Abstract:
A Bi base material of which a Miller index (202) face has the index of orientation of not less than 30% and in which the (202) face has the index of orientation assuming a maximum value as compared with those of other faces forms a minute structure and has a surface which is not a mirror finished surface but a fine, irregular surface on which minute and uniform projections in the form of a triangular pyramid or a quadrangular pyramid congregate. Therefore, the surface easily retains oil thereon to be improved thereby in oil wettability, as a result of which an improvement in anti-seizure is achieved.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a slide member with an overlay layer provided on a slide alloy layer, and more particular, to a slide member comprising an overlay layer formed from Bi or Bi alloy. 
     In a plain bearing (slide member) used for a main shaft of a crankshaft, a large end of a connecting rod, and the like for internal combustion engines, a constitution is general, in which a Cu base or Al base bearing alloy (slide alloy) is lined on an inner peripheral surface of steel back metal and plating is used to cover a surface of the bearing alloy with an overlay layer through an intermediate layer or not. 
     As the overlay layer, Pb alloy has been mainly used heretofore and Sn alloy has been partly used. Since Pb is an environmental contamination substance, however, there is a tendency of avoiding its use, and JP-A-2001-20955 has proposed Bi or Bi alloy as its substitute material. 
     While Bi is a low melting point metal like Pb, it is harder than Pb and inferior thereto in lipophilic property, so that it is low in anti-seizure. An improvement in anti-seizure is earnestly requested in using Bi or Bi alloy for an overlay layer. 
     The invention has been thought of in view of the above situation, and has its object to provide a slide member which is excellent in anti-seizure. 
     BRIEF SUMMARY OF THE INVENTION 
     The inventors of the present application have fabricated various plain bearings with an overlay layer formed from Bi or Bi alloy and repeated characteristic tests thereon. As a result, the inventors have found a Bi base material as a Bi base material which is excellent in anti-seizure, separate from ones disclosed in JP-A-2001-20955 described above. Further, in measuring the crystal configuration of the Bi base material in terms of X-ray diffracted intensity, it has proved that one in which a Miller index (202) face has the index of orientation of not less than 30% and the X-ray diffracted intensity R (202)  of the (202) face assumes a maximum value as compared with that of other faces is especially excellent in anti-seizure. The Bi base material has a surface of a minute structure as shown in  FIG. 1 , and the minute surface is not a mirror finished surface but a fine, irregular surface on which projections in the form of a triangular pyramid or a quadrangular pyramid congregate. Such fine, irregular surface easily retains oil thereon to be improved thereby in oil wettability, as a result of which an improvement in anti-seizure is thought to be achieved. 
     In view of the above, the invention provides a slide member comprising a back metal layer, a slide alloy layer provided on the back metal layer, and an overlay layer provided on the slide alloy layer, and wherein the overlay layer is formed from Bi or Bi alloy, and in a crystal configuration thereof, a Miller index (202) face has the index of orientation of not less than 30% and the X-ray diffracted intensity R (202)  of the (202) face assumes a maximum value as compared with those of other faces. 
     Here, an explanation is given to the index of orientation. First, since Bi is composed of trigonal crystal, its Miller index is represented in three figures (h, k, l). Bi or Bi alloy in the invention shows an intermediate orientation between a complete random orientation as in fine powder and a particular one orientation as in single crystal, and a Miller index (202) face among respective crystal faces of Bi aligns in one direction at a high rate. A rate, at which such particular crystal face aligns in one direction, is denoted by an index of orientation. 
     An index of orientation Ae of a particular face is
 
 Ae=R   (h, k, l) ×100÷Σ R   (h, k, l) 
 
where R (h, k, l)  indicates the X-ray diffracted intensity of respective faces of a crystal of Bi or its alloy in an overlay layer.
 
