Abstract:
A sintered friction material especially suitable for use in a braking system has a matrix of a copper-system metal such as copper, tin, nickel and aluminum, and contains a specific additive, graphite and potassium titanate as friction conditioners. The specific additive consists of at least one material selected from a group consisting of zirconium oxide, silica, dolomite, orthoclase and magnesium oxide. The specific additive, the graphite and the potassium titanate are preferably blended in volume ratios of 1 to 15%, 10 to 50% and 5 to 30% respectively. The form of the potassium titanate is at least one of whiskery, platy and spherical forms and preferably plate-like or spherical. The sintered friction material has good abrasion resistance, low abrasion of the counterpart, a high friction coefficient, excellent material strength, good chattering resistance, and good squealing resistance.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a friction material, and more particularly, it relates to a friction material which is optimum for a sliding surface of a brake lining, a disc pad, a clutch facing or the like in a braking system of an automobile, rolling stock, an aircraft, an industrial machine or the like. 
     2. Description of the Prior Art 
     A friction material prepared by dispersing a base material in a binder of resin such as phenolic resin or epoxy resin, adding a friction conditioner as needed and binding and molding the mixture under heat and pressure is known for use as a friction material in the aforementioned braking system. 
     The friction coefficient of such a friction material is generally reduced as the temperature is increased. When an automobile continuously goes down descents or the like, therefore, the braking performance is remarkably reduced through so-called fading as the friction material becomes frictionally heated. To this end, a friction material employed under a high load condition is prepared from a sintered alloy based on a metal such as copper with addition of a friction conditioner such as graphite or ceramics in recent years. 
     However, some conventional friction material of a sintered alloy (hereinafter referred to as a sintered friction material) is insufficient in lubricity and remarkably abrades the counterpart although the friction material itself is less abraded. Another conventional friction material is remarkably abraded itself, although it abrades the counterpart to a larger degree. Thus, these conventional sintered friction materials have unsatisfactory characteristics under the present circumstances. 
     Still another conventional sintered friction material is insufficient in lubricity and remarkably abrades the counterpart although it exhibits a high friction coefficient. A further friction material is remarkably reduced in friction coefficient although it abrades the counterpart to a larger degree. Thus, these conventional sintered friction materials have unsatisfactory characteristics under the present circumstances. 
     A further conventional sintered friction material is insufficient in material strength although the same exhibits a high friction coefficient. A further friction material is remarkably reduced in friction coefficient although the same is sufficient in material strength. Thus, these conventional sintered friction materials have unsatisfactory characteristics under the present circumstances. 
     A further conventional sintered friction material is insufficient in judder resistance or chatter resistance although the friction material itself is less abraded. A further friction material is remarkably abraded itself although the same is sufficient in judder resistance. Thus, these conventional sintered friction materials have unsatisfactory characteristics under the present circumstances. 
     A further conventional sintered friction material is insufficient in creak resistance or squealing resistance although the same exhibits a high friction coefficient. A further friction material is remarkably reduced in friction coefficient although the same is sufficient in creak resistance. Thus, these conventional sintered friction materials have unsatisfactory characteristics under the present circumstances. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a sintered friction material compatibly improving its abrasion resistance and suppressing abrasion of the counterpart. 
     Another object of the present invention is to provide a sintered friction material compatibly attaining a high friction coefficient and suppressing abrasion of the counterpart. 
     Still another object of the present invention is to provide a sintered friction material compatibly attaining both a high friction coefficient and excellent material strength. 
     A further object of the present invention is to provide a sintered friction material compatibly attaining both abrasion resistance and judder resistance. 
     A further object of the present invention is to provide a sintered friction material compatibly attaining both a high friction coefficient and excellent creak resistance. 
     The sintered friction material according to the present invention has a matrix of a copper-system metal and contains a specific additive, graphite and potassium titanate as friction conditioners, while the specific additive consists of at least one material selected from a group consisting of zirconium oxide, silica, dolomite, orthoclase and magnesium oxide. 
