Study On Mechanics And High Temperature Oxidation Of Fe-Cr-Al Cladding Materials By Al Element

With the introduction of the fourth-generation nuclear energy system,the fuel cladding materials currently in use cannot meet the requirements of the fourth-generation nuclear energy system,so it is necessary to seek and develop new fuel cladding materials capable of meeting the fourth-generation nuclear energy system.Fe-Cr-Al alloy is considered as one of the candidate materials for the nuclear fuel cladding material of the new generation nuclear energy system due to its excellent high temperature strength and high temperature oxidation resistance and its good performance in thermal power generation applications.In this paper,the preparation,heat treatment,thermal processing,microstructure,mechanical properties and high temperature oxidation performance of nuclear fuel cladding material Fe-Cr-Al alloy were systematically carried out,and the phase and microstructure of the material were controlled.The crack distribution and oxide film structure were analyzed.The oxidation mechanism of air atmosphere and water vapor atmosphere was studied.The following conclusions were obtained:?1?After homogenizing annealing treatment of Fe-13Cr-6Al alloy at 1150 ? for 20 min,the grain size of the air-cooled sample is moderate and uniform,and the structure of the obtained alloy is better;the Fe-13Cr-6Al alloy prepared by hot rolling at 800 ? and recrystallization annealing at 1000 ? is not only complete in crystallization,but also fine in grain,and the obtained alloy structure is better.?2?With the increase of Al content,Fe-Cr-Al alloy is still ?-Fe single-phase structure,which belongs to ferrite,its phase structure does not change with the change of Al element,and the hardness is obviously improved;the elastic modulus of the alloy is not obviously changing with the increase of Al content;the yield strength and tensile strength of Fe-Cr-Al alloy increase with the increase of Al content,and the highest yield strength and tensile strength of Fe-13Cr-6Al are 421 MPa and 495 Mpa respactively;the elongation at break decreases with the increase of Al content.The Fe-Cr-Al alloy with Fe-13Cr-6Al composition has the best tensile strength and the smallest elongation at break,and its mechanical properties are better than those of traditional cladding materials such as zirconium alloy.?3?From the results of the oxidation experiment,when the aluminum content in the Fe-Cr-Al alloy reaches 5% by weight in an air atmosphere of 1200?,an oxide film with better protective effect can be formed;in a water vapor environment of 1200? Al content needs to reach 6wt.%;from the surface phase,the continuous Al₂O₃ film can be formed only when Al element reaches at least 3wt.% in air at 1200?,and at least 4wt.% in water vapor at 1200?.According to the oxidation thermodynamic calculation,the reaction of Al oxidation to form Al₂O₃ has the highest Gibbs free energy in both air and water vapor environment of 1200 ?.Moreover,Al element can react with Cr₂O₃,Fe₂O₃ and FeCr₂O₄,and the increase of Al element content can increase the speed and quality of the formation of Al₂O₃ thin films,so that it can rapidly generate continuous and dense Al₂O₃ thin films with a certain thickness,which can delay or even prevent the formation of oxide films.In general,the mechanical properties and high temperature oxidation resistance of Fe-Cr-Al alloys are far superior to other traditional cladding materials,and are the primary choice for nuclear reactor accident-tolerant nuclear fuel?ATF?cladding.