Abstract
The synergistic effects of B and N on the microstructure evolution, mechanical properties and fracture behavior of Ti46Al4Nb1Mo alloy were investigated by adding BN particles. Ti46Al4Nb1Mo-xB-xN (x = 0, 0.4%, 0.8%, 1.2%, 1.6%, atomic percent, hereafter in at.%) alloys were prepared by vacuum arc melting. Compared with Ti46Al4Nb1Mo alloy, B2 phase disappeared and curvy TiB phase appeared at the interdendritic region in the Ti46Al4Nb1Mo-0.4B-0.4 N alloy. When 0.8% B and 0.8% N were added, Ti2AlN particles appeared in α2/γ lamellar colonies, tiny TiB particles and a few curvy TiB phases formed both at lamellar boundaries and lamellar colonies. With further increasing B and N content, the volume fraction of Ti2AlN and tiny TiB phases increased, and some long TiB phases appeared in the Ti46Al4Nb1Mo-1.6B-1.6 N alloy. Ti2AlN and TiB phases formed by the reaction between Ti46Al4Nb1Mo alloy and BN particles. The different formation mechanism between Ti2AlN and TiB was related to the different solid solubility of B and N in the Ti46Al4Nb1Mo alloy and solute redistribution during solidification process. When the content of B and N increased from 0 to 1.2%, the average lamellar colony size decreased from 358.4 μm to 48.7 μm, which resulted from synergistic effect of Ti2AlN and TiB. Compression results showed that the strength was improved from 1961 MPa to 2493 MPa without decreasing compressive strain. The fracture morphology showed inter-granular and inter-lamellar fracture mode in the Ti46Al4Nb1Mo alloy, while the fracture morphology showed trans-lamellar mode in the reinforced composites. The second phase strengthening of Ti2AlN and TiB, grain boundary strengthening by refined α2/γ lamellae, and elimination of B2 phase contributed to the improvement of strength.
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