Patent Application
20070296967
As used herein, the term “turbine component” refers to any turbine component that comprises a metal substrate (i.e., the substrate is formed from metals or metal alloys), and includes turbine components comprising airfoils (e.g., blades, vanes, etc.), turbine disks (also referred to sometimes as “turbine rotors”), turbine shafts, turbine seal elements that are either rotating or static, including forward, interstage and aft turbine seals, turbine blade retainers, other static turbine components, etc. The metal substrate of the turbine component may comprise any of a variety of metals, or more typically metal alloys, including those based on nickel, cobalt and/or iron alloys. The metal substrate typically comprises a superalloy based on nickel, cobalt and/or iron. Such superalloys are disclosed in various references, such as, for example, U.S. Pat. No. 4,116,723 (Gell et al.), issued Sep. 26, 1978; and commonly assigned U.S. Pat. No. 4,957,567 (Krueger et al.), issued Sep. 18, 1990; U.S. Pat. No. 5,399,313 (Ross et al.), issued Mar. 21, 1995; and U.S. Pat. No. 6,521,175 (Mourer et al.), issued Feb. 18, 2003, the relevant portions of which are incorporated by reference. Superalloys are also generally described in Kirk-Othmer's Encyclopedia of Chemical Technology, 3rd Ed., Vol. 12, pp. 417-479 (1980), and Vol. 15, pp. 787-800 (1981). Illustrative nickel-based superalloys are designated by the trade names Inconel®, Nimonic®, René® (e.g., René® 80, René® 88, René® 104, and René® N5 alloys), and Udimet®.
As used herein, the term “metallic coating” refers to a coating that consists essentially of metal or metal alloys (i.e., is a not a ceramic coating, such as a metal oxide). The metallic coating may be a protective coating for the metal substrate of the turbine component, a bond coat layer for adhering a thermal barrier coating comprising a ceramic (e.g., yttria-stabilized zirconia) to the metal substrate, etc. These metallic coatings may comprise diffusion coatings, overlay metal alloy coatings, etc.
As used herein, the term “diffusion coating” refers to coatings comprising various noble metal aluminides such as nickel aluminide, platinum aluminide, etc., as well as simple aluminides (i.e., those formed without noble metals), and may be formed on metal substrates by chemical vapor phase deposition (CVD), pack cementation, vapor phase aluminiding, “over the pack” aluminizing, pack aluminizing, flash electroplating of nickel and platinum onto a metal substrate followed by application of aluminum, etc. Diffusion coatings normally comprise two distinct zones or layers, the outermost of which is an additive layer containing an environmentally-resistant intermetallic; beneath this additive layer is a diffusion zone or layer comprising various intermetallic phases that form during the coating process as a result of diffusional gradients and changes in elemental solubility in the local region of the adjacent metal substrate.
As used herein, the term “overlay metal alloy” refers to metal alloys having the formula MCr, MAl, MCrAl, MCrAlX, or MAlX, wherein M is nickel, cobalt, iron, etc., or an alloy thereof, and wherein X is hafnium, zirconium, yttrium, tantalum, platinum, palladium, rhenium, silicon, lanthanum, etc., or a combination thereof. Typically, the overlay metal alloys used herein are MCrAlY alloys, and more typically wherein M is nickel, cobalt, or a nickel-cobalt alloy and wherein X is yttrium (i.e., Y).
