Abstrakt
Only zirconium alloys with a very low amount of alloying elements have been studied for utilization in nuclear reactors in order to preserve low cross section for neutron capture. However, experience with titanium alloys, whose are in the same group of periodic table of elements and therefore undergo similar phase transformations, show that adding higher amount of alloying elements and utilize well-known strengthening mechanisms of multi-phase microstructure enhance the mechanical properties significantly. This enhancement could compensate higher cross section for neutron capture.
Phase transformations of metastable beta Zr12Nb alloy were studied by high energy X-ray diffraction (HEXRD) in-situ during linear heating. HEXRD was complemented by differential scanning calorimetry (DSC), electrical resistance and dilatometry. Evolution of ω phase was observed post-mortem using transmission electron microscopy (TEM). In accordance to Zr-Nb phase diagram, two bcc phases occur during the linear heating. The initial solution treated condition consist of metastable bcc βZr phase and nanometer-sizes ωath particles. Around 300 °C, Nb-rich bcc βNb with a lower lattice parameter starts to precipitate while the weight fraction of ω phase increases and βZr gradually disappears. At 560 °C, the ω solvus was found. Above this temperature, α phase precipitates.