Nondestructive Testing of Thermal Barrier Coated
Turbine Blades using Microwave Techniques
Publication: Publication Date: 1 April 2016Testing Method:
Zirconia-based thermal barrier coatings (TBCs) are
widely used to protect turbine blades against hightemperature
and pressurized steam, increasing the
lifetime of the whole system. A turbine blade
crack, which normally begins from the metal
surface due to corrosion and stress, must be
inspected nondestructively to avoid catastrophic
failure. Although there are several established
nondestructive testing (NDT) techniques available,
microwave testing using a broad frequency sweep
with an open-ended rectangular waveguide energy
launch, in conjunction with signal processing, is
proposed in this paper as an inspection technique.
Electromagnetic signals at microwave frequencies
are capable of providing inspection of metals
coated with dielectric materials such as TBC. In
this paper, the principle of this technique is
described, along with 3D electromagnetic software
simulation using various measurement scenarios
and a number of measurements of representative
turbine blade models with discontinuities on the
metal surface, visibly hidden by the TBC. This
research is aimed at delivering an in-situ
microwave test capable of detecting surface and
subsurface discontinuities and may form part of
quality control in manufacturing as well as portable
field service inspection. As such, the system is
comparable in size to current NDT systems, as well
as robust, affordable, and capable of providing
real-time data about the nature of an anomaly
such as discontinuity location and size.
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