Patent Publication Number: US-2017369981-A1

Title: Treated gas turbine components and processes of treating gas turbine systems and gas turbine components

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to EPO Patent Application No. 16461527.0 filed Jun. 22, 2016, which is hereby incorporated by reference herein in its entirety. 
     FIELD OF THE INVENTION 
     The present embodiments are directed to methods of treatment and treated components. More specifically, the embodiments are directed to methods of treating a gas turbine component having a base coating and a treated gas turbine component. 
     BACKGROUND OF THE INVENTION 
     Gas turbine components are subjected to thermally, mechanically, and chemically hostile environments. For example, in the compressor portion of a gas turbine, atmospheric air is compressed, for example, to 10-25 times atmospheric pressure, and adiabatically heated, for example, to 427-677° C. (800-1250° F.), in the process. This heated and compressed air is directed into a combustor, where it is mixed with fuel. The fuel is ignited, and the combustion process heats the gases to very high temperatures, for example, in excess of 1650° C. (3000° F.). These hot gases pass through the turbine, where airfoils fixed to rotating turbine disks extract energy to drive the fan and compressor of the turbine and the exhaust system. The gases provide sufficient energy to rotate a generator rotor to produce electricity. 
     Gas turbines, such as aircraft engines and power generation systems, must satisfy the highest demands with respect to reliability, power, efficiency, economy, and operating service life. The use of coatings on turbine components, such as combustors, combustion liners, combustion transition pieces, combustion hardware, turbine blades (buckets), vanes (nozzles), and shrouds, is important in commercial as well as military gas turbine engines. Coatings, such as bond coatings and thermal barrier coatings (TBCs), contribute to desirable performance characteristics when operating in certain harsh environmental conditions. To avoid oxidation/corrosion damage at high temperatures, coatings have been applied to the surface of metallic components and cooling schemes have been implemented, so that the components function well and meet the designed life expectancy. 
     The bond coating is often a MCrAlY metallic bond coating, where M is Ni, Co or a combination thereof. Some conventional bond coatings, such as GT33 (available from Sulzer Metco, Westbury, N.Y.), which is a MCrAlY bond coating alloy for turbine engine applications, have operational temperature limits of about 950° C. (1750° F.). At temperatures higher than the operational temperature limit, the bond coating deteriorates much faster due to accelerated oxidation, which increases the chances of spallation of the thermal barrier coating (TBC) applied to the bond coating and hence reduces the component service life. Typical MCrAlY bond coatings have a two-phase structure of fine γ-(M) (face-center cubic) and β-(M)Al (body-center cubic). The β-(M)Al phase is the aluminum (Al) reservoir. 
     Aluminum in the bond coating is depleted during service by diffusion either to the bond coating/TBC interface, forming α-Al 2 O 3  a thermally grown oxide (TGO), or into the substrate. Spallation of the TBC occurs when the TGO layer is very thick or there is no more aluminum from the bond coating to form the adherent α-Al 2 O 3  scale. Aluminum diffusion and TGO growth depend on bond coating temperatures, i.e., higher bond coating temperatures accelerate aluminum diffusion and TGO growth, and hence TBC spallation, and reduce component service life. Therefore, bond coating temperatures are limited due to oxidation, spallation, and depletion of the aluminum reservoir in the bond coating. High temperatures deplete β-phase material from the MCrAlY coatings. Upon reaching a predetermined depletion of the β-phase material, such MCrAlY coatings are treated. 
     Known MCrAlY coating treatment techniques include stripping MCrAlY coatings, for example, with an acid, and re-coating the article with a MCrAlY coating. Such techniques undesirably extend the duration of service periods for turbine components. Such stripping and re-coating can also result in undesirably high costs. The steps of stripping the old base coating and applying a new base coating accounts for more than 30 to 40% of the treatment cost for a turbine component. Thus, there is considerable cost saving potential in avoiding stripping off the old base coating. Furthermore, improper stripping and re-coating can have an undesirable effect on alloys in the substrate. 
