Patent Publication Number: US-9410868-B2

Title: Methods for producing strain sensors on turbine components

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to strain sensors and, more specifically, to methods for producing ceramic strain sensors on turbine components for high temperature applications. 
     In gas turbine engines, such as aircraft engines for example, air is drawn into the front of the engine, compressed by a shaft-mounted rotary-type compressor, and mixed with fuel. The mixture is burned, and the hot exhaust gases are passed through a turbine mounted on a shaft. The flow of gas turns the turbine, which turns the shaft and drives the compressor and fan. The hot exhaust gases flow from the back of the engine, driving it and the aircraft forward. 
     During operation of gas turbine engines, the temperatures of combustion gases may exceed 3,000° F., considerably higher than the melting temperatures of the metal parts of the engine which are in contact with these gases. Operation of these engines at gas temperatures that are above the metal part melting temperatures may depend in part one or more protective coatings and/or on supplying a cooling air to the outer surfaces of the metal parts through various methods. The metal parts of these engines that are particularly subject to high temperatures, and thus require particular attention with respect to cooling, are the metal parts forming combustors and parts located aft of the combustor. 
     Moreover, the turbine components may experience stress and/or strain from various forces over its operational lifecycle. While various tools may be utilized to measure imparted stress and strain in relatively standard environments, the turbine components in turbine engines may experience hotter and/or more corrosive working conditions that may be unsuitable for such measurement tools. 
     Accordingly, alternative strain sensors and methods for producing ceramic strain sensors on turbine components would be welcome in the art. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a method for manufacturing a strain sensor on a turbine component is disclosed. The method includes providing a turbine component comprising an exterior surface, and, depositing a ceramic material onto a portion of the exterior surface. The method further includes ablating at least a portion of the ceramic material using a laser to form a strain sensor comprising at least two reference points. 
     In another embodiment, a method of monitoring a turbine component is disclosed. The method includes providing a turbine component comprising an exterior surface, depositing a ceramic material onto a portion of the exterior surface, and ablating at least a portion of the ceramic material using a laser to form a strain sensor comprising at least two reference points. The method further includes measuring a second distance between a first of the at least two reference points of the strain sensor and a second of the at least two reference points of the strain sensor at a second time internal. Finally, the method includes comparing the second distance to a first distance between the first of the at least two reference points of the strain sensor and the second of the at least two reference points of the strain sensor from a first time interval. 
     In yet another embodiment, a turbine component is disclosed. The turbine component includes an exterior surface, and, a strain sensor deposited on a portion of the exterior surface, wherein the strain sensor comprises a partially ablated ceramic material comprising at least two reference points. 
     These and additional features provided by the embodiments discussed herein will be more fully understood in view of the following detailed description, in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments set forth in the drawings are illustrative and exemplary in nature and not intended to limit the inventions defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: 
         FIG. 1  is an exemplary turbine component comprising a strain sensor according to one or more embodiments shown or described herein; 
         FIG. 2  is an exemplary strain sensor according to one or more embodiments shown or described herein; 
         FIG. 3  is cross section of ceramic material deposited on a turbine component according to one or more embodiments shown or described herein; 
         FIG. 4  is a cross section of another exemplary strain sensor on a turbine component according to one or more embodiments shown or described herein; 
         FIG. 5  is a cross section of yet another strain sensor on a turbine component according to one or more embodiments shown or described herein; 
         FIG. 6  is a cross section of even yet another strain sensor on a turbine component according to one or more embodiments shown or described herein; 
         FIG. 7  is an exemplary method for manufacturing a strain sensor on a turbine component according to one or more embodiments shown or described herein; and, 
         FIG. 8  is an exemplary method for monitoring a turbine component according to one or more embodiments shown or described herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     Referring now to  FIG. 1 , a turbine component  10  is illustrated with a strain sensor  40  comprising ceramic material  30  deposited on a portion of the turbine component&#39;s exterior surface  11 , wherein at least a portion of the ceramic material is ablated by a laser. 
     The turbine component  10  can comprise a variety of specific components such as those utilized in high temperature applications (e.g., components comprising nickel or cobalt based superalloys). For example, in some embodiments, the turbine component  10  may comprise a combustion component or hot gas path component. In some particular embodiments, the turbine component  10  may comprise a bucket, blade, vane, nozzle, shroud, rotor, transition piece or casing. In other embodiments, the turbine component  10  may comprise any other component of a turbine such as a component for a gas turbine, industrial gas turbine, steam turbine or the like. 
