Data from: Formation of property gradient in coarse-grained niobium using a wedge tool - experiment and analysis

The processes of severe plastic deformation are an effective approach for creating an ultra-fine grain structures and increasing mechanical properties of bulk materials. However, there are usually size limitations for the processed workpieces. Surface treatment processes typically deform only a surface layer of limited thickness in a workpiece or finished part. 

A novel severe plastic deformation process for coarse-grained niobium is introduced in the current work, which employs a tool with an inclined (wedge) surface for deforming the material by reverse shear scheme. The process increases the intensity of shear deformations and the depth of plastic deformation in the body of the workpiece when a wedge tool acts on a surface. The essence of the process is the repeated displacement of the workpiece material in opposite directions during the asymmetrical introduction of a wedge tool until the required degree of deformation is accumulated in the tool-affected volume. This deformation scheme applies a 15° angle wedge tool to a workpiece of 21 mm height. After 9 cycles of plastic deformation, it enabled to create a gradient of the accumulated degree of deformation in the range of true strain e = 0.3 – 4.5. At maximum deformation, the microhardness of the workpieces increased by 1.86 times and the tensile strength by 1.6 times. Fractograms show a significant influence of the accumulated degree of deformation on the nature of fracture. The finite element method simulation of the deformation process showed that creating a uniformly strengthened layer requires at least five deforming operations.

The proposed reverse shear process with a wedge tool can be used, for example, for improving the structure of the surface layers of niobium ingots for subsequent forming. Due to the creation of a significant gradient of properties, the reverse shear process can be used as an express method for determining the mechanical characteristics of different materials in a wide range of accumulated degree of deformation.