Microstructure, tensile properties and creep behavior of high-Al TiAlNb alloy using electromagnetic cold crucible continuous casting

Abstract

Newly designed Ti–47Al–10Nb alloy was prepared at growth rates ranging from 0.3 mm/min to 1 mm/min under power of 45 kW using electromagnetic cold crucible continuous casting technique. The macro/microstructure, tensile properties and creep behavior are studied. Results show that this alloy can be directionally solidified at growth rates from 0.3 mm/min to 0.7 mm/min, and this alloy exhibits the β-solidification at growth rates from 0.3 mm/min to 1 mm/min. The lamellar spacing decreases with the increasing of growth rate, and the relationship between lamellar spacing and growth rate can be fitted by d=371.2V−0.56. The directional solidification structure has little effect on room temperature ultimate tensile strength, and the creep properties strongly depend on the directional solidification structure. At the optimum preparation parameters of 0.5 mm/min and 45 kW, this alloy exhibits the good room-temperature tensile properties with ultimate tensile strength 562 MPa and elongation 1.42%, and the minimum strain rate is 4.31 × 10−8s−1 during creep at 800 °C/200 MPa. Moreover, in directional solidification structure, the plastic incompatibility of lamellar colonies leads to the local stress concentration at the steps of vertical colony boundary, which promotes the formation of cavities and cracks at colony boundary.