Research on the processes of deformation and failure in coarse- and ultrafine-grain states of Zr1-Nb alloys by digital image correlation and infrared thermography

The mechanical behavior of coarse- and ultrafine-grained (CG/UFG) Zr-1Nb alloy specimens under quasi-static tensile testing, the distribution of epsilon(xx), epsilon(yy), epsilon(xy) strains and the evolution of temperature patterns have been studied using the techniques of digital image correlation and infrared thermography. The microstructure of the Zr-1Nb alloy in the initial CG and UFG states, as well as after deformation at the prefracture stage, has been investigated. A study of the accumulation and dissipation of energy in these materials under tensile load has demonstrated the influence of the alloy heat capacity on these processes. It has been found that, under tensile testing, the Zr-1Nb alloy in the UFG state is characterized by a stage with constant temperature, which takes place up to epsilon(true) approximate to 0.04 thus indicating that UFG materials, unlike CG ones, more efficiently use the structural energy absorption channel during deformation. The prefracture stage of the Zr-1Nb in the UFG state is characterized by the sharp temperature increase up to 60 degrees C. At this stage, the strain hardening coefficient becomes negative reaching values up to -6.5 GPa thus indicating local material softening before fracture. The formation of large local areas with disoriented mesh structure of dislocations is another feature of structural transformations in the Zr-1Nb alloy in the UFG state before fracture that also indicates a local material softening.