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Home  > Raw materials & technologies  > Applications  > Protective & Marine coatings  > Mullite coatings exhibit suitable structur...

Tuesday, 17 September 2019
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Raw materials & technologies, Applications, Protective & Marine coatings

Mullite coatings exhibit suitable structural integrity as EBCs

Thursday, 21 November 2013

The mechanical properties and structural integrity of mullite (3 Al2O3 • 2 SiO2) environmental barrier coatings (EBCs) are key factors towards the implementation of these systems in real applications.

Mullite coatings can optimise corrosion protection

Quelle: Sasha Radosavljevic - Fotolia.com

Mullite coatings can optimise corrosion protection

Quelle: Sasha Radosavljevic - Fotolia.com

By using chemical vapor deposition, the chemical composition of mullite in these coatings may be tailored to obtain high Al/Si ratios in the outer surface, for an optimum corrosion protection in gas turbine environments.

Hardness increases with raising Al/Si ratio

Researchers from the Universitat Politècnica de Catalunya in Barcelona, Spain, and the Boston University in Massachusetts, USA, evaluated the influence of such Al/Si ratio on the mechanical properties and structural integrity of different Al-rich mullite coatings by means of nanoindentation and nanoscratch tests. It is found that hardness and elastic modulus of the coating increases as the Al/Si ratio raises. On the other hand, an inverse trend is discerned for the apparent fracture toughness, although this is stated to be an indirect consequence of the resulting residual stress state, without any relevant effect on the intrinsic toughness of the mullite coatings.

Brittle-like damage did not translate into critical decohesion

Regarding structural integrity, an increasingly brittle response to the sliding contact is evidenced as chemical composition moves towards higher Al/Si ratios. However, within the load range studied, brittle-like damage at the coating surface did not translate into critical decohesion at the coating/substrate interface. It sustains the effective protective role of the studied layers as EBCs. Therefore, all the studied coatings are found to exhibit a suitable structural integrity for their potential use as EBCs.

This study will be published in Surface and Coatings Technology.

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