HIP Preparation, Interface Structure And Irradiation Stability Of Aluminum-based Boron Carbide Composites

Nuclear power industry is in a stage of rapid development in our country,the nuclear power plant will produce a large amount of highly radioactive spent fuel over the coming decades,and how to dispose the spent fuel safely and reliably will become increasingly important.Boron carbide reinforced aluminum matrix composites not only have excellent thermal neutron absorption and radiation resistance,but also have great mechanical properties,and these composites have been applied in the storage and transportation of spent fuel successfully.Different preparation process of Al/B4Cp composite will lead to different interface structures;the difference and poor stability of the interface structure will influence the the long-term service life of the composites.This paper systematically studied the fabrication route of Al/B4Cp composite by the ball milling mixing,cold isostatic pressing(CIP),hot isostatic pressing(HIP)sintering and hot rolling,and investigated the influence of these preparation process parameters on the microstructure and mechanical properties of Al/B4Cp composite.Combine the high resolution transmission electron microscopy(HRTEM)experiment and the first principles calculation to emphatically research the interface structure,interface stability and interface reaction of the Al/B4Cp composites;simulating the wet storage radiation environment of spent fuel,the accelerated irradiation test was carried out in the reactor,and the effect of accelerated irradiation on properties of Al/B4Cp composite was studied.The main research contents and results of this paper are as follows:(1)Al/B4Cp and Al/B4Cp/B composites were designed,the dry ball milling and wet ball milling were implemented,and the results revealed that the use of anhydrous alcohol as a liquid medium for wet milling can not only avoid the oxidation and agglomeration of particles,but also contribute to the uniform distribution of B4C particles in the aluminum alloy matrix.The influence of CIP technology on the density of green billets was studied and high density of CIP green billet was obtained.The interface reaction can be controlled effectively by controlling the temperature of the HIP,the high density and good mechanical properties composites can be obtained,and B4C particles are homogeneously dispersed in aluminum alloy matrix.The variable temperature hot rolling method was adopted,and the effect of hot rolling temperature on Al/B4Cp composite sheet defect.Finally the large size composite plate without obvious void defect was successfully achieved,and B4C particles were uniform distributed in the composite plate.The effect of B4C particle size on the tensile properties of Al/B4Cp was studied,reinforcement effect of different strengthening mechanism were analyzed,it was found that the tensile properties of composites increases with the decrease of particle size of B4C,when the B4C particles is?3.5 ?m,the yield strength and ultimate tensile strength of 6061 Al-31%B4Cp are?288 MPa and?351 MPa,respectively;fine grain strengthening has the largest contribution to the reinforcement effect of composite.(2)HRTEM experiment and the first principles calculation methods were combined to investigate the interface structure,interface stability and interface reaction of the Al/B4Cp composites systematically.Results revealed that Al(200)and B4C(012)formed a clean and impurity free interface structure without debonding,holes,cracks and other defects,and a transition layer with 2-6nm width was found in some interfacial region.In the first principle study,B11Cp(CBC)configuration was adopted as the basic unit of the B4C structure,then four kinds of B4C(001)surface slab were established with different terminal atoms,next the most stable C-terminated B4C(001)surface slab was used to built the Al(111)/B4C(001)interface model;According to the different stacking relationship of Al,C atoms in interface zone,the interface model was further divided into three geometries including top-site,hollow-site and bridge-site structure.The calculation results revealed that the top-site interface structure transformed into a new structure,which looks like hollow-site,has relatively the strongest interfacial adhesion and the best interface stability.Interfacial Al atom diffusion occurred both in hollow-site and bridge-site interface structure after relaxation,and the transition regions was formed.The results of HRTEM experiment also confirmed the formation of interfacial transition layer,which is produced by the diffusion of interfacial Al atoms.(3)The wet storage radiation environment of spent fuel was simulated,and the accelerated irradiation test was carried out in the reactor,the total irradiation dose was more than 40 years of service life during the test,and the average neutron flux was about 7.185E+19n/cm2,the average gamma irradiation dose was about 4.021E+11 rads(E?1MeV).The irradiation behavior of Al/B4Cp composites with different surface treatment process were researched through accelerated irradiation experiment.The results showed that both the surface polishing samples and anodized samples occurred slight irradiation swelling after accelerated irradiation;The average increasement of length,width and thickness for surface polishing samples was?0.061%?0.076%?0.084%respectively,while the corresponding average increasement for anodized samples was?0.046%??0.073%?0.042%respectively;For all samples,the dry weight increase rate was not more than 0.35%,and the density reduction amount was less than 0.6%,the change degree of the surface polishing samples is slightly larger than that of the anodized samples.The 10B areal density of all specimens was about 0.03615 g/cm2 after accelerated irradiation test,it had little change.Both of the two kinds of samples occurred slight rradiation hardening,Rockwell hardness,the yield strength and ultimate tensile strength improved a little while the elongation decreased slightly.After simulating the wet storage radiation environment of spent fuel for more than 40 years service life,both the surface polishing and anodized samples exhibited great anti-radiation stability,the macroscopical properties,physical performance and mechanical properties lived up to requirements of the spent fuel storage and transportation application after accelerated irradiation test.