Sliding member with a sintered copper alloy layer
BACKGROUND OF THE INVENTION 
     The present invention relates to a composite sliding member to be preferably used as bushes and washers in automobiles, industrial machines, agricultural machines, and the like. More specifically, the present invention relates to a composite sliding member exhibiting greater wear resistance in the boundary lubrication condition of a severe lubricating condition. 
     Sintered copper alloys such as bronze, lead bronze and graphite-containing bronze have been used principally in the bushes, washers and the like described above. These alloys exhibit good sliding performance under the condition of use when a lubrication oil is present. However, such alloys are poor particularly in wear resistance in a boundary lubrication region, so sliding performance has not satisfactorily been obtained. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved on such technical background. A primary object of the present invention is to provide a sliding member having a sintered copper alloy layer with improved wear resistance under the boundary lubrication condition. 
     According to the invention, a hard Ni-B compound is added in the sintered copper alloy. The sliding members of the invention are provided in the following forms: 
     a. A sliding member comprising a backing steel and a sintered copper alloy layer mounted integrally on one surface of the backing metal, wherein the sintered copper alloy comprises, by weight, 1 to 15% Sn, 1 to 20% Ni-B compound, 1% or less P, and the balance of Cu and impurities. 
     b. A sliding member comprising a backing steel and a sintered copper alloy layer mounted integrally on one surface of the backing metal, wherein the sintered copper alloy is composed of, by weight, 1 to 15% Sn, 1 to 20% Ni-B compound, 1 to 30% Pb, 1% or less P, and the balance of Cu and impurities. 
     c. A sliding member comprising a backing steel and a sintered copper alloy layer mounted integrally on one surface of the backing metal, wherein the sintered copper alloy is composed of, by weight, 1 to 15% Sn, 1 to 20% Ni-B compound, 0.5 to 8% graphite, 1% or less P, and the balance of Cu and impurities. 
     d. A sliding member comprising a backing steel and a sintered copper alloy layer mounted integrally on one surface of the backing metal, wherein the sintered copper alloy is composed of, by weight, 1 to 15% Sn, 1 to 20% Ni-B compound, 1 to 30% Pb, 0.5 to 8% graphite, 1% or less P, and the balance of Cu and impurities. 
     It is preferable to use a Ni-B compound of which chemical composition is 7 to 15 wt. % B and the balance of Ni and impurities, while as the backing steel plate, those with no surface treatment or the steel plate with a copper plating or with copper alloy plating can be used. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     There will now be explained the reason to limit the content of each alloying element in the sintered copper alloys. 
     Sn (1 to 15%): Tin dissolves in copper as to produce a solid solution and strengthen the matrix. At tin content less than 1%, the alloy is insufficient in strength and poor in wear resistance. At tin content above 15%, the alloy becomes brittle. 
     Graphite (0.5 to 8%): Graphite exhibits a lubrication function as a component having a self lubrication property in the metal to metal contact condition in which no lubricant film is formed. At graphite content less than 0.5%, the lubrication function is insufficient, while at the content above 8%, the alloy strength is deteriorated extremely. 
     Ni-B compound (1 to 20%): It is preferably used a Ni-B compound consisting of 7 to 15% B and the balance of nickel and impurities. The hardness is above HV 1000 or more. The Ni-B compound disperses in the copper alloy and improves the wear resistance. At boron content of less than 7% in the compound, elemental nickel co-exists besides the Ni-B compound, which is unsuitable as a wear resistant material. At boron content above 15%, elemental boron co-exists besides the Ni-B compound, which deteriorates the sintering property of the copper alloy. At the content of Ni-B compound less than 1%, less effect is obtained on the improvement of wear resistance. At the content above 20%, the alloy becomes brittle and also incurs abrasive wear in a mating sliding member. 
     P (1% or less); Phosphorus in a level of 1% or less is added in the alloy in order to improve the wear resistance and the sintering properties. At phosphorus content above 1%, the toughness is deteriorated among mechanical properties. 
     Pb (1 to 30%); Lead exhibits a good lubrication function as a soft component. In case that a lubricant oil is present, lead also exhibits a lubrication function as a component of having a good affinity to oil. At lead content less than 1%, the lubrication function is insufficient. At the content above 30%, the alloy strength is deteriorated and thus the alloy is unsuitable as a sliding member. 
     EXAMPLE 
     Each of the alloy powders as samples 1 to 12 shown in Table 1 was laid on a steel plate with a copper plating layer previously plated on the surface thereof, and then was heated at a temperature of 700° to 900° C. in a furnace under a hydrogen atmosphere for 10 to 30 minutes in order to sinter the powder on the steel plate. A rolling and a resintering treatments were effected one after another on the composite member obtained by the first sintering treatment. The rolling is effected in order to press a sintered copper alloy layer to a high density so that a composite member with a predetermined thickness is obtained. The term &#34;resintering treatment&#34; means a treatment to make a previously sintered copper alloy layer strengthen by heating in a furnace under hydrogen atmosphere at a temperature of 700° to 900° C. for 10 to 30 minutes. Each of the composite sliding members thus obtained had a size of a total thickness of 2.2 mm, 0.6 mm thickness of a sintered copper alloy layer and a width of 100 mm. 
