Thermal barrier coating on metallic substrates by
preceramic route
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A low cost, easily processable, multi layered functionally graded ceramic coating of
thickness ~1000 µm was developed to protect metallic substrates from the risk of thermal oxidation.
It consists of a four layered functionally graded coating consisting of aluminide layer followed by an
intermediate zirconia as thermal insulative layer, an alumina layer serving as buffer layer with the
outer most high emissivity layer to provide the required emissivity. All the layers were brush coated
and the specimens were cured at 150°C. The solar absorptivity and emissivity of the coating was
found to be 0.82 and 0.88 respectively. 15CDV6 plate of 150 x 150 x 5 mm was coated with
multilayer thermal barrier coating of thickness ~ 1 mm. The coated sample was subjected to a heat
flux of 8.5 W/cm
2
for 1035 secs to evaluate the thermo-responsive behaviour of the coating.
Maximum back wall temperature measured was 299°C. The coating methodology is simple
compared to complicated plasma techniques which can be applied on complex shaped substrates
and all operations are carried out at low temperatures, below 150°C ensuring no deterioration of
structural properties of the substrate.
Metallic material systems with potential for high temperature operations are critical for many
land based and space based systems where high mechanical strength and extreme service
temperatures are required. Metals exhibit high mechanical strength which makes it extremely
attractive for high temperature structural applications for aircraft engines, hypersonic aerospace
vehicles, automotive industry biomedical, refractory and thermonuclear fusion applications. But the
oxidation of these materials under high pressure and temperature and the deterioration of
mechanical properties limits their use. The inherent reactivity of these materials makes it necessary
to design a complex system of inhibitors, sealants and coatings for its use at high temperature[1,2].
So there arises a need to develop light weight, high temperature resistant thermal barrier protective
coatings for emerging high temperature metals/alloys.
In recent years, multilayer protective coatings were designed which can reduce oxidation,
increase emittance and reduce catalytic efficiency for recombination of dissociated species for the
candidate materials. Ceramic thermal barrier coatings (TBC) are used to protect metallic surfaces
from harsh combustion environments and extend the structure’s life time[3-6]. The coating systems
must be designed with high temperature stability, lower thermal conductivity and improved thermal
stress. Application of ceramic coatings derived from preceramic polymers will provide an
economical solution to high temperature corrosion required by conventional composite coatings
containing several functional phases. Thus it provides an effective means of improved performance
Materials Science Forum Vol. 710 (2012) pp 786-791
© (2012) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/MSF.710.786
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,
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