Influence of beryllium addition on the microstructural evolution and mechanical properties of Zr alloys

The microstructural evolution and mechanical properties of Zr-chi Be binary alloys with different contents of Be (chi = 0, 0.25, 0.50, 0.75 and 1.00 wt.%) were studied in this paper. X-ray diffraction results showed that the phase composition of alloys underwent a series of changes from alpha phase to alpha phase + Be2Zr after Be addition. Moreover, the content of Be2Zr increased with increased Be. Microscopic analysis showed that the shape of prior-beta grains gradually transformed from inerratic planar crystallization to cellular crystal and then irregular arborization. In addition, it would have an obvious effect on grain refinement with Be added. The average prior-beta grain size in the pure Zr exceeded 1000 mu m. The addition of 0.25 wt.% Be dramatically decreased the average size of prior-beta grain to 170 mu m. With the beryllium further increased gradually to 1.00 wt.%, the average size of prior-beta grain in Zr-chi Be (chi = 0.50, 0.75, 1.00 wt.%) decreased gradually to 26 mu m. The key factor affecting significant refinement is the enhancement in nucleation rate and the growth restriction factor values of Zr alloys resulting from Be addition. The microstructural variation of Zr-Be alloys with Be greatly affected mechanical properties. In this paper, the tensile strength of pure Zr was only approximately 560 MPa, and the ductility remained above 14%. In the Zr-based alloys, adding Be element is beneficial to the improvement of the tensile properties. Zr-chi Be (chi = 1.00 wt.%) possessed the highest tensile strength (sigma(b) = 848 MPa) and retained an elongation of 8.6%. Scanning electro microscope results indicated that the fracture modes of Zr alloys with gradually added Be changed from ductile fracture to brittle fracture. (C) 2014 Elsevier Ltd. All rights reserved.