Fundamental Research On The Removal Of Metal Impurities During The Electromagnetic Directional Solidification Of Titanium-silicon Alloys

The migration and segregation of impurities in the directional solidification process have an important influence on the purification of Si enriched layer and Ti-Si eutectic alloy layer.In this paper,on the basis of the separation of silicon and Ti-Si alloy by electromagnetic induction directional solidification,the experimental research on impurity removal of titanium silicon alloy by electromagnetic induction directional solidification was carried out.high silicon Ti-Si alloy is taken as the research object.In different mass ratio of Ti-Si alloy directional solidification ingot,the migration rule and solidification segregation behavior of impurities in silicon enrichment layer,Ti-Si eutectic alloy layer and impurity enrichment layer are studied respectively.The distribution and composition phase of impurities in each layer are studied in order to be impurities in silicon enrichment layer and titanium silicon eutectic alloy layer The further purification in is the foundation.Taking the Ti-Si alloy ingot with Ti-Si mass ratio of 1:9 as the research object,the impurity removal in the silicon enrichment layer was studied.The experimental results show that under the experimental conditions,the most suitable pull-down rate is 5?m/s,which can shorten the time of directional solidification as much as possible on the premise of ensuring high impurity removal efficiency.At this pull-down rate,the average content of silicon enriched layer decreased from 2800 ppmw,1700 ppmw and 260 ppmw to 29.65 ppmw,12.55 ppmw and 36.85ppmw,respectively,with the average removal rate of 98.94%,99.26%and 85.83%.Impurities in the silicon enrichment layer are mainly concentrated at the bottom and top of the silicon enrichment layer.The residual impurity phase at the bottom is caused by heterogeneous nucleation.The impurity phase is mainly Si C and Ti Si₂,while the top is mainly caused by the continuous directional solidification.The concentration of impurities in the melt increases gradually,and then reaches its segregation limit.The impurity phase is mainly Ti Si₂,?₅ and?₁.The removal of impurities in eutectic alloy layer was studied by directional solidification of Ti-Si alloy ingot with Ti-Si mass ratio of 2:8.The experimental results show that the impurities in the whole eutectic alloy layer increase gradually in the longitudinal distribution.When the pull-down rate is 5?m/s,the content of Fe,Al and Ca in the bottom of the eutectic alloy layer decreases from 3600 ppmw,1900 ppmw and 200 ppmw to 45 ppmw,24 ppmw and 32 ppmw,respectively.The removal rates are 98.75%,98.74%and 84%.Because the pushing rate of impurities at the liquid-solid interface is lower than the pulling rate,there is impurity phase residue at the top of the Ti-Si eutectic alloy layer.The residual impurity phase is mainly composed of two parts,?₅ phase formed by solid solution in Ti Si₂ crystal and Fe Ti Si₂ phase formed on Ti Si₂ crystal boundary.In this paper,the solidification segregation behavior of impurities in the Ti-Si alloy ingot with Ti-Si mass ratio of 1:9 and 2:8 was studied.The experimental results show that with the directional solidification,the iron impurity phase in the impurity enrichment layer is mainly formed by the transformation from Ti Si₂ phase to?₅ phase and from?₅ phase to?₁ phase,and the precipitation of silicon phase exists in the transformation process,which makes the grain volume of the impurity phase in the ingot increase gradually,the proportion area of silicon phase increases,and the distribution of Ti Si₂ decreases gradually.In addition,the precipitation of impurities in the impurity enrichment layer has obvious directionality.As the directional solidification proceeds,the grain direction gradually changes from the direction parallel to the longitudinal axis of the ingot center to the top of the ingot to the direction of the melt to the crucible.