Abstract:
A method for coating a component of a track roller frame track tensioning and recoil system is disclosed. The method includes irradiating a surface of the component with a continuous laser to heat the component&#39;s surface. The method also includes coating the surface of the component with a thermal spray coating after irradiating.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part application based on U.S. Ser. No. 12/285,309, filed Oct. 1, 2008. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure is directed to a thermal spray coating and, more particularly, to surface preparation for bond enhancement of a thermal spray coating to track roller frame components. 
       BACKGROUND 
       [0003]    Several well known high temperature thermal spray methods for coating a substrate exist in the industry, such as high-velocity oxygen fuel (HVOF) spraying. HVOF is a combustion process in which oxygen is mixed with a fuel gas and ignited, forming an exhaust gas. The exhaust gas is accelerated toward a substrate via a spray torch as a metal, ceramic, or composite material is injected into the gas stream. The injected material becomes molten and is propelled at a high velocity toward the substrate to be coated. One possible shortcoming of thermal spray methods such as HVOF in some applications is that the bond strength achieved between a coating and a substrate may be limited. 
         [0004]    U.S. Pat. No. 5,688,564 (&#39;564), issued to Coddet et al., discloses a process for the preparation of a substrate surface to increase bond strength. The &#39;564 patent discloses irradiating a substrate surface via a pulse laser beam immediately before applying a thermal spray coating. The pulse laser beam imparts a large amount of energy into the substrate surface in a very brief amount of time. The pulse laser may improve bond strength of the coating by creating a plasma of vaporized material that expands to cause a shockwave. The shockwave may have a cleaning and roughening effect on the substrate surface that may improve bond strength between the coating and the substrate surface. 
         [0005]    Although the process disclosed in &#39;564 may provide a method for affecting a shockwave effect to roughen a substrate surface, it does not allege to disclose a method for improving the coating bond for metallurgically joining the coating and the substrate. The process described in &#39;564 does not provide a significant increase in thermal energy available at a contact surface between the substrate and the thermal spray particles. 
         [0006]    The present disclosure is directed to overcoming one or more of the shortcomings set forth above and/or other deficiencies in the art. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    In accordance with one aspect, the present disclosure is directed toward a method for coating a component of a track tensioning and recoil system of a work machine. The method comprises irradiating a surface of the component with a continuous laser to heat the component and coating the surface of the element with a thermal spray coating after irradiating. Here, coating the surface occurs between about 1 and about 20 milliseconds after irradiating the surface. 
         [0008]    The present disclosure is also directed toward a method for coating a component of a track tensioning and recoil system of a work machine where the method comprised irradiating a surface of the component with a laser, controlling a rate of movement of the laser to produce a desired laser-affected zone of the component; and coating the surface of the component with a thermal spray coating after irradiating. 
         [0009]    According to another aspect, the present disclosure is directed toward a component of a track tensioning and recoil system of a work machine having a coating. The component includes a substrate material, a thermal spray layer, and an interface layer bonding the substrate material to the thermal spray layer, the interface layer being about 75% or greater contaminant-free. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic illustration of an exemplary coating system; 
           [0011]      FIG. 2  is a detailed view of the coating system of  FIG. 1 ; 
           [0012]      FIG. 3  is a second detailed view of the coating system of  FIG. 1 ; and 
           [0013]      FIG. 4  is a flow chart of the coating system of  FIG. 1   
       
    
    
     DETAILED DESCRIPTION 
       [0014]    As illustrated in  FIG. 1 , a coating system  10  may include a depositing device  14 , a laser  18 , and a coating  15 . Depositing device  14  may apply coating  15  to a substrate  12 , and laser  18  improves a bond strength between coating  15  and substrate  12 . Coating system  10  may also include an application of flux prior to the process to clean substrate  12  by thermally activating the flux via laser  18 . 