     The matrix of a copper-system metal, having excellent expandability and high hot conductivity, can stabilize the friction coefficient and disperse heat spots, while improving the friction coefficient through adhesion to the counterpart. The graphite improves the abrasion resistance of the friction material, while the potassium titanate suppresses adhesion to the counterpart for inhibiting abrasion of the counterpart and matches with the matrix material for maintaining the material strength. 
     When prepared from any of zirconium oxide, silica and dolomite (CaCO 3  ·MgCO 3 ), the specific additive improves the frictional force by removing an oxide film or the like adhering to the surface of the counterpart. When prepared from orthoclase K 2  O·Al 2  O 3  ·6SiO 2 ), the specific additive has proper hardness and small attackability to the counterpart, and improves the judder resistance. When prepared from magnesium oxide, the specific additive improves the creak resistance by improving the damping property of the friction material. 
     In order to sufficiently attain the aforementioned effects, the sintered friction material preferably contains the specific additive, the graphite and the potassium titanate by 1 to 15%, 10 to 50% and 5 to 30% in volume ratio respectively. 
     The frictional force is insufficiently improved if the volume ratio of zirconium oxide is smaller than 1%, while the effect of suppressing abrasion of the counterpart is reduced due to removal of the counterpart if this volume ratio exceeds 15%. Zircon (ZrSiO 4 ) may be employed in place of or along with zirconium oxide. 
     The frictional force is insufficiently improved if the volume ratio of silica is smaller than 1%, while the effect of suppressing abrasion of the counterpart is reduced due to removal of the counterpart if this volume ratio exceeds 15%. Silica is preferably prepared from at least one of crystal silica obtained by crushing natural ore as such, fused silica obtained by fusing and vitrifying ore at a high temperature of at least 1800° C. and thereafter crushing the same, and industrially synthesized amorphous silica. 
     The frictional force is insufficiently improved if the volume ratio of dolomite is smaller than 1%, while the matrix is inhibited from sintering and the material strength is reduced if this volume ratio exceeds 15%. 
     The judder resistance is insufficiently improved if the volume ratio of orthoclase is smaller than 1%, while the matrix is inhibited from sintering and the material strength is reduced if this volume ratio exceeds 15%. 
     The creak resistance is insufficient if the volume ratio of magnesium oxide is smaller than 1%, while the matrix is inhibited from sintering and the material strength is reduced if this volume ratio exceeds 15%. 
     The abrasion resistance of the friction material is insufficiently improved if the volume ratio of graphite is smaller than 10%, while the material strength is remarkably reduced to deteriorate the abrasion resistance if this volume ratio exceeds 50%. 
     The effect of suppressing abrasion of the counterpart is insufficient and the effect of maintaining the material strength is not attained if the volume ratio of potassium titanate is smaller than 5%, while the effect of maintaining the material strength is saturated to result in reduction of the material strength and deterioration of the abrasion resistance if this volume ratio exceeds 30%. 
     While potassium titanate is a compound expressed in a general formula K 2  O·nTiO 2 , a practical friction conditioner is obtained when n is equal to 2, 4, 6 or 8. Potassium hexatitanate is particularly preferable. Alternatively, a composite material prepared by granularly sintering potassium titanate and calcium titanate may be employed. 
     The grain size of zirconium oxide is suitably in the range of 0.5 to 200 μm. If the grain size is smaller than the lower limit of this range, the zirconium oxide cannot remove an oxide film adhering to the surface of the counterpart and no improvement of the frictional force is attained. If the grain size exceeds the upper limit of the above range, on the other hand, the zirconium oxide removes not only an oxide film adhering to the surface of the counterpart but also the counterpart itself, and hence the effect of suppressing abrasion of the counterpart is deteriorated. 
     The grain size of silica is suitably in the range of 0.5 to 200 μm. If the grain size is smaller than the lower limit of this range, the silica cannot remove an oxide film adhering to the surface of the counterpart and no improvement of the frictional force is attained. If the grain size exceeds the upper limit of the above range, on the other hand, the silica removes not only an oxide film adhering to the surface of the counterpart but also the counterpart itself, and hence the effect of suppressing abrasion of the counterpart is deteriorated. 
