Abstract:
The present disclosure is directed to a method of making a textured coating on a wear surface of a component. The method includes applying a mask on the surface and depositing a tribological coating on the surface. The method further includes removing the mask.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part to U.S. patent application Ser. No. 11/606,178, filed on Nov. 30, 2006. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to a method of making a textured coating on a component surface, and more particularly, to a method of making a textured coating on the surface of a component that is subject to friction. 
       BACKGROUND 
       [0003]    In a machine, there are component parts that are designed to rub together during operation. Some examples are bearings, gears, cams, tappets, pistons, rings, fuel injector plungers, bearings, cams/followers, transmission components and hydraulic system components such as hydraulic pumps. In these components, two surfaces come into contact, support (or subject to) a load, and move with respect to each other (hereinafter referred to as frictional contact). While these surfaces may look smooth on a macroscopic scale, they may contain many irregularities (called asperities) on a microscopic scale. When two microscopically rough component surfaces undergo frictional contact, physical contact and load transfer occur at the asperities. The high local pressure at points of contact cause the asperities to deform plastically and form microscopic adhesive junctions at the contact points. When these components undergo relative motion, the adhesive junctions are sheared and new junctions are formed. This repeated shearing and reestablishment of adhesive junctions cause material removal. This process is referred to as wear. Wear may also be caused in surfaces under frictional contact by other mechanisms. Due to the various wear mechanisms, the dimensions of the component and/or the strength of the component may change. Wear limits the durability of a machine component that undergoes frictional contact. A component that includes surfaces, which undergo frictional contact, will be referred to as wear components, and the surfaces that undergo frictional contact will be referred to as wear surfaces. 
         [0004]    Engineered surface treatments are applied to surfaces under frictional contact to reduce friction and wear, and thereby improve durability. These surface treatments can be broadly classified as treatments that alter the surface texture of the component and treatments that change the surface chemistry of the component. Examples of treatments that alter the surface texture of a component include chemical and/or mechanical polishing of the surface using vibratory finishing, laser texturing, stone honing, shot-peening, mechanical dimpling/grooving etc. Examples of treatments that change the surface chemistry of a component include tribological coatings. 
         [0005]    Tribological coatings include doped/undoped amorphous carbons (diamond like carbon, “DLC”), amorphous hydrocarbons, metal carbides, metal nitrides, metal dichalcogenides, metal borides, etc. Surface texture modifications reduce wear by reducing the heights of the asperities and/or by providing miniature reservoirs to trap the lubricant and/or debris. Tribological coatings decrease component wear by reducing the formation of adhesive joints and by providing a hard surface to resist material removal or, in other words, to increase wear resistance. To harness the wear resistant qualities of both types of engineered surface treatments, textured surfaces can be formed on tribological coatings. A tribological coating may be first deposited on a surface and the texture formed on the coating. Surface texturing techniques such as machining, laser surface texturing, etc. are most often used to create these textured surfaces on the tribological coating. 
         [0006]    Textured tribological coatings and methods of making these coatings on surfaces under frictional contact are described in U.S. Patent Publication No. US 2005/0175837 A1 issued to Massler et al. on Aug. 11, 2005 (hereinafter the &#39;837 publication). In the methods of the &#39;837 publication, uniform layers of different tribological coatings are applied to a component surface using physical vapor deposition or chemical vapor deposition processes. Grooving (texturing) of the tribological coatings is then carried out using an excimer laser system. While the textured tribological coatings of the &#39;837 publication may improve the wear resistance of the component, making the textured tribological coatings as disclosed in &#39;837 publication have significant limitations. For instance, surface-texturing using a laser may damage the component due to excessive localized heat. Individually forming the grooves (that make up the surface texture) using a laser may be expensive for mass produced components, both due to high equipment costs and increased process time/complexity. In addition, the method of the &#39;837 publication does not disclose a method of re-applying the tribological coating when the initial coating wears out. Therefore, although the wear resistance of the component may be increased by methods disclosed in the &#39;837 patent, the component may still require replacement when the initial textured tribological coating wears out. Other known processes rely upon the use of chemical vapor deposition (CVD), which requires temperatures exceeding 500° C., and is therefore unsuitable for many components or substrates. 
         [0007]    The present disclosure is directed at overcoming one or more of the shortcomings of the prior art textured tribological coatings. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    In one aspect, the present disclosure is directed to a method of making a textured coating on a surface of a component including, but not limited to as fuel injector plungers, gears, pistons, rings, bearings, cams/followers, transmission components and hydraulic system components such as hydraulic pumps. The method includes applying a mask on the surface and depositing a tribological coating on the surface. The method further includes removing the mask. 
