macrosegregation observed at normal gravity levels is eliminated. 2. Limited data suggests that interdendritic solute enrichment increases under conditions of micro gravity. 3. Larger dendrite arm spacings are observed when solidification takes place under micro gravity conditions. 4. No consistent effects of microgravity on eutectic interphase spacing are observed. 5. Most driving forces for grain multiplication are absent under conditions of micro gravity. Evaluations of ferrous alloys will give the following results: 1. As in the case of nonferrous alloys, dendrite arm spacings increase under conditions of micro gravity. 2. Interphase spacing in the metastable Fe-Fe{sub}3C lamellar eutectic decreases under micro gravity conditions. 3. Solidification under micro gravity increases graphite flake size in the Fe-graphite eutectic. 4. Eutectic cell count decreases under conditions of microgravity. 5. Approximately 20-23% of eutectic nuclei results from convection-induced heterogeneous nucleation. The effect of inoculation on convection-induced nucleation requires more study. Proposals are presented to evaluate the effect of microgravity on the solidification of hypoeutectic cast irons. Experiments are proposed to evaluate the role of gravity in the segregation of silicon and manganese, and to study the role of sulfur in the nucleation of eutectic graphite under micro gravity conditions. It is also proposed that work be carried out to more completely define the effect of inoculants on eutectic nucleation. Experiments to examine the effect of micro gravity on the solidification of C and alloy steels are discussed. Finally, it is proposed that the mechanical properties of solidification structures developed under micro gravity conditions be determined.