Microstructure and Microhardness of V–W–Cr–Zr Alloy Depending on Deformation in Bridgman Anvils

Abstract

Using the methods of transmission and scanning electron microscopy, the microstructure of a V–W–Cr–Zr alloy is studied as a function of its plastic deformation value under the condition of high-pressure torsion in the Bridgman anvils. The main stages of structure transformation and the respective mechanisms are identified. It is found out that the grain and defect structure transformation up to e ≈ 1.1 is provided by the dislocation and dislocation-disclination mechanisms, which when combined activate the processes of submicrocrystalline structure formation. The deformation impact in the strain interval from e ≈ 1.1 to e ≈ 3 is characterized by a significant increase in the grain-boundary length. A high strength state is achieved in the course of this deformation, where the dislocation modes of plastic deformation are suppressed. This is accompanied by the activated processes of formation of two-level nanostructured states, wherein the principal mechanism is a quasi-viscous re-orientation by the flows of non-equilibrium point defects. A further increase in the deformation to e ≈ 5.3 gives rise to refinement of the submicrocrystalline grains and formation of two-level nanostructured states in the entire material volume. The main contribution to the grain- and subgrain transformations comes from the disclination and quasi-viscous modes of plastic deformation. At higher strain degrees (e > 5.3), the size of submicrocrystalline grains does not virtually change, and the transformation of two-level nanostructured states makes itself evident in the rotations of some of the fragments of this structure with respect to the other by small angles from tens of fractions of a degree to several degrees. The formation of the submicrocrystalline state is followed by a multiple increase in the microhardness; its values are observed to saturate at e ≈ 3.3.