     However, R (h, k, l)  of a numerator in the above formula indicates the X-ray diffracted intensity of a face of which an index of orientation is to be found, and ΣR (h, k, l)  indicates the sum total of the X-ray diffracted intensities of respective faces. 
     In the invention, the Miller index (202) face can have the index of orientation of not less than 40% and the X-ray diffracted intensity R (012)  of a Miller index (012) face can be made not more than 45% of the X-ray diffracted intensity R (202)  of the (202) face. 
     The above constitution makes it possible to obtain a further excellent anti-seizure. 
     According to the invention, the overlay layer can have a thickness of 3 to 15 μm. When the thickness is less than 3 μm, the overlay layer cannot realize its function, and when the thickness exceeds 15 μm, the overlay layer is reduced in fatigue resistance. 
     Also, according to the invention, an intermediate layer formed from one or more selected from Ni, Cu, Ag, Co, Ni alloy, Cu alloy, Ag alloy, or Co alloy can be provided between the slide alloy layer and the overlay layer. Thereby, the overlay layer can be enhanced in bond strength to the slide alloy layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a microphotograph of a surface of an overlay layer of a product sample of the invention; 
         FIG. 2  is a view showing a X-ray diffraction pattern of the surface of the overlay layer of a product sample of the invention; 
         FIG. 3  is a schematic view showing a microphotograph of a surface of an overlay layer of a product sample of comparative examples; and 
         FIG. 4  is a view showing a X-ray diffraction pattern of the surface of the overlay layer of a product sample of comparative examples. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the invention will be described hereinunder. 
     A slide member according to the invention is formed by lining a Cu base or Al base slide alloy on a surface of a back metal layer and covering the slide alloy with an overlay layer composed of Bi or Bi alloy through an intermediate layer or not. The slide member can be made a plain bearing used for a main shaft of a crankshaft, a large end of a connecting rod, and the like for internal combustion engines. 
     The following electroplating condition was employed to perform plating of the overlay layer by means of electroplating. 
     Bath composition: bismuth oxide; 10 to 70 g/l, methanesulfonic acid; 30 to 150 ml/l, HS-220S (trade mark; manufactured by EBARA-UDYLITE CO. LTD.,); 20 to 60 ml/l 
     Bath temperature: 25 to 40° C. 
     Current density: 1 to 6 A/dm 2    
     In order to obtain an index of orientation of at least 40% for a Miller index (202) face, the PR electrolytic method (Period Reverse Electroplating) is effective. The PR electrolytic method is one in which cathode current is periodically switched over to anode current, and switching is commonly performed with time of anode current being 10 to 20% of time of cathode current. The longer time of anode current, the smoother a plated surface, but the slower a speed of plating. The index of orientation can be changed by regulating anode current, cathode current, and a switching cycle thereof. 
     Using the plating method, product samples 1 to 8 of the invention and product samples 1 to 4 of comparative examples shown in the following TABLE 1 were obtained. An oil wettability test and a anti-seizure test were carried out on the product samples 1 to 8 of the invention and the product samples 1 to 4 of comparative examples. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 MAXIMUM 
               
               
                   
                 COMPOSITION 
                   
                   
                   
                   
                   
                   
                 SURFACE 
               
               
                   
                 (MASS %) OF 
                 INDEX OF 
                 INTENSITY 
                   
                   
                 THICKNESS 
                   
                 PRESSURE 
               
               
                   
                 OVERLAY 
                 ORIENTATION 
                 RATIO 
                   
                 INTER- 
                 (μm) OF 
                 RANK 
                 (MPa) 
               
               
                 SAMPLE 
                 LAYER 
                 (%) 
                 (012)/ 
                 SLIDE 
                 MEDIATE 
                 OVERLAY 
                 OF OIL 
                 WITHOUT 
               
             
          
           
               
                 NO. 
                 Bi 
                 Cu 
                 (012) 
                 (202) 
                 (202) 
                 ALLOY 
                 LAYER 
                 LAYER 
                 WETTABILITY 
                 SEIZURE 
               
               
                   
               
             
          
           
               
                 PRODUCTS 
                   
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 OF THE 
               
               
                 INVENTION 
               
               
                 1 
                 100 
                 — 
                 4.5 
                 69 
                 0.065 
                 Cu ALLOY 
                 NONE 
                 10 
                 A 
                 80 
               
