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Effect of solid solution temperature on the structure and properties of Ti6246 titanium alloy
Ti6246 titanium alloy (Ti-6Al-2Sn-4Zr-6Mo) is a high-temperature titanium alloy with high Mo content developed by the American Timet Company in the 1960s. The service temperature is around 420°C. The low-cycle fatigue strength of this alloy after solution aging or double annealing is significantly higher than that of the corresponding Ti6Al4V titanium alloy. It also has high high-temperature creep strength and instantaneous strength, and can be used to manufacture medium and high-power compressor discs and blades. Since Ti6246 titanium alloy contains 6% of the strong beta stabilizing element Mo, the mechanical properties and heat treatment regime of the alloy are very sensitive. However, there are few research reports on the heat treatment of Ti6246 alloy, especially there are fewer domestic published literature reports. Therefore, it is extremely important to study the effects of different solution aging heat treatment systems on the microstructure and mechanical properties of alloys. Researchers studied the changes in the microstructure and mechanical properties of Φ200mm rods under different heat treatment regimes to provide a theoretical basis for the engineering application of the alloy.
The test material is a Ti6246 titanium alloy ingot prepared by three times of vacuum consumable electric arc furnace melting. Its chemical composition complies with the requirements of standard AMS4981 and GB/T3620.1-2007 "Titanium and Titanium Alloy Grades and Chemical Compositions". The (α+β)/β phase transformation point of the ingot was measured by metallographic method to be 955~960°C. The ingot is opened and forged, and finally forged into a Φ200mm bar. The forged state (R state) structure of the bar is a typical equiaxed structure. Cut the sample blank from the bar body and perform solution aging treatment on it. The solution temperatures are 860, 880, 900, 915, 925 and 935°C, maintained for 2 hours, and air-cooled. The aging temperature is 593°C, kept warm for 8 hours, and air cooled. Then test the room temperature tensile properties according to ASTM E 8/E8M, test the 427℃ high temperature tensile properties according to ASTM E21, and test the creep properties according to ASTM E139 (427℃×655MPa×35h, test the residual deformation under this condition, standard requirements ≤0.2%), and used LEICA MEF4A inverted metallographic microscope and SUPRATM55 scanning electron microscope for microstructural observation and analysis. The results showed that:
(1) When the solid solution temperature is between 860 and 900°C, the microstructure is a typical equiaxed structure. When the solid solution temperature is higher than 915°C, the primary α phase content decreases significantly and the microstructure shows a two-state structure. Changes in solid solution temperature have little effect on the size of the primary α phase. The content of secondary α phase increases significantly with the increase of solid solution temperature, and its size increases and broadens significantly.
(2) After solid solution treatment at 860~900℃, the room temperature and high temperature tensile strength of the alloy do not change much. When the solid solution temperature is higher than 915°C, both room temperature and high temperature tensile strength continue to decrease, and vice versa, and the increase in high temperature plasticity is significantly greater than that of room temperature plasticity. As the solid solution temperature increases, the creep properties gradually improve.
