Role of Boundaries in Control of Deformation Rate and Strength of Crystalline Materials
|Periodical||Materials Science Forum (Volumes 604 - 605)|
|Main Theme||Processing and Applications of Structural Metals and Alloys|
|Edited by||Marcello Cabibbo and Stefano Spigarelli|
|Citation||Wolfgang Blum, 2008, Materials Science Forum, 604-605, 391|
|Online since||October, 2008|
|Keywords||Annihilation of Dislocations, Creep Rate, Deformation Resistance, Dislocation Structure, Flow Stress, Generation of Dislocation, High-Angle Boundaries, Low-Angle Boundaries, Nanostructured Materials, Phase Boundaries, Steady State Deformation|
Plastic deformation of crystalline materials is not controlled by interaction among free dislocations only, but the interaction of free dislocations with internal boundaries. i) Low-angle boundaries: Modeling of deformation of pure materials with conventional grain size on the basis of structure evolution indicates that low-angle boundaries act as obstacles of free dislocations. The migration of the low-angle boundaries constitutes an essential recovery process determining the deformation resistance in the steady state. ii) High-angle boundaries: Severe plastic deformation transforms low-angle boundaries into high-angle ones. They differ in obstacle and recovery characteristics from low-angle boundaries, which explains the special properties of ultrafine-grained and nanocrystalline materials with regard to strength, strain rate sensitivity and ductility. iii) Phase boundaries in Ni-base superalloys enhance the strengthening by hard phases with strengthening by dense dislocation networks serving to reduce coherency stresses. It is concluded that internal boundaries play a crucial role in controlling the evolution of structure and strength in crystalline materials.