               
                 2 
                 100 
                 — 
                 14.3 
                 52 
                 0.275 
                 Cu ALLOY 
                 NONE 
                 10 
                 B 
                 80 
               
               
                 3 
                 100 
                 — 
                 8.5 
                 49.5 
                 0.172 
                 Cu ALLOY 
                 NONE 
                 5 
                 B 
                 80 
               
               
                 4 
                 100 
                 — 
                 5.6 
                 60.6 
                 0.092 
                 Cu ALLOY 
                 Ag 
                 15 
                 A 
                 85 
               
               
                 5 
                 100 
                 — 
                 5.3 
                 61.6 
                 0.086 
                 Al ALLOY 
                 Cu 
                 10 
                 A 
                 75 
               
               
                 6 
                 98 
                 2 
                 15.5 
                 41 
                 0.378 
                 Cu ALLOY 
                 Ni 
                 5 
                 B 
                 75 
               
               
                 7 
                 98 
                 2 
                 13.6 
                 31 
                 0.439 
                 Cu ALLOY 
                 NONE 
                 5 
                 B 
                 70 
               
               
                 8 
                 98 
                 2 
                 15.9 
                 30 
                 0.53 
                 Cu ALLOY 
                 NONE 
                 10 
                 B 
                 70 
               
               
                 PRODUCTS OF 
               
               
                 COMPARATIVE 
               
               
                 EXAMPLES 
               
               
                 1 
                 100 
                 — 
                 95 
                 0.3 
                 317 
                 Cu ALLOY 
                 Ni 
                 10 
                 C 
                 60 
               
               
                 2 
                 98 
                 2 
                 40 
                 7.1 
                 5.6 
                 Cu ALLOY 
                 NONE 
                 5 
                 C 
                 60 
               
               
                 3 
                 98 
                 2 
                 41.6 
                 6 
                 6.9 
                 Cu ALLOY 
                 NONE 
                 10 
                 C 
                 60 
               
               
                 4 
                 100 
                 — 
                 8.1 
                 28.8 
                 0.281 
                 Al ALLOY 
                 Cu 
                 10 
                 C 
                 55 
               
               
                   
               
             
          
         
       
     
     In the oil wettability test, oil of 0.02 g corresponding to SAE  20  was dropped on overlay layers of the product samples 1 to 8 of the invention and the product samples 1 to 4 of comparative examples in the form of a flat plate and spread (area) of the oil after two minutes was evaluated. The evaluation was performed on the basis of a rank A for an oil spread area of not less than 350 mm 2 , a rank B for an oil spread area of not less than 300 mm 2 , and a rank C for an oil spread area of less than 300 mm 2 . 
     Further, the anti-seizure test was carried out in conditions indicated in the following TABLE 2. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 CONDITIONS OF SEIZURE TEST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 TESTER 
                 SEIZURE TESTER 
               
               
                   
                 SPEED OF ROTATION 
                 7200 rpm 
               
               
                   
                 PERIPHERAL SPEED 
                 20 m/s 
               
               
                   
                 TEST LOAD 
                 INCREASED BY 10 MPa EVERY 
               
               
                   
                   
                 10 MINUTES 
               
               
                   
                 OILING TEMPERATURE 
                 100° C. 
               
               
                   
                 OILING QUANTITY 
                 150 ml/min 
               
               
                   
                 LUBRICATING OIL 
                 VG22 
               
               
                   
                 SHAFT BEING TESTED 
                 JIS S55C 
               
               
                   
                   
               
             
          
         
       
