Continuous Casting and Directional Solidification of Titanium Alloys with Cold Crucible

摘要

Titanium alloy billets were continuously cast and directionally solidified under vacuum and compelling cooling conditions by using round or rectangular cross-section cold crucible. It is found that hot crack is caused by friction between the skull and the inner wall of crucible, a coating of CaO and CaF_2 flux can eliminate the hot cracks. The experimental results show that the withdrawal velocity, where the changes was setting as 5, 3, 1, 0.5mm/min respectively, is the significant factor that affects the macrostructure and solidification front shape from concave to flat and then to convex. Directional columnar grains and a single crystal can be obtained when the velocity is controlled to either 1 or 0.5mm/min under a round cross-section crucible, and columnar grains can be also obtained at the speed of 2mm/min under a rectangular cross-section crucible. Finally, the temperature fields during the process are calculated and the trend of solidification front is in good agreement with the experiment. Specimens composed of columnar grains or single crystal exhibit excellent tensile properties.