     The grain size of dolomite is suitably in the range of 0.5 to 200 μm. If the grain size is smaller than the lower limit of this range, the dolomite cannot remove an oxide film adhering to the surface of the counterpart and no improvement of frictional force is attained. If the grain size of the dolomite exceeds the upper limit of the above range, on the other hand, the matrix is inhibited from sintering and the material strength is reduced. Dolomite is preferably prepared either by crushing natural ore as such or baking the same. 
     The grain size of orthoclase is suitably in the range of 0.5 to 200 μm. If the grain size of the orthoclase is smaller than the lower limit of this range, the matrix is inhibited from sintering and the material strength is reduced. If the grain size of the orthoclase exceeds the upper limit of the above range, on the other hand, judder resistance is insufficiently improved. 
     The grain size of magnesium oxide is suitably in the range of 0.5 to 200 μm. If the grain size of the magnesium oxide is smaller than the lower limit of this range, the matrix is inhibited from sintering and the material strength is reduced. If the grain size of the magnesium oxide exceeds the upper limit of the above range, on the other hand, no improvement of the damping property of the friction material is attained and the creak resistance is insufficiently improved. 
     The grain size of graphite is suitably in the range of 10 to 1000 μm. If the grain size of the graphite is smaller than the lower limit of this range, the matrix is inhibited from sintering and the material strength is reduced to deteriorate the abrasion resistance of the friction material. If the grain size exceeds the upper limit of the above range, on the other hand, segregation of the graphite is so remarkable that it is difficult to ensure a homogeneously dispersed state. 
     The form of potassium titanate is preferably at least one of whiskery, platy (or plate-like) and spherical forms. In particular, spherical potassium titanate is more preferable as compared with whiskery and platy ones in the following points: 
     (1) The spherical potassium titanate less reduces the material strength as compared with the whiskery and platy ones. 
     (2) The spherical potassium titanate is hardly crushed but homogeneously dispersed as such when mixed into the material powder. 
     (3) The spherical potassium titanate is less segregated due to excellent flowability of the mixed powder when introduced into a mold. 
     (4) The spherical potassium titanate has a remarkable effect of improving the damping property of the sintered body and suppressing creaking due to internal friction of spherical grains. 
     A further friction conditioner, a preservative and/or a lubricant may be added to the sintered friction material according to the present invention in a proper amount as needed as a matter of course. For example, barium sulfate, magnetite, fluorite and/or molybdenum disulfate may be added to the inventive sintered friction material. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Examples of the present invention are now described. 
    
    
     (TEST EXAMPLE 1) 
     Mixed powder materials were prepared by blending matrices, zirconium oxide, graphite and potassium titanate in the ratios shown in Table 1, molded into green compacts under a pressure of 2 to 5 tons/cm 2  and thereafter sintered in an N 2  atmosphere at 750° C. for 20 to 90 minutes, thereby preparing samples Nos. 1 to 31 of sintered friction materials. 
