From crack-prone to crack-free: Unravelling the roles of LaB6 in a β-solidifying TiAl alloy fabricated with laser additive manufacturing

Abstract

The 4th generation of intermetallic γ-TiAl based alloy, the so-called β-solidifying TiAl, has attracted great attentions due to its promising high-temperature properties. But it is intrinsically brittle and crack-prone, which lowers the processability of laser additive manufacturing (LAM) that offers an effective pathway for material processing and design. Thus, improving the mechanical properties, particularly the room temperature plasticity, of LAMed β-solidifying TiAl alloy is of technical interest and theoretical importance. Based on previous results, the present work investigates the synergistic roles of La and B in grain refinement and crack elimination in a LAMed β-solidifying TiAl alloy with LaB6 addition (0–2 wt%). Results show that La2O3 and TiB in-situ formed via reaction between the β-solidifying TiAl and the added LaB6 nanoparticles. Microstructural feature, phase transformation texture and mechanical properties at both room and high temperatures can be optimized through controlling the LaB6 addition level. 0.5 wt% LaB6 has been determined as the optimized addition, at which the balanced mechanical properties at both room temperature and 800 °C can be achieved for the LAMed β-solidifying TiAl alloy. Excessive LaB6 addition led to agglomeration of in-situ formed precipitates, reducing density and therefore deteriorating mechanical properties. The study offers an in-depth understanding of the effective grain refining approach to overcome the intrinsic brittle nature of β-solidifying TiAl through optimized doping of LaB6.