Deformation alloying and transformation reactions

Abstract

During intense deformation of multilayer samples, atomic mixing reactions can yield alloy synthesis and amorphization reactions and can control amorphous phase stability against nanocrystallization. A precondition for deformation-induced alloying is a mixing reaction at interphase boundaries. In multilayer samples the intermixing occurs on a nanostructured size scale. As a result of localized mixing reactions at the interfaces, very steep concentration gradients develop that act to suppress crystal nucleation and allow for the development of metastable states such as supersaturated solutions or amorphous layers. In systematic studies of the alloying reaction during intense deformation of elemental multilayers in isomorphous and glass forming systems, atomic level mixing is observed to proceed in stages. The initial reaction is characterized by a significant layer refinement to nanoscale levels and an asymmetric exchange across layer interfaces. With continued deformation, the length scales of the layer thickness and the deformation-induced mixing zone can approach each other to yield a bulk nanostructured alloy or a fully amorphous phase. In contrast, intense deformation of amorphous Al base alloys can catalyze crystallization behavior. The characteristic behavior during deformation driven alloying and transformation reactions reveal opportunities for new kinetic pathways and novel microstructures that are not accessible by thermally activated processes.