Severe plastic cold rolling effects in nickel–vanadium alloy: Microstructure, texture evolution and mechanical properties

Abstract

The microstructural characteristics and morphological attributes of the target material, along with its intrinsic properties, can significantly influence the performance of the resultant film. Currently, commercially available nickel-vanadium targets employed in the industry have not been subjected to investigations aimed at controlling grain size and grain orientation. This study examines the effects of unidirectional rolling at room temperature, combined with substantial deformation, on the alterations in microstructure, texture evolution, and mechanical properties of the NiV7 alloy. The process of severe plastic cold rolling leads to a continuous elongation and refinement of the grains. The changes in microstructure and texture of the cold-rolled sheets were analyzed using electron backscatter diffraction (EBSD) technology. At an 80% reduction, a significant number of sub-grains are observed, which transform into deformed grains as the reduction reaches 95%. With a thickness reduction of 96.6%, the average grain size is approximately 1.10 μm. Further increases in reduction do not lead to significant alterations in the grain structure; instead, the grain orientation progressively becomes more uniform with higher levels of deformation. The combination of substantial deformation and lower rolling rates results in an increased number of high-angle grain boundaries. The alloy displays various textures throughout the rolling process, including S-type, copper-type, brass-type, fiber, and cubic textures. Notably, the prevalence of S-type and fiber textures diminishes as the degree of deformation increases, while the cubic texture becomes increasingly prominent. Upon achieving a reduction of 95%, the cubic texture emerges as the dominant texture. A transmission electron microscope (TEM) was utilized to examine the extensive array of dislocations, dislocation cells, dislocation walls, and shear bands generated during the cold rolling process. At a deformation level of 96.6%, the ultimate tensile strength of the alloy demonstrates a significant enhancement, attributed to mechanisms of dislocation strengthening and grain strengthening, reaching a value of 1231 ± 20 MPa, accompanied by a post-fracture elongation of approximately 2%. The ultimate tensile strength exhibited an increase of 781 ± 20 MPa compared to the sample prior to the rolling process; however, there was a notable reduction in plasticity.