FORMING AND DEFORMATION BEHAVIOR OF THE ULTRAFINE-GRAINED Zr – 1Nb ALLOY

Abstract

The effect of the severe plastic deformation modes on the ultrafi ne-grained state forming in zirconium Zr – 1Nb alloy comprising precipitations of secondary phases in the form of particles in the volume and at the grain boundaries was studied. Pressing with a gradual temperature decrease in the range of (973 – 573) K was established to dissolution of the secondary phase precipitates and forming the ultrafi ne-grained grain-subgrain structure in the alloy with an average elements size (0.25 ± 0.10) mm. In the pressing process at room temperature with an intermediate hour annealing in the temperature range of (873 – 803) K forming of ultrafi ne-grained structure with an average size of elements (0.45 ± 0.18) mm was observed. At the same time the secondary phase particles were retained in structure. The ultra fi negrained structure forming leads to the increase in the values of tensile and yield strengths of Zr – 1Nb alloy in 1.5 – 2.0 times and the simultaneous increase in the propensity to the localization of plastic deformation and decrease of the values of uniform strain and deformation to failure. Presence of secondary phase’s particles in ultrafi ne-grained structure as an increase in the size of its elements prevents the development of the plastic deformation localization and increases the effect of strain hardening.