As used herein, the terms “Laser Plasma Spectroscopy (LPS)”, “Laser-Induced Breakdown Spectroscopy (LIBS)” and/or Laser-Induced Plasma Spectroscopy (LIPS) (collectively referred to herein as “LPS”) refer to a type of atomic emission spectroscopy which utilizes a highly energetic laser pulse as the excitation source. LPS analyzes matter regardless of its physical state, be it solid, liquid or gas. Because all elements emit light when excited to sufficiently high temperatures, LPS may detect all elements, limited only by the power of the laser as well as the sensitivity and wavelength range of the spectrometer and detector. The elemental composition of the material irradiated during LPS may then be accurately determined through spectral analysis of light radiation emitted from the plasma generated. LPS may also have certain advantages over other types of elemental analytical techniques, for example, in not requiring extensive preparation of a sample to be analyzed, vaporizing only a small quantity of the sample (e.g., on the order of nanograms) during analysis, performing the analysis of the sample fairly rapidly, identifying multiple constituent elements at the same time, etc. In accordance with an embodiment of an LPS analytical technique, light output from a pulsed laser may be focused onto the surface of the sample to be analyzed. Assuming the focused laser pulse has sufficient intensity, a small amount of material at the surface of the sample is vaporized, thus forming a high-temperature plasma which corresponds to the elemental constituents of the vaporized material and which comprises ions and excited atoms that emit light radiation as the ions and excited atoms de-excite. The elemental composition of the irradiated material may then be accurately determined through temporally resolved spectral analysis of the light radiation emitted from the plasma. Multiple plasma generating laser pulses may be used in succession to obtain additional spectral data to improve the accuracy of the analysis.
As used herein, the terms “spectrophotometer” and “spectrometer” (hereafter collectively referred to as “spectrometer”) refer to an analytical device used to separate the optical emissions from the plasma by their wavelength. In combination with an appropriate detector (e.g., an ICCD camera), the spectrometer enables a determination of the intensity of the plasma emissions as a function of wavelength. The ionic and atomic emissions from each element are unique, and may thus be used to identify the presence, absence and/or concentration of an element in the vaporized portion of the sample.
As used herein, the term “qualitative analysis” refers to an analysis that yields an identification of the elements present in the plasma generated by LPS. Qualitative analysis may be used, for example, to determine the presence or absence of a metallic coating in an analyzed sample, the elemental composition of any metallic coating present in an analyzed sample, the identification of a particular coating type as opposed to another coating type in an analyzed sample, etc.
As used herein, the term “quantitative analysis” refers to an analysis that determines the particular concentration or concentrations of the elements by evaluation of the plasma plume generated by LPS. Quantitative analysis may be used to determine elemental concentrations in the metallic coating present in an analyzed sample, elemental concentration as a function of depth into the coating in an analyzed sample, etc. The thickness of the metallic coating present on an analyzed sample may also be determined by monitoring one or more spectral emissions from a laser-generated plasma using LPS as a function of depth, together with a known calibration (e.g., ablation rate calibration curve) which has been performed to associate depth penetration with a number of successive laser shots or pulses (or time associated with such shots or pulses) applied to or striking the sample surface.
As used herein, the term “ablation rate calibration curve” refers to a curve such at that shown in
As used herein, the term “ablation depth” refers to the depth that a laser pulse or pulses penetrates into a coating, substrate or both during LPS.
As used herein, the term “ablation time” refers to amount of time that a laser pulse or pulses strike a sample during LPS.
As used herein, the term “marker element” refers to an element measured by LPS which may be used to differentiate alone, or in combination with one or more other marker elements, the elemental composition, elemental concentration and/or thickness of the metallic coating, metal substrate, or both.
As used herein, the term “resolved spectra” refers to a signal or signals generated by LPS which have been spectrally and temporally resolved such that the signal or signals have been identified and correlated to differentiate one or more metallic coatings and/or metal substrates.