         [0009]    In another aspect, the present disclosure is directed to a method of making a textured coating on a surface of a machine component including, but not limited to as fuel injector plungers, gears, pistons, rings, bearings, cams/followers, transmission components and hydraulic system components such as hydraulic pumps. The method includes applying a first mask to the surface in a first pattern and depositing a first tribological coating on the surface. The method also includes removing the first mask to obtain a first tribological coating pattern. The machine component is then operated such that the first tribological coating pattern will be subject to wear. The method further includes depositing a second tribological coating pattern on the surface. 
         [0010]    In yet another aspect, the present disclosure is directed to a method of making a coating on a surface of a machine part including, but not limited to as fuel injector plungers, gears, pistons, rings, bearings, cams/followers, transmission components and hydraulic system components such as hydraulic pumps. The method includes attaching a resin mask to the surface to cover a first portion of the surface and expose a second portion of the surface. The method also includes applying a coating on the second portion and removing the resin mask from the surface after applying the coating. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagrammatic illustration of an exemplary method of making a textured coating on the surface of a component; 
           [0012]      FIG. 2  is a flow chart illustrating an exemplary application of the method of making the textured coating of  FIG. 1 ; and 
           [0013]      FIG. 3  is a flow chart illustrating another exemplary application of the method of making the textured coating of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  illustrates a method  1000  of making a textured coating  50  on a surface  20  of a machine component  15 . In this specification, the term-textured coating is used to refer to a tribological coating with an intentionally created pattern on the surface of the coating. The surface  20  may be any surface of a component  15 , such as, but not limited to as fuel injector plungers, gears, pistons, rings, bearings, cams/followers, transmission components and hydraulic system components such as hydraulic pumps. The component  15  may be any component of a machine or more complex component  10 , such as a fuel injector as shown in  FIG. 1 . The component  15  may include a new component or a used component. A new component may be a newly manufactured component, and a used component may be a component that has previously been used. The used component may include components that have any degree of wear due to the prior use. The machine component  10  may be any part of a machine that performs some type of operation associated with an industry. Such a machine could be used for mining, construction, farming, transportation or any other industry known in the art. For example, component  15  may be a bearing of a motor used in a hedge trimmer or other types of bearings, a plunger of a fuel injector used in an internal combustion engine, a component of a transmission, a component of a hydraulic system such as a hydraulic pump, a piston, a ring or liner of an engine, a cam or follower, etc. 
         [0015]    During routine operation of the machine component  10 , surface  20  of the component  15  may undergo frictional contact with another surface. In other words, the surface  20  may rub, slide and/or roll on another surface. For example, contacting surfaces of gears of a gearbox rub, slide or roll on surfaces of other gears. To improve the tribological properties of the surface, a textured coating  50  may be applied to the surface  20 . 
         [0016]    To apply the textured coating  50 , the component  15  may first be subjected to a cleaning process  100  to remove impurities from the surface  20 . These impurities may include dirt, oil and/or other residue. The cleaning process  100  may involve ultrasonic cleaning using a cleaning solution. The component may be immersed in a cleaning solution and agitated using ultrasonic waves. The ultrasonic waves may cause bubbles to form and collapse (ultrasonic cavitation) in the cleaning solution loosening and removing (dislodging) impurities from the surface  20  of the component  15 . The cleaning solution may be water (deionized or regular water), or a solvent (organic or chemical). The component  15  may be cleaned by the ultrasonic process until the surface  20  is sufficiently clean. In some cases, one or more inspection steps may be instituted during the cleaning operation  100 . These inspection steps may involve visual, physical or chemical analyses to determine the presence of impurities on the surface  20 . It is contemplated that, in some embodiments, other methods of cleaning the surface  20  may be used in the cleaning process  100 . 
         [0017]    After impurities are removed from the surface  20  of the component  15 , the component  15  may be subjected to a mask application process  200 . In the mask application process  200 , a mask  25  may be applied to the surface  20  of the component  15 . The mask  25  may be applied to create any pattern on the surface  20 . This pattern may expose some portions of the surface  20  (exposed region), while covering other portions of the surface  20  below the mask (shadow region). For instance, the mask  25  applied to the surface  20  may form a pattern of lines on the surface  20 . These lines may be straight lines, curved lines, parallel lines, intersecting lines or lines of any type. These mask pattern on the surface  20  may have lines of any width, thickness, and pitch. Other patterns like dots or irregular shapes may also be formed by the mask  25  on the surface  20 . It is also contemplated that different regions of the surface  20  may have different patterns. In some cases, tribological models (fluid flow models or other models) may be used to determine the pattern of the mask  25  on the surface  20 . 
