Non-transformable tetragonal YSZ nanostructured feedstocks for plasma spraying-physical vapor deposition

Significance 

Composition and microstructure properties of materials are the main processing attributes that material scientists have been focusing on in a bid to bridge the gaps that exist between the two. Based on this, the scientists have been able to design composition of materials that can achieve excellent performance, a case in point, thermal barrier coatings: which have been broadly applied in aircraft and gas turbine engines. Presently, the most popular material for thermal barrier coatings is the 8% by weight yttria stabilized zirconia (8YSZ) with non-transformable tetragonal prime phase (t´).

Recently, a novel fabrication technique: plasma spraying-physical vapor deposition (PS-PVD), has been developed and employed for the fabrication of the yttria based material since it can combine the benefits of atmosphere plasma spraying and electron-beam physical vapor deposition. However, for the PS-PVD, a lower particle size for feedstocks is necessary to facilitate the vaporization of feedstocks. Currently, M6700 powders are most popular for this purpose and have a detrimental drawback in that the remnant monoclinic zirconia has damaging effects to the thermal shock resistance capability of the resultant coating. Therefore, there is need to fabricate high performance YSZ feedstocks as substitutes for the M6700 powders.

To this note, a team of researchers at Harbin Institute of Technology in China led by professor You Wang investigated the t´ phase in yttria stabilized zirconia feedstocks used for plasma spraying-physical vapor deposition. They also hoped to pioneer in the preparation of non-transformable tetragonal (t´) n-8YSZ feedstocks by the nanopowder reconstitution method and establish a good foundation for future work. Their work is now published in the research journal, Ceramics International.

The research team commenced their work by selecting a raw nanopowder of 8YSZ of specific grain size. The 8YSZ feedstocks were synthesized by the powder reconstitution method. Next, they exposed the powders to sintering at 1250 oC for a specific duration. For comparison purposes, the researchers used 7% by weight yttria stabilized zirconia agglomerated powders of specific particle sizes (M6700). The surface morphology of the resultant powders was examined and eventually characterized.

The authors observed that surface morphology of n-8YSZ feedstocks was composed of spherical or equiaxed agglomerates which satisfied the demands of particle size for PS-PVD. When compared with the control sample, the team noted that the control sample yielded poorer sphericity. Again, an X-ray diffractometer analysis of the samples revealed that the n-8YSZ feedstocks were composed of t prime tetragonal zirconia (t´).

Feifei Zhou and colleagues demonstrated the successful fabrication of n-8YSZ feedstocks for PS-PVD using the powder reconstitution technique for the first time. It has been seen that the grain size of n-8YSZ feedstocks is below 20 nm and the n-8YSZ feedstocks are composed of spherical agglomerates whose particle size is below 23 µm. Altogether, the fabricated feedstock is advantageous over the current/control sample powders used for PS-PVD. Adopting the new n-8YSZ feedstocks would present wider applications for the PS-PVD. Currently, The spherical t´-8YSZ feedstocks with nanostructure have been industrialized in Fujian Dilong Innovation Development Co., Ltd, Quanzhou, China.

non-transformable tetragonal YSZ nanostructured feedstocks for plasma spraying-physical vapor deposition. Advances in Engineering

About the author

Feifei Zhou is currently a Ph.D. student in Materials Science department, Harbin Institute of Technology (HIT), China. He gained his bachelor degree in Materials Science from Chongqing University, China, in 2015. He was conferred the First prize in Science and Technology Award in Colleges and universities of Heilongjiang Province in 2018. His current research focuses on the fabrication of nanostructured thermal-sprayed (atmospheric plasma spraying, plasma spray-physical vapor deposition) feedstocks used for thermal barrier coatings (TBCs) such as yttria stablized zirconia (YSZ), rare-earth zirconates RE2Zr2O7 (RE=La, Gd, Sm, and so on), ultra-high temperature oxidation and calcium-magnesium-alumina-silicate (CMAS) corrosion of TBCs.

About the author

Yaming Wang is a professor in Materials 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 holds 13 patents and 1 coauthored BOOK.

He has authored / coauthored more than 100 papers in refereed journals, with SCI indexed citation of >2000 and H index of 28. The wear resistance ceramic coating and high emissivity ceramic coating were successfully applied in aerospace components. He was conferred the Second prize in Natural Science Award of Heilongjiang Province in 2011. He is now focusing on elevated temperature thermal protective ceramic coatings, bioceramic coatings and new energy ceramics.

About the author

Professor You Wang is a Professor of Materials Science and Engineering of Harbin Institute of Technology, China. Now, Professor Wang is the President of Surface Engineering Society of Heilongjiang province, a member of the New Materials Expert Committee of Heilongjiang province, Senior member of the Chinese Society for Metals, a member of the editorial board of “Journal of Materials Science and Technology”, a member of the editorial board of “transactions of materials and heat treatment”, a member of the editorial board of “nano technology”, a guest editor of “Applied Surface Science”, a guest editor of “Journal of Thermal Spray Technology”, a guest editor of “Surface and Coatings Technology”, also the reviewer for “Wear”, “Thin Solid films”, “Materials Science and Engineering A”, “Tribology letters”, “Corrosion Science” and so on more than 20 domestic and foreign journals.

Professor Wang has conducted funded research on tribology, surface engineering and nano-modified materials. Up to now, He has published more 290 papers in the national and international journals, SCI cited more than 3000 times. Also, he has obtained 5 US and international patents and about 20 China patents. From 2013 to 2017, Professor Wang has been selected for the list of Chinese Most Cited Researchers by Elsevier for five years.

Based on Professor Wang’s invention, new nanostructured coatings have been developed, which are much more durable than the coatings used today. The thermal sprayed nanostructured Al2O3/TiO2 ceramic coatings, has been called a “revolutionary new coating”, and were studied since 1997. Test results from different sources showed that the modified nanostructured Al2O3/TiO2 coating properties – such as bond strength, toughness, thermal shock resistance, wear resistance, etc. – were remarkably increased. In 2000, the nanostructured ceramic coatings surpassed the US Navy’s standards and obtained the Navy’s application certificate. The modified nanostructured Al2O3/TiO2 coatings were recognized in 2001 by a World R&D100 Award and a DoD Dual Use Achievement Award. In 2004, the coating technology was recognized by a Technology Pioneer Award of the World Economic Forum. Now, the modified nanostructured Al2O3/TiO2 coatings have been widely used in US Navy’s systems as wear and/or corrosion resistant coatings.

Reference

Feifei Zhou, You Wang, Yaming Wang, Liang Wang, Junfeng Gou, Wenlong Chen. A promising non-transformable tetragonal YSZ nanostructured feedstocks for plasma spraying-physical vapor deposition. Ceramics International, volume 44 (2018) pages 1201–1204

 

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