Structural Characteristics Of Second Phase Particle And Microstructure Evolution Of New Zirconium Alloys

The technical level of nuclear fuel assembly manufacturing is an important condition for ensuring the normal operation of pressurized water reactor nuclear power plants.The key core components are composed of different inner and outer strips made of zirconium alloy sheet strip.At present,the resea rch on zirconium alloys for thin-plate strips mainly focuses on the second-phase particles and corrosion resistance,and there are few studies related to the close microstructure of the punching properties.In this paper,a new zirconium alloy w ith good punching performance was taken as the research object.The field emission scanning electron microscopy,transmission electron microscopy,scanning electron microscopy and X-ray diffractometer combined with the first-principles calculation were used to study the microstructure of the annealed strip and the structural characteristics of the second phase particles.The evolution of the second phase particles and microstructure of the strip with annealing temperature was explored under vacuum heat treatment conditions.The main reason and factors for the good punching performance of the new zirconium alloy were revealed.The research results were expected to provide a theoretical basis for the development of commercial new zirconium alloys with independent intellectual property rights.Firstly,the microstructure and the structural characteristics of the second phase particle of the new zirconium alloy were carried out.It was found that the grain morphology of the finished strip is equiaxed,and the average grain size is 3.39?m;There are two textures of{0001}<101^—0>and{0001}<112^—0>,most of the grains{0001}<112^—0>parallel strip RD direction,less grain with<101^—0>parallel strip RD direction;The second phase particles are distributed inside the grain and at the grain boundary,with an average size of 114nm,the large size is the irregular elliptical Zr-Nb-Fe phase,and the smaller is the circular?-Nb phase;wherein,the Zr-Nb-Fe second phase particles were ZrCr₂ type close packed hexagonal?HCP?crystal structure,lattice constant is a=0.54nm and c=0.88nm,in which Fe tends to occupy the position of Cr???,Nb tends to occuoy the position of Cr???.Secondly,the effects of different annealing temperatures on the microstructure and second phase particles of the new zirconium alloy under vacu um heat treatment conditions were studied.It was found that the grain morphology of the new zirconium alloy sheet annealing strip is not significantly different from that of the finished strip as the annealing temperature changes;As the heat treatment temperature decreases,the grain size of the strip decreases.The second phase particles are fine and uniformly dispersed;As the annealing temperature increases,the recrystallization process proceeds sufficiently,the texture strength of{101^—0}becomes weak,the texture strength of{112^—0}becomes stronger,and the grain orientation gradually changes from the{0001}<101^—0>texture of the as-rolled state to the recrystallized state{0001}<112^—0>;The second phase particles Zr-Nb-Fe is unstable at high temperature and is easily soluble in matrix phase.With the increase of temperature,the structure of?-Zr particles is the most stable,followed by?-Nb,?-Zr particles worst.Finally,this paper analyzed the main reasons for the good punching performance of the new zirconium alloy sheet.It was believed that annealing and rolling deformation are the main factors affecting the stripping.Among them,the annealing temperature has little effect on the morphology and distribution of the grains and the second phase particles,but has a great influence on the texture of the strip.The annealing temperature increases,the texture of the new zirconium alloy changes,and the grain orientation is changed from the{0001}<101^—0>texture of the as-rolled state to the recrystallized state{0001}<112^—0>,and the grain recrystallizes and restores the plastic processing ability of the strip,which is beneficial to the improvement of the strip punching performance;The small amount of rolling is co ntinuously accumulated,and the grain refinement of the new zirconium alloy during the recrystallization process is induced,which causes the twin crystal to break or eliminate the twinning,so that the slip to realize the dislocation motion is easier to carry out,under the joint action of annealing and rolling deformation,the finished strip of the new zirconium alloy sheet has good punching performance.