Study On Martensite Structure Of M5Zirconium Alloy

With the development of nuclear power technology in the word, zirconium in nuclear power has been localized gradually in China. M5zirconium alloys are used as the fuel cladding tubes in nuclear reactors and are one of the key researches on the nuclear fuel cladding materials. The cladding tube materials are not only withstood strong neutron irradiation, high temperature and high pressure, mechanical stress and complex corrosion environment, but also satisfied with the demand of increasing nuclear fuel consumption. The zirconium alloys especially Zr-Nb alloys are pointed out the correct development direction by those demands. M5zirconium alloys which used in nuclear reactor are processed by recrystallization annealing, while cladding tubes would occur martensite transformation after rapid cooling on high temperature. At present, there are few researches on the mechanical properties and corrosion resisting properties of martensite structures quenched in β phase zone.The processes by comparisons the variations of M5zirconium microstructures with different heat treatment conditions, different heat treatment parameters, different aging times and plastic deformations have been conducted in this study. The influence of thermal aged M5zirconium substructures on mechanical properties is analyzed and verified by ring tensile test. The possibility about M5zirconium alloys after quenching and tempering applied in nuclear reactor has been studied.The microstructure of M5zirconium after annealing was small equiaxed grain and it occurred to martensite transformation which grains grew obviously after quenching. Quenching temperature and time have great influence on twin width. Elevating temperature and prolonging temper time can fragment the twins and the temperature fragment worse. The microstructures of M5zirconium alloys after aging test are still martensitic crystals which the size are stabilized. With the extension of aging time, the fragmented degree of twin martensitic is increased and the dislocation configuration is changed.The substructure changes according to different states of M5zirconium after plastic deformation can be seen in this text. Annealed samples after room temperature tensile become grain deformation; grains are drawn out and second-phase particles are declined after high temperature tensile. Twinned martensitic of quenching and tempering treatment is drawn out and thin after room temperature tensile; the twins fractured and dislocation density decreased after high temperature tensile. The twins of aging sample after room temperature tensile are stretched and fractured, and dislocation cells in grains while dislocation line in grains after high temperature tensile.Strength of extension, yield strength and static toughness of M5zirconium sample after aging are both decreased with aging time extension, plasticity is decreased slightly and micro-hardness changes little.The tensile macro-fractures of aging sample are gray fibrous fractures and have some plastic deformations on fractures and the plastic deformations after high temperature tensile are obviously. A lot of dimples on the fracture, secondary cracks increase by aging time extension and quasi cleavage steps exist in cracks after room temperature tensile. The dimples were drawn out and the quasi cleavage planes increase by aging time extension after high temperature tensile. The fractures are mixed fractures include dimple feature and quasi-cleavage.