Tailored Porosity for Polymer Infiltration in Stainless Steel Coatings
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In this work, a new method for the development of polymer-infiltrated bond coatings is presented. Substrate surfaces are coated by high-velocity oxygen fuel spraying, with a powder mixture containing a stainless steel (SS444) matrix and an iron aluminide (Fe3Al) pore former. Prior to polymer infiltration, acid leaching in 0.5 M HCl solution was used to remove the pore-forming phase. To control total porosity and pore size distribution, nine different feedstock blends were prepared with varying volume fractions and size distributions of SS444 and Fe3Al particles. It was found that the leaching rates are strongly dependent on the solution temperature. Moreover, higher in-flight oxidation leads to significant chemical and mechanical degradation of the deposited SS444 splats. The as-leached coatings mechanical integrity was poor, and a sintering heat treatment at 1300 °C for 1 h was crucial for the development of appreciable coating strength. It was shown that a mixture of polyimide binder and 25 wt.% graphite can be infiltrated in pores with pore openings as narrow as 10 µm. The present research results could be impactful for any application requiring large surfaces to be coated with a metal-polymer composite layer without the use of adhesives or glues.
Keywordsbond coatings porosity sealing stainless steel
The authors would like to express their gratitude to Prof. Dr. Richard Chromik and Dr. Yinyin Zhang for their suggestions in the methodology for the preparation of the polyimide composites which proved essential for the achieved results. The authors are also grateful for the financial support provided by NSERC and Hydro-Québec.
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