         [0015]    Depositing device  14  may be any suitable thermal spraying device for depositing a coating material  16  onto substrate  12 . Coating material  16  may be deposited onto substrate  12  via any suitable method known in the art such as, for example, combustion wire spraying, combustion powder spraying, twin wire arc spraying, plasma transfer wire arc spraying, wire or powder high-velocity oxygen fuel (HVOF) spraying, or combustion flame spraying. HVOF is a combustion process where oxygen may be mixed with a fuel gas and ignited, forming an exhaust gas stream. The exhaust gas stream may be accelerated toward a substrate at high velocities such as, for example, velocities in excess of about 1000 m/s, about 1200 m/s, or even in excess of about 1400 m/s. 
         [0016]    Coating material  16  may include powder metals or ceramic cermets that are injected generally axially or radially into the exhaust gas stream and become molten as they are propelled toward substrate  12 . In some settings, high velocities of coating material  16  contribute to mechanical bond strength between coating material  16  and substrate  12 . Depositing device  14  may be any suitable application device such as, for example, an HVOF spray gun, a wire arc spray gun, or a plasma arc spray gun. Coating material  16  may be in any suitable form such as, for example, powder, liquid, or wire, and may be introduced into a plasma jet produced by depositing device  14 . Depositing device  14  may deposit coating material  16  via any suitable technique such as, for example, a raster motion on flat surfaces or a spiral pattern on rotating elements. Depositing device  14  forms a thermal spray layer  24  on substrate  12 . 
         [0017]    Laser  18  may be a continuous laser suitable for preparing a surface for a coating such as, for example, a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser, a carbon dioxide laser, or a high power diode laser (HPDL). Further, laser  18  may be a continuous wave (CW) laser and may operate at a suitable power level for coating such as, for example, of between about 100 and about 2000 W/mm 2 . For example, laser  18  may operate at a power level of between about 500 and about 1500 W/mm 2 . Laser  18  may also operate at a power level of about 400 W/mm 2 . Power level may be determined based on laser spot, which may be a surface area irradiated by laser beam  22 . Laser spot may be measured based on the full width at half maximum (FWHM) of the laser power distribution across laser beam  22 . 
         [0018]    Laser  18  may be mounted on a same fixture as depositing device  14  or, alternatively, on a different fixture that precedes depositing device  14  in a direction of motion  25  to form coating  15 . Laser  18  may be moved in direction of motion  25  at a suitable rate for coating such as, for example, between about 200 and about 3000 mm/s relative to substrate  12 , such as between about 500 and about 1500 mm/s. Alternatively, substrate  12  may be moved at a rate of between about 200 and about 3000 mm/s relative to laser  18  and depositing device  14 . For example, laser  18  may be moved at a rate of between about 500 and about 1500 mm/s. Depositing device  14  is configured to follow closely behind laser  18  in the direction of motion  25 , with coating material  16  contacting a surface location at an interval such as, for example, between about 1 and about 20 milliseconds after laser  18  irradiates the surface location. 
         [0019]    Laser  18  may emit a laser beam  22  that contacts a surface  20  of substrate  12  and/or a previously applied layer  24 . As illustrated in  FIG. 2 , heat from laser beam  22  may produce a laser-affected zone  26  within substrate  12 . Laser-affected zone  26  includes portions of substrate  12  and layers  24  having material properties that are changed by laser beam  22 . For example, laser-affected zone  26  may include portions of substrate  12  and layers  24  that are heated by laser beam  22 . Laser-affected zone  26  has a depth  27  that may result from a combination of parameters such as laser power, laser spot, and traverse speed. In accordance with the disclosed method, depth  27  is less than about 500 μm, such as, for example, between about 100 μm and about 200 μm. For example, depth  27  may be between about 125 and about 175 μm. The substrate properties within laser-affected zone  26 , such as hardness, may vary based on rapid heating, quenching, and/or tempering. The characteristics of laser-affected zone  26  is a result of a heat gradient, in which a temperature closer to surface  20  may be higher than a temperature further away from surface  20 . Laser beam  22  may heat substrate  12 , within laser-affected zone  26  and near surface  20 , to a maximum temperature such as, for example, of between about 0.7 and about 1.0 of the solidus temperature of substrate  12 . Portions of laser-affected zone  26  near surface  20  may be any desired maximum temperature for coating such as, for example, between about 500° C. and about 1500° C. For example, laser-affected zone  26  may be between about 800° C. and about 1200° C. near surface  20 . 
