| With more and more serious problems about environmental pollution and energy crisis, nuclear energy has attracted more and more attentions because of its high efficiency, no greenhouse gas emissions and so on. So far, the advanced nuclear power system has been developed to the fourth generation fission reactor and fusion reactor. Due to people put forward higher request to the security, nuclear waste and efficiency of the advanced nuclear power system, the service environment of the key structure material in the reactor is more severe.9Cr oxide dispersion strengthened (ODS) steel has become one of the most promising candidate materials for advanced nuclear power system due to its excellent mechanical properties and radiation resistance, which can be mainly ascribed to the strengthening effect and the function of trapping helium bubbles by the dispersed particles in the matrix, respectively.In this paper, the optimization of preparation process, microstructure and mechanical properties, the strengthening mechanism, and the performance evaluation in service environment were studied. It can be concluded that 9Cr ODS steel, which is optimized by hot working, has excellent mechanical properties (strength and plasticity), which mainly attributed to the microstructure improved by hot working and the enhancement of the dispersion phases. The analysis results of microstructure show that the larger particles in the matrix are TiN with an average size of 240 nm; the smaller particles are Y-Ti-O with an average diameter of 6nm, and the number density is as high as 2.36×1023/m3. The atomic ratio of Y/Ti changes with particle size:Y/Ti for particles (larger than 10nm) is about 1, which were identified as face centered cubic (BCC) Y2Ti2O7 particles; The Y/Ti for particles (less than 5nm) is about 0.5, which may be crystal Y-Ti-Cr-O particles.The deformation behavior of 9Cr ODS steel from room temperature to 600℃ was studied by in situ tensile experiments using synchrotron radiation high energy X-ray. The results of lattice strain and internal stress for three phase (matrix. TiN and Y2Ti2O7) in 9Cr ODS steel during tensile process showed an obvious size effect on strengthening ability, nano-sized Y2Ti2O7 particles can bear higher force than the larger size TiN particles. The average internal stress of matrix shows that dispersed phase has a good strengthening effect from room temperature to high temperature. The dislocation density and character were also measured during tensile deformation. The dislocation character was determined by best-fit methods for different dislocation average contrasts with various levels of uncertainty. The results shows edge type dislocations dominate the plastic strain at room temperature (RT) and 300℃, while the screw type dislocations dominate at 600 ℃.The thermal stability, irradiation resistance and corrosion resistance of 9Cr ODS steel were also studied. The results of thermal aging at 700℃ showed the preferred growth of some grains, the change of composition and distribution for nano-sized particles during prolonged aging time, which caused the change of mechanical properties. The results of dual ion beam irradiation (Kr+and He+) at 500℃ proved the effect of oxide dispersion particles and fine grains on trapping helium bubbles induced by radiation. The results of corrosion test in melt Pb showed that 9Cr ODS steel performed in different ways in liquid Pb with different oxygen content. All in all, the corrosion resistance of 9Cr ODS steel is very poor. In order to improve the corrosion resistance of 9Cr ODS steel, the Al added 9Cr ODS steel was preliminary explored. The results showed that Al can improve the oxidation resisitance of 9Cr ODS steel effectively, while Zr can inhibit the formation of multi-scale and different structured Y-Al-O particles, and form uniform size Y-Zr-O nanoparticles to keep the good mechanical properties. |
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