Individual and synergistic effects of Ta and Mn on optimizing the microstructures and mechanical properties of TiB reinforced high Nb–TiAl composites

In order to further optimize the microstructure and mechanical properties of TiB/TiAl composites, the individual and synergistic effects of Ta and Mn were investigated in this study. Ti43Al6Nb1.6B-xTa-yMn (x + y = 1, at%) composites, termed as TNB, TNB-1Ta, TNB-1Mn and TNB-0.5Ta0.5Mn, were fabricated by vacuum arc melting. X-ray diffraction results showed that the diffraction peak of B2 phase appeared in TNB-1Ta and TNB-1Mn composites, while it was not obvious in TNB-0.5Ta0.5Mn counterpart, which indicated that higher content of B2 phase formed with individual 1% Ta or 1% Mn addition. According to the solidified microstructures, Ta and/or Mn addition changed the α₂/γ lamellar colonies from elongated to equiaxed morphology, which was due to the constitutional undercooling by Ta and/or Mn addition. Compressive results showed that individual and synergistic addition of Ta and Mn all increased the compressive strength and strain at room temperature, while the highest compressive properties were obtained in TNB-0.5Ta0.5Mn, which were 2142 MPa and 25.7%, respectively. Compared with individual addition of Ta or Mn, the synergistic addition of 0.5% Ta and 0.5% Mn not only induced less brittle B2 phase, but also had a stronger solid solution strengthening effect, because Ta atoms existed in TiB phase and Mn atoms existed in α₂/γ lamellae. Therefore, the enhanced properties of TNB-0.5Ta0.5Mn resulted from the refinement of α₂/γ lamellar colonies, solid solution strengthening of Ta and Mn, and lower content of brittle B2 phase.