Microstructure evolution behavior of near alpha type high temperature titanium alloy during long-term aging
Microstructure evolution behavior and mechanism of high temperature Ti600 titanium alloy during long-term aging at 550℃ for 0-2000 h were studied by means of optical microscope,scanning electron microscopy and transmission electron microscopy.The results show that the rare earth phase in the Ti600 alloy is maintained relatively stable during long-term aging at 550 ℃,but α2 phase and silicide S2 phase are promoted to precipitate and grow up.At the early stage of aging,the size and number of spherical α2 phase coherent with the matrix increase as the aging time increases from 0 to 500 h.However,after aging for 500 h,the precipitation and growth of the α2 phase tend to be stable.After aging for 2000 h,the size of the α2 phase remains within 10 nm.The silicide S2 phase is induced to precipitate at the interface between the lamella α and β phase or within the α phase,and its growth gradually becomes obviously after the aging time exceeds 200 h,and it grows along the long axis direction,gradually transforming its shape into a rod shape.After aging for 2000 h,the average size of the S2 phase in the alloy has reached about 175 nm.After calculation,the growth rate of the S2 phase during long-term aging at 550℃ is K=2.69×103 nm3·h-1.The diffusion of Zr mainly controls the growth of the S2 phase.
near α titanium alloyheat treatmentlong-term agingsilicideα2 phase
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