Methods and devices for evaluating the thermal exposure of a metal article

• US 20060256833A1
• Filed: 05/10/2005
• Published: 11/16/2006
• Est. Priority Date: 05/10/2005
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Jiang, Liang, Hardwicke, Canan Uslu, Lee, Ching-Pang, Kool, Lawrence Bernard, Zhao, Ji-Cheng, Jackson, Melvin Robert, Ritter, Ann Melinda
• Granted Patent: US 7,654,734 B2
• Time in Patent Office: Days
• US Class Current: 374/5
• CPC Class Codes: G01K 7/02 using thermoelectric elements, e.g. thermocouples
• CPC Class Codes: G01N 17/00 Investigating resistance of materials to the weather, to corrosion, or to light

Abstract

A method for evaluating the thermal exposure of a selected metal component which has been exposed to changing temperature conditions is described. The voltage distribution on a surface of the metal component, or on a metallic layer which lies over the component, is first obtained. The voltage distribution usually results from a compositional change in the metal component. The voltage distribution is then compared to a thermal exposure-voltage model which expresses voltage distribution as a function of exposure time and exposure temperature for a reference standard corresponding to the metal component. In this manner, the thermal exposure of the selected component can be obtained. A related device for evaluating the thermal exposure of a selected metal component is also described.

Claims

1. A method for evaluating the thermal exposure of a selected metal component which has been exposed to changing temperature conditions, comprising the following steps:

(a) determining the voltage distribution on a surface of the metal component, or on a metallic layer which lies over the component, said voltage distribution resulting from a compositional change in the metal component; and

(b) comparing the voltage distribution to a thermal exposure-voltage model which expresses voltage distribution as a function of exposure time and exposure temperature for a reference standard corresponding to the metal component, so as to evaluate the thermal exposure of the selected component.

2. The method of claim 1, wherein the thermal exposure evaluation comprises an approximate, average temperature reading over a selected time period.

3. The method of claim 1, wherein the thermal exposure evaluation comprises a time period of exposure at a selected temperature.

4. The method of claim 3, wherein the time period is expressed in temperature cycles.

5. The method of claim 1, wherein the voltage distribution is determined by an electrical measurement device which comprises a sensing probe and a reference probe, both in contact with the component surface, wherein heating of the sensing probe while the reference probe is maintained at ambient temperature results in the development of a measurable voltage.

6. The method of claim 1, wherein the thermal exposure-voltage model is obtained from a set of test specimens having known voltage distribution (EMF) characteristics, wherein the test specimens are formed of the same type of material as the selected metal component.

7. The method of claim 6, wherein each test specimen is subjected to a different time/temperature schedule for thermal exposure, and the corresponding EMF value for each specimen is recorded.

8. The method of claim 1, wherein the compositional change in the metal component is caused by migration of one or more elements from the component to a layer which overlies the component.

9. The method of claim 1, wherein the compositional change is caused by oxidation of the metal component.

10. The method of claim 1, wherein the metal component comprises aluminum and at least one of nickel or cobalt;

and an aluminum-containing coating lies over the component.

11. The method of claim 10, wherein the component is a nickel-based superalloy, and the overlying coating comprises at least one composition selected from the group consisting of MCrAlX, aluminide, platinum-aluminide;

nickel-aluminide; and

platinum-nickel-aluminide, wherein M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing; and

X is selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C, and combinations thereof.

12. A method of temperature-mapping the selected metal component of claim 1, wherein multiple thermal exposure values are measured, and each value corresponds to a different location on the surface of the component.

16. The method of claim 1, further comprising the step of determining the remaining service life of the metal component, by calculating the difference between the thermal exposure value obtained for the component and a predicted thermal exposure value for a standard metal component of similar composition, wherein the predicted thermal exposure value corresponds to the projected service life of the standard metal component.

13. A method for evaluating the thermal exposure of a selected superalloy turbine component which has been exposed to high-temperature conditions, comprising the following steps:

(a) determining the voltage distribution on a surface of the turbine component, or on a protective layer which lies over the component, said voltage distribution resulting from a compositional change in the superalloy component; and

(b) comparing the voltage distribution to a thermal exposure-voltage model which expresses voltage distribution as a function of exposure time and exposure temperature for a reference standard corresponding to the turbine component, so as to evaluate the thermal exposure of the selected component.

14. The method of claim 13, wherein the turbine component comprises a nickel-based superalloy, and the protective layer comprises a material selected from the group consisting of MCrAlX compositions, aluminide compositions, platinum-aluminide compositions, nickel-aluminide compositions;

and platinum-nickel-aluminide compositions, wherein M is selected from the group consisting of Fe, Ni, Co, and mixtures of any of the foregoing; and

X is selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C, and combinations thereof.

15. The method of claim 14, wherein the compositional change results from oxidation of the protective layer, or from migration of elements from the superalloy into the protective layer.

17. A device for evaluating the thermal exposure of a selected metal component which has been exposed to changing temperature conditions, comprising:

(i) means for measuring the voltage distribution on a surface of the metal component, said voltage distribution resulting from a compositional change in the component; and

(ii) means for comparing the voltage distribution to a thermal exposure-voltage model which expresses voltage distribution as a function of exposure time and exposure temperature for a reference standard corresponding to the metal component.

18. The device of claim 17, wherein element (i) comprises an EMF-measurement device which functions according to the Seebeck Principle.

19. The device of claim 17, wherein element (i) comprises an EMF-measurement device which itself comprises a sensing probe which can be maintained at a constant, elevated temperature, and a reference probe;

wherein both probes are connected in circuit with an electrical measuring mechanism, and both probes are capable of simultaneously contacting the component surface;

wherein heating of the sensing probe while the reference probe is maintained at ambient temperature during the time the probes contact the component surface results in the development of a measurable voltage (EMF) which is characteristic of the component.

20. The device of claim 17, wherein component (ii) comprises at least one computer processor and associated computer software.