         [0020]    Depth  27  and the temperature gradient of laser-affected zone  26  may affect bond strength between coating  15  and substrate  12 . Although heating substrate  12  may improve bond strength, bond strength may be weakened by too much heat, i.e., by laser-affected zone  26  being too large and/or temperatures being too high. Bond strength may also be weakened by laser-affected zone  26  being too small and/or temperatures being too low. Decreasing a rate of movement of laser  18  may increase the amount of time that laser beam  22  imparts heat into a given location of substrate  12 , thereby imparting more heat into substrate  12  than when laser  18  moves at a faster rate. Therefore, controlling the rate of movement of laser  18  is typically also related to the amount of heat imparted to substrate  12 , and may produce a desired laser-affected zone  26  of an appropriate size and temperature for optimizing bond strength for a given coating material and substrate material. Laser-affected zone  26  may be controlled via laser  18  to avoid melting of substrate  12 . Melting may be undesirable because it may significantly reduce a hardness of substrate  12 . 
         [0021]    As illustrated in  FIG. 3 , thermal coating  15  may include a plurality of layers  24 . Each layer  24  may be applied by a pass of depositing device  14  and laser  18  across substrate  12 . Coating  15  may be composed of numerous layers such as, for example, about twenty to thirty layers  24 . Each layer  24  may be of any suitable dimension for coating such as, for example, between about 5 μm and about 20 μm thick, or between about 10 μm and about 15 μm thick. Further, the layer may be between about 5 mm and about 100 mm wide, such as between about 40 mm and about 60 mm wide. As laser  18  makes passes across substrate  12 , an interface layer  28  may be produced within laser-affected zone  26 . Interface layer  28  is a dilution zone in which substrate  12  and layers  24  are metallurgically bonded. Based on coating system  10 , interface layer  28  may be substantially free of contaminants such as, for example, oxide compounds. Interface layer  28  may be at least about 75% contaminant-free. For example, based on coating system  10 , interface layer  28  may be at least about 90% contaminant-free, at least about 95% contaminant-free, or at least about 99% contaminant-free. 
         [0022]    Laser beam  22  may affect at least one previously applied layer  24  and a portion of substrate  12  to combine together to form a single interface layer  28  within laser-affected zone  26 . After a suitable amount of passes of laser  18  and depositing device  14  such as, for example, between about twenty and thirty passes, interface layer  28  may have a thickness of up to about 150 μm. For example, interface layer  28  may be between about 1 μm and 100 μm thick, or between about 1 μm and 50 μm thick. Interface layer  28  may have a hardness that is greater than a hardness of substrate  12 . Hardness may be measured by a suitable micro-hardness test that measures hardness of a small volume of material such as, for example, a Vickers or Knoop hardness test. 
         [0023]    Coating system  10  may include an application of flux to clean surface  20  of substrate  12 , and/or surfaces of previously applied layers  24 , before irradiation by laser  18 . The flux may be any suitable flux known in the art for preventing oxidation such as, for example, fluoride-containing or calcium-containing flux. Oxidation occurs when oxygen molecules interact with molecules of a surface, causing an oxide film to form that may decrease bond strength. Oxidation may occur nearly instantaneously such as, for example, when oxygen molecules contact surface  20 . Any suitable method known in the art for applying a thin film of material may be used to apply the flux over an area of surface to be coated such as, for example, via a dispensing device that sprays a thin layer of flux onto a surface. The flux may be inert at relatively low temperatures such as, for example, an ambient outdoor temperature. When subjected to relatively high temperatures such as, for example, laser beam  22 , the flux may react with any oxide film that has formed on surface  20  and/or surfaces of layer  24  due to oxidation, to vaporize both the flux and the oxide film. The removal of oxides prior to coating may improve a bond strength between coating  15  and substrate  12 . 
