Effect of Solution Temperature on Microstructure and Tensile Properties of a Metastable b -Ti Alloy Ti-4Mo-6Cr-3Al-2Sn

Plates of a novel metastable β-Ti alloy Ti-4Mo-6Cr-3Al-2Sn (mass fraction, %) were solid solution treated at different temperatures for 0.5 h and subsequently aging treated at 400℃ for 4 h. Then the microstructure and room temperature tensile properties of the treated plates were examined by means of SEM, TEM and electronic universal testing machine. Results show that the primary α-phase decreases gradually with the increase of solution temperature. When the temperature rises above the phase transformation point the primary α-phase disappears completely, whilst almost all the plates present the microstructure of coarse β -grains, and the β -grains grow obviously. The 900℃ solution-treated plate presents good compromise in strength and plasticity with yield strength 898.7 MPa, tensile strength 962.5 MPa, and elongation at break 12.7%. Fine secondary α-phase precipitates occurred for the aged plates after solution treated at different temperatures. When the solution temperature is lower than the transformation point, the secondary α-phases are arranged in parallel or at a 60-degree inclination to the primary ones. When the solution temperature is higher than the phase transformation point, the primary α -phase almost disappeared, the precipitated secondary α -phase became coarser with larger spacing. Continuous chain of α-phases precipitated along the original β-grain boundaries in the aged plates, which were subjected to solution treatment in the temperature range 700~900℃, and the plasticity of the alloy is poor at the same time. After a combination solution and aging-treatment of 750℃/0.5 h plus 500℃/4 h, the alloy plate exhibits good compromise in strength and plasticity with tensile strength 1282 MPa, yield strength 1210.6 MPa, and the elongation at break 5.3%. © All right reserved.