Translated Abstract
Ti-1300 alloy possesses high strength and high toughness and has been used in areaspace field. As a near-β-type titaniμm alloy, Ti-1300 alloy is mainly strengthened through the precipitation of the α phase during aging. In this paper, the precipitation behavior of α phase and the effect of aging microstructure on the strength and plasticity of Ti-1300 alloy have been studied, to provide the experimental basis for the microstructure and properties optimized design of the alloy.The microstructures and mechanical properties of the experimental materials after different heat treatment were characterized by means of optical microscope, scanning electron microscope, transmission electron microscopy, X-ray diffraction, Vickers hardness, tensile curve and fracture morphology. The following results were found by the experiments above.
The pre-aging time of Ti-1300 alloy in β solid solution is 1h, 3h and 5h respectively. It is found that the pre-aging time has little effect on the precipitation of α phase. For the heat treatment of 850℃ solution plus 350℃ for 3h aging, the second phase is ω phase. After aging at 500℃ for 1h, the precipitation of the α phase is not sufficient, and when the time is prolonged to 4h, the α phase is fully precipitated.
After the heat treatment of 850℃ solution, there are a large number of uniformly distributed small ω phase at 4℃•min-1 to 350℃ for 10min. When the aging temperature rises to 400℃ at 4℃•min-1, the ω phase and the α phase coexist. It is found that the growth of α phase is close to that of ω phase, which indicates that ω phase does promote α nucleation in Ti-1300 alloy.
After the heat treatment of 870℃ solution plus step-quench and held at 530℃, 580℃, 630℃ for 15min, the areal density of α is largest at 580℃,which is 819 laths•μm-2. The alloy composition is close to the intersection of Gibbs free energy curve of α phase and β phase at 580℃, the pseudo-spinodal decomposition has occurred.
Four processes, including single aging and 850℃, 820℃,790℃ solid solution plus low rate heat aging, were set up to investigate the effect of α on the mechanical properties of Ti-1300 alloy. It was found that after solution at 790℃ plus low rate heat aging, the content of primary α content is 6.7%. The tensile strength of the alloy is 1557Mpa, and the elongation is 10.7%, which reached a good matching of strength and plascity. However, the elongation is less than 2% when the samples soluted at 850℃ or 820℃ plus low rate heat aging.
Translated Keyword
[anisotropy, core-shell structure, mechanical properties, single crystal cementite]
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