       INDUSTRIAL APPLICABILITY 
       [0024]    Coating system  10  may be used in any coating application. For example, coating system  10  may be used in any manufacturing and remanufacturing applications requiring a thermal spray coating. Laser  18  may improve bond strength by producing a desired laser-affected zone  26  via laser beam  22 . 
         [0025]    Coating system  10  may be used for new manufacturing of an article, remanufacturing of an article, sealing of an article, and wear resistance applications on an article. Coating system  10  may be used on track assembly undercarriage structures, such as the track tensioning and recoil system. Such track tensioning and recoil systems are generally well known in the art, see, e.g., U.S. Pat. Nos. 4,223,878; 4,283,093; and 4,881,786, incorporated herein by reference. These track tensioning and recoil systems are the components of an undercarriage that enable appropriate constant tension to be applied to the tracks of a machine during operation, yet allow service at necessary times. The method disclosed herein may be used to apply a coating to any wear surfaces comprised therein. For example, most track tensioning and recoil systems comprise an outer member and an inner member, both of which are generally tubular, with the inner member slidably disposed within the outer member by means of bearings, such as sleeve bearings. Further, suitable seals are employed to enclose the arrangement by sealing against various features, referred to herein as seal surfaces, of the outer member, inner member, and any other moving parts that may encounter wear, such as piston surfaces. Any one of these track tensioning and recoil system components may be coated using the method disclosed herein. 
         [0026]    As illustrated in  FIG. 4 , coating  15  may be applied to substrate  12  according to method steps  30 ,  32 ,  34 , and  36 . In step  30 , flux may be applied to surface  20 . If coating  15  is being applied as part of a remanufacturing application, an appropriate amount of material may be removed from substrate  12  prior to step  30  such as, for example, about 75 μm or greater of material. In step  32 , laser beam  22  may irradiate surface  20 , affecting the flux to react with and vaporize any oxides that have formed on surface  20 , cleaning and thereby improving characteristics of substrate  12  for bonding with coating  15 . Laser beam  22  may also preheat substrate  12  within laser-affected zone  26 , the preheating action improving characteristics of substrate  12  for bonding with coating  15 . The rate of movement of laser  18  may be controlled to produce a desired laser-affected zone  26  that is appropriate for increasing bond strength between coating  15  and substrate  12 . In step  34 , depositing device  14  may apply coating material  16  to surface  20 . Because depositing device  14  follows closely behind laser  18 , as described above, there may not be enough time for an oxide film to be produced on surface  20 . In step  36 , additional layers  24  may be applied to substrate  12  in a manner similar to steps  30 ,  32 , and  34 , in which flux may be applied to a surface of each applied layer  24  to improve bonding of each subsequent layer  24 . Iterative passes of laser  18  and depositing device  14  may produce a coating  15  having an interface layer  28  that is substantially oxide-free. Coating  15  may be machined, if required. 
         [0027]    Coating system  10  may improve the bond strength between coating  15  and substrate  12 . Controlling a rate of movement of laser  18  may produce a desired laser-affected zone  26  of substrate  12 , which may improve bond strength. A desired laser-affected zone  26  may be selected, based on material properties of substrate  12  and coating  15 , to achieve a desired bond strength. Controlling laser-affected zone  26  may thereby achieve a desired, uniform bond strength. Coating system  10  may also provide a relatively small interface layer  28  having metallurgical properties that may improve bonding between coating  15  and substrate  12 . Metallurgical properties of interface layer  28  may also reduce the probability of feathering (i.e., removing coating and exposing uncoated substrate material) during machining after applying coating  15 . Laser  18  may also clean a surface to be coated, which may improve bond strength of coating  15  and may eliminate the need for grit-blasting the surface. 
         [0028]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed coating system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed method and apparatus. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.