     The turbine component  10  has an exterior surface  11 . As should be appreciated herein, the exterior surface  11  may have one or more exposed portions  12  and can include any area suitable for the location of a strain sensor  40  for the subsequent capturing of strain measurements. As used herein, “exposed portion” refers to an area of the exterior surface  11  that is, at least initially, absent of ceramic coatings (e.g., thermal barrier coating or the like). In such embodiments, the absence of ceramic coatings may allow for the base metal/alloy to be more visibly identifiable when analyzing the at last two reference points  41  and  42  of the strain sensor  40  as should be appreciated herein. As should also become appreciated herein, in some embodiments, the exposed portion  12  may subsequently be coated with a supplemental material such as a visually contrasting material  35  (as illustrated in  FIGS. 4 and 5 ) that is visually distinct from the strain sensor  40 . 
     Referring now to  FIGS. 1-6 , the ceramic material  30  is deposited on a portion of the exterior surface  11  of the turbine component  10  ( FIG. 3 ). A portion of the ceramic material  30  is subsequently ablated by a laser  25  ( FIG. 4 ) for form the strain sensor  40 . The strain sensor  40  generally comprises at least two reference points  41  and  42  that can be used to measure the distance D between said at least two reference points  41  and  42  at a plurality of time intervals. As should be appreciated to those skilled in the art, these measurements can help determine the amount of strain, strain rate, creep, fatigue, stress, etc. at that region of the turbine component  10 . The at least two reference points  41  and  42  can be disposed at a variety of distances and in a variety of locations depending on the specific turbine component  10  so long as the distance D there between can be measured. Moreover, the at least two reference points  41  and  42  may comprise dots, lines, circles, boxes or any other geometrical or non-geometrical shape so long as they are consistently identifiable and may be used to measure the distance D there between. 
     The strain sensor  40  comprises a ceramic material that is deposited by a deposition apparatus  20  and then partially ablated by a laser  25 . More specifically, the strain sensor  40  itself comprises any ceramic material or materials suitable for deposition (such as utilizing a ceramic powder through an automated additive manufacturing process), ablation (such as by a laser  25 ), and optical recognition (such as for measuring the distance D between the at least two reference points  41  and  42  as discussed above). The ceramic strain sensor  40  may provide increased temperature survivability compared to other strain sensor materials. For example, in some embodiments, the ceramic material  30  may comprise a thermal barrier coating such as yttria-stabilized zirconia (also referred to as YSZ). In such embodiments, the YSZ may comprise, for example, YSZ-D111. In even some embodiments, the strain sensor  40  may comprise a metallic bond coat and/or thermally grown oxide to assist in the deposition of the ceramic top coat (e.g., YSZ). While some particular turbine components  10  (or at least particular locations thereon) may not experience the elevated temperatures to require thermal barrier coatings, such utilization for the strain sensor  40  may ensure its longevity where other strain sensor materials (e.g., polymeric materials, chemical dyes, etc.) could potentially break down and disappear from the relatively harsh environment. 
     In even some embodiments, the strain sensor  40  may comprise a visually contrasting material  35  in addition to the ceramic material  30 . As used herein, “visually contrasting material”  35  refers to any material that visually contrasts with the ceramic material such as through different colors or patterns. The visually contrasting material  35  may help facilitate identification of the first and second reference points  41  and  42  of the strain sensor  40  by visually highlighting their locations for an operator and/or machine. The visually contrasting material  35  may comprise any additional metal, alloy, ceramic or the like that can similarly survive on the turbine component  10  during operation. For example, in some embodiments, the visually contrasting material  35  may comprise a doped version of the ceramic material  30  that changes its color. 
     In some embodiments, such as that illustrated in  FIG. 5 , the visually contrasting material  35  may be deposited directly within the negative space  45  of the strain sensor (i.e., where the ceramic material  30  was ablated by the laser  25 ) such that the ceramic material  30  and the visually contrasting material  35  form one substantial layer. In even some embodiments, such as that illustrated in  FIG. 6 , the visually contrasting material  35  may be deposited directly on the turbine component  10  and then the ceramic material  30  may be deposited on top of the visually contrasting material  35 . 
     In some embodiments, the strain sensor  40  itself may comprise any other detectable type of contrasting characteristic that sets it apart from the underlying turbine component  10 . For example, the strain sensor  40  may comprise a different height, roughness, pattern or the like, may emit distinct energy (e.g., photoluminescence, radiation, etc.), or may comprise any other differentiating characteristic compared to the turbine component  10 . These and similar embodiments may facilitate the identification of, and measurements between, the first and second reference points  41  and  42  such as through surface metrology, energy emission analysis or the like. 
     The ceramic material  30  may be deposited using any deposition apparatus  20  suitable for depositing with high enough precision to form the strain sensor  40  as should be appreciated herein. For example, in some embodiments, the deposition apparatus  20  may comprise an aerosol jet coater (e.g., Aerosol Jen and LENS systems from Optomec), Micro Dispensing Machine (e.g., Micropen or 3Dn from Ohcraft, Inc. or nScrypt, Inc), MesoPlasma from MesoScribe Technologies, Inc., plasma spray, or any other suitable apparatus or combinations thereof. In even some embodiments, the ceramic material  30  may be airbrushed so long as suitable thickness levels can be obtained. 
