Sintering densification, microstructure and mechanical properties of Sn-doped high Nb-containing TiAl alloys fabricated by pressureless sintering

Abstract

The challenge of producing high-density TiAl alloys is hereby addressed by a simple pressureless sintering approach. A systematic study has been made on the effect of Sn addition on the sintering densification, microstructure and mechanical properties of Ti–45Al-8.5Nb-0.2W-0.2B-0.02Y alloy. The results show that Sn addition significantly reduces the alloy's melting point, directly affecting the sintering behavior and with increasing Sn content the optimum sintering temperature decreases. A high-density (≥99.0%) and fine fully lamellar microstructure with a colony size of 40–60 μm can be achieved by a small amount of Sn addition. The lamella has a specific orientation relationship of (110)γ∥(0001)α2 and [11‾0]γ∥[11‾01‾]α2. Sn element is dissolved in TiAl matrix and the soluble Sn content in α2 phase is almost two times than that in γ phase. Benefitting from the optimized microstructure and Sn solid solution strengthening, the as-sintered TiAl–1Sn alloy exhibits the best mechanical properties, with a compressive strength of 3029 ± 49 MPa, yield strength of 685 ± 57 MPa and strain to failure of 32.5 ± 0.49%, respectively. The optimal Sn content should be between 1 and 2 at.% and beyond this the samples fails prematurely.