     Corrosion pits in a service-returned base coating are a deterrent to life extension of the base coating. These coatings often include corrosion pits that may be due to any of a number of various causes including, but not limited to, small particle impingement, foreign object impingement, hot corrosion, particles coming from the gas and fuel, or combinations thereof. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In an embodiment, a process of treating a component includes mechanically removing surface debris from a base coating of the component, identifying at least one surface feature in the base coating, and applying an overlay coating layer over the at least one feature of the base coating without stripping off the base coating. 
     In another embodiment, a treated gas turbine component includes a gas turbine component substrate and a base coating on the gas turbine component substrate having at least one healed surface feature. The healed surface feature includes an overlay coating layer on the base coating. 
     In another embodiment, a process of treating a gas turbine component includes mechanically removing surface debris from a base coating of the gas turbine component, identifying at least one surface feature in the base coating selected from the group consisting of corrosion pits, dents, spalls, and combinations thereof, and applying an overlay coating layer over the at least one feature of the base coating without stripping off the base coating. 
     Other features and advantages of the present invention will be apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a treatment process with a selectively-applied overlay coating in an embodiment of the present disclosure. 
         FIG. 2  is a schematic view of a treatment process where the heat treatment heals the base coating in an embodiment of the present disclosure. 
         FIG. 3  is a schematic view of a treatment process where applying a selectively-applied overlay coating heals the base coating in an embodiment of the present disclosure. 
         FIG. 4  is a schematic view of a treatment process with a uniformly-applied overlay coating in an embodiment of the present disclosure. 
     
    
    
     Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Provided is a process of extending the life of a base coating during treatment of a component with the base coating. The overlay coating preferably gives new life to the base coating and thereby enhances the overall coating life on the component and hence the performance of the component. In some embodiments, the component is a turbine component. 
     Embodiments of the present disclosure, for example, in comparison to concepts failing to include one or more of the features disclosed herein, enable life extension of a coating without having to strip and recoat, enable a practical and simple method of reusing an external coating, allow for a cost-effective treatment without additional steps being involved, allow for a faster turnaround time for treatment, allow for fewer process steps in the repair router, or any combination thereof. 
     As shown in  FIG. 1  through  FIG. 4 , prior to being treated, a component  101  includes a substrate  103  and a base coating  105  positioned on at least a portion of the substrate  103 . The base coating  105  may include at least one surface feature  113 . The component  101  may also include surface debris  109  and the surface feature  113  may include a corrosion region  111 . The component  101  may be any suitable component, including, but not limited to, a turbine component or an engine component. In some embodiments, the turbine component is a gas turbine component. Exemplary components include, but are not limited to, combustor liners, transition ducts (for example, between combustion and turbine sections), stationary nozzles, rotating buckets, shrouds, other metal or metallic components, or combinations thereof. 
     The component  101  is treated to form the treated component  107  according to the treatment process  100 . The treatment process  100  may include mechanically removing surface debris  109  from the base coating  105  (step  121 ), identifying at least one surface feature  113  in the base coating  105  (step  123 ), and applying an overlay coating layer  115  over the surface feature  113  of the base coating  105  without stripping off the base coating  105  (step  125 ). The surface feature  113  may be, but is not limited to, at least one corrosion pit, dent, spall, cavity, discontinuity, porosity defect, shrinkage defect, scratch, void, impurity-derived fault, or combinations thereof. 
     The overlay coating layer  115  may be selectively applied to the surface feature  113 , as shown in  FIG. 1 ,  FIG. 2 , and  FIG. 3 , but may also be applied substantially uniformly to the rest of the base coating  105 , as shown in  FIG. 2 . In some embodiments, the selectively-applied overlay coating layer  115  serves as a patch to patch one or more surface features  113  on the base coating  105 . Alternatively, the overlay coating layer  115  may be applied substantially uniformly to the base coating  105 , as shown in  FIG. 4 , such as when no surface features are identified, when surface features  113  are wide-spread over the base coating  105 , or when the surface features are smaller than a predetermined dimension. 
     Applying the overlay coating layer  115  (step  125 ) may heal the surface feature  113  by removing some of the corrosion in the corrosion region  111 , as shown in  FIG. 1 , or all of the corrosion, as shown in  FIG. 3 . In other embodiments, applying the overlay coating layer  115  (step  125 ) does not remove any of the corrosion in the corrosion region  111 , as shown in  FIG. 2  and  FIG. 4 . The treatment process  100  preferably also includes a heat treatment (step  127 ) to complete the healing process by removing any, most, or all of the remaining corrosion, as shown in  FIG. 1 ,  FIG. 2 , and  FIG. 4  and bonding the overlay coating layer  115  to the base coating  105 . 
