Plastic instability in an omega forming Ti-l5% Mo alloy

The plastic flow behavior of a β-titanium alloy (Ti-15% Mo) was investigated over a wide range of temperatures and strain rates covering those conditions where the ω-phase forms dynamically. Portevin-Le Chatelier (PLC) effect was observed in this alloy at temperatures between 575 and 775 K at a strain rate of 1.31 x 10-4 s-1. The serrated flow behavior of this alloy could be suppressed by rendering the matrix β-phase more stable against the β to ω transformation. PLC bands formed in this alloy, studied at different levels of magnification using light, scanning electron and transmission electron microscopy, showed a high density of deformation bands within the macroscopic PLC band. The following mechanism of serrated flow is proposed; the load drop is ascribed to the sudden flow associated with the formation of deformation bands within which ω-particles were destroyed while the subsequent load rise results from pinning of dislocations by ω-particles forming dynamically