金属氧化物陶瓷涂层高温阻氘渗透性能研究

采用射频磁控溅射方法在316L不锈钢表面沉积了Al₂O₃,Cr₂O₃,Y₂O₃和ZrO₂(8%Y₂O₃)4种单层氧化物陶瓷涂层。选用X射线衍射(XRD)和扫描电镜(SEM)对4种氧化物陶瓷涂层相组成、微观组织结构进行表征,结果表明,Al₂O₃涂层为非晶态,其他3种氧化物陶瓷涂层均为晶体结构,且涂层沉积致密,无明显微观缺陷产生。采用气相氢渗透装置对各涂层的氘渗透性能进行测试,结果表明,受氧化物中金属离子与氧的结合能的影响,在973 K@80 kPa氢渗透压下,厚度约为250 nm的Al₂O₃,Cr₂O₃,Y₂O₃和ZrO₂(8%Y₂O₃)涂层氘渗透阻挡因子(DPRF)分别为103,46,112和256,表明4种氧化物陶瓷涂层均具有良好的阻氘渗透性能,其中Y₂O₃陶瓷涂层阻氘渗透性能最好。因此,以Y₂O₃陶瓷涂层为例,研究厚度对涂层阻氘渗透性能的影响,在涂层厚度为139~251 nm范围内,氘渗透激活能和D-PRF随着涂层厚度的增加而线性增大。随着Y₂O₃涂层厚度增加,氘渗透量减少,阻氘渗透性能提高。

Deuterium Permeation Resistance of Metal Oxide Ceramic Coatings at High Temperature

Deuterium and tritium with tiny atomic radius,as nuclear fuel,have the extremely strong permeability,which will lead to hydrogen embrittlement and surface corrosion of the metallic structure materials.In addition,tritium has strong radioactivity and is in direct contact with the inner wall of the vessels and pipes.The high permeation rate of deuterium and tritium will lead to waste of nuclear fuel,and also cause radioactive contamination of the surroundings.The four oxide ceramic coatings were prepared on the inner wall of the structural material in order to suppress the permeation rate of hydrogen and its isotopes.The method of the radio frequency magnetron sputtering was used to prepare four single oxide ceramic coatings,namely Al₂O₃,Cr₂O₃,Y₂O₃ and ZrO₂(8%Y₂O₃)on the 316 L stainless steel.Then the coatings were annealed at 973 K and held for 2 h.The purpose was to improve the density of structure and the uniformity of the composition of the coatings.X-ray diffraction(XRD)and scanning electron microscope(SEM)were used to characterize the phase composition and microstructure of the oxide ceramic coatings.In addition,the gas permeation method was used to measure the deuterium resistance of the coatings.The range of measure temperature was 973-973 K,and the range of measure permeation pressure was 40-100 kPa.By characterizing the crystalline state of the four coatings,the results showed that Al₂O₃ coating was amorphous,and the Cr₂O₃,ZrO₂(8%Y₂O₃)and Y₂O₃ coatings were all crystalline structures.Cr₂O₃ coating was the R-3 C space group(hexagonal crystal system;lattice constant a=b=0.4959 nm,c=1.3594 nm).ZrO₂(8%Y₂O₃)coating was belonged to the P42/nmc space group(tetragonal crystal structure;lattice constants a=b=0.3629 nm,c=0.5143 nm).Y₂O₃ coating was the body-centered cubic with the lattice constant of a=b=c=1.0611 nm.It could be seen from SEM images that the four coatings were intensely deposited along the depth direction.ZrO₂(8%Y₂O₃)and Y₂O₃ coatings grew in an equiaxed manner.However,Cr₂O₃ coating initially grew in an equiaxed manner,then transformed into columnar crystal growth.The thickness of Al₂O₃,Cr₂O₃,ZrO₂(8%Y₂O₃)and Y₂O₃ coatings were 245,360,252 and 251 nm,respectively.Compared with the other three coatings,the surface of Al₂O₃ coating was rougher.The atomic percentage of each element in the four coatings was calculated.The results showed that the ratio of metal ions and oxygen atoms was stoichiometric,which indicated that there were no oxygen vacancies and metal phases in the four coatings.The deuterium resistance of the coating was closely related to the temperature and the permeation deuterium pressure.When the thickness of the coatings was similar,the deuterium permeability of the four coatings was 2-4 orders of magnitude lower than that of the 316 L stainless steel substrate.The results indicated that the presence of the coating could effectively reduce the deuterium permeation flux.The permeation reduction factor(PRF)of Al₂O₃,Cr₂O₃,ZrO₂(8%Y₂O₃)and Y₂O₃ coatings were103,46,112 and 256,respectively at 973 K@80 kPa.Y₂O₃ coating had better deuterium resistance.The main reason was that the permeation and diffusion of deuterium in the oxide ceramic coating needed enough energy to break the chemical bond between metal ion and oxygen atom.The oxygen atoms combined with deuterium atoms to form OD-1.Subsequently,the deuterium atom broke away from original OD-1 and combined with nearby oxygen atoms to form new OD-1 under the drive of the concentration difference.The binding energy of metal ions and oxygen atoms in oxide ceramics was different,leading to differences in the energy barriers during the deuterium permeation process.In Y₂O₃ coating,one O2-combines with four Y3+,and the bond energy of Y-O was 714 kJ·mol-1.The release of one O2-needed to overcome the energy barrier of 2856 kJ·mol-1.Compared with the other three coatings,Y₂O₃ coating needed to overcome the highest energy barrier in the deuterium permeation process,so its deuterium resistance performance was the best.When the thickness of the Y₂O₃ ceramic coating was between 190 and 251 nm,the permeation activation energy and permeation reduction factor of the coating increased linearly.The deuterium permeation activation energy was 93-137 kJ·mol-1.The corresponding PRF was 142-256 at 973 K@80 kPa.In summary,the following conclusions could be drawn:(1)Al₂O₃,Cr₂O₃,Y₂O₃ and ZrO₂(8%Y₂O₃)ceramic coatings were prepared by radio frequency magnetron sputtering method.The coating structure was dense,without obvious microscopic defects.In addition,except for non-crystalline Al₂O₃ coating,the other three coatings were crystalline structures.(2)When the thickness of the coating was similar,the binding energy of metal ions and oxygen atoms had an important impact on the deuterium resistance performance of the coating.The higher the binding energy,the better the deuterium permeation resistance.The comparison showed that Y₂O₃ coating had the best deuterium resistance among the four coatings.Its PRF was 256 at 973 K@80 kPa.Furthermore,the deuterium permeation behavior was the synergistic effect of bulk diffusion and surface diffusion.(3)The deuterium resistance performance varied with the thickness of the coating.When the thickness of Y₂O₃ ceramic coating was in the range of 190-251 nm,the permeation activation energy and PRF of Y₂O₃ coating increased linearly as the coating thickness increases.