     The base coating  105  is preferably a bond coating and more preferably a MCrAlY bond coating. In some embodiments, the life of an external oxidation coating, including, for example, a GT33 MCrAlY bond coating, is extensible up to 96,000 hours without having to strip and recoat. A MCrAlY bond coating, as used herein, refers to a commercially available bond coating having a composition of about 30-35 wt % nickel, about 20-25 wt % chromium, about 8-12 wt % aluminum, about 0.1-0.5 wt % yttrium, and about 30-40 wt % cobalt. In some embodiments, the process enables coating life extension by healing the base coating  105 , by adding an overlay coating layer  115  of the same type of coating, with a fewer number of passes, either via thermal spray or by using a gel coating. Application of the overlay (step  125 ) and subsequent heat treatment (step  127 ) serves to heal the base coating  105 . 
     The treatment process  100 , according to the present disclosure, enables treatment of the component  101  without stripping the base coating  105 , even if the base coating  105  includes some corrosion pits. The treatment process  100  preferably retains and treats the base coating  105  and overcomes the corrosion that is found on the base coating  105 . 
     In some embodiments, the base coating  105  is a damaged coating that was damaged during service. In some embodiments, the treatment repairs the damaged coating on the component. In some embodiments, the overlay coating layer  115  is a repair coating layer. 
     In some embodiments, a treatment process  100  includes removing a component  101  having a base coating  105  from service in the system, mechanically removing (step  121 ) surface debris  109  from the base coating  105 , identifying (step  123 ) at least one surface feature  113  in the base coating  105  as a corrosion pit, dent, spall, cavity, discontinuity, porosity defect, shrinkage defect, scratch, void, impurity-derived fault, or combinations thereof, and applying (step  125 ) an overlay coating layer  115  over the surface feature  113  of the base coating  105  without stripping off the base coating  105 . In some embodiments, the system is a turbine system. In some embodiments, the turbine system is a gas turbine system. 
     The state of the base coating  105  is often difficult to assess when a gas turbine component  101  is first removed from service. Mechanically removing (step  121 ) any surface debris  109  from the base coating  105  permits visual assessment and measurement of any surface features  113  on the base coating  105 . Mechanically removing (step  121 ) surface debris  109  is preferably performed by a cosmetic grit blasting, preferably of the entire coated surface of the gas turbine component. 
     Once the surface debris  109  has been removed (step  121 ), surface features  113 , including, but not limited to, corrosion pits, dents, spalls, cavities, discontinuities, porosity defects, shrinkage defects, scratches, voids, and impurity-derived faults, may be identified (step  123 ) and then characterized. Based on previous observations, 40 to 50% of gas turbine components removed from service are expected to have corrosion pits. Methods of identifying (step  123 ) these surface features  113  may include, but are not limited to, manually visually inspecting the surface; automatically inspecting the surface of the base coating  105 , such as by an automated inspection directed by a computer using a visual sensor, a chemical sensor, or a topographical sensor; or combinations thereof, of the gas turbine component after mechanically removing (step  121 ) the surface debris  109 . Characterization of these surface features  113  may include, but is not limited to, measuring the area, dimensions, or depth of the surface feature  113 ; assessing the presence or degree of corrosion in a corrosion region  111  present in the surface feature  113 ; or combinations thereof. In some embodiments, a depth gauge measures the depth of the surface feature  113 . In some embodiments, the characterization includes accurately gauging the depth of a corrosion pit. 
     The type of overlay coating layer  115  and the method of application (step  125 ) are preferably then selected based on the assessed condition of the base coating  105  as a result of the identification (step  123 ) and characterization of any surface features  113 . In some embodiments, the method of application (step  125 ) is selected based on the gauged depth of a surface feature  113 , which may be a corrosion pit. In some embodiments, the method of application (step  125 ) is selected based on whether the gauged depth of the surface feature  113  is greater than or less than a predetermined depth. The overlay coating layer  115  is applied (step  125 ) over the at least one surface feature  113  of the base coating  105  without an acid rinse of the component  101  and without stripping off the base coating. Surface features  113  up to at least 75 to 100 microns (3 to 4 mils) in depth have been successfully treated on turbine components  101  by the treatment process  100 . 