     The ceramic material may then be ablated by any suitable laser. As used herein, “ablate” (and variations thereof) refers to any material removal via the laser  25 . The laser can comprise any suitable power and configuration to ablate enough ceramic material to form the at least two reference points  41  and  42 . For example, in some embodiments the laser  25  may comprise a power of from about 40 watts to about 80 watts. In even some embodiments, the laser  25  may comprise a power of less than 40 watts such as, for example, an 8 Watt YVO4 crystal YAG laser. In some embodiments, the laser  25  may comprise a pulsed laser. In even some embodiments, the laser  25  may ablate the ceramic material  30  via multiple passes. Such factors may facilitate the ablation of ceramic material  30  without substantially burning the underlying turbine component  10 . 
     In some embodiments, the ceramic material  30  may be at least partially cured prior to ablation. Such curing may help ensure the ceramic material  30  is stable on the exterior surface  11  of the turbine component  10  prior to ablation. Curing may occur at any suitable temperature and for any suitable time such as, for example, at from about 50° C. to about 100° C. for at least about 2 hours. It should be appreciated, however, that any other suitable curing conditions may also be utilized. 
     As discussed herein, the strain sensor  40  may be utilized in conjunction with different recognition techniques to help determine one or more distance measurements between at least the first and second reference points  41  and  42 . Accordingly, the laser  25  may ablate the ceramic material  30  with a suitable resolution to define a strain sensor  40  that comprises at least first and second reference points  41  and  42  that are identifiable, such as optically by a machine or individual. In some embodiments, the laser  25  may ablate the ceramic material  30  with a resolution of at least 15 microns. In even some embodiments, the laser  25  may ablate the ceramic material  30  with a submicron resolution. 
     In some embodiments, the ceramic material  30  (and potentially any visually contrasting material  35 ) may undergo one or more additional curing and/or sintering stages, either prior to or after ablation. Any curing and/or sintering may depend on the specific type of ceramic material  30  and can comprise any suitable temperature and time to substantially solidify the strain sensor  40  onto the exterior surface  11  of the turbine component  10 . In some particular embodiments, the ceramic material  30  may be at least partially cured prior to ablation and then fully sintered after ablation. 
     As best illustrated in  FIGS. 2-6 , the strain sensor  40  may comprise a variety of different configurations and cross-sections such as by incorporating a variety of differently shaped, sized, and positioned reference points  41  and  42 . For example, as illustrated in  FIG. 2 , the strain sensor  40  may comprise a variety of different reference points comprising various shapes and sizes. Such embodiments may provide for a greater variety of distance measurements D such as between the outer most reference points (as illustrated), between two internal reference points, or any combination there between. The greater variety may further provide a more robust strain analysis on a particular portion of the turbine component  10  by providing strain measurements across a greater variety of locations. 
     Furthermore, the dimensions of the strain sensor  40  may depend on, for example, the turbine component  10 , the location of the strain sensor  40 , the targeted precision of the measurement, deposition technique, ablation technique, and optical measurement technique. For example, in some embodiments, the strain sensor  40  may comprise a length and width ranging from less than 1 millimeter to greater than 300 millimeters. Moreover, the strain sensor  40  may comprise any thickness that is suitable for deposition, ablation and subsequent optical identification without significantly impacting the performance of the underlying turbine component  10 . For example, in some embodiments, the strain sensor  40  may comprise a thickness of less than from about 0.1 millimeters to greater than 1 millimeter. In some embodiments, the strain sensor  40  may have a substantially uniform thickness. Such embodiments may help facilitate successful ablation and more accurate measurements for subsequent strain calculations between the first and second reference points  41  and  42 . 
     In some embodiments, the strain sensor  40  may comprise a positively deposited square or rectangle (such that surrounding material was ablated) wherein the first and second reference points  41  and  42  comprise two opposing sides of said square or rectangle. In other embodiments, the strain sensor  40  may comprise at least two deposited reference points  41  and  42  separated by negative space  45  (i.e., an area in which ceramic material  30  was ablated). The negative space  45  may comprise, for example, an exposed portion  12  of the exterior surface  11  of the turbine component  10 . Alternatively or additionally, the negative space  45  may comprise a subsequently deposited visually contrasting material  35  that is distinct from the material of the at least two reference points  41  and  42 . 
