PROCESSING MAP FOR THE HOT-WORKING OF NEAR-ALPHA TITANIUM-ALLOY-685

Using a dynamic materials model, processing and instability maps have been developed for near-alpha titanium alloy 685 in the temperature ra nge 775-1025 degrees C and strain-rate range of 0.001-10 s(-1) to opti mise its hot workability. The alloy's beta-transus temperature lies at about 1020 degrees C. The material undergoes superplasticity with a p eak efficiency of 80% at 975 degrees C and 0.001 s(-1), which are the optimum parameters for alpha-beta working. The occurrence of superplas ticity is attributed to two-phase microduplex structure, higher strain -rate sensitivity, low flow stress and sigmoidal variation between log flow stress and log strain rate. The material also exhibits how local isation due to adiabatic shear-band formation up to its beta-transus t emperature with strain rates greater than 0.02 s(-1) and thus cracking along these regions. (C) 1997 Published by Elsevier Science S.A.