Effect of cold rolling strain on the microstructural evolution in equimolar MoNbTaTiZr refractory complex concentrated alloy: Comprehensive characterization

TL;DR

This study investigates how cold rolling affects the microstructure of a MoNbTaTiZr refractory alloy, revealing phase transformations, grain fragmentation, and twinning, which influence its deformation behavior and potential ductility.

Contribution

It provides a comprehensive microstructural analysis of the effects of cold rolling on a refractory complex concentrated alloy, highlighting phase evolution and deformation mechanisms.

Findings

Formation of a new FCC phase after rolling

Identification of Zr segregation and phase transformations

Presence of deformation twinning enhancing ductility

Abstract

This work presents a pilot study on a strained complex concentrated alloy based on refractory elements: MoNbTaTiZr. Initially, the as-cast and homogenization-annealed conditions were characterized. After casting, the alloy consists of two solid solutions with BCC 1 and BCC 2 crystal structures. Homogenization annealing promotes the growth, ordering, and refinement of the BCC 2 phase. TEM and AES analyses indicate possible Zr segregation at grain boundaries in the as-cast state. In contrast, annealing followed by cooling results in the formation of Ti-Zr-based particles without segregation. Subsequently, the annealed alloy was cold-rolled, and its microstructure was investigated. During rolling, grain fragmentation occurs within the structure. In addition to the two BCC solid solutions, a phase with an FCC crystal structure is identified after rolling. Its composition corresponds to the Zr2Ta phase, which is a Laves phase of the A2B type. Rotational relationships, relatively rare in rolled materials with BCC structures, are identified. The texture components found after 10% rolling deformation are related to that present after 20% deformation by a 45 degrees <110> rotation, and this component is related to that appearing after 30% deformation by a 20 degrees <100> rotation. However, no distinct rolling texture or clear texture development was observed, although some mutual relationships among preferred orientations can be identified. Schmid and Taylor factor maps demonstrate that, despite deformation, the alloy remains capable of further strain accumulation and plastic deformation. Twinning is also observed after rolling, which may be beneficial, as deformation twinning contributes to improved ductility in the alloy.