Enhanced fracture toughness stability of (B,Y)-contained TiAl-based alloy prepared by cold crucible directional solidification

Abstract

Cold crucible directional solidification (CCDS) can be used to prepare the well-DS TiAl-based alloys with good mechanical properties. However, when the DS columnar grains are coarsened, the stability of fracture toughness will not be guaranteed due to the internal random-direction (α2+γ) lamellas. In this study, in order to improve the fracture toughness stability of CCDS TiAl-based alloys, (B,Y) refinement element was added, and the model alloys Ti–44Al–6Nb–1Cr–2V and Ti–44Al–6Nb–1Cr–2V-(0.1B,0.15Y) were used. The two alloys were fabricated by CCDS under the same parameters, and their macro/microstructure and fracture toughness were studied. The results showed that the B/Y compounds hindered the growth of dendrites, narrowed the DS window, and significantly refined the columnar grains. The fracture toughness of well-DS Ti–44Al–6Nb–1Cr–2V-(0.1B,0.15Y) alloy with the refined columnar grains was still at a higher level, and the key was that the stability of its fracture toughness was significantly improved comparing with that of the well-DS Ti–44Al–6Nb–1Cr–2V alloy with the coarsened columnar grains. It was found that the well-DS Ti–44Al–6Nb–1Cr–2V-(0.1B,0.15Y) alloy could provide more longitudinal grain boundary barriers for the radial crack propagation, create more crack deflection when the crack entered the next columnar grain (lamella colony) and avoid the crack long-distance propagation along the bad-orientation (α2+γ) lamellas.