     When corrosion pits and other surface features  113  are observed, but observed to be few, sporadically located, or located in one or more clusters on the surface, the overlay coating layer  115  is preferably a gel aluminide applied (step  125 ) selectively as one or more patches only to the area or areas where the corrosion pits or other surface features  113  are located, as shown in  FIG. 1  and  FIG. 3 . 
     When corrosion pits and other surface features  113  are observed to be somewhat spread around the component  101 , the overlay coating layer  115  is preferably applied (step  125 ) over the entire base coating  105  by thermal spraying, although a thicker overlay coating layer  115  may be applied to the locations of one or more of the surface features  113 , such as any surface features  113  larger than a predetermined size or deeper than a predetermined depth. The thermal spraying is preferably a high-velocity oxygen fuel (HVOF) spraying or a high-velocity air-fuel (HVAF) spraying, but other thermal spraying techniques, including, but not limited to, vacuum plasma spraying (VPS), may alternatively apply (step  125 ) the overlay coating layer  115 . When corrosion pits and other surface features  113  are observed to be concentrated in one or more particular portions of the turbine component, the overlay coating layer  115  is preferably selectively applied (step  125 ) by thermal spraying to those particular portions rather than to the entire component  101 . 
     In some embodiments, the thermal spray process of applying (step  125 ) the overlay coating layer  115  at a high temperature, by way of melting and solidification of the overlay coating, completely or partially heals the surface features  113  by dissolving some or all of one or more corrosion products located in or on a corrosion region  111  of the surface feature  113 . In some embodiments, the corrosion product is the result of low temperature hot corrosion or high temperature hot corrosion. In some embodiments, the corrosion product resulted from operation with one or more elemental impurities in the system, which may include, but is not limited to, sodium, vanadium, sulfur, potassium, chlorine, lead, or combinations thereof. In some embodiments, the dissolved corrosion product may include, but is not limited to, sodium chloride (NaCl), sodium sulfate (Na 2 SO 4 ), nickel sulfate (NiSO 4 ), cobalt sulfate (CoSO 4 ), vanadium (V) oxide (V 2 O 5 ), sodium vanadate (Na 2 V 2 O 6 ), or combinations thereof. In some embodiments, the corrosion product resulted from operation with one or more contaminants in the system, which may include, but are not limited to, sand particles, calcium-magnesium aluminosilicate (CMAS), or combinations thereof. The applied overlay coating layer  115  preferably forms a molten pool on the surface feature  113  during the healing process. 
     In some embodiments, the overlay coating is a gel aluminide diffusion coating. The gel aluminide coating may be applied (step  125 ) selectively to only the regions with surface features  113 , applied (step  125 ) substantially uniformly to the base coating  105 , or applied (step  125 ) to the entire base coating  105  as a thin layer over most of the base coating  105  but as a thicker layer selectively applied (step  125 ) over one or more surface features  113 . A heat treatment (step  127 ) of the component  101  after application of the aluminide diffusion coating preferably bonds the overlay coating layer  115  to the base coating  105  and heals the surface features  113  to form the treated component  107 . 
     In some embodiments, the base coating  105  is observed to contain no surface features  113  or only surface features  113  that are smaller than a predetermined size, that have no corrosion, or that have less corrosion than a predetermined level such that no overlay coating or only a thin overlay coating layer  115  is applied to the base coating  105 . The thin overlay coating layer  115  preferably has a thickness less than 100 microns (4 mils), alternatively less than 75 microns (3 mil), alternatively less than 50 microns (2 mil), alternatively in the range of 25 to 50 microns (1 to 2 mils), or any suitable combination, sub-combination, range, or sub-range thereof. In some embodiments, the thin overlay coating  115  is a MCrAlY coating applied (step  125 ) by a thermal spraying technique or a gel aluminide coating, preferably followed by a heat treatment (step  127 ) of the component. 
     In some embodiments, the component  101  is a gas turbine component and the treated component  107  is a treated gas turbine component. 
