Bottom-Up Synthesis and Mechanical Behavior of Refractory Coatings Made of Carbon Nanotube-Hafnium Diboride Composites

Carly Sandin, Tushar K. Talukdar, John R Abelson, Sameh H Tawfick

Research output: Contribution to journalArticle

Abstract

We use aligned carbon nanotube (CNT) forests as scaffolds to deposit hafnium diboride (HfB 2 ) and fabricate millimeter-thick ultrahigh-temperature composite coating. HfB 2 has a melting temperature of 3250 °C, which makes it an attractive candidate for applications requiring operation in extreme environments. Compared to typical refractory HfB 2 processing, which requires temperatures exceeding 1500 °C, we use conformal HfB 2 chemical vapor deposition (CVD) to coat CNT forests at a low temperature of 200 °C. During this process, nanometer-thin HfB 2 films grow on the CNT surface and uniformly fill tall CNT forests, thus transforming nanometer film deposition to a scalable HfB 2 coating technology. The conformal HfB 2 coating process uses static (S-) CVD, where the precursor is fed into a closed system, enabling highly conformal coating and economically efficient utilization of the HfB 2 precursor reaching 85%. The modulus and compressive strength of the composites are measured using flat-punch indentation of micropillars having various coating thickness. Filling the CNTs with HfB 2 strengthens their node morphology and effectively enhances the mechanical properties. We study the nonlinear behavior of the material to extract a unique modulus value that describes the stress-strain response at any applied compression. At the highest HfB 2 coating thickness of 45 nm, the solid fraction is increased from 2% for the bare CNTs to 36% for the composite; the modulus and strength reach 107 and 1.5 GPa, respectively. An analytical model is used to explain the mechanism of the measured structure-mechanical property scaling. Finally, the process is used to fabricate CNT-HfB 2 films having 1.7 mm height, a centimeter square area, and only 5.8 × 10 -6 nm/nm thickness gradient to demonstrate the potential for scalability.

Original languageEnglish (US)
Pages (from-to)1487-1495
Number of pages9
JournalACS Applied Materials and Interfaces
Volume11
Issue number1
DOIs
StatePublished - Jan 9 2019

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Hafnium
Carbon Nanotubes
Refractory materials
Carbon nanotubes
Coatings
Composite materials
Chemical vapor deposition
Mechanical properties
Composite coatings
Indentation
Scaffolds
Temperature
Compressive strength
Melting point
Scalability
Analytical models
Compaction
Deposits
Processing

Keywords

  • chemical vapor deposition
  • conformal coating
  • porous material
  • refractory
  • thermal protection system

ASJC Scopus subject areas

  • Materials Science(all)

Cite this

Bottom-Up Synthesis and Mechanical Behavior of Refractory Coatings Made of Carbon Nanotube-Hafnium Diboride Composites. / Sandin, Carly; Talukdar, Tushar K.; Abelson, John R; Tawfick, Sameh H.

In: ACS Applied Materials and Interfaces, Vol. 11, No. 1, 09.01.2019, p. 1487-1495.

Research output: Contribution to journalArticle

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abstract = "We use aligned carbon nanotube (CNT) forests as scaffolds to deposit hafnium diboride (HfB 2 ) and fabricate millimeter-thick ultrahigh-temperature composite coating. HfB 2 has a melting temperature of 3250 °C, which makes it an attractive candidate for applications requiring operation in extreme environments. Compared to typical refractory HfB 2 processing, which requires temperatures exceeding 1500 °C, we use conformal HfB 2 chemical vapor deposition (CVD) to coat CNT forests at a low temperature of 200 °C. During this process, nanometer-thin HfB 2 films grow on the CNT surface and uniformly fill tall CNT forests, thus transforming nanometer film deposition to a scalable HfB 2 coating technology. The conformal HfB 2 coating process uses static (S-) CVD, where the precursor is fed into a closed system, enabling highly conformal coating and economically efficient utilization of the HfB 2 precursor reaching 85{\%}. The modulus and compressive strength of the composites are measured using flat-punch indentation of micropillars having various coating thickness. Filling the CNTs with HfB 2 strengthens their node morphology and effectively enhances the mechanical properties. We study the nonlinear behavior of the material to extract a unique modulus value that describes the stress-strain response at any applied compression. At the highest HfB 2 coating thickness of 45 nm, the solid fraction is increased from 2{\%} for the bare CNTs to 36{\%} for the composite; the modulus and strength reach 107 and 1.5 GPa, respectively. An analytical model is used to explain the mechanism of the measured structure-mechanical property scaling. Finally, the process is used to fabricate CNT-HfB 2 films having 1.7 mm height, a centimeter square area, and only 5.8 × 10 -6 nm/nm thickness gradient to demonstrate the potential for scalability.",
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