| The evolution of microstructure and the enhancement of strength and ductility of Zrhave been investigated in this research by cryorolling via the liquid nitrogen cooling withfollowed low-temperature annealing. The results of this research demonstrate these pointsfollowed: The use of the low temperature suppresses dynamic recovery, allowing thedensity of the accumulated dislocations to reach a higher steady-state level than thatachievable at room temperature. A multimodal grained structure composed of nanoscalegrains and subgrains (20%,<100nm), ultrafine grains (56%,100nm-1000nm), coarsegrains (24%,>1000nm) has been introduced in pure Zr by employing cryorolling withaverage strain rate2.238s-1and strain2.869, combined with subsequent low-temperatureannealing at450℃for1hour. This kind of pure Zr exhibits a high ultimate strength(658MPa), a good uniform elongation (8.5%) and a large elongation to failure (20.7%).Its strength is1.8times as the raw coarse-grained Zr that is processed by annealing. At thesame time, It has a larger toughness127.5×106J/m3than the second one's110.7×106J/m3. The mechanism of the simultaneous enhancement of strength andductility is the introduction of multimodal grained structure and high-angle grainboundaries. The high strength results from the contribution of nanoscale and ultrafinegrains, while the good ductility is provided by the coarse grains and the strain hardeningcapability is improved by the coarse grains and complex deformation strain paths causedby the multimodal grains. While the strain rate increases, the deformation is more severe,much more dislocations are put in the pure Zr to a higher density. And its distributionbecomes regular as lamellas. The high energy stored lead to more recrystallizationnucleation evens and secondary recrystallization. These have benefits for the production ofmultimodal grained structure Zr. |
