FLOW SOFTENING MECHANSIM OF A Ti ALLOY WITH LAMELLAR STRUCTURE DURING SUBTRANSUS DEFORMATION

The flow stress has a considerable flow softening after a peak strain hardening at very low strains for Ti alloys with lamellar structure during subtransus deformation.In order to study the mechanism of such flow softening behavior,the deformation behavior of TC11 Ti alloy with a lamellar structure was studied using isothermal hot compression tests under a temperature range of 890—995℃and a strain rate range of 0.01-10 s~(-1).Theoretical calculation shows the Hall-Petch strengthening effects induced byα/βinterface as well as the twin boundary inαlamellar are far more significant than that of the colony boundary.The flow softening can be related to reduction of Hall-Petch strengthening effects due to transfer from the hard slip mode to the soft one.