Grain refinement in commercial alloys due to high plastic deformations and phase transformations

The results of investigations of grain refinement methods are presented in this paper. Titanium alloys, stainless steels and superalloys are the materials that were studied. The most significant effect of microstructure refinement was observed during severe plastic deformations in alloys with an initial lamellar type microstructure due to dynamic recrystallization and phase transformation. The combination of dynamic recrystallization and phase transformation makes it possible to produce micro and sub-microcrystalline structures in massive billets. Hydrogen alloying of Ti-base alloys decreases the temperature of beta --> alpha transition, and it becomes possible to generate a highly dispersed microstructure upon quenching. After that during subsequent severe plastic deformation a nanocrystalline state can be formed. Conditions for sub-microcrystalline structure formation in austenitic stainless steels and Ni-based alloys are considered, too. On the basis of the results of the investigations the general principles of grain refinement methods in commercial alloys are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.