Grain Refining and Microstructural Modification during Solidification.

The objective of the program is to study grain refining and microstructural modification during solidification, as affected by supercooling, solidification rate, andor inoculation. The report summarizes some of the findings from the first year of the program and covers details of the current investigations on the structure and phase transformations in Cr-Ni alloys, the effect of electromagnetic stirring on the structure of Cr-Ni alloys, and grain refining via peritectic transformations in Cu. The effect of iron and niobium additions on the grain size of copper was studied. The experiments showed that iron is effective in reducing as-cast grain size of copper in concentrations as low as 1.0 percent, and the grain size decreased with increasing the amount of iron. Research on the solidification of Cr-Ni alloys has led to the observation of various phase transformations in the alloy system. The results indicate that the accepted phase diagram for Cr-Ni, consisting of a eutectic transformation only, is incorrect. The effect of electromagnetic stirring on the structure of Cr-Ni alloys has been shown to cause considerable dendrite fragmentation, and consequently grain refinement.