Mechanical behavior and superplasticity of a severe plastic deformation processed nanocrystalline Ti-6Al-4V alloy

Mechanical behavior of a severe plastic deformation (SePD) processed nanocr ystalline Ti-6Al-4V alloy has been studied in the temperature range 25-675 degreesC. Compared with the microcrystalline state, the nanocrystalline sta te material had higher strength up to 400 degreesC and comparable strength above that. The ductility was significantly higher for the nanocrystalline state above 500 degreesC, including superplasticity above 600 degreesC. Tra nsmission electron microscopy showed considerable grain growth and dislocat ion activity during superplastic deformation. A comparison of the superplas tic data across the nanocrystalline and microcrystalline range showed an in teresting discrepancy in the kinetics of superplastic deformation. Contrary to the general expectation, the kinetics of superplastic deformation was s lower in ultrafine grained materials after normalizing the data for grain s ize and temperature dependence. The slower superplastic deformation kinetic s in the nanocrystalline materials is discussed in terms of the difficulty associated with slip accommodation of grain boundary sliding. (C) 2001 Else vier Science B.V. All rights reserved.