Investigation of macro/microstructure evolution and mechanical properties of directionally solidified high-Nb TiAl-based alloy

Abstract

Newly designed Ti44Al6Nb1.0Cr2.0V0.15Y0.1B (at.%) alloy was prepared by vacuum consumable melting technology (melted two times), and then it was processed by cold crucible directional solidification (CCDS) technology at input power of 45kW and a range of pulling velocities. The macro/microstructure evolution and mechanical properties are investigated in detail, and the results can be concluded as follows. Directional macrostructure can be acquired at pulling velocity of 8.33μm/s or 10μm/s, however, when pulling velocity is higher, the refined colonies are presented instead of the directional macrostructure. After CCDS, microcrack can be eliminated, and higher percentage of small angle lamellas can be acquired for the well directionally solidified billets. Solidification course and CCDS macro/microstructure evolution are expressed by schematic. The Desirable CCDS macro/microstructure contributes to the better mechanical properties including tensile properties at room temperature and high temperature, three-point bending property and fracture toughness, and the related mechanism are discussed. Moreover, the relationship between pulling velocity and interlamellar space, and the relationship between nanoindentation hardness and interlamellar space are also given.