Extraordinary Toughening by Cryorolling in Zr

Abstract

High strength and good ductility are essential for the applications of structural materials. However, the strength and ductility of materials are often mutually exclusive. For example, deformed materials always exhibit a hardening behavior, i.e. enhanced strength accompanied with reduced ductility. [1] This is attributed to the mutual entanglement and blockage of high-density dislocations induced by plastic deformation, which greatly inhibit the motion of dislocations. [2] Thermal annealing is indispensable for enhancing the ductility of deformed materials at the expense of their strength.Recently, studies show that dislocations in some special configurations are movable, which prevents localized shear deformation and contributes to the ductility of deformed materials. [3] To tailor dislocation configurations in deformed materials, high-density dislocations induced by plastic deformation are indispensable. This can be achieved by suppressing the dynamical recovery of deformed materials using cryogenic deformation that has been successfully employed to study lowtemperature properties of materials, [4] tailor their microstructures and mechanical properties. [5,6] More recently, our studies demonstrate strain rate has a significant effect on the dislocation configurations of cryorolled Zr, and the dislocations in lamella configurations are movable under high stress and contribute to plastic deformation. [7] Moreover, dislocation dynamics simulations show that in hcp Zr no dislocation junction forms between intersecting screw dislocations at low temperature, which results in a weak forest hardening. [8] These studies hint a work toughening behavior, not hardening behavior, may be observed in the hcp Zr if appropriate dislocation configurations, in which dislocations are moveable under high stress, are yielded through cryogenic deformation. To unambiguously confirm this supposition through experimentally procedure, both room temperature (RT) and cryogenic deformation experiments of metal Zr with increased strain were designed and performed in this study, and an extraordinary work toughening behavior is observed in the cryogenically deformed Zr, in contrast to the work hardening behavior of RT-cryorolled Zr. ExperimentalHigh-purity Zr (99.95%) sheets with a fully recrystallized microstructure (average grain size $30 mm) were rolled at RT and liquid nitrogen (LN) temperature at a strain rate of 2.63 s À1 with various strains e ¼ 0.5-2.95, respectively. The cryorolling was performed by immersing the samples into liquid nitrogen for 10 min before and after each rolling pass. The rolling temperature was determined to be À90 to À160°C by using both a Pt100 resistance thermometer and an adiabatic calorimeter. Cryorolled Zr sheets were annealed from 100 to 150°C for 1 h, and the annealed specimens were air-cooled to RT after annealing. The microstructure of cryorolled Zr in the RD-TD plane was characterized using a transmission electron microscope (TEM) and an X-ray diffractometer (XRD) with Cu Ka radiation. Dislocation densi...

Enhanced mechanical properties of ARB-processed aluminum alloy 6061 sheets by subsequent asymmetric cryorolling and ageing

“…The higher strength of samples subjected to cryogenic deformation is seen to result from grain refinement and suppression of dynamic recovery. On the other hand, the higher ductility of samples subjected to cryogenic deformation is attributed to the change in (i) the fraction of high-angle boundaries, (ii) the density of pre-existing deformation twins [16] and (iii) the density of dislocations [17]. Shi et al [17] found that dislocations in some special configurations are movable, which prevents localized shear deformation and contributes to the improved ductility of CR-processed Zr.…”

“…On the other hand, the higher ductility of samples subjected to cryogenic deformation is attributed to the change in (i) the fraction of high-angle boundaries, (ii) the density of pre-existing deformation twins [16] and (iii) the density of dislocations [17]. Shi et al [17] found that dislocations in some special configurations are movable, which prevents localized shear deformation and contributes to the improved ductility of CR-processed Zr. Recently, Yu et al [18] found that simultaneous grain growth and grain refinement appear in CR-processed UFG Cu sheets, which results in a high-true failure strain of 1.5.…”

Special Rolling Techniques for Improvement of Mechanical Properties of Ultrafine‐Grained Metal Sheets: a Review

“…The UFG/NG grains result in an increase in strength while the coarse grain facilitated good ductility. Shi et al [72] found that cryorolled Zr showed an extraordinary toughening with increasing strain, as shown in Fig. 7.…”

“…[72] CR also finds applications in the fabrication of UFG/NG Ti alloys. During CR, intensive twinning in Ti accelerates the kinetics of microstructure refinement, and a grain/subgrains size of approximately 80 nm can be obtained when the rolling reduction ratio reaches 93%.…”

Effects of Nd addition on microstructure and mechanical properties of Mg–6Zn–1Mn–4Sn alloy

“…Recent investigations have reported that the age hardening response of Mg-Zn alloys could be enhanced by various elements alloying [9][10][11]. The addition of alloying elements such as Mn, Sn, Y and Nd can enhance the age hardening response by improving the number density of fine precipitates for a given volume fraction and forming new phases [12][13][14][15][16][17]. Sn is a low cost alloying element that refines the grains and improves the number density of precipitates due to the formation of Mg 2 Sn phase [18,19].…”