Graded Microstructure and Texture in Ultrafine Grained Multi-Layered Immiscible Bimetallic System

Abstract

In this investigation we report the formation of a graded microstructure in copper/tantalum ultrafine grained (UFG) multi-layered composite fabricated by cross accumulative roll bonding (CARB) process at high temperatures. The gradient microstructure develops as a consequence of the strain gradient present along the thickness of the specimen during the CARB process. The correlation of strain gradient with the microstructure, micro-texture and bulk texture in copper/tantalum composite was established. The fragmentation of tantalum in between copper layers and the grain refinement with evolving passes has been explained. The deformed copper layers show rotated cube texture and deformed tantalum layers show cube texture with γ- fibre. The overall texture of copper/tantalum composite weakens after the process of ARB; copper undergoing texture randomization. The crucial role of interfaces on the evolution of texture is demonstrated. The effect of strain on orientation relationship (OR) between copper and tantalum layers was studied, confirming higher misorientation in OR at regions under high strain. Dynamic recrystallization taking place at the copper/tantalum interface has been elaborated with the aid of microtexture analysis.