         [0018]    The mask  25  may be any material that will form a pattern on the surface  20  of the component  15 , survive the conditions of the subsequent coating deposition process  300 , and will be removable at the subsequent mask removal process  400 . The mask  25  may include a synthetic or an organic resin, which may be applied to the surface  20 . In some cases, the resin may include additives, such as adhesion promoters, flow enhancers, viscosity modifiers, etc. After application to the surface  20 , the mask  25  may cure or harden in air and adhere to the surface  20 . It is also contemplated that the component  15  may be exposed to a particular ambient condition, such as a high temperature environment, to speed up or enhance the hardening process. In some cases, the mask  25  may include an ink or a paint material that is applied to the surface  20  of the component  15 . The mask  25  may also include an adhesive tape, which is attached to the surface  20  in a pattern. 
         [0019]    The mask  25  may be applied to the surface  20  by any application method. In some cases, a pattern of mask  25  may be painted, brushed or drawn on to the surface  20 . The pattern may also be formed on the surface  20  by printing the mask material on to the surface  20  through a stencil or a screen (similar to screen-printing). The stencil may be a part with apertures arranged in a pattern corresponding to a desired mask pattern on the surface  20 . The stencil may be placed atop the surface  20 , and a quantity of mask material may be placed on top of the stencil. A squeegee may then spread the mask material evenly across the top of the stencil making an image of the apertures on the surface  20 . In applications where the surface  20  of the component  15  is curved, the component  15  may also be turned or rotated while the mask material is moved by the squeegee across the stencil. The thickness of the stencil and/or the speed of the squeegee across the stencil may control the thickness of the mask  25  applied to the surface  20 . It is also contemplated that other automated, semi-automated or manual processes may be used to apply the mask  25  on the surface  20  of the component  15 . For instance, if the mask  25  is an adhesive tape, it may be stuck to the surface  20  of the component. 
         [0020]    After the mask  25  is applied to the surface  20  in the desired pattern, a coating  30  may be deposited on the component  15  in a coating deposition process  300 . The coating  30  may be deposited on the surface  20  using any technique known in the art. For instance, the coating  30  may be deposited on the surface  20  using a vapor deposition technique, such as chemical vapor deposition or physical vapor deposition. The deposited coating  30  may conform to the shape of the surface  20  with the applied mask  25 . The coating deposition process  300  may deposit the coating material on the exposed region of the surface  20  and on the exposed surfaces of mask  25 . 
         [0021]    Although the coating  30  may be applied for any purpose, in some applications, the coating  30  may improve the tribological properties of the surface  20 . The coating  30  may be made of a wear resistant material and/or solid lubricant materials. The coating material may include, among others, doped/undoped amorphous carbon (DLC), amorphous hydrocarbons, metal carbides, metal nitrides, metal dichalcogenides, metal borides or ceramic materials. The coating  30  may also include particles of one material embedded in another material. For instance, the coating  30  may include tungsten carbide particles embedded in a DLC matrix. The tungsten carbide particles may provide the wear resistant properties, while the amorphous carbon matrix may provide lubrication and impact absorbing properties. The coating  30  may also include multi-layer coatings. For instance, the coating  30  may be made of a layer of chromium followed by a layer of tungsten carbide containing DLC. While the tungsten carbide containing DLC layer may improves the tribological properties of the surface  20 , the chromium layer may serve as an adhesion layer to improve the adhesion of the tungsten carbide containing DLC layer to the surface  20 . It is contemplated that the coating  30  may include any single or multi-layer coating used in the art to improve the tribological properties of a surface. 