     
     The evaluation was performed in such a manner that when a back surface temperature of a sample exceeded 200° C., or a shaft-driving belt for rotating a mating shaft slipped due to fluctuation in torque, seizure was judged and a maximum surface pressure was defined by a value obtained by dividing a test load immediately before judgment of such seizure by a pressure receiving area. 
     Results of the above oil wettability test and anti-seizure test are described in TABLE 1. 
     As seen from TABLE 1, it has been confirmed that with respect to oil wettability, all the product samples 1 to 8 of the invention belong to the rank A or the rank B while all the product samples 1 to 4 of comparative examples belong to the rank C, and that the product samples 1 to 8 of the invention are superior to the latter in oil wettability. Further, as the result of the favorable oil wettability, the product samples 1 to 8 of the invention are large in maximum surface pressure without seizure to be excellent in anti-seizure as compared with the product samples 1 to 4 of comparative examples. 
       FIG. 1  is a view schematically showing a microphotograph of a surface of an overlay layer of the product sample 2 of the invention, and  FIG. 3  is a view schematically showing a microphotograph of a surface of an overlay layer of the product sample 2 of comparative examples. As understood from comparison between  FIG. 1  and  FIG. 3 , the product sample 2 of the invention has that surface of an overlay layer on which minute and uniform projections congregate to define a fine, irregular surface. Although being not seen in  FIG. 1 , the projections assume a shape close to that of a triangular pyramid and a quadrangular pyramid. 
     In contrast, the product sample 2 of comparative examples has that surface of an overlay layer which is a coarse surface composed of relatively large irregularities being uneven in size. While it is generally said that a surface on which small irregularities are minutely present is excellent in oil wettability, the product sample 2 of the invention has a surface of an overlay layer which is exactly in the form of a minute, irregular surface said to be excellent in oil wettability, and it has been confirmed that the surface of the overlay layer is excellent in oil wettability owing to its surface configuration. 
     A test for taking a X-ray diffraction figure of the structure of an overlay layer was carried out on the product samples 1 to 8 of the invention and the product samples 1 to 4 of comparative examples, which had the surface configurations, respectively.  FIG. 2  shows a X-ray diffraction pattern of the overlay layer of the product sample 2 of the invention, and  FIG. 4  shows a X-ray diffraction pattern of the overlay layer of the product sample 2 of comparative examples. As apparent from  FIGS. 2 and 4 , a Miller index (202) face of the product sample 2 of the invention is especially higher in X-ray diffracted intensity than other faces while a Miller index (012) face of the product sample 2 of comparative examples is especially higher in X-ray diffracted intensity than other faces and a Miller index (202) face thereof is low in X-ray diffracted intensity. The tendency of X-ray diffracted intensity for the Miller index (202) face and the Miller index (012) face, as described with respect to the product sample 2 of the invention and the product sample 2 of comparative examples is the same as that for the product samples 1, 3 to 8 of the invention and the product samples 1, 3, 4 of comparative examples. 
     Indices of orientation of a Miller index (202) face and a Miller index (012) face, and intensity ratios of the both faces were calculated for the product samples 1 to 8 of the invention and the product samples 1 to 4 of comparative examples, results of which are indicated in TABLE 1. 
     According to the results, with all the product samples 1 to 8 of the invention which are excellent in anti-seizure, the index of orientation of a Miller index (202) face is not less than 30% and the X-ray diffracted intensity of the (202) face assumes a maximum value as compared with the X-ray diffracted intensities of other faces, while the index of orientation of a Miller index (202) face in all the product samples 1 to 4 of comparative examples is less than 30%. 
     From the above, it can be said that Bi or Bi alloy in which the index of orientation of a Miller index (202) face is not less than 30% and the X-ray diffracted intensity of the (202) face assumes a maximum value as compared with those of other faces forms a structure which is excellent in anti-seizure. 
     Further, for the product samples 1 to 6 of the invention, the index of orientation of a Miller index (202) face is not less than 40% and the X-ray diffracted intensity R (012)  of a Miller index (012) face is not more than 45% of the X-ray diffracted intensity R (202)  of the Miller index (202) face, so the product samples 1 to 6 of the invention are more excellent in anti-seizure than the product samples 7 and 8 of the invention which do not meet with the above conditions. 
     In addition, the invention is not limited to the embodiment described above and shown in the drawings, but can be extended or modified in the following manner. 
     The plating method for formation of the overlay layer is not limited to that described above. 
     The overlay layer is not limited to ones formed by means of plating. 
     Metal making an alloy with Bi is not limited to Cu. 
     In order to achieve improvement in characteristics, the overlay layer may contain hard substances and other substances. 
     The slide member is not limited to the use for plain bearings.