     As illustrated in  FIG. 2 , in even some embodiments, the ceramic material  30  of the strain sensor  40  may be ablated to form a unique identifier  47  (hereinafter “UID”). The UID  47  may comprise any type of barcode, label, tag, serial number, pattern or other identifying system that facilitates the identification of that particular strain sensor  40 . In some embodiments, the UID  47  may additionally or alternatively comprise information about the turbine component  10  or the overall turbine that the strain sensor  40  is deposited on. The UID  47  may thereby assist in the identification and tracking of particular strain sensors  40 , turbine components  10  or even overall turbines to help correlate measurements for past, present and future operational tracking. 
     The strain sensor  40  may thereby be deposited in one or more of a variety of locations of various turbine components  10 . For example, as discussed above, the strain sensor  40  may be deposited on a bucket, blade, vane, nozzle, shroud, rotor, transition piece or casing. In such embodiments, the strain sensor  40  may be deposited in one or more locations known to experience various forces during unit operation such as on or proximate airfoils, platforms, tips or any other suitable location. Moreover, since the strain sensor  40  comprises a ceramic material, the strain sensor  40  may be deposited in one or more locations known to experience elevated temperatures (wherein strain sensors comprising other materials may corrode and/or erode). For example the strain sensor  40  comprising ceramic material may be deposited on a hot gas path or combustion turbine component  10 . 
     In even some embodiments, multiple strain sensors  40  may be deposited on a single turbine component  10  or on multiple turbine components  10 . For example, a plurality of strain sensors  40  may be deposited on a single turbine component  10  (e.g., a bucket) at various locations such that the strain may be determined at a greater number of locations about the individual turbine component  10 . Alternatively or additionally, a plurality of like turbine components  10  (e.g., a plurality of buckets), may each have a strain sensor  40  deposited in a standard location so that the amount of strain experienced by each specific turbine component  10  may be compared to other like turbine components  10 . In even some embodiments, multiple different turbine components  10  of the same turbine unit (e.g., buckets and vanes for the same turbine) may each have a strain sensor  40  deposited thereon so that the amount of strain experienced at different locations within the overall turbine may be determined 
     Referring additionally to  FIG. 7 , a method  100  is illustrated for manufacturing a strain sensor  40  on a turbine component  10 . The method  100  first comprises providing a turbine component  10  in step  110 . As discussed herein, the turbine component  10  can comprise any component having an exterior surface  11 . The method further comprises depositing a ceramic material  30  onto a portion of the exterior surface  11  in step  120 . The method then comprises ablating at least a portion of the ceramic material  30  to form the strain sensor  40  in step  130 . As also discussed herein, the strain sensor  40  formed via the ablation comprises at least two reference points  41  and  42 . In some particular embodiments, the at least two reference points  41  and  42  may be at least partially separated by an exposed portion of the exterior surface  11 . In some embodiments, ablation in step  130  may occur prior to sintering the ceramic material  30  of the strain sensor  40 . In such embodiments, the strain sensor  40  may be partially cured such that it is in a green state, ablated by a laser, and then fully sintered. In other embodiments, the strain sensor  40  may be ablated after the ceramic material  30  is fully sintered. Furthermore, in some of these embodiments, the method  100  may further comprise depositing a visually contrasting material  35  in the exposed portion in step  140  to assist in the identification of the at least two reference points  41  and  42 . Method  100  may be repeated to produce multiple strain sensors  40  on the same turbine component  10 , multiple strain sensors  40  on different turbine components  10 , or combinations thereof. 
     Referring additionally to  FIG. 8 , another method  200  is illustrated for monitoring a turbine component  10 . Similar to method  100 , method  200  further comprises depositing a ceramic material  30  onto a portion of the exterior surface  11  in step  220 . The method  200  then comprises ablating at least a portion of the ceramic material  30  to form the strain sensor  40  in step  230 . Method  200  further comprises determining a first distance D between a first  41  and a second  42  of the at least two reference points of the strain sensor  40  in step  240 . In some embodiments, determining the first distance D can be accomplished through measuring. In even some embodiments, such as when ablation of the ceramic material  30  is accomplished with high resolution, determining the first distance D may be accomplished by simply knowing the distance based on the ablation specifications of the strain sensor  40  in step  220 . Method  200  then comprises utilizing the turbine component  10  in a turbine in step  250 . Subsequently, method  200  comprises measuring a second distance D between the same first  41  and second  42  of the at least two reference points of the strain sensor  40  in step  260 . Finally, method  200  comprises comparing the first distance to the second distance in step  270 . By comparing the distances measured at different times in step  270 , the strain experienced by the turbine component  10  at the location of the strain sensor  40  may be determined 
     It should now be appreciated that ceramic strain sensors may be deposited on turbine components. The ceramic strain sensors may facilitate the monitoring of the turbine components performance while withstanding the potentially harsh operating conditions. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.