| With the development of nuclear power technology, zirconium in nuclear power has been gradually localized in China. Without the strong neutron irradiation, high temperature and pressure, mechanical stress, as well as the complex corrosion environment, the nuclear fuel cladding materials also need to satisfy the increasing fuel consumption requirement, which is the new direction for the development of zirconium alloy, especially Zr-Nb alloy. M5 zirconium alloy in nuclear reactor was processed with recrystallization annealing. At present, there are few researches on the oxidation behavior of M5 alloy.The oxidation behavior of M5 alloy was investigated under as annealed and as quenchedcondition in this experiment. First, the oxidation test for M5 alloy with the two different states was carried out in high-temperature high-pressure water vapor and ambient air with the temperature of 350℃ and 400℃, after which their oxidation rates was studied. In addition, the micro-morphology and compositional change of the oxide layers were observed after these three different oxidation treatments. Besides, in order to analyze their mechanical properties and to observe their fracture morphology, the ring tensile test for M5 alloy was carried out. Therefore, through comparing, the effects of different oxidation conditions and different heat treatments on the oxidation behavior of M5 alloy can be analyzed.The analysis showed:The oxidation kinetics curves of annealed M5 and quenched M5 alloys which were oxidized in high-temperature high-pressure water vapor laws y annealed =13.55×0.224 and yquenehed=10.99×0.36, in 350℃ air laws yannealed=4.6x0.2707 and yquenched=11.68x0.261, in 400 ℃ laws yannealed=5.55x0.43 and y quenched=9.82x0.44. Besides, the oxidation resistance of the as annealed M5 alloy was superior to that of the as quenched M5 alloy in all of these three different oxidizing environments. By comparing the three different oxidation conditions, the oxidation rate and the oxidation degree of M5 alloy in ambient air at 400℃ was the highest, which was followed by high-temperature high-pressure water vapor. The oxidation rate and the oxidation degree of M5 alloy in ambient air at 350℃ was the lowest.M5 alloys were oxidized in ambient air at 350℃ and 400 ℃ for 3000 hours and the observation of the micro-morphology of the oxide layers showed that a thin layer of oxide film has been developed on the surface of the M5 alloy with two kinds of heat treatment states after 100 hours’oxidation. What’s more, the surface of the oxide layer of the annealed M5 alloy appears to have holes and their area and depth increase with the increase of the oxidation time. However, there is no significant change on the surface of the quenched M5 alloy with increasing the oxidation time but the thickness of the oxide film is obviously increased when compared with that of the annealed M5 alloy. When the M5 alloys were oxidized in high-temperature high-pressure water vapor for 3000 hours, a thin layer of oxide film has been developed on the surface of the M5 alloy with two kinds of heat treatment states after 100 hours’ oxidation. In addition, the oxidation products on the surface of the annealed M5 alloy were grown from needle-shaped particles to be disc-shaped particles with a certain thickness with the increase of the oxidation time and the entire surface was covered by these disc-shaped particles uniformly and compactly. However, the oxidation products on the surface of the quenched M5 alloy were changed from needle-shaped particles which were gathered into nodular form to be Hake-like particles which were gather into clusters with the increase of the oxidation time and they were scattered on the surface of the samples discontinuously.The ring tensile test for M5 alloy with two kinds of heat treatment states was carried out after different oxidation treatments and their tensile mechanical properties were analyzed. The experimental results showed that the tensile strength, yield strength, the percentage elongation after fracture, the percentage reduction in area, static toughness and average static toughness decreased with the increase of the oxidation time. Furthermore, the mechanical properties of the as quenched M5 alloy are superior to that of the as annealed M5 alloy but the mechanical properties of the quenched M5 alloy decline more dramatically after 3000 hours’ oxidation when compared with those of the annealed M5 alloy. Therefore, the mechanical properties of the as annealed M5 alloy were more stable after oxidation treatment.The ring tensile test for M5 alloy with two kinds of heat treatment states was carried out after different oxidation treatments and their fracture micro-morphology was observed. The experimental results showed that the micro-morphology of the ring tensile fracture wasmicro porous aggregation type ductile fracture. With the increase of oxidation time, the deformation of the macro fracture morphology decreases gradually, the dimple of the fracture micro-morphology becomes smaller and shallower and the plastic property of the alloy becomes poorer. Thequenched M5 alloyexperienced smaller deformation in macro fracture and had smaller dimple size and more secondary crack in micro fracture and showed poorer plasticity when compared with those of the annealed M5 alloy after oxidation. |
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