Investigation of Low Temperature Creep Deformation Behavior of a Metastable Beta Titanium-14.8Wt%Vanadium Alloy

Abstract

This dissertation presents the results of investigated low temperature creep behavior of a metastable beta phase Ti-14.8Weight%V alloy (Ti-14.8V). It is the first such study which relates the activation energy and microstructure with low temperature creep deformation mechanisms in the temperature range of 298K to 800K. A Ti-14.8V alloy with a grain size of 350 m was tensile and creep tested in the temperature range of 298 - 458 K; creep tests were conducted at 95% of the 0.2% yield stress. Activation energies were determined by utilizing strain rate models and resulting least squared Arrhenius plots, which were found to be in the range of 36.6-112.42 kJ/mole for the measured temperature range of 298 - 458K. The resulting activation energies plotted as a function of strain was found to be linear dependent. The determined activation energy values of 36.6 57.55 kJ/mole at the low end of the strain are within the range of activation energy values for dislocation motion. The higher activation energy value of 112.42 kJ/mole is within range of for activation energy value for diffusion of oxygen in beta titanium alloy. These activation energy values are consistent with SEM and TEM observations of deformation mechanisms as dislocations, slip, and stress induced plates (SIP) in the form of twinning were the dominant creep deformation mechanisms for this alloy. The deformation mechanisms changed from predominantly slip to SIP in the form of twins at the higher test temperatures. Further, these findings are consistent with observations, characterization by TEM analysis identified slip dislocations of the 1/2<111> type and twins of the {332}<113> type, which are consistent with time dependent twinning deformation. The results strongly support the mechanism of oxygen controlled time dependent twinning deformation as proposed earlier.