Patent Publication Number: US-2016230274-A1

Title: Multilayer coating for a component

Description:
TECHNICAL FIELD 
     The present disclosure relates to a multilayer coating for a component. More specifically, the present disclosure relates to the multilayer coating to protect a metallic surface of the component from wear and tear. 
     BACKGROUND 
     Internal combustion engines running on diesel fuel employ pumps, valves and/or fuel injectors for injecting fuel at high pressure in to the cylinders for combustion. The fuel injector includes a plunger/check which, in idle position, rests against a seat of the injector. During operation, when the fuel may be required to be injected in to the cylinder, the plunger/check may move away from the seat, thus, opening a passage for the fuel to enter the cylinder via the seat. When the fuel injection process may need to be stopped, the plunger/check may come back to its idle position with considerable force and may rest on the seat thus closing the passage. 
     Typically, depending on engine parameters, the plunger/check may translate with respect to the seat a couple of hundreds of times per minute. This movement of the plunger/check may create continuous impacts on the seat when the plunger/check may contact the seat. As a result, the plunger/check and/or the seat may experience accelerated wear and tear in the form of erosion, scuffing, chipping, and so on. Additionally, a pressure and a velocity of the fuel passing across the plunger/check and the seat may also be considerably high to cause wear and tear of the plunger/check and/or the seat. 
     U.S. Pat. No. 8,178,213 discloses a multilayer coating for a metallic surface. The coating includes at least two anti-wear layers each consisting of a diamond-like carbon (DLC) material and an intermediate layer arranged between first and second anti-wear layers. The first anti-wear layer is closer to the metallic surface. The intermediate layer is comprised of a material composition containing the DLC material. The intermediate layer includes a first transition region extending away from the first anti-wear layer over which a content of the DLC material decreases as a function of an increasing distance from the metallic surface. The intermediate layer also includes a second transition region towards the second anti-wear layer over which the content of the DLC material increases as a function of the increasing distance from the metallic surface. The intermediate layer has at least 5% by weight of the DLC material at every point. 
     Generally, properties of the multilayer coating may not be sufficient to resist erosion and/or crack propagation in heavy duty engine components such as the plunger/check. Hence, there is a need for an improved multilayer coating for such components. 
     SUMMARY OF THE DISCLOSURE 
     In an aspect of the present disclosure, a multilayer coating for a metallic surface of a component is provided. The multilayer coating includes a first coating having a metal nitride. The first coating at least partially overlaps the metallic surface. The multilayer coating also includes a second coating having a metal. The second coating at least partially overlaps the first coating. The multilayer coating further includes a third coating having a Diamond Like Carbon (DLC) material. The third coating at least partially overlaps the second coating. The first coating, the second coating, and the third coating differ from one another with respect to at least one of hardness, elasticity, corrosion resistance, and lubricity. The multilayer coating includes at least ten overlapping layers having successive layers of the first coating, the second coating, and the third coating in repeating sequence. 
     Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is cross sectional view of a component, according to one embodiment of the present disclosure; and 
         FIG. 2  is a cross sectional view of a multilayer coating, according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or the like parts. Referring to  FIG. 1  an exemplary component  10  is illustrated. More specifically, the component  10  is a fuel injector  12 . In other embodiments, the component  10  may be any component such as a valve, a pump, a bearing, and so on. 
     The fuel injector  12  is configured to inject fuel wider high pressure in to one or more cylinders of an engine (not shown). The fuel injector  12  includes a body  14  having an elongate and hollow configuration defining a passage  16 . The passage  16  is configured to provide a path for a flow of the fuel through the fuel injector  12 . The body  14  further includes a seat  18 . The seat  18  includes a conical configuration defining an inner surface  20 . The body  14  includes one or more apertures  22  provided on the seat  18 . The apertures  22  are configured to inject the fuel from the passage  16  into the cylinder. The body  14  and the seat  18  may be made of any metal known in the art such as steel. 
     The fuel injector  12  also includes a plunger  24  provided within the passage  16  of the body  14 . The plunger  24  includes an elongate configuration having a conical tip  26  on one end thereof. The conical tip  26  defines an outer surface  28 . During operation, the plunger  24  is configured to translate longitudinally within the passage  16 . More specifically, in an idle position, the conical tip  26  of the plunger  24  may contact and rest against the seat  18 . As a result, in the idle position, the plunger  24  may block the aperture  22  and prevent injection of the fuel therethrough. During an injection process, the plunger  24  may move away from the seat  18 , thus, opening the aperture  22  and allowing the fuel to flow past the seat  18 . The plunger  24  serves as a valving element to control the injection of the fuel through the fuel injector  12 . The plunger  24  may be made of any metal known in the art such as steel. 
