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RESEARCH LETTER|2 Article(s)
Wenhao YE, Qiang WEI, Jiamin LIANG, Jie ZHOU, Fanping MENG, Per EKLUND, and Qing HUANG
Zircaloy coating is one of the crucial technical ways to improve the accident tolerance of nuclear fuel cladding, which enables the zirconium-water reaction problems to be solved. Zr2Al3C4 coating is one type of candidate solutions to improve the high-temperature oxidation resistance of zirconium claddings. However, little study has been performed on the synthesis of Zr2Al3C4 coatings on zirconium alloy substrates due to the inter-diffusion, as well as the difference of the thermal expansion coefficients between the Zr2Al3C4 coating and the substrates. In this study, Zr2Al3C4 coatings were prepared through room-temperature magnetron sputtering and post annealing on zirconium alloy (ZIRLO) substrates with magnetron-sputtered Al/Mo-C interlayers. The effects of Al/Mo-C interlayers on phases and microstructures of Zr-Al-C coatings after annealing were studied by different methods. It is found that the coatings without interlayer are broken and no Zr2Al3C4 phase is formed due to significant interdiffusion between the Zr-Al-C coating and the substrate during annealing at 800 ℃ for 3 h. The Al/Mo-C interlayers prevented elemental diffusion between Zr-Al-C coatings and substrates during the post-annealing process. The Al/Mo-C interlayers act as diffusion barriers and greatly reduce the stoichiometric deviations from Zr2Al3C4 phase, which facilitates the formation of the Zr2Al3C4 phase in the final coating. Moreover, this diffusion-barrier layers contribute to eliminating cracks induced by the difference of the thermal expansion coefficients between the Zr2Al3C4 coatings and substrates. At the same time, the adhesions between Zr-Al-C coatings with Al/Mo-C interlayers and substrates were improved after annealing, with their strength exceeding 30 N. Zircaloy coating is one of the crucial technical ways to improve the accident tolerance of nuclear fuel cladding, which enables the zirconium-water reaction problems to be solved. Zr2Al3C4 coating is one type of candidate solutions to improve the high-temperature oxidation resistance of zirconium claddings. However, little study has been performed on the synthesis of Zr2Al3C4 coatings on zirconium alloy substrates due to the inter-diffusion, as well as the difference of the thermal expansion coefficients between the Zr2Al3C4 coating and the substrates. In this study, Zr2Al3C4 coatings were prepared through room-temperature magnetron sputtering and post annealing on zirconium alloy (ZIRLO) substrates with magnetron-sputtered Al/Mo-C interlayers. The effects of Al/Mo-C interlayers on phases and microstructures of Zr-Al-C coatings after annealing were studied by different methods. It is found that the coatings without interlayer are broken and no Zr2Al3C4 phase is formed due to significant interdiffusion between the Zr-Al-C coating and the substrate during annealing at 800 ℃ for 3 h. The Al/Mo-C interlayers prevented elemental diffusion between Zr-Al-C coatings and substrates during the post-annealing process. The Al/Mo-C interlayers act as diffusion barriers and greatly reduce the stoichiometric deviations from Zr2Al3C4 phase, which facilitates the formation of the Zr2Al3C4 phase in the final coating. Moreover, this diffusion-barrier layers contribute to eliminating cracks induced by the difference of the thermal expansion coefficients between the Zr2Al3C4 coatings and substrates. At the same time, the adhesions between Zr-Al-C coatings with Al/Mo-C interlayers and substrates were improved after annealing, with their strength exceeding 30 N.
Journal of Inorganic Materials
- Publication Date: May. 20, 2021
- Vol. 36, Issue 5, 541 (2021)
Hanqin LIANG, Jinwei YIN, Kaihui ZUO, Yongfeng XIA, Dongxu YAO, and Yuping ZENG
Si3N4 ceramics with improved and tailorable dielectric constant are desirable for microwave dielectric substrate application in harsh environment. Effect of BaTiO3 addition on the mechanical and dielectric properties of the hot-pressed Si3N4 ceramics with Al2O3 and Nd2O3 as sintering additives were investigated. Relative density, flexural strength and Vickers’ hardness of Si3N4 ceramics all decreased, while indentation fracture toughness increased monotonically with the increase of BaTiO3 content. Flexural strength of Si3N4 ceramics was higher than 600 MPa and dielectric constant of Si3N4 ceramics increased to 9.26-11.50 when 5wt%-20wt% of BaTiO3 was added. The dielectric loss was at the level of 10-3. The improvement of dielectric constant was attributed to the formation of TiN during hot pressing, as crystalline BaTiO3 was not detected in the sintered samples. These findings can make a significant contribution to the new applications of Si3N4 ceramics. Si3N4 ceramics with improved and tailorable dielectric constant are desirable for microwave dielectric substrate application in harsh environment. Effect of BaTiO3 addition on the mechanical and dielectric properties of the hot-pressed Si3N4 ceramics with Al2O3 and Nd2O3 as sintering additives were investigated. Relative density, flexural strength and Vickers’ hardness of Si3N4 ceramics all decreased, while indentation fracture toughness increased monotonically with the increase of BaTiO3 content. Flexural strength of Si3N4 ceramics was higher than 600 MPa and dielectric constant of Si3N4 ceramics increased to 9.26-11.50 when 5wt%-20wt% of BaTiO3 was added. The dielectric loss was at the level of 10-3. The improvement of dielectric constant was attributed to the formation of TiN during hot pressing, as crystalline BaTiO3 was not detected in the sintered samples. These findings can make a significant contribution to the new applications of Si3N4 ceramics.
Journal of Inorganic Materials
- Publication Date: May. 20, 2021
- Vol. 36, Issue 5, 535 (2021)
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