Effect Of Grain Size Or Gallium Doping On The Behavior Of Helium In Aluminum

With the development of society's demand for clean energy,nuclear energy has become one of the representative new energy sources.However,since the structural materials of nuclear fuel reactors are exposed to extreme environments,they will be affected by a large number of particles,which will cause radiation damage,which will lead to vacancies,gap atom eccentric defects and impurity atoms(helium).Most of the irradiated vacancies can be recovered spontaneously,but helium(He)atoms are inert atoms with full shell electronic structure and do not combine with any metal atoms.It is foreseeable that if there are these foreign helium atoms incompatible with the matrix atoms in the metal,their own aggregation and growth,or interaction with defects such as vacancies,will inevitably cause irrecoverable damage to the material.How to effectively improve the anti-irradiation performance of the material is a major challenge.Aluminum(AI)and its alloys are used as deuterium barrier coatings for fusion reactors.It is of engineering and scientific significance to study the behavior of helium.In this paper,aluminum with different grain sizes and samples of aluminum and aluminum-gallium alloys(Al-1.8 at.%Ga)with the same grain size were prepared respectively in terms of grain size effect and doped gallium(Ga)atoms.These samples were exposed to low-energy(50 eV)He plasma has been investigated with the fluence of 1.8×1024 He/m2 at room temperature(RT).Combining X-ray diffraction(XRD),electron scanning microscope(SEM),slow beam positron annihilation(SPAS),transmission electron microscope(TEM),thermal desorption spectroscopy(TDS)and other analytical testing methods to explore the effect of grain size or Ga doping on the behavior of helium in Al,separately.By analyzing the experimental results.the main conclusions of this work are as follows:(1)After analysis and testing,it was found that helium implantation would distort the crystal lattice and make the XRD characteristic peak half width(FWHM)of Al significantly wider.Helium atoms "self-trap" in the matrix,introducing vacancy-type defects into the sample to form a helium-vacancy complex,which migrates,aggregates,merges,and nucleates into helium bubbles through dislocations or grain boundaries,as the radiation dose further Increase,the helium bubble increases.Eventually,when the internal pressure of the helium bubble is greater than the yield limit of the sample,the surface of the material is bubbled,and in severe cases,the surface of the material is peeled off.(2)Reducing the grain size will improve the material's resistance to helium irradiation and also affect the thermal desorption behavior of Al.According to the TDS results,as the grain size increases,the peak of helium thermal desorption moves to a high temperature region,the spectrum of helium thermal desorption broadens,and there are obvious satellite peaks.This is because the smaller the grain size,helium can quickly diffuse through the grain boundaries.When the grain size is 20 ?m,the helium heat release signal cannot be detected in the low temperature region,which proves that the grain boundary has a solid helium effect at a certain temperature.(3)The addition of gallium atoms will distort the lattice of matrix and make the dislocations in Al difficult to disappear.The surface bubble of the irradiated Al-1.8 at.%Ga alloy is smaller in size and larger in surface density than the irradiated Al surface.This is because the addition of gallium introduces vacancy-type defects and forms more helium capture trap.The temperature of helium thermal desorption peak of Al-1.8 at.%Ga alloy(480 K)is lower than that of Al(580 K),and the amount of helium thermal desorption of Al-1.8 at.%Ga alloy(1.76×1021 He/m2)is much higher than Al's helium thermal desorption amount(8.92×1018 He/m2).This is because the increase in trapping means that more vacancies are combined with helium,and the dislocations in the aluminum-gallium alloy are not easy to disappear,so that helium has more opportunities to diffuse out along the dislocations and reduce the peak of its thermal desorption spectrum.(4)TDS experiments were performed on deuterium(D)in aluminum uder different heating rates,and the thermal activation energy of deuterium in aluminum was determined to be 0.19 ± 0.02 eV based on the experimental results.In addition,it was also found that deuterium hinders the movement of the grain boundary and increases the high-temperature strength of Al during the temperature increase process.This is because deuterium and vacancy combine to move to the grain boundary,which is not conducive to the movement of the grain boundary.