THERMAL IMAGING METHOD AND APPRATUS FOR EVALUATING COATINGS

• US 20120050537A1
• Filed: 08/27/2010
• Published: 03/01/2012
• Est. Priority Date: 08/27/2010
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Ringermacher, Harry Israel, Howard, Donald Robert, Knight, Bryon Edward
• Granted Patent: US 8,692,887 B2
• Time in Patent Office: Days
• US Class Current: 348/164
• CPC Class Codes: G01B 11/0658 with measurement of emissivity or reradiation
• CPC Class Codes: G01B 21/085 using thermal means
• CPC Class Codes: G01J 5/0088 in turbines
• CPC Class Codes: G01J 5/0896 using a light source, e.g. for illuminating a surface
• CPC Class Codes: G01J 5/48 Thermography; Techniques using wholly visual means

Abstract

An apparatus is provided for determining variable thickness of a coating on a surface of a substrate using in part a flash-lamp source, capable of generating a thermal pulse at the coating surface, and a image capture and processing device capable of capture sequential image frames of the coating surface, whereas each sequential image frame corresponds to an elapsed time and comprises a pixel array, and wherein each pixel of the array corresponds to a location on the coating surface. A method of calculating coating thickness is also provided.

Claims

1. An apparatus for determining variable thickness of a coating disposed on a substrate, the apparatus comprising:

a flash-lamp source capable of generating a thermal pulse at the coating surface;

an optical trigger coupled to the flash-lamp source and capable of initiating the flash-lamp firing;

a transistor coupled to the flash lamp source and capable of quenching the thermal pulse

a reflective filter positioned between the flash-lamp source and the coating surface capable of preventing residual heat from the flash-lamp from heating the coating surface;

an IR image capture device positioned to capture sequential image frames of the coating surface, whereas each sequential image frame corresponds to an elapsed time and comprises a pixel array, and wherein each pixel of the array corresponds to a location on the coating surface;

a processor coupled to the IR image capture device capable of;

controlling the operation of the optical trigger and transistor;

receiving the image frames of the coating surface at the initiation of the flash-lamp firing and sequentially there after; and

determining the thickness of the coating at various points along the substrate using in part the sequential image frames to calculate a time-temperature response.

2. The apparatus of claim 1 wherein the IR image capture device comprises an infrared focal plane array camera.

3. The apparatus of claim 1 wherein the reflective filter is coated directly on the flash-lamp source and capable of reflecting radiation in the 3 to 5 micron range.

4. The apparatus of claim 1 wherein the coating is a least one of thermally barrier coating or environment barrier coating.

5. The apparatus of claim 1 wherein the processor is configured to calculate an inflection point value and delta log from the time-temperature response.

6. The apparatus of claim 1 further comprising a display device capable of projecting an image of the coating thickness along the substrate.

7. A method for determining the thickness of a coating at various points along the surface of a substrate comprising:

generating a short duration thermal pulse at the coating surface using a flash-lamp source equipped with a reflective filter to preventing residual heat from the flash-lamp from heating the coating surface;

capturing sequential image frames of the coating surface using an IR capture device, whereas each sequential image frame corresponds to an elapsed time and comprises a pixel array, and wherein each pixel of the array corresponds to a location on the coating surface;

processing the sequential image frames using a processor to store the sequential image frames;

determining the thickness and thermal conductivity of the coating along the substrate comprises the sequential image frames to calculate a time-temperature response curve independently for two or more pixels of the pixel array.

8. The method of claim 7 wherein the time of maximum slope on the time-temperature response curve is defined as an inflection point time (t_inflection) and wherein the equation of said time-temperature response curve is defined as:

9. The method of claim 8 wherein the inflection point time (t_inflection) is measured experimentally from the time-temperature response curve and R is determined from the material properties of the coating and substrate.

10. The method of claim 9 wherein determining the variation in coating thickness comprises calculating a value for L at two or more pixels of the pixel array wherein L is defined as

L=α

_cτ

_c;

where

α

_c is defined as

11. The method of claim 7 wherein the short duration thermal pulse is less than 4 milliseconds.

12. The method of claim 11 wherein a Gaussian function temporal smoothing of the sequential image frame data is used to generate the time-temperature response curve.

13. The method of claim 12 wherein imaging filters are applied to the sequential image frame data said imaging filters comprises spatial smoothing, initial and ending noise suppression, negative contrast suppression, contrast thresholding, and combinations thereof.

14. The method of claim 7 further comprising displaying a color-coded or gray scale-coded image of the coating thickness along the substrate.

15. The method of claim 7 wherein the coating is at least one of thermal barrier coating or environmental barrier coating.