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![]( "Buchcover ISBN 9783958061293")
Development of Embedded Thermocouple Sensors for Thermal Barrier Coatings (TBCs) by a Laser Cladding Process
von Yanli ZhangThermal barrier coatings (TBCs) are now being widely used on gas turbine engines to lower the
surface temperatures of metallic substrate from extreme hot gas stream in combustor and turbine
components. The thermally grown oxide (TGO) growth rate plays an important role in the life
time of TBC systems. The accurate real-time monitoring of bond-coat/ 8YSZ interface
temperature in thermal barrier coatings (TBCs) in hostile environments opens large benefits to
efficient and safe operation of gas turbines. A new method for fabricating high temperature
thermocouple sensors which can be placed close to this interface using laser cladding technology
has been developed.
K-type thermocouple powders consisting of alumel (Ni2Al2Mn1Si) and chromel (Ni10Cr) were
studied as candidate feedstock materials. A thermocouple sensor using these materials was first
produced by coaxial continuous wave (CW) or pulsed laser cladding process onto the standard
yttria partially stabilized zirconia (7~8 wt.% YSZ) coated substrate and afterwards embedded
with a second YSZ layer deposited by the atmospheric plasma spray (APS) process. The process
parameters of the laser cladding were optimized with respect to the degradation of the substrate,
dimensions, topography, thermosensitivity and embeddability, respectively. Infrared cameras
were used to monitor the surface temperature of clads during this process.
The manufacture of the cladded thermocouple sensors provides minimal intrusive features to the
substrate. The dimensions were in the range of two hundred microns in thickness and width for
CW laser cladding and less than 100 microns for pulsed laser cladding. Additionally, continuous
thermocouple sensors with reliable performance were produced. It is possible to embed sensors
manufactured by CW laser cladding rather than by pulsed laser cladding due to the limited
bonding strength between the clads and the substrate. Periodically droplets were formed along
the clads under improper parameters, the mechanism to this is discussed in terms of particle size
distribution after interaction with the laser beam, melts duration and Rayleigh’s theory.
To sum up, laser cladding is a prospective technology for manufacturing microsensors on the
surface of or even embedded into functional coatings that can survive in operation environments
for in-situ monitoring. Production of sensors within thermal barrier coatings (TBCs) increases
the application field of the laser cladding technique.
surface temperatures of metallic substrate from extreme hot gas stream in combustor and turbine
components. The thermally grown oxide (TGO) growth rate plays an important role in the life
time of TBC systems. The accurate real-time monitoring of bond-coat/ 8YSZ interface
temperature in thermal barrier coatings (TBCs) in hostile environments opens large benefits to
efficient and safe operation of gas turbines. A new method for fabricating high temperature
thermocouple sensors which can be placed close to this interface using laser cladding technology
has been developed.
K-type thermocouple powders consisting of alumel (Ni2Al2Mn1Si) and chromel (Ni10Cr) were
studied as candidate feedstock materials. A thermocouple sensor using these materials was first
produced by coaxial continuous wave (CW) or pulsed laser cladding process onto the standard
yttria partially stabilized zirconia (7~8 wt.% YSZ) coated substrate and afterwards embedded
with a second YSZ layer deposited by the atmospheric plasma spray (APS) process. The process
parameters of the laser cladding were optimized with respect to the degradation of the substrate,
dimensions, topography, thermosensitivity and embeddability, respectively. Infrared cameras
were used to monitor the surface temperature of clads during this process.
The manufacture of the cladded thermocouple sensors provides minimal intrusive features to the
substrate. The dimensions were in the range of two hundred microns in thickness and width for
CW laser cladding and less than 100 microns for pulsed laser cladding. Additionally, continuous
thermocouple sensors with reliable performance were produced. It is possible to embed sensors
manufactured by CW laser cladding rather than by pulsed laser cladding due to the limited
bonding strength between the clads and the substrate. Periodically droplets were formed along
the clads under improper parameters, the mechanism to this is discussed in terms of particle size
distribution after interaction with the laser beam, melts duration and Rayleigh’s theory.
To sum up, laser cladding is a prospective technology for manufacturing microsensors on the
surface of or even embedded into functional coatings that can survive in operation environments
for in-situ monitoring. Production of sensors within thermal barrier coatings (TBCs) increases
the application field of the laser cladding technique.