     Samples 1 to 8 are the composite sliding members of the invention. Samples 9 to 12 are conventional composite sliding members. Table 1 shows chemical compositions of powders used as raw materials. 
     Mechanical properties (hardness, tensile strength and bonding strength of a backing steel between a sintered alloy layer) and a wear performance of each of the sliding members were examined. The results are shown in Tables 2 and 3. Table 4 shows the condition of wear test. 
     
                                           TABLE 1
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       Samples       Chemical composition (wt. %)
Types  No.  Powder used
                     Cu Sn Pb
                             Ni--B
                                 Graphite
                                      P
__________________________________________________________________________
Invention
       1    Lead-bronze and
                     Bal.
                        3.3
                           22
                             5.5 --   0.02
alloy  2    Ni--B compound
                     Bal.
                        3.0
                           20
                             15  --   0.02
       3    (11% B and the
                     Bal.
                        3.5
                           23
                             1.5 --   0.02
            bal. Ni)
       4    Lead-bronze,
                     Bal.
                        3.3
                           22
                             5.5 1    0.02
       5    Ni--B compound
                     Bal.
                        10 10
                             1.5 8    0.02
       6    and graphite
                     Bal.
                        10  5
                             15  4    0.02
            (11% B and the
            bal. Ni)
       7    Bronze, Ni--B
                     Bal.
                        10 --
                              3  4    0.2
       8    compound and
                     Bal.
                        10 --
                             13  4    0.2
            graphite
Conventional
       9    Lead-bronze
                     Bal.
                        10 10
                             --  --   0.05
alloy  10            Bal.
                        3.5
                           23
                             --  --   0.02
       11   Bronze and
                     Bal.
                        10 --
                             --  4    0.2
       12   graphite Bal.
                        10 --
                             --  8    --
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                       TABLE 2
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           Mechanical Strength
                                    Bonding
                                    Strength
                                    between
                                    Backing
         Sam-    Hardness of
                            Tensile Steel and
         ples    Alloy Layer
                            Strength
                                    Alloy Layer
Types    No.     (Hv)       (kg/mm.sup.2)
                                    (kg/mm.sup.2)
______________________________________
Invention
         1       58         16      13
alloy    2       65         17      14
         3       51         15      12
         4       53         13      10
         5       40          8       6
         6       63         16      13
         7       76         13      10
         8       80         20      17
Conventional
         9       73         24      18
alloy    10      48         14      11
         11      57         11       9
         12      35          5       3
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                                           TABLE 3
__________________________________________________________________________
           Wear Amount (mm)
 Types  Sample No.
            ##STR1##
__________________________________________________________________________
Invention Alloy
        1
            ##STR2##
        2
            ##STR3##
        3
            ##STR4##
        4
            ##STR5##
        5
            ##STR6##
        6
            ##STR7##
        7
            ##STR8##
        8
            ##STR9##
Conventional Alloy
        9
            ##STR10##
       10
            ##STR11##
       11
            ##STR12##
       12
            ##STR13##
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                       TABLE 4
______________________________________
Test Condition             Unit
______________________________________
1.  Loading at A Bush End
                        250        kgf
2.  Rotation Speed of Shaft at
                        0.26       m/sec
    Surface
3.  Rotation Number of Shaft
                        250        rpm
4.  Driving of Shaft    Intermittent Repetition of
                        Rotation and Stop:
                        Each 30    sec
5.  Lubricant Oil       Kerosene   --
6.  Oil Supply          20 to 30   ml/min.
7.  Oil Temperature at A Discharge
                        55 to 65°
                                   C.
    Port
8.  Inner Diameter of Bush × Width
                        20 × 15.5
                                   mm
9.  Shaft Material      JIS S55C   --
                        (hardened by
                        quenching)
    Roughness           R.sub.max  1.0
                                   μm
    Hardness            650        Hv
10. Diameter Clearance  0.028 to 0.040
                                   mm
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     EVALUATION OF THE TEST RESULTS 
     Comparing the results of the wear test shown in Table 3 concerning the conventional alloy No. 10 and the invention alloy No. 1, the both having similar compositions, it is understood that the wear loss of the latter (No. 1), containing 5.5 wt. % of the Ni-B compound, is about 1/30 against that of the former (No. 10). 
     Comparing also the conventional alloy No. 11 and the invention alloy No. 7, it is understood that the wear loss of the latter (No. 7) containing 3 wt. % of the Ni-B compound is about 1/7 against that of the former (No. 11). This indicates that the addition of the Ni-B compound remarkably improves wear resistance. 
     As will be apparent from the above, the sliding members of the present invention each comprising a sintered copper alloy layer have a good wear resistance property due to containing the Ni-B compound in the copper alloy layer, comparing with those of conventional bronze, lead bronze, graphite-containing bronze and the like.