     
                                           TABLE 1__________________________________________________________________________      Matrix                              Potassium Titanate                  Total                      Zirconium Oxide                                Graphite               Total                  Ratio                      Ratio     Ratio                  RatioSample                 (Vol.                      (Vol.                         Grain Size                                (Vol.                                   Grain Size          (Vol.No. Classification      Cu Sn Ni Al %)  %) (μm)                                %) (μm)                                          Whiskery                                               Platy                                                  Spherical                                                       %)__________________________________________________________________________1   inventive      34 5  0  0  39  14 0.5˜200                                30 200˜400                                          0    0  17   172   inventive      33 5  0  0  38  2  0.5˜200                                45 200˜400                                          0    0  15   153   inventive      33 5  0  0  38  8  0.5˜200                                24 200˜400                                          0    0  30   304   inventive      33 5  0  0  38  14 0.5˜200                                20 200˜400                                          0    0  28   285   inventive      37.5         5.5            0  0  43  14 0.5˜200                                15 200˜400                                          0    0  28   286   inventive      36 5  0  0  41  14 0.5˜200                                40 200˜400                                          0    0  5    57   inventive      36 5  0  0  41  14 0.5˜200                                30 200˜400                                          0    0  15   158   inventive      33 5  0  0  38  8  0.5˜200                                40 200˜400                                          0    0  14   149   inventive      33 5  0  0  38  8  0.5˜200                                40 200˜400                                          0    14 0    1410  inventive      33 5  0  0  38  8  0.5˜200                                40 200˜400                                          14   0  0    1411  inventive      33 5  0  0  38  8  0.5˜200                                40 200˜400                                          0    7  7    1412  inventive      33 5  0  0  38  8  0.5˜200                                40 200˜400                                          7    0  7    1413  comparative      33 5  0  0  38  0.5                         0.5˜200                                43 200˜400                                          0    0  18.5 18.514  comparative      33 5  0  0  38  18 0.5˜200                                33 200˜400                                          0    0  11   1115  comparative      48 7  0  0  55  15 0.5˜200                                5  200˜400                                          0    0  25   2516  comparative      32 5  0  0  37  2  0.5˜200                                55 200˜400                                          0    0  6    617  comparative      33 5  0  0  38  15 0.5˜200                                44 200˜400                                          0    0  3    318  comparative      33 5  0  0  38  5  0.5˜200                                25 200˜400                                          0    0  32   3219  comparative      33 5  0  0  38  8  0.01˜0.4                                40 200˜400                                          0    0  14   1420  comparative      33 5  0  0  38  8  220˜400                                40 200˜400                                          0    0  14   1421  comparative      33 5  0  0  38  8  0.5˜200                                40 0.1˜8                                          0    0  14   1422  comparative      33 5  0  0  38  8  0.5˜200                                40 1200˜2000                                          0    0  14   1423  inventive      24 3  11 0  38  8  0.5˜200                                40 200˜400                                          0    0  14   1424  inventive      24 3  11 0  38  8  0.5˜200                                40 200˜400                                          0    14 0    1425  inventive      24 3  11 0  38  8  0.5-200                                40 200˜400                                          14   0  0    1426  inventive      23 3  10 2  38  8  0.5˜200                                40 200˜400                                          0    0  14   1427  inventive      23 3  10 2  38  8  0.5˜200                                40 200˜400                                          0    14 0    1428  inventive      23 3  10 2  38  8  0.5˜200                                40 200˜400                                          14   0  0    1429  comparative      40 6  0  0  46  14 0.5˜200                                40 200˜400                                          0    0  0    030  comparative      27 4  15 0  46  14 0.5˜200                                40 200˜400                                          0    0  0    031  comparative      27 4  12 3  46  14 0.5˜200                                40 200˜400                                          0    0  0    0__________________________________________________________________________ 
    
     A general performance test was made on the samples in accordance with the JASO C406-82 passenger car braking device dynamometer test method. The ranges of friction coefficients were measured at initial braking speeds of 50 km/h and 100 km/h and deceleration of 0.1 to 0.9 G in a second effectiveness test. Abrasion loss values of the samples and the counterparts of cast iron were measured before and after the general performance test. Table 2 shows the results. Referring to Tables 1 and 2, the samples Nos. 1 to 12 and 23 to 28 are inventive samples, and the samples Nos. 13 to 22 and Nos. 29 to 31 are comparative samples. In the columns of &#34;Classification&#34;, &#34;inventive&#34; and &#34;comparative&#34; indicate the inventive and comparative samples respectively. 