Embodiments of the method of this invention are based on the discovery that analysis of the surface of turbine components, such as turbine blades and vanes, may be carried out by using laser plasma spectroscopy (LPS) to determine: (1) the presence or absence of a metallic coating on the external surface of the metal substrate of a turbine component; (2) if a metallic coating is present, the type and composition of the metallic coating, the thickness, etc., of the metallic coating, etc.; (3) if the external surface has been subjected to treatment to remove the metallic coating, the degree of removal of the metallic coating from the treated surface. Because LPS may be carried out selectively on a very small portion or section of the turbine component, it is less invasive and destructive compared to heat tinting in analyzing for metallic coatings on the external surface of metal substrates of turbine components. This includes avoiding the need to subject the turbine component to treatments (e.g., grit blasting) to remove reaction products (e.g., metal oxides) that may be created on the external surface of the metal substrate by the analytical method. LPS may also be more accurate compared to heat tinting in determining the presence, composition, concentration, and thickness of the metallic coating present on the external surface of the metal substrate of the turbine component. In other words, LPS may provide a qualitative analysis, quantitative analysis, or both a qualitative and quantitative analysis of any metallic coating that may or may not be present on the surface of the turbine component.
An illustration of a turbine component for which embodiments of the LPS analytical method of this invention may be useful is illustrated in
As shown in
Airfoil 12 may also be provided with a metallic coating that may be applied to the external surfaces of sides 14 and 16, to internal surfaces 54, 58 and 62, or both external surfaces of sides 14 and 16 and internal surfaces 54, 58 and 62. For example, an external metallic coating (e.g., diffusion coating) represented by an external coating layer, indicated generally as 70, may be present on the external surfaces of sides 14 and 16,. For the internal surfaces 54, 58 and 62, an internal metallic coating (e.g., diffusion coating) represented by an internal coating layer, indicated generally as 78, may be present on these internal surfaces 54, 58 and 62. In some embodiments of blade 10, external layer 70 may differ in composition from internal layer 78. For example, external layer 70 may comprise a nickel aluminide diffusion coating, while internal layer 78 may comprise a simple aluminide diffusion coating. Because of the manner in which the internal layer 78 is applied to internal surfaces 54, 58 and 62, the diffusion coating comprising internal layer 78 may also be present on the external surfaces of sides 14 and 16, or if external layer 70 has already been applied to these external surfaces of side 14 and 16, on top of external layer 70.
One embodiment of the method of this invention broadly comprises analyzing the external surface of a metal substrate of a turbine component, such as blade 10, by LPS to determine whether a metallic coating is present on or absent from the external surface. For example, the external surface of sides 14 and 16 may be analyzed to determine whether a simple aluminide diffusion coating is or is not present on these external surfaces. An LPS system that may be used to analyze these external surfaces of sides 14 and 16 of blade 10 may comprise a pulsed laser (e.g., a neodymium doped yttrium aluminum garnet (Nd:YAG) solid state laser), a spectrometer with a wide spectral range and a high sensitivity, fast response rate, a time gated detector, as well as other components such as optical fibers, lenses, beam splitters, controllers, etc. This system may include or be coupled to a computing device which may rapidly process, interpret, display, etc., the acquired or collected data. Suitable LPS analytical systems for use herein may include those disclosed in commonly assigned U.S. Pat. No. 6,762,836 (Benicewicz et al.), issued Jul. 13, 2004; and commonly assigned published U.S. Patent Application No. 2005/0068524 (Wu et al.), published Mar. 31, 2005, the relevant disclosures of which are incorporated by reference.
An embodiment of an LPS system, indicated generally as 100, which may be used to analyze external surfaces of sides 14 and 16 of blade 10 is illustrated in
As shown in
As further shown in
In an embodiment of system 100 shown in
Once an emission spectral profile of plasma plume 110 is created, a comparison and matching of the spectral profile may be performed in situ either manually or automatically against a reference source of known emission spectra to determine the elemental composition (i.e., elemental constituents) of the vaporized portion of sample 102. A database containing reference spectral profiles of selected elements and/or compounds may be created and stored, for example, within computing device 116 for in situ access and display. Alternatively, computing device 116 may be provided with conventional means to access a remotely located database containing emission spectra information through a conventional wired or wireless communications link, a telephone line, the Internet, etc.
