Directional solidification of TiAl–W–Si alloy by electromagnetic confinement of melt in cold crucible

Abstract

The directional solidified Ti-46Al-0.5W-0.5Si alloy with lower oxygen content has been performed successfully by electromagnetic confinement of melt within a water-cooling inductive cold crucible device. By varying the growth rate from 0.5 to 1.5 mm/min, the effects of growth rate on primary phase selection and solidification path as well as structure characteristics either in macro- or micro- scale were determined. The results reveal that the alloys will display β phase primarily when the peritectic reaction completed at a growth rate of less than 1.0 mm/min, which implies that the brittle lamellae with orientation that is perpendicular to the crystal growth direction might be disappeared accordingly. It is also found that the average columnar grain size decreased from 312 to 126 μm with increasing of the growth rate, which is in balance with the similarity of primary dendrite arm spacing (PDAS) λ decreased according to a relationship of λ ∝ V−0.41. Due to the oxygen content is reduced to a lower degree for individual DS sample, the oxygen stabilizing effect on yielding α phase to participate primarily seems to be retarded to some extent. Thus, by controlling the directional solidification processing with cold crucible, the gamma based fully lamellar dual-phase DS Ti-46Al-0.5W-0.5Si alloy exhibits good combination of tensile properties at ambient temperature, in which it yields more than 479 MPa of yield strength and as much 3.6% in maximum of fracture elongation.