     
                       TABLE 2______________________________________                  Abra-                       AbrasionSam-          Friction sion Loss ofple  Classi-  Coeffi-  Loss Counter-                              Appearance afterNo.  fication cient    (mm) part (mm)                              Friction Test______________________________________1    inventive         0.40˜0.48                  0.12 0.05   excellent with neither                              chipping nor cracking2    inventive         0.33˜0.40                  0.10 0.05   excellent with neither                              chipping nor cracking3    inventive         0.35˜0.45                  0.13 0.04   excellent with neither                              chipping nor cracking4    inventive         0.40˜0.48                  0.14 0.04   excellent with neither                              chipping nor cracking5    inventive         0.40˜0.48                  0.15 0.04   excellent with neither                              chipping nor cracking6    inventive         0.40˜0.48                  0.10 0.09   excellent with neither                              chipping nor cracking7    inventive         0.40˜0.48                  0.12 0.05   excellent with neither                              chipping nor cracking8    inventive         0.38˜0.45                  0.10 0.05   excellent with neither                              chipping nor cracking9    inventive         0.35˜0.45                  0.10 0.05   excellent with neither                              chipping nor cracking10   inventive         0.35˜0.45                  0.10 0.05   excellent with neither                              chipping nor cracking11   inventive         0.37˜0.45                  0.10 0.05   excellent with neither                              chipping nor cracking12   inventive         0.37˜0.45                  0.10 0.05   excellent with neither                              chipping nor cracking13   compar-  0.15˜0.25                  0.25 0.06   excellent with neitherative                         chipping nor cracking14   compar-  0.35˜0.50                  0.22 0.30   corner chippedative15   compar-  0.35˜0.45                  0.50 0.09   excellent with neitherative                         chipping nor cracking16   compar-  0.30˜0.40                  0.45 0.08   corner chippedative17   compar-  0.35˜0.45                  0.20 0.30   corner chippedative18   compar-  0.35˜0.45                  0.45 0.25   corner chippedative19   compar-  0.15˜0.25                  0.25 0.09   excellent with neitherative                         chipping nor cracking20   compar-  0.25˜0.45                  0.20 0.30   corner chippedative21   compar-  0.32˜0.40                  0.30 0.09   corner chippedative22   compar-  0.25˜0.50                  0.35 0.18   corner chippedative23   inventive         0.36˜0.47                  0.12 0.05   excellent with neither                              chipping nor cracking24   inventive         0.36˜0.47                  0.12 0.06   excellent with neither                              chipping nor cracking25   inventive         0.36˜0.47                  0.12 0.06   excellent with neither                              chipping nor cracking26   inventive         0.38˜0.48                  0.13 0.05   excellent with neither                              chipping nor cracking27   inventive         0.38˜0.48                  0.13 0.06   excellent with neither                              chipping nor cracking28   inventive         0.38˜0.48                  0.13 0.06   excellent with neither                              chipping nor cracking29   compar-  0.35˜0.45                  0.30 0.50   corner chippedative30   compar-  0.36˜0.47                  0.32 0.52   corner chippedative31   compar-  0.38˜0.48                  0.35 0.55   corner chippedative______________________________________ 
    
     As understood from Table 2, the samples Nos. 1 to 12 having matrices of copper and tin exhibited high friction coefficients and small abrasion loss values of the friction materials and the counterparts. It is also understood that the samples Nos. 1 to 12 were sufficient in strength with neither chipping nor cracking on the appearances after the test. 
     On the other hand, the samples Nos. 13 to 22, similarly having matrices of copper and tin, were insufficient as friction materials as described below: 
     The sample No. 13 containing zirconium oxide in a ratio smaller than those of the remaining samples exhibited an insufficient friction coefficient for serving as a friction material. The sample No. 14 containing zirconium oxide in a high ratio removed not only an oxide film adhering to the surface of the counterpart but also the counterpart itself, which was remarkably abraded. 
     The sample No. 15 containing graphite in a ratio smaller than those of the remaining samples exhibited high abrasion loss. The sample No. 16 containing graphite in a high ratio was remarkably reduced in material strength and increased in abrasion loss. 
     The sample No. 17 containing potassium titanate in a ratio smaller than those of the remaining samples remarkably abraded the counterpart and had an insufficient effect of suppressing abrasion of the counterpart. The sample No. 18 containing potassium titanate in a ratio larger than those of the remaining samples was reduced in material strength and increased in abrasion loss. 
