| In the daily operation of nuclear reactor,control rod is an important device to regulate reactor reactivity,which has great significance for maintaining the stable operation and safety of nuclear reactors.The gray control rod is the first choice for reactivity regulation and load tracking for new generation nuclear power plant.It is urgent to develop new neutron-absorber materials for gray control rods,which will fill the technical gap and accelerate the development of nuclear power independence in China.In this paper,Fe-based Tm2O3 composites,Fe-based TmFeO3 composites,Fe-based TbFeO3-DyFeO3 composites and Fe-based Tb2O3-Dy2O3 composites were prepared by the process of ball milling,cold isostatic pressing and sintering.The evolution and mechanism during ball milling and sintering process were analyzed.The effects of preparation parameters on microstructure,mechanical properties and thermophysical properties of the composites were investigated.The phenomena and principles of composite materials during irradiation and corrosion experiments were studied.In the process of ball milling,Fe-Tm2O3 and Fe-Tb4O7-Dy2O3 mixure powders were refined,homogenize,nano-crystallized and amorphized.Finally rare earth oxide R2O3(R=Tm,Tb,Dy)phase were broke down into Tm,Tb,Dy and O elements,which were dissolved into the Fe crystals to form the supersaturated nanocrystalline solid solution.In addition,crystal transition and phase transition were observed in Fe-Tb4O7-Dy2O3 mixure powders.Th4O7 was transformed into Tb2O3.Cubic Dy2O3 was transformed into monocline Dy2O3.With the increase of ball-milling time,the grain size of Fe gradually decreases and ultimately tended to a constant value,however,the trend of lattice constant is opposite to that of grain size.Fe-Tm2O3 and Fe-Tb2O3-Dy2O3 mixure powders were shaped by cold isostatic pressing and then sintered at constant temperature.High temperature sintering promoted Tm,Tb,Dy and O atoms precipitating from Fe crystal structure.The formed precipitate with nanometer scale uniformly distributed in Fe matrix.Sintering atmosphere and temperature have great influence on phase composition.When the green bodies were sintered under the atmosphere containing trace oxygen,Fe matrix composites with oxide R2O3(R=Tm,Tb,Dy)were obtained.When the green bodies were sintered in the atmosphere absence of oxygen,Fe-based composites with RFeO3 were obtained.The special feature of Fe-Tm2O3 system was that its phase compositions were affected by not only sintering atmosphere but also sintering temperature.When the green bodies were sintered in the atmosphere containing trace oxygen,the formation of Fe-TmFeO3 composites were obtained at the sintering temperature of 600? to 1100? and Fe-Tm2O3 composites were papered at 1100?to 1200?.The mechanical and thermophysical properties of Fe-based composites were affected by the content of rare earth elements,ball-milling time and sintering temperature.With the increase of ball-milling time,the thermal expansion coefficient and compressive strength of Fe-based composites increase.With the increasing content of theoxides,the microhardness,thermal expansion coefficient and compressive strength of Fe-based composites increase.With the increase of sintering temperature,the microhardness of Fe-based composites increase.Four kinds of composite materials were obviously corroded in the deionized water with 340 °C and 15.16 MPa.With the increase of corrosion time,the corrosion weights increase and the dense of surface corrosion products gradually grow up.According to EDS and GIXRD results,the corrosion products are mainly Fe3O4 phase.Overall,the irradiation and corrosion resistance of Fe-based TbFeO3-DyFeO3 composite and Fe-based Tm2O3 composite is better than that of Fe-based Tb2O3-Dy2O3 composite and Fe-based TmFeO3 composite.In addition,compared with the non-irradiated Fe-based composites,it was found that Fe+ irradiation significantly promote the corrosion. |
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