International Seminar on Mechanics and Mechanisms of Solid-Solid Phase Transformations
J. Phys. IV France 06 (1996) C1-99-C1-108
Phase Transformation Kinetics and Mechanisms in Titanium Alloys Ti-188.8.131.52,ß-CEZ and Ti-10.2.3S. Bein and J. Béchet
Laboratoire de Métallurgie, Conservatoire National des Arts et Métiers, 292 rue St. Martin, 75141 Paris cedex 03. France
The precipitation mechanisms and kinetics in three titanium alloys of different ß-phase stabilities - the ß-rich a α+β titanium alloy Ti-6Al-2Sn-4Zr-6Mo and the near ß-titanium alloys Ti-5Al-2Sn-2Cr-4Mo-4Zr-1Fe(ß- CEZ) and Ti-10V-2Fe-3Al - were investigated by isothermal holding in the α+β field after a ß-solution treatment. For this purpose, the amount of transformation was determined by electrical resistivity measurements. The TTT diagrams of these alloys, plotted in the whole α+β field, show several independent C-curves. It is apparent from the cornparison of nose temperatures, that the transformation schemes should be quivalent for the thrre alloys in the two upper C-curves when temperatures are related to ß-transus temperatures, and for ß-CEZ and 10.2.3 in the two lower C-curves wheu absolute temperatiires are considered. This was confirmed by microstructiual observations (OM, SEM and TEM) of isothermal treated specimens. The nature and the morphologies of phases (ß-, α-, α"-, ω-phase) are specified. Furthermore, the ß-phase decomposition kinetics can be analysed by means of the Johnson- Mehl-Avrami relation from the electncal resistivity data at each studied temperahue. For the three alloys, the same n values are determined in the whole temperature range corresponding to similar C-curves. These coefficient values could be attributed to particular transformation mechanisms described by classical phase transformation theory. and coincide with the sequence of precipitation observed in these alloys.
© EDP Sciences 1996