     The sample No. 19 containing zirconium oxide in a grain size smaller than those of the remaining samples was incapable of removing an oxide film or the like adhering to the surface of the counterpart and exhibited an insufficient friction coefficient for serving as a friction material. The sample No. 20 containing zirconium oxide in a grain size larger than those of the remaining samples removed not only an oxide film adhering to the surface of the counterpart but also the counterpart itself, which was remarkably abraded. 
     The sample No. 21 containing graphite in a grain size smaller than those of the remaining samples was inhibited from sintering of the matrix, reduced in material strength and deteriorated in abrasion resistance. The sample No. 22 containing graphite in a grain size larger than those of the remaining samples was incapable of ensuring a homogeneous dispersed state and obtaining a stable friction coefficient due to remarkable segregation of graphite, and increased in abrasion loss. 
     The samples Nos. 23 to 25 having matrices of copper, tin and nickel exhibited higher friction coefficients as compared with those of the samples Nos. 1 to 12, with small abrasion loss of the friction materials and the counterparts. Further, the samples Nos. 23 to 25 were sufficient in strength for serving as friction materials with neither chipping nor cracking on the appearances after the test. 
     The samples Nos. 26 to 28 having matrices of copper, tin, nickel and aluminum exhibited higher friction coefficients as compared with those of the samples Nos. 23 and 25, with small abrasion loss of the friction materials and the counterparts. Further, the samples Nos. 26 to 28 were sufficient in strength for serving as friction materials with neither chipping nor cracking on the appearances after the test. On the other hand, the samples Nos. 29 to 31 of conventional sintered friction materials containing no potassium titanate exhibited insufficient effects of suppressing abrasion of the counterparts with remarkable abrasion loss of the counterparts due to the absence of potassium titanate. 
     (TEST EXAMPLE 2) 
     Mixed powder materials were prepared by blending matrices, silica, graphite and potassium titanate in the ratios shown in Table 3, molded into green compacts under a pressure of 2 to 5 tons/cm 2  and thereafter sintered in an N 2  atmosphere at 750° C. for 20 to 90 minutes, thereby preparing samples Nos. 101 to 125 of sintered friction materials. 
     
                                           TABLE 3__________________________________________________________________________      Matrix                              Potassium Titanate                  Total                      Silica    Graphite               Total                  Ratio                      Ratio     Ratio                  RatioSample                 (Vol.                      (Vol.                         Grain Size                                (Vol.                                   Grain Size          (Vol.No. Classification      Cu Sn Ni Al %)  %) (μm)                                %) (μm)                                          Whiskery                                               Platy                                                  Spherical                                                       %)__________________________________________________________________________101 inventive      23 3  10 2  38  14 0.5˜200                                30 200˜400                                          0    0  18   18102 inventive      23 3  10 2  38  2  0.5˜200                                45 200˜400                                          0    0  15   15103 inventive      23 3  10 2  38  8  0.5˜200                                26 200˜400                                          0    0  28   28104 inventive      23 3  10 2  38  14 0.5˜200                                20 200˜400                                          0    0  28   28105 inventive      26 3.4            11.3               2.3                  43  14 0.5˜200                                15 200˜400                                          0    0  28   28106 inventive      24.8         3.2            10.8               2.2                  41  14 0.5˜200                                40 200˜400                                          0    0  5    5107 inventive      24.8         3.2            10.8               2.2                  41  14 0.5˜200                                30 200˜400                                          0    0  15   15108 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜400                                          0    0  14   14109 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜400                                          0    14 0    14110 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜400                                          14   0  0    14111 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜400                                          0    7  7    14112 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜400                                          7    0  7    14113 comparative      23 3  10 2  38  0.5                         0.5˜200                                43 200˜400                                          0    0  18.5 18.5114 comparative      23 3  10 2  38  18 0.5˜200                                33 200˜400                                          0    0  11   11115 comparative      33.3         4.3            14.5               2.9                  