Evolution and micromechanical properties of interface structures in TiNb_f/TiAl composites prepared by powder metallurgy

TiNb_f/TiAl composite has enormous potential to serve on advanced aerospace equipment, but brittle reaction products limit the further improvement of overall toughness; meanwhile, the types and contents of interface reaction products remain controversial. This study is to clarify the evolution process of interface reaction structure in TiNb_f/TiAl composite and explain it from the perspective of thermodynamics. This study discovered that brittle interface can transform into a relatively ductile interface containing two kinds of α₂/γ lamella colonies above the transition temperature of 1200 °C. The relative sizes of γ and α₂ lamella thickness varied in two different lamellar colonies. Above 1200 °C, recrystallization process at the boundary of original TiAl particles was completed and all defects were eliminated completely either. Gibbs free energy (ΔG) of every phase (γ, α₂, β and other generated intermetallics) calculated based on element distribution model is consistent with the experiment results well. Micromechanical properties tested by nanoindentation suggest that the interface in the form of lamella colonies had relieved variation amplitudes of reduced modulus E_r and hardness H across the interface region which may show beneficial influences on improving toughness of TiNb_f/TiAl composite.