         [0022]    Following deposition of the coating  30  on the surface  20  of the component  15 , the mask  25  may be removed in the mask removal process  400 . The mask removal process  400  may involve washing/cleaning the component  15  using a solvent. In some applications, the component  15  may be immersed in a solvent and agitated using an ultrasonic cleaner. The resulting ultrasonic cavitation may dislodge the mask  25  from the surface  20 . Along with the dislodged mask  25 , the portion of the coating  30  deposited on the mask  25  may also be removed. The solvent used in the mask removal process  400  may be any solution that facilitates removal of the mask  25  from the surface  20 . In some cases, ethanol and/or water may be used as the solvent. In some applications, the mask removal process may also include a cleaning/rinsing process (step  500 ,  FIG. 2 ). The cleaning/rinsing process (step  500 ) may involve rinsing the component in water (deionized or regular) to remove any traces of the mask, solvent and other materials. In some applications, a separate cleaning step may be omitted if the component exiting the mask removal process  400  is sufficiently clean. Following the mask removal process  400 , the component  15  may have a layer of textured coating  50  on its surface  20 . The pattern of the textured coating  50  on the surface  20  corresponds to the exposed region (region of the surface not covered by the mask) of the surface  20 . That is, the pattern of the textured coating  50  may be a negative image of the pattern of the mask  25 . 
       INDUSTRIAL APPLICABILITY 
       [0023]    The disclosed method  1000  of making a textured coating  50  on a surface  20  of a component  15  may be applied to any surface  20  that undergoes frictional contact with another surface, including, but not limited to as fuel injector plungers, gears, pistons, rings, bearings, cams/followers, transmission components and hydraulic system components such as hydraulic pumps. Though the surface  20  may typically be made of metal, it may also be made of other materials. The method provides an inexpensive way of improving the tribological properties of the contacting surfaces without detrimentally affecting the components. The method also provides a way of re-applying the textured coating  50  on the surface  20  when the coating  30  wears off, thus prolonging the life of the component  15 . The textured coating  50  improves the tribological properties of the surface  20  both by providing a wear resistant layer and by providing lubricant and/or debris reservoirs on the wear resistant layer. 
         [0024]    To illustrate applications of the disclosed method, two embodiments are described. The first embodiment describes a method to create a textured DLC coating on the curved surface (surface  20 ) of a plunger (component  15 ) of a fuel injector (machine component  10 ) of  FIG. 1 . The second embodiment describes a method of re-applying a textured DLC coating on the surface  20  of the plunger, when the initial coating wears off. 
         [0025]      FIG. 2  illustrates the steps involved in the method  1000  of making a textured coating  50  on the surface  20  of the plunger. The plunger is initially cleaned (step  100 ) using deionized water in an ultrasonic cleaner. After cleaning, surface  20  of the plunger may be visually inspected for impurities. In some applications, the surface  20  may be cleaned for about half an hour to remove most impurities from the surface  20 . 
         [0026]    When the surface  20  appears free of impurities, a mask  25  may be applied (step  200 ) to the cleaned surface  20 . In some applications, ink from a Sharpie® marker pen may be used as the mask  25 . A mask pattern may be sketched on the surface  20 . In some applications, the pattern used may be a series of ink dots on the surface  20 . However, any mask material and any pattern can be applied to the surface  20 . 
         [0027]    After the mask pattern is applied (step  300 ) to the surface  20 , a coating  30  may be applied to the cleaned and masked surface  20 . Although any deposition process may be used to coat the surface  20 , in most applications, a physical vapor deposition (PVD) technique may be used to keep the process temperatures below 500°, such as below 300° or even about 200° or less. The plunger may be placed in the chamber of a closed field unbalanced magnetron-sputtering system containing tungsten carbide and chromium targets. The chamber may be pumped down to a pressure between roughly 10 −6  mbar and roughly 10 −4  and a precursor of argon gas, at a flow rate of about 200-400 SCCM, may be pumped into the chamber. A negative bias of a few hundred volts may be applied to the surface  20  of the plunger for about 20 minutes. The negative bias may cause argon ions to bombard the surface  20  of the plunger and the clean the surface  20  of contamination such as oxides. After about 20 minutes of cleaning, the negative bias on the surface  20  may be removed and the argon gas evacuated from the chamber. Acetylene gas, at a flow rate of 100-200 SCCM, may be introduced into the chamber and a negative bias applied to the chromium target. The negative bias on the chromium target may cause ion bombardment of the target releasing chromium atoms (sputtered), which may deposit on the surface  20 . The bias may be switched from the chromium to the tungsten carbide target after about 5 minutes. The tungsten carbide may then be sputtered for roughly 3-4 hours. The acetylene gas may contribute carbon to the coating  30  along with the sputtered tungsten carbide atoms. The resulting coating  30  on the surface  20  may consist of a roughly 100 nanometer layer of chromium followed by a roughly 1 micron layer of tungsten carbide atoms (1-10 atomic percent) embedded in an amorphous carbon matrix (DLC). The tungsten carbide atoms may provide hardness and wear resistant properties to the coating  30  while the DLC matrix may provide lubrication properties. Other deposition conditions may be used to control the thicknesses and/or properties of the resulting coating  30 . It is also contemplated that other coating materials may be deposited on the surface  20 . 
