| The concept of accident tolerant Fuel(ATF)was came up after several nuclear accidents occurred.The ATF system can minimize the oxidation rate of cladding material and the generation of hydrogen compared with exist nuclear system,which makes the ATF nuclear system have the ability of self-protection under severe condition.FeCrAl alloys have long been used as structural material under high temperature condition.Nowadays,FeCrAl alloy is considered as candidate for ATF cladding material in light water reactor(LWR)due to its high resistance to oxidation and relatively stability under irradiation condition.FeCrAl alloys can withstand high temperature steam compared with Zr alloys which have long been used as structural material in extreme environment and the matrix is ferritic(bcc)due to strong bcc stabilizing effect of chromium and aluminum in iron-based alloy.The formation of Al2O3 and Cr2O3 layer can protect FeCrAl alloy from oxidation.Therefore,FeCrAl alloys can be treated as a promising candidate of nuclear cladding material.Understanding the deformation mechanism under irradiation environment is very important for structural material used in neutron reactors.However,using neutron irradiation to achieve high dose to investigate the irradiation property of material is very expensive,time consuming and could cause activation of materials.The post-irradiation characterization is hard to perform.However,the ion penetration depth is limited to the order of tens of microns,make micro-scale test necessary to compare the mechanical behavior before and after irradiation in the same magnitude.At the same time,the micro-scale specimen can be less-cost and easy to manufacture,bridging micro-scale to macro-scale mechanical property measurements,and to develop capabilities for predicting performance limitations of FeCrAl alloys became very popular in field of nuclear material research.In this research,the crystal structure,grain size,and the structure of grain boundaries of FeCrAl alloy were studied.By using EBSD technology,the structure of FeCrAl alloy bulk sample were characterized.The micro-pillars of FeCrAl alloy were prepared with FIB and compressed by Pico-indenter.By observing the slip trace on the surface of micro-pillars after compression,we analyzed the effect of pillar size,crystallography orientation,and structure of grain boundaries on the deformation behavior of FeCrAl alloy.The result shows that when the pillar size is larger than 2 μm,the strength of the pillar is similar to that of bulk material,which means there is no size effect for the pillars larger than 2 μm.Therefore,the property of these pillars can well represent the property of bulk material.Comparing the strength of pillars with different orientations,the data indicates that the crystallography orientation has very little influence on the mechanical property of this material.The micro-pillar compression tests were also performed on the material,which was pre-strained.The result shows that the increase of dislocation density can increase the strength of FeCrAl alloy.Grain boundaries(GBs)have been regarded as barriers to dislocation motion and contributors to strain hardening.The slip transmission across GB can be classified into three groups:(a)Direct transmission with a residual Burgers vector in GB if the angle between two slip systems in each side of bi-crystal are very small.(b)Indirect transmission including residual dislocations in GB,the incoming and outgoing slip plane are not parallel leaves a partial residual Burgers vector in GB if the angle between slip planes are not very big.(c)No transmission: GB act a barrier to slip transmission and dislocations remain stay at GB if the angle between two slip systems with high Schmid factors are really large,this would cause the increase of yield strength and strain hardening. |
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