     The present disclosure relates to a multilayer coating  30  provided on the outer surface  28  of the plunger  24 . Alternatively, in other embodiments, the multilayer coating  30  may be provided on the inner surface  20  of the seat  18  of the fuel injector  12  based on application requirements. In yet other embodiments, the multilayer coating  30  may be provided on both the outer surface  28  of the plunger  24  and the inner surface  20  of the seat  18  of the fuel injector  12  based on application requirements. The multilayer coating  30  will be explained in more detail with reference to  FIG. 2 . 
     Referring to  FIG. 2 , the multilayer coating  30  includes a first coating  32 . The first coating  32  may include any metal nitride known in the art such as chromium nitride. The first coating  32  is provided in a manner such that the first coating  32  at least partially overlaps a metallic surface of the plunger  24 . More specifically, the first coating  32  is provided on the outer surface  28  of the conical tip  26  of the plunger  24  that contacts the inner surface  20  of the seat  18 . In other embodiments, the first coating  32  may be provided on the complete outer surface  28  of the plunger  24  based on application requirements. The metal nitride provides corrosion resistance to the outer surface  28  of the plunger  24 . In the illustrated embodiment, the first coating  32  includes a thickness in a range of 10-200 nanometers (nm). In other embodiments, the thickness of the first coating  32  may vary based on application requirements. 
     The multilayer coating  30  includes the second coating  34  provided on the first coating  32 . In the illustrated embodiment, the second coating  34  is provided on the outer surface  28  of the conical tip  26  of the plunger  24  in a manner such that the second coating  34  at least partially overlaps the first coating  32 . In other embodiments, the second coating  34  may be provided on the complete outer surface  28  of the plunger  24  based on application requirements. The second coating  34  may be made of any metal known in the art such as chromium. 
     The second coating  34  serves as an adhesion layer between the first coating  32  and a third coating  36 , In the illustrated embodiment, the second coating  34  includes a thickness in orange of 10-200 nm. In other embodiments, the thickness of the second coating  34  may vary based on application requirements. Also, material properties of the second coating  34  are different from material properties of the first coating  32 . More specifically, the second coating  34  differs from the first coating  32  with respect to the material properties including at least one of hardness, elasticity, corrosion resistance, and lubricity and will be explained in more detail later. 
     The multilayer coating  30  also includes the third coating  36  provided on the second coating  34 . In the illustrated embodiment, the third coating  36  is provided on the outer surface  28  of the conical tip  26  of the plunger  24  in a manner such that the third coating  36  at least partially overlaps the second coating  34 . In other embodiments, the third coating  36  may be provided on the complete outer surface  28  of the plunger  24  based on application requirements. The third coating  36  may be made of any Diamond Like Carbon (DLC) material known in the art such as tungsten DLC. 
     The DLC material provides lubricity to the outer surface  28  of the plunger  24 . In the illustrated embodiment, the third coating  36  includes a thickness in a range of 10-200 nm. In other embodiments, the thickness of the third coating  36  may vary based on application requirements. Also, material properties of the third coating  36  are different from material properties of the first coating  32  and the second coating  34 . More specifically, the third coating  36  differs from the first coating  32  and the second coating  34  with respect to the material properties including at least one of hardness, elasticity, corrosion resistance, and lubricity and will be explained in more detail later. 
     The multilayer coating  30  includes multiple layers of the first coating  32 , the second coating  34 , and the third coating  36  in order to achieve desired material properties. More specifically, the multilayer coating  30  includes successive layers of the first coating  32 , the second coating  34 , and the third coating  36  in repeating sequence. 
     In some embodiments, the sequence of layering of the first coating  32 , the second coating  34 , and the third coating  36  may be varied to vary the material properties of the multilayer coating  30 . For example, in some embodiments, the first coating  32  may be followed by the third coating  36 . The third coating  36  may be again followed by the second coating  34 . The second coating  34  may then be followed by the first coating  32 , and so on In some embodiments, any of the first coating  32 , the second coating  34 , and the third coating  36  may be omitted between a couple of alternating layers before being reintroduced again. Repeating layers of the first coating  32 , the second coating  34 , and the third coating  36  may be applied in any sequence and in a manner such that a total number of layers in the multilayer coating  30  may be at least ten. 
