Abstract:
A method of forming a valve seat of an engine head formed from a first composition includes forming a groove at a predetermined valve seat location of a bore defined by the engine head. A source of directed heat energy preheats at least the valve seat location to about a temperature of the melting point of the first composition with the source of directed heat energy. The source of directed heat energy is infused with a material having a second composition generating a melt pool upon the groove by direct metal deposition with the melt pool including the second composition. The second composition includes a heat conductivity generally equal to a heat conductivity of the first composition for providing efficient transfer of heat energy from the first composition to the second composition.

Description:
PRIOR APPLICATIONS 
       [0001]    The present application claims priority to U.S. provisional patent application Ser. No. 61/915,810, filed Dec. 13, 2013, the entire content of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally toward an application of a durable metallic material onto desired locations of a soft metallic substrate. More specifically, the present application is directed toward direct metal deposition of a first composition having desirable physical properties onto a second composition having different physical properties. 
       BACKGROUND 
       [0003]    Lightweight materials are being used to reduce mass of automotive vehicle on an ever-increasing basis. While lightweight materials are desirable to reduce mass, these materials do not often offer necessary durability to withstand the rigors known to automotive vehicles. For example, aluminum is being used to cast engine heads to provide a lightweight power train to an automotive vehicle. However, a valve seat of a bore formed in an aluminum engine head required for properly sealing a valve of an internal combustion engine does not provide necessary durability. Repeated thermal and load cycles on these valve seats demand a durable material capable of withstanding temperatures between 375° C. to 700° C. while providing sufficient oxidation and wear resistance. Most commercial engine valves use powder metallurgy fabricated steel inserts that are held in place within a valve pocket by way of interference fit. However, while adequate wear resistance has been achieved, other properties such as, for example sufficient, heat conductivity necessary to dissipate heat energy has not been achieved. 
         [0004]    Other attempts to improve the performance of a valve seat have included the use of different metallic alloys applied by using lasers, welding, or a thermal spray processes. Many of these efforts have relied on using a high energy laser beam with injected powder metal to form the valve seat on the engine block after which the deposited alloy is machined into a desired configuration. However, these efforts have also proven deficient. Poor process control that does not account for temperature differentials between the engine block and a melt pool formed by the deposited alloy during both application and subsequent cooling have resulted in deficient performance. Often, this has resulted in excessive liquidation of a substrate causing cracking, porosity, and poor quality of the deposited alloy. Additionally, known alloys used to form the valve seat have not provided desirable heat conductivity properties required of high performance internal combustion engines. Therefore, it would be desirable to provide an improved method of forming a valve seat along with an improved alloy composition providing desirable mechanical properties. 
       SUMMARY 
       [0005]    A method of forming a valve seat of an engine head that is formed from a first composition includes forming a groove at a predetermined valve seat location on a wall of a bore defined by the engine head. A source of directed heat energy preheats at least the valve seat location to about a temperature of the melting point of the first composition using the source of directed heat energy. A source of the directed heat energy is infused with material having a second composition generating a melt pool upon the groove by way of direct metal deposition. The melt pool includes the second composition. The second composition includes a heat conductivity generally equal to or higher than the heat conductivity of the first composition for providing efficient transfer of heat energy from the second composition to the first composition while the engine head is in service. 
         [0006]    Two aspects of the present invention overcome problems associated with the prior art of depositing a molten valve seat onto an engine head. For example, preheating the valve seat location to about the temperature of the melting point of the alloy comprising the engine head reduces the temperature differential during application and subsequent cooling of the molten valve seat that is known to cause defects. Additionally, the composition of the valve seat provides unique enhanced durability properties while facilitating the transfer of heat from the valve seat to the engine block while the engine block is in service. Improved heat conductivity of the inventive composition of the present application provides the benefit of cooling the valve seat in an efficient manner making optimal use of the cooling features included in the engine head. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
           [0008]      FIG. 1  shows a perspective view of an engine head; 
           [0009]      FIGS. 2A-2C  show cross-sectional views of a valve seat groove formed in the engine head; 
           [0010]      FIG. 3  shows a schematic view source of heat energy directed at a the valve seat groove; 
           [0011]      FIG. 4  shows a cross-sectional view of a deposited valve seat; 
           [0012]      FIGS. 5A and 5B  show alternative methods of depositing the valve seat; and 
