| The world's energy consumption is increasing day by day,and the proportion of nuclear energy is gradually increasing.Zirconium alloy is widely used in the field of nuclear fission due to its excellent nuclear material properties,strong mechanical properties and corrosion resistance,and is often used to make nuclear fuel cladding for reactors.It is well known that the diffusion behavior of elements has an important influence on the evolution of the microstructure and phase structure of zirconium alloys,and the physical properties.Especially mechanical properties of zirconium alloys are extremely important for the long-term stable service of nuclear reactors.Hence,studying the element diffusion properties and mechanical properties in zirconium alloys takes an important role in correlational researches.In this paper,binary diffusion couples such as Zr-Co,Zr-Cr,and Zr-V are prepared.A high-temperature and long-term annealing method is used to obtain a diffusion layer with a certain thickness.Then,an Electronic Probe Micro Analyzer(EPMA)and a Nano-indentation test instrument are used to characterize and analyze the diffusion behaviors and mechanical properties of the above-mentioned binary systems.The main conclusions of this work are as follows:(1)For the Zr-Co binary diffusion system,five intermetallic compounds(Zr3Co,Zr2Co,ZrCo,ZrCo2,and Zr6Co23)were determined to be generated in the diffusion layer,and only Zr2Co11 was not found.The composition of the diffusion layer was characterized by EPMA.The results showed that the thickness of the five intermetallic compounds increased linearly with the increase of annealing time,and the interdiffusion coefficients with?-Zr(BCC)and?-Co(FCC)as boundary conditions at different temperatures are calculated.The growth mechanism of each phase changes from the initial stage of incubation to the diffusion control mechanism.The Zr2Co phase has the maximum interdiffusion coefficient of 1.68×10-15 m2/s at 1223 K,and the minimum interdiffusion coefficient of ZrCo phase is 4.32×10-17 m2/s at 1148 K.(2)The Nano-hardness of the intermetallic compounds ZrCo2,Zr2Co and Zr3Co in the Zr-Co binary system was measured by the nanoindentation tester to be 13.30±0.24 GPa,12.40±0.56 GPa and 6.02±0.34 GPa,and Young's modulus are 252.85±6.92 GPa,205.63±18.27 GPa and 73.34±2.26 GPa,respectively.Precise tests of hardness and Young's modulus of Zr6Co23 and ZrCo were abandoned due to their thin diffusion layer thickness.(3)For the Zr-Cr and Zr-V binary diffusion systems,the only intermediate phase in the phase diagram appears in the diffusion layer,namely Laves phase ZrCr2 and ZrV2 with C15 structure respectively.Due to the difficulty of diffusion between Zr,Cr and V atoms,the diffusion process rate of these two Laves phases is low,so the diffusion layer grows slowly.The results show that with the increase of annealing temperature and the extension of annealing time,the thickness of Laves phase diffusion layer grows slowly,and the interdiffusion coefficient is very small.At 1273 K?1323 K?1373 K and 1423 K,the interdiffusion coefficients of intermetallic compounds ZrV2 and ZrCr2 are 9.36×10-19m2/s?12.8×10-19m2/s?16.99×10-19m2/s?21.4×10-19m2/s,and 5.35×10-18m2/s?7.86×10-18m2/s?10.64×10-18m2/s?18.34×10-18m2/s respectively.The comparison found that the diffusion between Zr-V is slower than that between Zr-Cr,and the interdiffusion coefficient of ZrV2 is an order of magnitude smaller than that of ZrCr2.(4)The Nano-hardness of the intermetallic compound ZrCr2 in the Zr-Cr binary system is 12.72±1.18 GPa,and the Young's modulus is 185.13±21.54GPa.However,due to its thin diffusion layer,ZrV2 could not be tested for mechanical properties. |
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