SOLUTE PARTITIONING DURING THE PROEUTECTOID ALPHA-TRANSFORMATION IN TI-X1-X2 ALLOYS

The alloying element concentration in the grain boundary allotriomorphs, sideplates and intragranular plates of proeutectoid alpha isothermally formed from the beta-matrix between 500 and 700-degrees-C was measured by scanning-transmission electron microscope equipped with energy dispersive X-ray analyzer (STEM-EDX) in four ternary titanium alloys, i.e. in Ti-Al-Cr and Fe, and Ti-V-Cr and Fe alloys. The local equilibrium theory which incorporates the diffusional interaction between alloying elements was extended to analyze the partition behavior of alloying elements having diffusivity of similar order of magnitude. Fairly good agreement was obtained between calculation and theory above and even below T0 (the upper limiting temperature at which the diffusionless beta to alpha-transformation can occur) where the formation of alpha is often considered to occur by massive or martensitic transformation.