     In some embodiments, a treated gas turbine component includes a gas turbine component substrate  103  and a base coating  105  on the gas turbine component substrate  103  having at least one healed surface feature  113 . The healed surface feature  113  includes an overlay coating layer  115  on the base coating  105 . 
     In some embodiments, a treatment process  100  for a gas turbine component  101  includes mechanically removing (step  121 ) surface debris  109  from a base coating  105  of the gas turbine component  101 , identifying (step  123 ) at least one surface feature  113  in the base coating  105  as a corrosion pit, dent, spall, cavity, discontinuity, porosity defect, shrinkage defect, scratch, void, or impurity-derived fault, and applying (step  125 ) an overlay coating layer  115  over the surface feature  113  of the base coating  105  without stripping off the base coating  105 . 
     In some embodiments, the base coating  105  is a MCrAlY bond coating alloy, where M is nickel, cobalt, iron, alloys thereof, or combinations thereof. In some embodiments, the MCrAlY bond coating alloy is GT33. In some embodiments, the base coating  105  is a corroded coating with at least one corrosion region  111 . The base coating  105  is overlaid, at least in part, with an overlay coating layer  115 . 
     In some embodiments, the overlay coating layer  115  is a MCrAlY bond coating alloy, where M is nickel, cobalt, iron, alloys thereof, or combinations thereof, applied to cover at least the corrosion pits on the existing coating. In some embodiments, the overlay coating layer  115  is GT33. In some embodiments, the thickness of the overlay coating layer  115  is in the range of 25-125 microns (1-5 mil). In some embodiments, the applied overlay coating is MCrAlY applied (step  125 ) using the same application technique as the application technique used to apply the base coating  105 . 
     In some embodiments, the overlay coating layer  115  is applied (step  125 ) by one or more thermal spraying techniques. In some embodiments, the thermal spraying technique is high-velocity oxygen fuel (HVOF) spraying, vacuum plasma spraying (VPS), high-velocity air-fuel (HVAF) spraying, wire arc spraying, flame/combustion spraying, or any combinations thereof. The thermal spraying technique preferably heats the overlay material to a temperature of at least 1900° C. (3450° F.), alternatively to at least 2000° C. (3650° F.). In some embodiments, the HVOF spraying technique heats the overlay material to the range of about 2750° C. to about 3600° C. (5000-6500° F.), alternatively about 2750° C. to about 3300° C. (5000-6000° F.), alternatively about 2750° C. to about 3050° C. (5000-5500° F.), alternatively about 3050° C. to about 3300° C. (5500-6000° F.), alternatively about 3300° C. to about 3600° C. (6000-6500° F.), or any suitable combination, sub-combination, range, or sub-range thereof. In some embodiments, the HVAF spraying technique heats the overlay material to the range of about 1900° C. to about 2000° C. (3450-3550° F.), alternatively about 1900° C. to about 1950° C. (3450-3550° F.), alternatively about 1950° C. to about 2000° C. (3550-3650° F.), or any suitable combination, sub-combination, range, or sub-range thereof. 
     In some embodiments, the applied overlay coating is an aluminide. In such embodiments, the overlay coating may be a slurry, a gel, or any other suitable material capable of application to the base coating  105 , such as vapor phase deposition. In some embodiments, the overlay coating is a gel aluminide coating applied to cover the corrosion pits on the existing base coating  105 . The aluminide in the overlay coating is preferably NiAl or Ni 2 Al 3 . In some embodiments, the overlay coating includes aluminum at a concentration, by weight, of about 8% to about 35%, alternatively about 12% to about 32%, alternatively about 15% to about 25%, alternatively about 15% to about 20%, alternatively about 20% to about 25%, alternatively about 20% to about 30%, alternatively about 25% to about 30%, alternatively about 15%, alternatively about 20%, alternatively about 25%, alternatively about 30%, or any suitable combination, sub-combination, range, or sub-range thereof. 
