Separating the effects of Ti3Al and silicide precipitates on the tensile and crack growth behavior at room temperature and 593 °C in a near-alpha titanium alloy

Aging of silicon-bearing, near-alpha titanium alloys produces two types of precipitate, Ti₃Al and (TiZr₆Si₃ (silicide). A postaging heat treatment that relies on the phenomenon of the critical ordering temperature is used to remove the Ti₃Al precipitate while leaving the silicide intact. Three materials—unaged (precipitate free), overaged (Ti₃Al plus silicide), and post aging heat treated (silicide only)— are compared. The objective is to identify the separate effects of the Ti₃Al and silicide precipitates on tensile and fatigue crack growth behavior at room temperature and 593 °C. The Ti₃Al precipitate is largely responsible for the increase in yield stress and for the decrease in ductility at both test temperatures. In contrast, the increase in room temperature fatigue crack growth rate associated with aging is attributed to the silicide, with Ti₃Al playing only a minor role. Aging produces a slight improvement in fatigue crack resistance at 593 °C, which also appears to be due to the presence of the silicide precipitate. Current address: Dept. of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.