Pressure-induced alpha-omega transformation in titanium Features of the kinetics data

Use is made of the increase in the electrical resistance of the specimen associated with the alpha-omega transformation in Ti in order to obtain the fraction zeta of the omega phase as a function of time under isobaric-isothermal conditions in the pressure range 4-9 GPa and at 300 + or - 3 K. Over the entire pressure range, zeta-t data fit an equation of the form zeta = 1-exp-(t/tau) to the n power, where tau and n are constants at a given pressure. The results suggest that tau decreases rapidly and n slightly with an increase in pressure. An analysis of tau-p data reveals that the activation free energy for the total process is very high at low pressures and decreases rapidly with increasing pressure and that the activation volume in the 6-9 GPa range is -4.3 cu cm/mol. The activation enthalpy is obtained by measuring tau at different temperatures; the average value in the pressure range 5-8 GPa is 12 + or - 0.5 kcal/mol