The widely used nickel-based superalloys for turbine engine materials showed a limited-service temperature of only 1200℃, and did not exceed 1500℃ even when coated with thermal barrier coatings, which is urgent to develop the advanced thermal protection system for turbine engines with higher thrust-weight ratios. Niobium alloy coated with silicide coating is undoubtedly considered the most efficient method to reach long-term service, since it can form a dense SiO2 layer with self-healing ability at high temperatures. However, the single silicide coating has a strong tendency to crack vertically and even peel off due to the accumulated growth thermal stress. Therefore, how to form a robust protective layer with high chemical stability and large strain tolerance at elevated temperatures is the key scientific issue for the long-term service of silicide protective coating. Motivated by such considerations, depositing an extra protective layer to form the silicide-based composite coating is a potential solution to the long-term service problem, and lots of works have been focused on fabricating the modified silicide-based coating to gain the improvement of thermal protective performance.
Recently, a team of material scientists led by Yaming Wang from Harbin Institute of Technology, China first reported a new approach for improving hot corrosion resistance and anti-oxidation performance in silicide coating on niobium alloys, that is constructing a modified silicide-based coating with a preset porous outer layer. This work proposes a reliable and efficient method, named liquid plasma-assisted particle deposition and sintering (LPDS), achieving the construction of a robust HfC-HfO2 modified silicide coating on niobium alloys, endowing the composite coating with excellent hot corrosion resistance and high-temperature oxidation resistance.
The team published their work in Journal of Advanced Ceramics on December 5, 2024.
“In this report, we propose a reliable and efficient method, named liquid plasma-assisted particle deposition and sintering (LPDS). It is developed from the conventional plasma electrolytic oxidation (PEO) and is characterized by high voltage and high temperature, accompanied by instant and dense plasma spark discharges at the coating/electrolyte interface. As a result, the added HfC nanoparticles in the electrolyte are migrated and deposited on the silicide coating surface, forming a NbSi2/HfC-HfO2 composite coating.” said Yaming Wang, professor at School of Materials Science and Engineering at Harbin Institute of Technology (China), a senior expert whose research interests focus on the field of thermal protection ceramic coating.
“LPDS technique has been unexpectedly found to achieve our design that the perfect combination of dense inner layer and functional outer layer, which is expected to endow the composite coating with excellent thermal protective performance. For a new approach, it is necessary to explore its formation mechanism of particle deposition and sintering outer layer,” said Yaming Wang.
NbSi2/HfC-HfO2 composite coating shows a significant improvement of the hot corrosion resistance and high-temperature oxidation resistance compared with single NbSi2 coating, possessing the lowest corrosion gain of 13.94 mg·cm-2, and the residual thickness of the NbSi2 layer after hot corrosion at 900℃ for 200 h and high-temperature oxidation at 900℃ for 500 min are ~ 91 μm and 72 μm, respectively. “The superior hot corrosion resistance and anti-oxidation properties of the composite coating to that of single NbSi2 coating have spurred inquiries to lucrative leverage it as a new thermal protection coating material,” said Yaming Wang.
Multiple stress release mechanisms of NbSi2/HfC-HfO2 composite coating at high temperatures are critical factors for the improvement, they are respectively: (i) a certain porosity of LPDS-coating provides the extra strain tolerance; (ii) the robust Hf-Si-O network structure with high thermal/chemical stability possesses large strain tolerance; (iii) there exists a smaller volume change within the deposition HfC-HfO2 layer due to the low volume expansion rate of the possible reactions. “From the perspective of long-term service, NbSi2/HfC-HfO2 composite coating pertains to an eligible thermal protection coating material for refractory metals.” said Yaming Wang.
However, more delicate research works are still needed to explore the suitability of NbSi2/HfC-HfO2 composite coating as a new thermal protection coating material. “In future work, our experiment designs might consider the oxidation test in a higher temperature and hot corrosion test in other molten salt environments such as CMAS or CMAS + molten salt. Moreover, the effort for the exact measurement of the coating residual stress value after different high-temperature service environments never stops.” said Yaming Wang.
Other contributors include Zhiyun Ye, Shuqi Wang, Shuang Yu, Xinrui Zhao, Yongchun Zou, Guoliang Chen, Jiahu Ouyang, Dechang Jia, Yu Zhou from the School of Materials Science and Engineering at Harbin Institute of Technology in Heilongjiang, China; Lei Wen from the University of Science and Technology Beijing in Beijing, China; Lina Zhao, Guangxi Zhang from Xi'an Aerospace Composites Research Institute in Xi'an, China.
This work was supported by the National Natural Science Foundation of China (Nos. 523B2010, U21B2053, 52071114, 52301084, and 52001100), China Postdoctoral Science Foundation (2023M730843), Heilongjiang Touyan Team Program, Heilongjiang Postdoctoral Science Foundation (No. AUGA4110004823), and Research start-up Fund by HIT are gratefully acknowledged.
About Author
Yaming Wang is a professor in Material Science and vice leader at Institute for Advanced Ceramics (IAC), Harbin Institute of Technology (HIT). He got his Bachelor’s degree and PhD from HIT in 2001 and 2006, respectively. Then he has a position as a lecture in HIT, and shortly got the Award of New Century Excellent Talents in Ministry of Education due to his good academic achievements in 2008. He went to Manchester University for 1-years visiting research supported from Chinese Scholarship Council in 2012. He is Fellow of the Chinese Society of Mechanical Engineering, Chinese Society for Materials Research, and Surface Engineering Branch of China Mechanical Engineering Society. He holds 30 patents and 2 coauthored BOOK. He has authored / coauthored more than 180 papers in refereed journals, with SCI indexed citation of >6000 and H index of 47. The wear resistance ceramic coating and high emissivity ceramic coating were successfully applied in aerospace components. He was conferred the First prize in Technological Invention Award of Heilongjiang Province in 2024. He is now focusing on high temperature multifunctional thermal protective ceramic coating for extreme environment applications.
About Journal of Advanced Ceramics
Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in “Materials Science, Ceramics” category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508
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