Eutectic growth kinetics and microstructure evolution of highly undercooled Ti86.33Si13.67 alloy at electrostatic levitation state

Abstract

Eutectic growth kinetics and microstructure evolution of highly undercooled Ti86.33Si13.67 alloy were systematically investigated using electrostatic levitation technique, and the maximum undercooling achieved was up to 343 K (0.21 TE). The experimental undercooling is rather low if the overheating degree is below a critical value, while that is high at the overheating degree beyond this value. The critical overheating degree is in the range from 60 to 86 K. The average eutectic growth velocity increases dramatically with the undercooling. The microstructure was proven to be consisted of α-Ti phase and Ti5Si3 phase. A small amount of metastable β-Ti phase inside the α-Ti phase was found for the alloy solidified at 343 K undercooling, and the orientation relationship between α-Ti phase and β-Ti phase is (110) β-Ti // (002) α-Ti. For the primary Ti5Si3 phase, it can be obtained in the microstructure solidified at low undercoolings, but cannot be found when the undercooling is larger than 200 K. The cluster like eutectic gradually occupied the whole alloy space with the increasing undercooling, and the irregular eutectic microstructure is confirmed to be directly generated from the undercooled liquid phase at high undercoolings.