LYU Meiyuan, SUN Weihao, YIN Quanfeng, XU Changcheng, LENG Xinlin, TANG Mingyao, TIAN Siyu, MA Mingqing, REN Yuping, CAI Minghui, JIANG Min, QIN Gaowu
The work aims to systematically compare the microstructural evolution and changes in mechanical properties of medical TC4ELI alloy bars at different stages of continuous hot working and reveal the corresponding relationship among microstructural reconstruction, texture evolution, and mechanical properties under multi-stage hot working conditions, so as to provide a reference for hot working process optimization and microstructure-property regulation of medical TC4ELI alloy bars. Optical microscopy (OM), electron backscatter diffraction (EBSD), and room-temperature tensile testing were employed to investigate the microstructure and mechanical properties of TC4ELI alloy in the as-cast, forged, rolled, and drawn states. The Widmanstätten microstructure formed in the as-cast alloy was transformed into a fine lamellar basketweave microstructure after forging in the high-temperature β phase region, and the α lamellar spacing was refined to 0.96 μm. After subsequent hot rolling in the α+β two-phase region, the microstructure was further refined, and the average α grain size was reduced to 0.9 μm. The grains were slightly elongated along the rolling direction, with the preferred orientation concentrated near <10-10>. During further hot drawing in the α+β two-phase region, although the average α grain size was about 0.7 μm, the microstructure exhibited obvious fibrous characteristics along the drawing direction, and the preferred orientation remained <10-10> parallel to the drawing direction. Finally, the rolled TC4ELI alloy exhibited the best overall mechanical properties, with a yield strength, ultimate tensile strength, and elongation of 937 MPa, 1 022 MPa, and 16.9%, respectively. In contrast, the drawn alloy showed higher yield strength and ultimate tensile strength, reaching 1 022 MPa and 1 208 MPa, respectively, but the elongation decreased significantly to 8.2%. Continuous hot working can promote the refinement and reconstruction of the microstructure of as-cast TC4ELI alloy and lead to obvious changes in texture and mechanical properties. Among the different states, the rolled alloy shows the best strength-ductility balance, whereas the drawn alloy achieves the highest strength.