55  15 0.5˜200                                5  200˜400                                          0    0  25   25116 comparative      22.4         2.9            9.7               2.0                  37  2  0.5˜200                                55 200˜400                                          0    0  6    6117 comparative      23 3  10 2  38  15 0.5˜200                                44 200˜400                                          0    0  3    3118 comparative      23 3  10 2  38  5  0.5˜200                                25 200˜400                                          0    0  32   32119 comparative      23 3  10 2  38  8  0.01˜0.4                                40 200˜400                                          0    0  14   14120 comparative      23 3  10 2  38  8  220˜400                                40 200˜400                                          0    0  14   14121 comparative      23 3  10 2  38  8  0.5˜200                                40 0.1˜8                                          0    0  14   14122 comparative      23 3  10 2  38  8  0.5˜200                                40 1200˜2000                                          0    0  14   14123 comparative      27 4  12 3  46  14 0.5˜200                                40 200˜400                                          0    0  0    0124 comparative      26 3.4            11.3               2.3                  43  14 0.5˜200                                43 200˜400                                          0    0  0    0125 comparative      24.8         3.2            10.8               2.2                  41  14 0.5˜200                                45 200˜400                                          0    0  0    0__________________________________________________________________________ 
    
     A general performance test was carried out on the samples in accordance with the JASO C406-82 passenger car braking device dynamometer test method. The ranges of friction coefficients were measured at initial braking speeds of 50 km/h and 100 km/h and deceleration of 0.1 to 0.9 G in a second effectiveness test. Abrasion loss values of the samples and the counterparts of cast iron were measured before and after the general performance test. Table 4 shows the results. Referring to Tables 3 and 4, the samples Nos. 101 to 112 are inventive samples, and the samples Nos. 113 to 125 are comparative samples. In the columns of &#34;Classification&#34;, &#34;inventive&#34; and &#34;comparative&#34; indicate the inventive and comparative samples respectively. 
     
                       TABLE 4______________________________________                       Abrasion                               Abrasion LossSample            Friction  Loss    of CounterpartNo.    Classification             Coefficient                       (mm)    (mm)______________________________________101    inventive  0.48˜0.55                       0.12    0.06102    inventive  0.45˜0.50                       0.09    0.05103    inventive  0.46˜0.53                       0.13    0.04104    inventive  0.48˜0.55                       0.14    0.04105    inventive  0.48˜0.56                       0.15    0.04106    inventive  0.48˜0.54                       0.10    0.09107    inventive  0.48˜0.54                       0.12    0.05108    inventive  0.46˜0.52                       0.10    0.05109    inventive  0.46˜0.52                       0.10    0.05110    inventive  0.46˜0.52                       0.10    0.05111    inventive  0.46˜0.52                       0.10    0.05112    inventive  0.46˜0.52                       0.10    0.05113    comparative             0.20˜0.28                       0.25    0.06114    comparative             0.45˜0.55                       0.22    0.45115    comparative             0.40˜0.48                       0.50    0.09116    comparative             0.30˜0.40                       0.45    0.08117    comparative             0.45˜0.50                       0.20    0.30118    comparative             0.46˜0.53                       0.45    0.25119    comparative             0.18˜0.28                       0.25    0.09120    comparative             0.45˜0.58                       0.20    0.30121    comparative             0.46˜0.53                       0.40    0.09122    comparative             0.35˜0.58                       0.35    0.18123    comparative             0.48˜0.58                       0.30    0.55124    comparative             0.48˜0.56                       0.26    0.52125    comparative             0.48˜0.54                       0.22    0.50______________________________________ 
    
     As understood from Table 4, the samples Nos. 101 to 112 having matrices of copper, tin, nickel and aluminum exhibited high friction coefficients and small abrasion loss values of the friction materials and the counterparts. It is also understood that the samples Nos. 101 to 112 were sufficient in strength with neither chipping nor cracking on the appearances after the test. 
     On the other hand, the samples Nos. 113 to 125, similarly having matrices of copper, tin, nickel and aluminum, were insufficient as friction materials as described below: 
     The sample No. 113 containing silica in a ratio smaller than those of the remaining samples exhibited an insufficient friction coefficient for serving as a friction material. The sample No. 114 containing silica in a high ratio removed not only an oxide film adhering to the surface of the counterpart but also the counterpart itself, which was remarkably abraded. 
