Microstructural control and mechanical properties of Ti–47Al–2Cr–2Nb alloy by directional solidification electromagnetic cold crucible technique

Directional solidification experiments were performed on the intermetallic Ti–47Al–2Cr–2Nb (at.%) alloy by directional solidification electromagnetic cold crucible technique. The oxygen content was lower than 200 wt.ppm and this alloy solidified in fully primary β phase in cold crucible so that the lamellar orientations in the columnar grains were successfully controlled to be parallel or inclined to the growth direction. Then the effect of growth rate and temperature gradient on microstructure parameters was determined. It was found that the grain size and the interlamellar spacing decreased with increasing of growth rate or temperature gradient. Furthermore, the interlamellar spacing decreased with increasing of cooling rate according to the relationship λ ∝ v′−0.5. As-processed microstructure exhibited yield strength greater than 540 MPa at 800 °C and about 5% ductility at room temperature. The yield stress increased with decreasing of interlamellar spacing according to the Hall–Petch relationship at room and elevated temperatures.

► This alloy solidified in fully primary β phase in cold crucible.
► Lamellar orientations were aligned to the growth direction.
► Relationship between interlamellar spacing (λ) and cooling rate (v′) is: λ ∝ v′−0.5.
► Yield stress increased with decreasing of λ according to Hall–Petch relationship.