Effect of Zr addition on the microstructure and mechanical properties of hot-rolled TiZrAlSn alloys

In this study, the microstructure and mechanical properties of hot-rolled chi Zr-Ti-5Al-2.5Sn (chi = 0, 10, 20, 30 and 35, wt%) alloys were systematically investigated. With the increase of Zr addition, phase constitutions of TiZrAlSn alloys change from single alpha phase to alpha + alpha,' alpha ' and alpha '+ alpha" + beta phases in sequence while the beta transformation temperature decreases. A lower content of alpha"+beta phases appears in the 35Zr-Ti-5Al-2.5Sn alloy. The yield strength of TiZrAlSn alloys increased monotonically from 612 +/- 15 MPa for basal Ti-5Al-2.5Sn alloy to an ultra-high strength of 1386 +/- 11 MPa for 35Zr-Ti-5Al-2.5Sn alloy, which is -126% higher than that of basal alloy. The high content of Zr solute atoms, high density of dislocations and interfaces/boundaries in alpha ' martensite phase render the ultra-high yield strength and high strain hardening rate in 35Zr-Ti-5Al-2.5Sn alloy. With respect to ductility, the uniform and total elongations increase initially from Ti-5Al-2.5Sn alloy to 10Zr-Ti-5Al-2.5Sn alloy and decrease afterward until 35Zr-Ti-5Al-2.5Sn alloy. The bimodal microstructure of primary alpha grains and secondary alpha ' martensite (beta trans region) rendered 20Zr-Ti-5Al-2.5Sn alloy the best comprehensive mechanical properties which included the tensile strength of 992 +/- 11 MPa, total elongation of 17.2 +/- 1% and a high strain hardening rate. This high strain hardening ability of 20Zr-Ti-5Al-2.5Sn alloy comes from the compatible deformation of soft primary alpha and hard secondary alpha ' martensite phases with high density of dislocations and boundaries. In addition, the 20Zr-Ti-5Al-2.5Sn alloy shows a high elongation during tensile necking. The corresponding ductile fracture morphologies of TiZrAlSn alloys are also analyzed. These high-strength TiZrAlSn alloys could be helpful for developing novel Ti-Zr alloys with a high strength and ductility.