Microstructure evolution, hot deformation behavior and mechanical properties of Ti-43Al-6Nb-1B alloy

A novel high Nb, low Al contained TiAl alloy Ti-43Al-6Nb-1B (at %) was fabricated by induction skull melting (ISM) technique. The as-cast alloy exhibits fully lamellar (FL) microstructure with mean colony size of 90 μm. By means of thermophysical simulation, the hot deformation mechanism at 1250 °C is concluded as dislocation slip and twinning in γ phase; bending, rotating and elongation of lamellar colonies are the primary deformation modes. A large-size TiAl pancake was successfully produced by triple-step canned forging at 1250 °C. The forged alloy displays duplex (DP) microstructure consisting of elongated lamellar colonies and γ grains. Typical DP and FL microstructures were further obtained by different heat treatments. The tensile strength increases rapidly from 670 MPa in as-cast state to 975 MPa in as-forged condition at room temperature, with elongation increasing from 0.4% to 1.5%. The as-forged alloy maintains strength higher than 950 MPa until 750 °C; also the DP and FL materials hold excellent strength more than 830 MPa and 770 MPa respectively. The superior tensile properties after forging are mainly ascribed to the microstructure refinement and homogenization, the lamellar spacing reducing, as well as the low Al and relatively low Nb additions in this novel high Nb containing TiAl alloy.