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Journal of Advanced Ceramics 2018, 7(1): 17-29 https://doi.org/10.1007/s40145-017-0252-2
Research Article | Open Access | Issue | Published: 28 December 2017

Epitaxial growth and cracking of highly tough 7YSZ splats by thermal spray technology

Show Author's Information Lin CHEN,  Guan-Jun YANG( )
State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China
Keywords:
epitaxial growth, crack patterns, transverse cracking/spallation, stress, locally heated substrate
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CHEN L, YANG G-J. Epitaxial growth and cracking of highly tough 7YSZ splats by thermal spray technology. Journal of Advanced Ceramics, 2018, 7(1): 17-29. https://doi.org/10.1007/s40145-017-0252-2
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Abstract Full text About this article

Thermally sprayed coatings are essentially layered materials and contain large numbers of lamellar pores. It is thus quite necessary to clarify the formation mechanism of lamellar pores which significantly influence coating performances. In the present study, to elaborate the formation mechanism of lamellar pores, the yttria-stabilized zirconia (ZrO2–7 wt% Y2O3, 7YSZ) splats, which have high fracture toughness and tetragonal phase stability, were employed. Interestingly, anomalous epitaxial growth occurred for all deposition temperatures in spite of the extremely high cooling rate, which clearly indicated chemical bonding and complete contact at splat/substrate interface before splat cooling. However, transverse spallation substantially occurred for all deposition temperatures in spite of the high fracture toughness of 7YSZ, which revealed that the lamellar pores were from transverse cracking/spallation due to the large stress during splat cooling. Additionally, fracture mechanics analysis was carried out, and it was found that the stress arose from the constraint effect of the shrinkage of the splat by locally heated substrate with the value about 1.97 GPa. This clearly demonstrated that the stress was indeed large enough to drive transverse cracking/spallation forming lamellar pores during splat cooling. All of these contribute to understanding the essential features of lamellar bonding and further tailoring the coating structures and performance.


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About this article

Epitaxial growth and cracking of highly tough 7YSZ splats by thermal spray technology

Show Author's information Lin CHEN, Guan-Jun YANG( )
State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an, Shaanxi 710049, China

Abstract

Thermally sprayed coatings are essentially layered materials and contain large numbers of lamellar pores. It is thus quite necessary to clarify the formation mechanism of lamellar pores which significantly influence coating performances. In the present study, to elaborate the formation mechanism of lamellar pores, the yttria-stabilized zirconia (ZrO2–7 wt% Y2O3, 7YSZ) splats, which have high fracture toughness and tetragonal phase stability, were employed. Interestingly, anomalous epitaxial growth occurred for all deposition temperatures in spite of the extremely high cooling rate, which clearly indicated chemical bonding and complete contact at splat/substrate interface before splat cooling. However, transverse spallation substantially occurred for all deposition temperatures in spite of the high fracture toughness of 7YSZ, which revealed that the lamellar pores were from transverse cracking/spallation due to the large stress during splat cooling. Additionally, fracture mechanics analysis was carried out, and it was found that the stress arose from the constraint effect of the shrinkage of the splat by locally heated substrate with the value about 1.97 GPa. This clearly demonstrated that the stress was indeed large enough to drive transverse cracking/spallation forming lamellar pores during splat cooling. All of these contribute to understanding the essential features of lamellar bonding and further tailoring the coating structures and performance.

Keywords: epitaxial growth, crack patterns, transverse cracking/spallation, stress, locally heated substrate

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Received: 16 June 2017
Revised: 22 August 2017
Accepted: 27 October 2017
Published: 28 December 2017
Issue date: March 2018

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