Study On Damage Effect Of Ti₂AlC And Fe₂AlB₂ Materials Irradiated By Helium Ions

In recent years,with the increasing emphasis on the utilization of nuclear energy in the world,nuclear reactors have transitioned from the first generation fission reactors to the fourth generation fission reactors.At present,the fourth generation fission reactor（Gen IV）is still the focus of nuclear reactor research.The reactor puts forward stricter requirements for cladding materials and structural materials:thermal shock resistance,high dose radiation resistance and corrosion resistance.MAX-phase materials/MAX-like materials,such as Ti₂AlC and Fe₂Al B₂materials,have the combination characteristics of metal and ceramic,corrosion resistance,oxidation resistance,high temperature resistance and radiation resistance,because of their unique composite structure of metal and ceramic.However,helium atoms produced by（n,α）reaction in the nuclear reactor will cause the material swelling,which will lead to the increase of micro-stress and cracks in the material.Therefore,studying the damage behavior of helium ion irradiation of the two materials can better explore their application potential.In this paper,Ti₂AlC material and Fe₂Al B₂material sintered by spark plasma are selected as the research subjects.The samples were irradiated with 50 keV He²⁺at room temperature and 400℃at two different doses(5×10¹⁵ions/cm²and 5×10¹⁶ions/cm²)and 500 keV He²⁺at 500℃and 700℃at the same dose(1×10¹⁷ions/cm²).The main conclusions are as follows:（1）Under the irradiation of 50 keV He²⁺at room temperature,with the increase of irradiation dose,the diffraction peaks of the main crystal planes of the two materials become more obvious,but the Fe₂Al B₂material is more serious,indicating that the Fe₂Al B₂material has poor radiation resistance;The diffraction peak of crystal plane of Ti₂AlC material shifted to the right,and it is considered that the lattice distortion was caused by micro-stress of He bubbles in Ti₂AlC material.The diffraction peak of Fe₂Al B₂material shifted to the left,which indicates Fe₂Al B₂material was not affected by micro-stress,but only slightly swollen.The Raman peaks of the two materials disappeared at high dose,and the chemical bonds of the materials were completely destroyed by He atoms.With the increase of irradiation dose,cracks appear on the surface of Ti₂AlC,and white scratches appear on the surface of Fe₂Al B₂,indicating the latter has better swelling resistance.The concentration or size of vacancy defects in Ti₂AlC material is smaller than the as-fabricated sample,while that in Fe₂Al B₂material is just the opposite,indicating that there are differences in the density and size of vacancy defects in the preparation state of the two materials.（2）The samples were irradiated at room temperature followed by annealed from 200℃to800℃with temperature interval of 200℃for 1 h.With the temperature rising to 800℃,the damaged crystal structure of the two materials gradually recovered,the peak broadening degree decreased,and the diffraction peak shifted to the original vicinity.After annealing at400℃,the diffraction peak of the crystal plane of Fe₂Al B₂material broadens,and the irradiated layer appears amorphous in TEM images.This may be due to the formed He V complexes or He bubbles squeezeing the lattice,leading to amorphization.At the highest annealing temperature,the internal stress of the two materials is released,the swelling degree is reduced and the surface is smooth.The density and size of vacancy defects in Ti₂AlC materials do not change obviously in the range of 0～600℃,but increase at 800℃.The S parameter of Fe₂Al B₂material has increased at 200℃,and it is difficult to be captured by positrons at 800℃because of the large size of vacancy clusters,which shows the decreasing of density and size of vacancy defects.The lower vacancies migration can make Fe₂Al B₂materials show such characteristics.（3）The experiment of 50 keV-400℃irradiation shows that the crystal damage of the two materials is light,but the chemical bond damage is heavy.There is no obvious crack on the surface,and the size and density of vacancy defects have increased.The TEM image of Fe₂Al B₂material also shows the good crystallinity of material and the size of He bubble（0.8nm）is slightly larger than that annealed at 400℃.Irradiation experiments at 500 keV-500℃and 700℃show that Fe₂Al B₂material has more obvious damage effect.The damaged degree of crystal structure is not great,but the existence of large He bubbles（～10nm）at 700℃greatly increases the internal stress in some crystal planes of the material,resulting in cracks and exfoliation on the surface.The change of vacancy defects in materials also proves that.Large-sized He bubbles and He V complexes increase the S value at the maximum damage,indicating that the increase of the size and density of vacancy defects.（4）Compared with the irradiation at room temperature followed by annealing,the crystal damage caused by high temperature irradiation is slight,as is the chemical bond damage.In addition,the surfaces of the two samples are almost the same under the two experimental conditions.However,it is found that the vacancy-type defects show different trait between Fe₂Al B₂and Ti₂AlC.The size and density of vacancy defects under high temperature irradiation are larger and vacancy defects grow faster,which is cause by ion irradiation that produces vacancy defects and high temperature promotes their migration at the same time.Ion irradiation at room temperature can not achieve that above.