Effect of Aging Treatment on Microstructure and Mechanical Properties of a Two-Phase Titanium Alloy

In present work, microstructure of Ti-6Al-2Mo-1.5Cr-2Sn-2Zr-1V-0.15Si-0.4Fe alloy as a function of aging temperature was investigated using optical microscopy, scanning electron microscopy (SEM), x-ray diffraction (XRD) and transmission electron microscopy (TEM).Three types of precipitates were found in this alloy, they were α2 phase (Ti3Al), silicides, and Sn rich phase. Ti3Al were observed in all aged specimens covering a range 500-740°C. A method of quantitative analysis toward α2 based on high resolution images and Flourier transformation is used. The results showed that the ordering in α phase was highly related to the property of fracture toughness. Silicides were first found at 580°C ageing and later determined in the formulate (Ti5+xZr3-x)Si3 in the specimens aged at 740°C, and they were found to influent the fracture toughness significantly. The Sn rich phase was emerged with large area during the 780°C aging. And its direct correlation to property was not found. The density of acicular α phase was found almost invariable by calculating through the modification XRD quantitative analysis during the elevated aging temperature.