     It should be noted that the sequence of application of the first coating  32 , the second coating  34 , and the third coating  36  disclosed herein is merely exemplary. In other embodiments, the sequence of application of the first coating  32 , the second coating  34 , and the third coating  36  may be interchanged to vary the material properties of the multilayer coating  30  based on application requirements. Also, in some embodiments, the second coating  34  of the metal disclosed herein may be optional. As such, in such situations, the multilayer coating  30  may include repeated layers of the first coating  32  and the third coating  36  with the second coating  34  omitted. 
     A thickness of each of the first coating  32 , the second coating  34 , and the third coating  36  may also be varied throughout the ten layers of the multilayer coating  30  in order to vary the material properties of the multilayer coating  30 . Further, the multilayer coating  30  may be provided on the outer surface  28  of the plunger  24  by any known deposition process known in the art such as Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), and so on. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure relates to the multilayer coating  30  for metallic surfaces. The multilayer coating  30  includes the alternating layers of the first coating  32 , the second coating  34 , and the third coating  36 . The alternating layers provide a combination of different material properties in a single coating. The thickness of each of the first coating  32 , the second coating  34 , and the third coating  36  may be varied or maintained constant throughout the multilayer coating  30  to optimize the multilayer coating  30  for material properties such as impact wear, debris wear, rolling wear, sliding wear, scuffing wear, conosion resistance, and so on. 
     The multilayer coating  30  may be used for any component which may impact another component thus resulting in cyclic loading and impact wear such as a check valve, a valve seat of an engine, the seat  18  of the fuel injector  12 , and so on. Also, the multilayer coating  30  may be used for sliding applications such as the plunger  24  of the fuel injector  12 , the pump, a bearing, and so on where protection against rolling wear, scuffing wear, sliding wear, and lubricity may be required. In some embodiments, the multilayer coating  30  may be used for applications requiring protection against a combination of impact wear, rolling wear, scuffing wear, sliding wear, and lubricity. It should be noted that the multilayer coating  30  may be used for any component having applications other than the engine such as a drivetrain without limiting the scope of the disclosure. 
     In some embodiments, the metal nitride used in the respective first coatings  32  of the multilayer coating  30  may include different metals for differing the material properties of the respective first coatings  32  of the multilayer coating  30 , In some embodiments, a concentration of the metal of the metal nitride used in the respective first coatings  32  of the multilayer coating  30  may be varied for differing the material properties of the respective first coatings  32  of the multilayer coating  30 . 
     The multilayer coating  30  provides alternating layers of the first coating  32 , the second coating  34 , and the third coating  36  to reduce generation of corrosion pathways. The multilayer coating  30  provides difference of material properties such as elasticity between the alternating layers of the first coating  32 , the second coating  34 , and the third coating  36 . This results in an impedance mismatch which in turn reduces crack propagation through dissipation of crack energy, reflection of energy, blunting of crack tip, nanoscale plastic deformation, and so on. 
     The multilayer coating  30  provides controlled wear due to controlled sacrifice of the alternating layers of the first coating  32 , the second coating  34 , and the third coating  36 . More specifically, the wear is limited to the thickness of individual layers of the alternating layers and may prevent removal of the complete multilayer coating  30 . 
     The multilayer coating  30  provides tuning of the hardness due to the alternating layers. By altering the thicknesses of each of the alternating layers, the hardness of each of the alternating layers may be tuned and increased while maintaining an elastic modulus of each of the alternating layers as constant. More specifically, a Hardness to Elastic Modulus (H/E) ratio of the multilayer coating  30  may be tuned by varying the thickness of each of the first coating  32 , the second coating  34 , and the third coating  36  of the alternating layers. A higher H/E ratio may provide better wear performance. Further, low thickness of the alternating layers of the multilayer coating  30  may increase the hardness due to pinning of dislocations at interfaces and reducing plastic deformation. An overall effect of the alternating layers of the first coating  32 , the second coating  34 , and the third coating  36  may provide accurate tuning and/or increasing of the H/E ratio which may not be achieved by mixing of different material properties. 
     The multilayer coating  30  includes the alternating layers of the first coating  32 , the second coating  34 , and the third coating  36  in order to control and limit grain size and columnar growth. More specifically, low thickness of the alternating layers of the multilayer coating  30  allows for stress relief, growth of coatings with more repeatability, less sensitivity to fabrication parameters, and allow fabrication of thicker alternating layers when needed with improved adhesion between the alternating layers. The multilayer coating  30  also provides improved lubricity and improved corrosion resistance in the same multilayer coating  30 . The first coating  32  provides corrosion resistance and the third coating  36  provides lubricity in the same multilayer coating  30 . The multilayer coating  30  thus provides improved wear properties, improved lubricity, and improved anti-corrosion properties for both impact wear and sliding/scuffing wear. 
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of the disclosure. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.