     The base coating  105  may be soaked or dipped in the overlay coating. Alternatively, the overlay coating may be poured, sprayed, or brushed onto the base coating  105 , and/or applied by any other application process capable of applying (step  125 ) the overlay coating. In some embodiments, the overlay coating diffuses into the base coating  105 , for example, by a diffusion depth. The diffusion depth may be at least about 25 microns (1 mil), alternatively at least about 38 microns (1.5 mils), alternatively at least about 50 microns (2 mils), alternatively about 25 microns (1 mil), alternatively about 38 microns (1.5 mils), alternatively about 50 microns (2 mils), alternatively within a range of about 25 microns (1 mil) to about 50 microns (2 mils), alternatively within a range of about 25 microns (1 mil) to about 38 microns (1.5 mils), alternatively within a range of about 38 microns (1.5 mils) to about 50 microns (2 mils), or any suitable combination, sub-combination, range, or sub-range thereof. 
     In some embodiments, the applying (step  125 ) of the overlay coating is under operational conditions. In some embodiments, the overlay coating is applied (step  125 ) for a predetermined duration, such as, for example, about 1 to about 6 hours, about 1 to about 3 hours, about 3 to about 6 hours, about 1 hour, about 3 hours, about 6 hours, or any suitable combination, sub-combination, range, or sub-range thereof. In some embodiments, the applying (step  125 ) of the overlay coating is followed by or done while heating the overlay coating and/or the component  101 . For example, in one embodiment, the component  101  is positioned in an atmospheric furnace and the heating is performed, for example, in an inert atmosphere, such as with argon gas and/or with low oxygen content. In some embodiments, the heating is performed under a reduced pressure or a vacuum. 
     The treatment process  100  preferably further includes heat treating (step  127 ) at a predetermined elevated temperature to form a treated protective coating on the treated component  107 . Post-coat heat treatment (step  127 ) of the overlay coating preferably restores or tends to heal the base coating  105  to have equal or substantially equal properties to a new base coating. In some embodiments, the healing includes precipitation of a beta phase during the heat treatment (step  127 ) in the new base coating, such as to a similar state as in the original base coating  105 . Heat treating (step  127 ) may include, for example, heating with a furnace to bring up the temperature of the gas turbine component. The heat treatment (step  127 ) preferably alters the metal of the base coating  105  or substrate  103  to allow the material from the diffusion zone to flow into the base coating  105  or substrate  103  and bond with the base coating material to form a treated protective coating. The treated protective coating may have a coating microstructure and a coating chemistry matching an original coating of a new gas turbine component prior to service in a turbine. 
     A heat treatment (step  127 ) includes suitable temperatures, for example, temperatures of about 870° C. to about 1200° C. (1600° F. to 2200° F.), alternatively about 1040° C. to about 1180° C. (1900° F. to 2150° F.), alternatively about 1070° C. to about 1150° C. (1950° F. to 2100° F.), alternatively at about 1080° C. (1975° F.), alternatively at about 1090° C. (2000° F.), alternatively at about 1120° C. (2050° F.), or any suitable combination, sub-combination, range, or sub-range thereof. In one embodiment, heat treating (step  127 ) is at a temperature capable of forming a ductile intermetallic material, such as a ductile aluminide, for example, having a strain range of about 4% and/or permitting the treated component  107  to be devoid or substantially devoid of cracking formed by application of a brittle aluminide. 
     In some embodiments, the applying (step  125 ) of the overlay coating and the heating (step  127 ) heals the surface feature  113  region of the base coating  105  to form the treated component  107 . The formation of the treated component  107  preferably includes outwardly forming β-phase material as the outwardly-formed β-phase material from the base coating  105  into the aluminide overlay coating layer  115 . Use of the term “outwardly” refers to having a greater characteristic of outward forming β-phase material than inward formed coatings which include NiAl and Ni 2 Al 3  β-phase material. For example, outwardly-formed aluminides include primarily β-NiAl as nickel diffuses outward to react with the aluminum source. 
     The component  101  for the treatment process  100  may be any suitable coated component. In some embodiments, the component  101  is a gas turbine component. In some embodiments, the component  101  is a stage  1  (S 1 ) turbine bucket of a gas turbine system. The component  101  has preferably been used in service for at least a predetermined period of time before being subjected to the treatment process  100 . 
     While the invention has been described with reference to one or more embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. In addition, all numerical values identified in the detailed description shall be interpreted as though the precise and approximate values are both expressly identified.