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Formation of Pores in Thermal Spray Coatings due to Incomplete Filling of Crevices in Patterned Surfaces

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Abstract

Molten particles in a thermal spray land on a rough surface, coalesce with each other and freeze to form a coating. Surface tension prevents liquid splats from completely filling crevices in the substrate, forming pores. An analytical model is developed to estimate the volume of such pores by calculating the equilibrium shape of a liquid meniscus pressing down on a surface asperity. Predictions from the model are compared with experimental results for the volume of voids formed under plasma sprayed yttria stabilised zirconia (YSZ) particles (average diameter 18 μm) landing with an average velocity of 250 m/s on patterned silicon surfaces that had vertical posts on them. The model predicted, to within an order-of-magnitude, the volume of voids on a surface in which the posts were tall (3 μm high) and closely spaced (1 μm apart), where pores were principally formed by incomplete filling of gaps.

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Abbreviations

e :

length of meniscus

g :

gravity acceleration

h :

liquid height

h s :

height of deformed liquid bottom

i :

number of post, counting from point of droplet impact

p :

pressure

r :

radial direction

R :

splat radius

R a :

average surface roughness

s :

theoretical height of deformed liquid surface of the underside of a splat

V :

impact velocity

V in :

Volume of incompletely filled voids

x :

Cartesian coordinate

y :

Cartesian coordinate

z :

Cartesian coordinate

α :

capillary length

β :

radius of the surface asperities

θ :

angle of perfect contact

σ :

surface tension

ρ :

liquid density

\( \phi _{v} \) :

meniscus contact angle

\( \phi _{t} \) :

meniscus contact angle

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Acknowledgement

The authors would like to acknowledge the support and assistance of GE Global Research Centre, NY, USA, in providing the patterned surfaces and FIB micrographs.

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Authors and Affiliations

  1. Centre for Advanced Coating Technologies, University of Toronto, Toronto, Canada

    M. Xue, S. Chandra, J. Mostaghimi & H. R. Salimijazi

Authors
  1. M. Xue
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  2. S. Chandra
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  3. J. Mostaghimi
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  4. H. R. Salimijazi
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Correspondence to M. Xue.

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Xue, M., Chandra, S., Mostaghimi, J. et al. Formation of Pores in Thermal Spray Coatings due to Incomplete Filling of Crevices in Patterned Surfaces. Plasma Chem Plasma Process 27, 647–657 (2007). https://doi.org/10.1007/s11090-007-9097-8

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  • DOI: https://doi.org/10.1007/s11090-007-9097-8

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