Heterogenous Activation of Dynamic Recrystallization and Twinning During Friction Stir Processing of a Cu-4nb Alloy

Abstract

An interplay between high degree of shear deformation and deformation-induced heating occurs during friction stir processing (FSP) of metals. In medium-to-low stacking fault energy Cu alloys, this can lead to a complex spatially heterogenous activation of dynamic recrystallization (DRX) and twinning mechanisms. Within the Cu-Nb system, the presence of Nb is further expected to influence the DRX mechanism of the Cu matrix. However, the microstructural changes induced by the co-deformation of Nb during FSP are still not well understood. Therefore, this study uses a combination of multimodal microstructural characterization, solution thermodynamics based predictions, and computational crystal plasticity simulation to reveal the various microstructrural evolution mechanisms that can occur during FSP of a Cu-4at.%Nb binary model alloy. The formation of softer DRX zones, and harder shear localization regions are revealed using electron backscatter diffraction, transmission electron microscopy, atom probe tomography, and crystal plasticity modeling. The detailed understanding developed by this work can guide future efforts to tailor the microstructure and local mechanical properties in Cu-Nb alloys by using friction stir processing.

Keywords: dynamic recrystallization, twinning, friction stir processing, copper-niobium