Segregation and grain refinement in cast titanium alloys

The growth restriction factor is a parameter derived from binary phase diagrams and is a useful predictor for the grain refining response when a solute is added to a base alloy. This work investigates the relevance of growth restriction theory to titanium alloys where solidification rates are an order of magnitude faster than previous studies in aluminum- and magnesium-based systems. In particular, the segregation of Fe and Cr in titanium is investigated and the effects on grain size studied. It was found that the Scheil equation reasonably modeled solidification of titanium where cooling rates approach 120 degrees C/s, and the growth restriction factors for Fe and Cr were useful in predicting prior-beta grain refinement. However, it was found that caution must be used when calculating growth restriction factors from binary phase diagrams.

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