         [0028]    After the coating  30  is deposited on the surface  20 , the mask  25  (ink) may be removed (step  400 ). To remove the ink, the plunger may be immersed in a beaker of ethanol and cleaned using an ultrasonic cleaner. The surface  20  may be visually inspected during cleaning. In some applications, after less than an hour of cleaning, the mask  25  and the coating  30  deposited on the mask  25  may be removed. The plunger may then be rinsed in deionized water (step  500 ), and dried. The resulting plunger with a textured coating  50  on its surface may be installed (step  600 ) in a fuel injector. 
         [0029]    After a period of use of the fuel injection system, the effectiveness of the textured coating decreases due to inevitable wear of the coating  30 . Wear of the coating  30  may decrease the thickness of the coating, and thereby the depth of the reservoirs formed on the surface. In extreme cases, the coating  30  may also be substantially worn off the surface  20 . 
         [0030]      FIG. 3  describes the steps involved in re-applying a textured coating on a surface  20  when the effectiveness of the coating  30  decreases. The coating  30  may be inspected for wear (step  70 ). The inspection may be performed in-situ, or may involve removing the component  15  from the machine part. Inspection of the coating  30  may involve visually inspecting the surface  20  to detect signs of wear, or measurement of some parameter using measurement tools. For example, the depth or surface texture of the coating  30  may be checked using a surface profilometer. 
         [0031]    When inspection indicates that the coating  30  is worn out (step  80 ), the textured coating  50  may be reapplied. The inspection to detect wear of the coating  30  may be direct visual inspection or may be based on sensors or other means. Determination of when the coating  30  is to be reapplied may be based on experience or mathematical models. In some applications, the coating  30  may be reapplied periodically. If the inspection indicates that the coating  30  is to be reapplied, the component  15  may be removed from the machine component  10  (step  90 ). In applications where the inspection step (step  70 ) involves removal of the component  15  from the machine component  10 , this step is eliminated. After removal, the component  10  may then be cleaned (step  100 ), masked (step  200 ), coated (step  300 ), unmasked (step  400 ), and rinsed (step  500 ) as described earlier. After the textured coating  50  is re-applied on the surface, the component  15  may be re-installed (step  650 ) in the machine component  10 . The same or a different textured coating  50  may be applied to the surface  20  during re-application. The re-application of the textured coating  50  may also be repeated numerous times. 
         [0032]    The disclosed method  1000  of making a textured coating  50  on a surface  20  of a component  15  does not expose the component  15  to conditions that may adversely affect the component  15 . Since material removal processes such as machining or laser texturing is not involved in creating the textured surface of the disclosed method, the component surface will not be exposed to localized high temperatures that may damage the component  15 . 
         [0033]    The disclosed method  1000  of making a textured coating  50  creates the texture on the surface during the coating process  300 . An additional process step (such as machining) is not required to create the textured pattern. The elimination of a process step to create the texture simplifies the method and enables the creation of complex patterns of texture on the surface. Use of a relatively simple and inexpensive mask to selectively prevent deposition of the coating on some regions (and thereby create the texture pattern), eliminates the need for expensive equipment (laser based or other machining equipment) to create the pattern. 
         [0034]    The disclosed method  1000  of making a textured coating  50  also increases the durability of the component  15  by providing a way to reapply the textured coating  50  when an existing coating  30  deteriorates. Unlike texture patterns created by machining, the re-application of the textured coating  50  can be repeatedly performed. Therefore, the durability of the component  15  will not be limited by durability of the textured coating  50 . 
         [0035]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed method. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the method of making a textured coating. 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. 
       LIST OF ELEMENTS 
       [0036]      10  component 
         [0037]      15  component 
         [0038]      20  surface 
         [0039]      25  mask 
         [0040]      30  coating 
         [0041]      50  textured coating 
         [0042]      70  step 
         [0043]      80  step 
         [0044]      90  step 
         [0045]      100  cleaning operation step 
         [0046]      200  mask application step 
         [0047]      300  coating step 
         [0048]      400  mask removal step 
         [0049]      500  cleaning/rinse step 
         [0050]      600  installation step 
         [0051]      650  reinstallation step 
         [0052]      1000  overall method