Microstructure analysis on enhancing mechanical properties at 750 °C and room temperature of Ti-22Al-24Nb-0.5Mo alloy tubes fabricated by hot gas forming

In this paper, the integrated hot gas forming was processed to fabricate Ti-22Al-24Nb-0.5Mo alloy quadrate tubes, in which the tubular component was cooled in the forming die by pressured airflow. The effect of airflow pressure on microstructure and mechanical properties was investigated. The results illustrated that the volume fraction and geometrical morphology of O phase was crucial to the mechanical properties, which could be tailored by adjusting the cooling rate. As the airflow pressure increased from 2 MPa to 15 MPa, the volume fraction and average width of O platelets reduced from 47.5%, 105 nm to 3.9%, 50 nm, respectively. But, the aspect ratio of O platelets increased from 5.6 to 9.8. In addition, the tensile strength decreased from 1378 MPa to 1196 MPa at room temperature, but increased from 801 MPa to 880 MPa at 750 °C. Comparing to the microstructure obtained by post ageing-treatment, the microstructure from in-die cooling had finer O platelets with high aspect ratio. The elongation at room temperature could be improved from 4.1% to 18.4% and the tensile strength at 750 °C increased from 788 MPa to 880 MPa.