Once a spectrally and temporally resolved signal or signals have been identified and correlated (i.e., “resolved spectra” have been obtained) to differentiate the various coatings 106 and substrates 104, the spectrometer 112/detector 152 pair of system 100 may be replaced with a detector/filter pair to acquire or collect only selected emissions of interest from sample 102, as is illustrated by the schematic diagram of an alternative analytical system, indicated generally 200, and shown in
As shown in
Another embodiment of the method of this invention may comprise analyzing the external surface of the metal substrate of the turbine component by LPS to determine the coating composition, the quantitative elemental concentration in the coating, the coating thickness, etc. For example, LPS may be used to determine: (a) the presence or absence of external layer 70 on surfaces 14 and 16 of blade 70; (b) the elemental composition of external layer 70; (c) the elemental concentration in external layer 70; (d) the thickness of external layer 70; (e) etc.
In determining the thickness of the analyzed coating 106 of sample 102, an ablation rate calibration curve, such as that shown in
In another embodiment of the method of this invention, the external surface of the metal substrate of the turbine component may be analyzed by LPS after the external surface has been subjected to treatment to remove a metallic coating applied to the external surface to determine the degree of removal of the metallic coating from the treated external surface. For example, if the presence of an external layer 70 were detected by LPS (or if it is assumed that external layer 70 may be present), blade 10 may be subjected to a treatment step to remove the detected or assumed to be present external layer 70, followed by LPS analysis to determine the degree to which external layer 70 has been removed. If needed because the presence of external layer 70 is detected by LPS to a degree that requires further treatment, the treatment step may be repeated one or more times, followed by subsequent LPS analysis to determine the degree to which removal of the external layer 70 has progressed. For example, an ablation rate calibration curve such as that shown in
Various methods or combinations of methods known in the art for treating external layers 70 comprising diffusion coatings (e.g., simple aluminide diffusion coatings), overlay metal alloy coatings (e.g., MCrAlY coatings), etc., to remove such coatings may be used. For example, external layers 70 comprising aluminide diffusion coatings or overlay metal alloy coatings may be chemically stripped by using an inorganic acid such as hydrochloric acid, nitric acid, phosphoric acid, etc., or a mixture thereof. See, for example, commonly assigned U.S. Pat. No. 5,944,909 (Reeves et al.), issued Aug. 31, 1999; U.S. Pat. No. 6,355,116 (Chen et al.), issued Mar. 12, 2002; and U.S. Pat. No. 7,008,553 (Wustman et al.), issued Mar. 7, 2006, the relevant portions of which are incorporated by reference. These external layers 70 may also be subjected to chemically stripping by using organic sulfonic acids. See, for example, commonly assigned U.S. Pat. No. 5,976,265 (Sangeeta et al.), issued Nov. 2, 1999; and U.S. Pat. No. 6,494,960 (MacDonald et al.), issued Dec. 17, 2002, the relevant portions of which are incorporated by reference. These external layers 70 may also be subjected to chemically stripping by treatment with a halogen gas, for example, hydrogen fluoride gas (e.g., fluoride ion cleaning). See commonly assigned U.S. Pat. No. 5,728,227 (Reverman), issued Mar. 17, 1998, the relevant portions of which are incorporated by reference. These external layers 70 may also be subjected to chemical stripping by using electrochemical stripping. See commonly assigned U.S. Pat. No. 6,599,416 (Kool et al.), issued Jul. 29, 2003; and U.S. Pat. No. 6,969,457 (MacDonald et al.), issued Nov. 29, 2005, the relevant portions of which are incorporated by reference. External layers 70 may also be removed by abrasive treatment, for example, by grit blasting, alone or in combination with other stripping methods. See commonly-assigned U.S. Pat. No. 5,723,078 (Nagaraj et al.), issued Mar. 3, 1998 (especially col. 4, lines 46-66), the relevant portions of which are incorporated by reference.
While specific embodiments of the system and method of this invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of this invention as defined in the appended claims.
