Strain hardening and microstructure evolution during uniaxial compression of ultrafine grained zirconium at temperatures of 4.2–300 K

The mechanical properties of ultrafine grained (UFG) zirconium (grain size 200 nm) obtained by a combination of extrusion, drawing, and annealing, are studied experimentally under uniaxial compression at temperatures of 4.2–300 K and compared with the mechanical properties of coarse grained (CG) Zr. The evolution of the texture and microstructure of Zr during strain is studied by x-ray diffraction and transmission electron microscopy. The volume fractions of twinned material are determined for UFG and CG Zr. It is found that at room temperature and below, twinning activity is lower in coarse grained zirconium, but at the very lowest temperatures (4.2 K) the opposite effect is observed, i.e., increased twinning activity with decreasing grain size. The influence of internal thermal anisotropy stresses on twinning in CG and UFG zirconium is discussed. The effect of twinning on the mechanical properties of UFG Zr is analyzed.