Features of Low-Temperature Plasticity, Mechanisms of Plastic Deformation and Fracture of the V–Cr–W–ZrC Alloy in the Process of Toughness Testing

A study of fractographic features of fracture surfaces, patterns of structural-phase transformations, and mechanisms of plastic deformation and fracture of low-activation vanadium alloy V–Cr–W–ZrC in the process of toughness tests was carried out. The appearance of a qualitatively new (non-dislocation) mechanism of plastic deformation was revealed—the mechanism of bcc → hcp → bcc transformation with a change in the systems of reverse transformations and (or) the participation of quasi-viscous mass transfer in the fields of high local pressure gradients. An important feature of this mechanism is its activation at the nanoscale level with the formation of nanovolumes several nanometers in size—new carriers of homogeneous transformation deformation of the Bain type. A significant feature of these carriers is the absence of any effective obstacles such as dislocations or disorientation boundaries for both homogeneous tensile/compressive deformation and quasi-viscous mass transfer. The activation of bcc → hcp → bcc transformations as a new non-dislocation deformation mode is based on the phenomenon of phase instability of the bcc crystal in fields of high local stresses and high local gradients of the nanoscale level. The above transformations (both direct and reverse) can be carried out under conditions of thermodynamic gain with a local (in the transformation zone) decrease in energy in the transformation region. This leads to intense softening of the material and high deformation and relaxation rates of highly defective substructures of deformation and deforming and local internal stresses.