           [0013]      FIG. 6  shows a cross-sectional view of machined valve seat. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 1 , an engine head for an internal combustion engine is generally shown at  10 . The engine head  10  is formed of an aluminum alloy in a known manner providing a lightweight solution for reducing mass of an internal combustion engine associated with powertrain of an automotive or other vehicle. It should be understood by those of ordinary skill in the art that the description of a valve seat of an internal combustion engine is merely exemplary and the present invention may be used on other components requiring efficient heat transfer and wear resistance. The engine head  10  includes a plurality of bores  12  that receive a valve seat  14  against which an intake or exhaust valve (not shown) rests during the portion of the engine operating cycle when the valve is closed. Therefore, the valve seat  14  is subject to intense heat from internal combustion and wear from opening and closing the valve. 
         [0015]    The engine head  10  includes a cooling line  16  through which engine coolant flows to prevent the engine head  10  from overheating. Therefore, it is desirable that the valve seat  14  provide sufficient heat transfer to the engine head  10  so that the coolant flowing through the coolant lines  16  provides sufficient heat dissipation to the valve seat  14 . It has been determined that it is desirable to have the heat conductivity value of the valve seat  14  to be generally equivalent to that of the engine head  10 . 
         [0016]    Referring now to  FIG. 2A-C , a bore wall  18  is shown with alternative valve seat grooves  20 ,  22 ,  23 . As best represented in  FIG. 2A , the first valve seat groove  20  is shown having a generally constant radius R. The generally constant radius R ranges from about 3 millimeters to 10 millimeters, the value of which is dependent upon the desired application. As best represented in  FIG. 2B , the second, or alternative, valve seat groove  22  is represented as a chamfered wall  24  having a normal wall  26  that is substantially perpendicular to the bore wall  18 . The angle of the chamfered wall  24  to the normal wall  26  ranges between 30° and 70°, which is dependent up on the physical needs of a particular application. The third, or additional alternative embodiment, valve seat groove  23  is best represented in  FIG. 2C  as an alternative chamfer wall  28  that intersects directly with the bore wall  18 . 
         [0017]    Referring now to  FIG. 3 , a source of directed heat energy such as, for example, a laser, a welding arch, or a plasma jet is directed through a nozzle  30 . The heat source covers substantially all of the valve seat groove  20 , either in a single pass or multiple number of passes to heat the valve seat groove to about the temperature of the melting point of a first composition used to form the engine head  10 . Therefore, in the event a laser is used, a focal point  32  of a laser beam  34  is contemplated to be spaced from the surface  36  of the valve seat groove  20  spaced a sufficient distance to known provide necessary heat energy. Should the engine head  10  be formed from an aluminum alloy, it is contemplated that the surface  36  of the valve seat groove  20  is heated to between about 250° C. and 450° C. in a preheating step to reduce the heat differential between the substrate of engine head and the formation of the melt pool. It is further contemplated that the surface of the valve seat groove  20  is melted by the source of directed heat energy raising the temperature of the surface of the valve seat to between 550° C. and 660° C., the purpose of which will be explained further below. 
         [0018]    A second composition forming the valve seat alloy is injected into the nozzle  30  in the form of a powder, or wire. A melt pool  38  is generated at the location of the valve seat  14 , as best represented in  FIG. 4 , from the second composition in the manner similar to that disclosed in U.S. Pat. No. 6,122,564, the content of which is included herein by reference. A dilution zone  40  is formed by melting the valve seat groove  20 . The dilution zone  40  forms a transitional alloy between the composition of which forms the melt pool  38  and the alloy composition of the engine head  10 . Therefore, transfer of heat from the valve seat  14  to the engine head  10  is efficient, unlike that of a mechanically-inserted valve seat, which generally includes a gap between the valve seat and an engine head  10 . 
         [0019]    As is known to those of skill in the art, the valve seat  14  circumscribes each of the plurality of bores  12  defined by the engine head  10 . The nozzle  30  relatively circumferentially traverses each bore  12  to apply the second composition defining the valve seat  14 . This is best represented in  FIGS. 5A and 5B . In one embodiment best represented in  FIG. 5A , the engine head  10  is stationary and the nozzle  30  and laser beam  34  circumscribes the bore  12  to apply the second composition defining the valve seat  14 . In an alternative embodiment shown in  FIG. 5B , the nozzle  30  and laser beam  34  are stationary and the engine head  10  pivots around a bore axis aligning the laser beam  34  with the valve seat groove  20  to apply the second composition defining the valve seat  14 . 
         [0020]    Referring now to  FIG. 6 , a complete application of the second composition is represented as a bead  42  having a geometric configuration proximate the desired geometric configuration of the valve seat  14  as represented by the perforated line of  FIG. 6 . A precise geometric configuration required of the valve seat  14  is obtained by machining the bead  42  to the desired geometric configuration shown  FIG. 6 . 
         [0021]    As set forth above, it is desirable to provide a deposited valve seat  14  having substantially similar heat conductivity to that of the aluminum engine head  10 . However, it is still required that the second composition comprising the valve seat provides sufficient hardness and durability to withstand the rigors of an internal combustion engine. As such, a first chemical composition is included below: 
         [0022]    A first embodiment of the second chemical composition includes the following percent by weight elemental ranges: 
         [0023]    copper in the amount of 40-50 percent by weight; 
