Microstructural changes during aging of a near-α titanium alloy

This paper describes the evolution of precipitation at a selected aging temperature of 593 °C in a new silicon-bearing near-α titanium alloy designated Ti-1100. This particular aging temperature was chosen to simulate the aging process occurring during service in a gas turbine engine. Over-aging results in the formation of silicide precipitates along the α platelet boundaries and the formation of Ti3Al distributed homogeneously throughout the matrix. The overall hardness response with aging exhibits two peaks: a minor peak at 800 min and a major peak at 10 000 min. Transmission electron microscopy evidence suggests that the silicide forms prior to the Ti3Al and that the minor peak is associated with silicide formation. The major peak is related to the silicide and/or Ti3Al. Metallurgical stability is only achieved after 60 000 min aging time. Since precipitation occurs over both short and long time periods (800-60 000 min), aging effects should be considered when characterizing high temperature mechanical behavior in this and similar near-α titanium alloys. © 1993