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The temperature dependence of the flow stress behavior has been measured from 77 to 740 K for age-hardenable beta-phase (bcc) Ti-40V-1Si alloy single crystals. For solution-treated and aged crystals, an increase in the athermal yield stress at 740 K is accompanied by a decrease in the temperature dependence of the yield stress. Direct electron microscopy observations, slip character, and work hardening behavior indicate that the precipitate particles are predominantly sheared in the conditions tested. It is suggested that the reduced temperature dependence of the yield stress with aging results from: (a) the relative flow stress difference of screw vs. edge dislocations moving through penetrable obstacles and (b) solute association which may occur during aging.
Precipitation hardened single crystals of a beta (bcc) Ti - 40 a/0 V + 1.0 a/o Si alloy were deformed in compression at 77K and 298K. The dependence of the yield stress upon aging time at 570C for solutionized and quenched crystals shows two maxima, caused by the formation of silicide precipitates. The orientation dependence of the yield stress and of the active macroscopic slip plane were determined as a function of aging time. The results indicate that the effect of the dislocation core structure on dislocation motion is independent of the presence of precipitates. The results also suggest that matrix hardening is independent of and additive to precipitation hardening. (Modified author abstract).