         [0024]    cobalt in the amount of 15-25 percent by weight; 
         [0025]    carbon in the amount of less than 0.1 percent by weight; 
         [0026]    chromium in the amount of 7-10 percent by weight; 
         [0027]    molybdenum in the amount of 8-12 percent by weight; 
         [0028]    nickel in the amount of 10-15 percent by weight; 
         [0029]    silicon in the amount of 2-5 percent by weight; 
         [0030]    iron in the amount of less than 1.5 percent by weight; 
         [0031]    hafnium in the amount of less than 1.5 percent by weight; 
         [0032]    niobium in the amount of 0.5-2 percent by weight; 
         [0033]    manganese in the amount of less than 2 percent by weight 
         [0034]    In one experimental composition A, a target weight percent of the elements forming the first embodiment of the second composition include: 
         [0035]    copper in the amount of 42.10 percent by weight; 
         [0036]    cobalt in the amount of 19.80 percent by weight; 
         [0037]    carbon in the amount of 0.10 percent by weight; 
         [0038]    chromium in the amount of 8.60 percent by weight; 
         [0039]    molybdenum in the amount of 10.00 percent by weight; 
         [0040]    nickel in the amount of 12.80 percent by weight; 
         [0041]    silicon in the amount of 2.90 percent by weight; 
         [0042]    iron in the amount of 0.70 percent by weight; 
         [0043]    hafnium in the amount of 0.90 percent by weight; 
         [0044]    niobium in the amount of 1.10 percent by weight; 
         [0045]    manganese in the amount of 1.10 percent by weight 
         [0046]    The copper based alloy of composition A provides the high thermal conductivity of copper leading to a lower temperature for the valve seat and enabling a higher efficiency of the engine. Several laves phase formers such as molybdenum, niobium and iron are added for creation of hard phases for wear resistance. Presence of Carbon allows formation of carbides in combination with chromium, molybdenum and/or niobium to provide further hardness. Nickel provides solid solution strengthening and cobalt provides hot hardness property. Hafnium is included to scavenge oxygen. 
         [0047]    A second embodiment of the second chemical composition includes the following percent by weight elemental ranges: 
         [0048]    aluminum in the amount of 50-66 percent by weight; 
         [0049]    copper in the amount of 20-30 percent by weight; 
         [0050]    silicon in the amount of 5-12 percent by weight; 
         [0051]    iron in the amount of 5-12 percent by weight; 
         [0052]    manganese in the amount of less than 1.5 percent by weight; 
         [0053]    zirconium in the amount of less than 2.0 percent by weight; 
         [0054]    magnesium in the amount of less than 2.0 percent by weight; 
         [0055]    germanium in the amount of less than 2.0 percent by weight 
         [0056]    In an experimental composition B, a target weight percent of the elements forming the first embodiment of the second composition include: 
         [0057]    aluminum in the amount of 66.00 percent by weight; 
         [0058]    copper in the amount of 8.00 percent by weight; 
         [0059]    silicon in the amount of 9.00 percent by weight; 
         [0060]    iron in the amount of 15.00 percent by weight; 
         [0061]    manganese in the amount of 0.50 percent by weight; 
         [0062]    zirconium in the amount of 0.50 percent by weight; 
         [0063]    magnesium in the amount of 0.50 percent by weight; 
         [0064]    germanium in the amount of 0.50 percent by weight 
         [0065]    The high thermal conductivity of aluminum leads to a lower temperature for the valve seat and allows higher efficiency of the engine. Presence of alloying elements such as silicon, copper and iron forms hard intermetallic phases providing the superior wear resistance for the valve seat. Manganese, zirconium, Magnesium and germanium may or may not be present for as additional strengtheners. 
         [0066]    As set forth above, it was discovered that establishing a thermal conductivity for the valve seat  14  to be generally equal to or greater than the engine head  10  alloy composition efficient heat transfer making use of the cooling apparatus  16  of the engine head  10  could be achieved. The table below sets forth the relevant Thermal conductivity and specific heat capacity of the experimental compositions A and B. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Stainless 
                 Aluminum 
                   
               
               
                   
                   
                 Steel 
                 Base 
                 Copper Base 
               
               
                 Properties 
                 Unit 
                 insert 
                 Alloy B 
                 Alloy A 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Density 
                 g/cc 
                 7.74 
                 3.99 
                 8.736 
               
               
                 Thermal Conductivity 
                 w/m-K 
                 24.90 
                 215.20 
                 227.912 
               
               
                 Sp. Heat Capacity 
                 J/g-K 
                 0.46 
                 0.76 
                 0.399 
               
               
                   
               
             
          
         
       
     
         [0067]    The unique chemical composition and processing characteristics of the present application provide additional benefits to that of improved heat transfer and thermal conductivity. The valve seat  14  is thinner than prior art valve seats. For example, the valve seat includes a depth D of between about 0.5 mm and 4 mm while prior art valves seat are more up to 8 mm. Additionally, the ration of length L to depth D is unique ranging from about one to ten. 
         [0068]    The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the specification, the reference numerals are merely for convenience, and are not to be in any way limiting, the invention may be practiced otherwise than is specifically described.