Flexible Assessment of Thermal Transport Properties of Thermal Barrier Systems Measured by The Hot Disk Method

Caroline Goddard1, Tobias Öhman2; Nicolaie Markocsan2; Mattias Gustavsson3, Lars Östergren4

1-University of Manchester; 2-University West; 3-Hot Disk AB; 4-Volvo Aero

Project Supported by VINNOVA

Participants: Univ. West / Univ. Manchester, Hot Disk AB, VAC

Requirements of Thermal Conductivity of TBCs

Performance of layers (lab) – LFLower-cost/flexible testing – HDQuality Control? (on-line) – HD

Hot Disk Sensor

Laser Flash Technique Transient Plane Source (Hot Disk)

Most accepted method New possibility

Non Contact method Contact method

Laboratory method only Potential to be used directly on components

Measures Thermal Diffusivity then calculates Thermal Conductivity

Measures Thermal Conductivity directly

Higher equipment cost Lower equipment cost

Need to know the thickness, density and specific heat capacity

Need to know the thickness of the sample and its dimensions

Must be a specific size and shape

HD Technique – Apparent (Thin Film) vs. Bulk Properties

Apparent Coating Properties - Setup

Influence of Surface Roughness

Comparisons LF vs. HD

• The results show that it is possible to obtain comparable results between the Hot Disk method and the Laser Flash method for coatings A and B.

• Coating C did not show agreement with LF.

Comparisons LF vs. HD

• The surface roughness has a significant effect.

• It is possible to develop a method for measuring thermal conductivity of TBC by “Thin Films” apparent property approach.

• Approach does not allow non-destructive testing.

• Zirconia coatings range from 300µm thick to over 700µm thick and the method cannot reliably measure coatings 550µm or thicker.

• ( Presently preparing for tests at elevated temperatures. )

Other Possibilities – Quality Control?

• APPARENT properties (less stable) if coating thinner than 0.5 mm

• BULK properties (stable), only if coating thicker than 0.5 mm

• Investigating inhomogeneous variations vs. depth from surface, for thicker coatings basis (on-line testing)