Effect Of Annealing Treatment Of Duplex Zr-Nb Alloy And Study Of New Zr-Nb-Al Alloy

The Zr-based alloys(Zr-2.5Nb and Zr-Nb-Al)are studied in this paper.The microstructure and properties of the Zr-based alloys are investigated through chemical optimization and heat treatment controlling.Effect of annealing treatment on microstructure evolution and mechanical propertries of duplex Zr-2.5 Nb alloy obtained by air cooling and water cooling are studied.Result shows that the microstructure after air cooling is composed of α,residual β and ωisolation while the the microstructure after water cooling consists of α′ and ωisolation.The pre-existed ωisolation transforms to α+β in accompany with the aging precipitated phase ωathermal under the annealing treatment whithin 300-600℃.With the increase in annealing temperature,the volume fraction of ωathermal reduces.Under the annealing treatment the transformation from α and α′ to α+β through Nb diffusion leads to the decrease of volume fraction of the primary α,and coarsening of the secondary α phase.After the annealing treatment,the strength of the specimen after air cooling reaches maximum at 300℃ while the strength of the specimen after water cooling obtains the maximum value at 400℃.As the annealing temperature further increasing,the strength and hardness decreases.Both of the specimens have the similar elongation at the same annealing temperature.However,the specimen after water cooling exhibits lower uniform elongation and poor deformation compatible capability.In order to enhance the mechanical property,Al element is added into Zr-Nb alloy according to Zirconium alloying principle.A series of Zr-Nb-Al alloys are prepared using a vacuum non-consumable electro-arc furnace and the effect of composition on phase structure and mechanical property is investigated.Adding Al contents in Zr-Nb-Al alloys within 1 wt.% ~ 2 wt.% enhance the strength obviously without loss of the plasticity.The alloys containing Nb in the range of 2.5 wt.%-4 wt.% possesses the highest static toughness.According to the results of composition optimization,Zr-3Nb-1.5Al alloy is prepared by vacuum consumable electro-arc furnace in industry.Phase structure of as-cast and forging alloys are composed of α phase and β phase.The basket weave microstructures are obtained in the as-cast alloy and forging alloy along axial direction.Widmannstatten structure is obtained in the forging alloy along the vertical axial direction.Zr-3Nb-1.5Al alloy prepared along axial direction direction exhibits the best mechanical properties.The yield strength,tensile strength,ductility and static toughness is 789 MPa,858 MPa,28.6%,and 24.5 GPa%,respectively.