     The sample No. 115 containing graphite in a ratio smaller than those of the remaining samples exhibited high abrasion loss. The sample No. 116 containing graphite in a high ratio was remarkably reduced in material strength and increased in abrasion loss. 
     The sample No. 117 containing potassium titanate in a ratio smaller than those of the remaining samples remarkably abraded the counterpart and had an insufficient effect of suppressing abrasion of the counterpart. The sample No. 118 containing potassium titanate in a ratio larger than those of the remaining samples was reduced in material strength and increased in abrasion loss. 
     The sample No. 119 containing silica in a grain size smaller than those of the remaining samples was incapable of removing an oxide film or the like adhering to the surface of the counterpart and exhibited an insufficient friction coefficient for serving as a friction material. The sample No. 120 containing silica in a grain size larger than those of the remaining samples removed not only an oxide film adhering to the surface of the counterpart but also the counterpart itself, which was remarkably abraded. 
     The sample No. 121 containing graphite in a grain size smaller than those of the remaining samples was inhibited from sintering of the matrix, reduced in material strength and deteriorated in abrasion resistance. The sample No. 122 containing graphite in a grain size larger than those of the remaining samples was incapable of ensuring a homogeneous dispersed state and obtaining a stable friction coefficient due to remarkable segregation of graphite, and increased in abrasion loss. 
     The samples Nos. 123 to 125 of conventional sintered friction materials containing no potassium titanate exhibited insufficient effects of suppressing abrasion of the counterparts with remarkable abrasion loss of the counterparts due to the absence of potassium titanate. 
     (TEST EXAMPLE 3) 
     Mixed powder materials were prepared by blending matrices, dolomite, graphite and potassium titanate in the ratios shown in Table 5, molded into green compacts under a pressure of 2 to 5 tons/cm 2  and thereafter sintered in an N 2  atmosphere at 750° C. for 20 to 90 minutes, thereby preparing samples Nos. 201 to 225 of sintered friction materials. 
     
                                           TABLE 5__________________________________________________________________________      Matrix                              Potassium Titanate                  Total                      Dolomite  Graphite               Total                  Ratio                      Ratio     Ratio                  RatioSample                 (Vol.                      (Vol.                         Grain Size                                (Vol.                                   Grain Size          (Vol.No. Classification      Cu Sn Ni Al %)  %) (μm)                                %) (μm)                                          Whiskery                                               Platy                                                  Spherical                                                       %)__________________________________________________________________________201 inventive      23 3  10 2  38  14 0.5˜200                                30 200˜500                                          0    0  18   18202 inventive      23 3  10 2  38  2  0.5˜200                                45 200˜500                                          0    0  15   15203 inventive      23 3  10 2  38  8  0.5˜200                                26 200˜500                                          0    0  28   28204 inventive      23 3  10 2  38  14 0.5˜200                                20 200˜500                                          0    0  28   28205 inventive      26 3.4            11.3               2.3                  43  14 0.5˜200                                15 200˜500                                          0    0  28   28206 inventive      24.8         3.2            10.8               2.2                  41  14 0.5˜200                                40 200˜500                                          0    0  5    5207 inventive      24.8         3.2            10.8               2.2                  41  14 0.5˜200                                30 200˜500                                          0    0  15   15208 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜500                                          0    0  14   14209 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜500                                          0    14 0    14210 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜500                                          14   0  0    14211 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜500                                          0    7  7    14212 inventive      23 3  10 2  38  8  0.5˜200                                40 200˜500                                          7    0  7    14213 comparative      23 3  10 2  38  0.5                         0.5˜200                                43 200˜500                                          0    0  18.5 18.5214 comparative      23 3  10 2  38  18 0.5˜200                                33 200˜500                                          0    0  11   11215 comparative      33.3         4.3            14.5               2.9                  55  15 0.5˜200                                5  200˜500                                          0    0  25   25216 comparative      22.4         2.9            9.7               2.0                  37  2  0.5˜200                                55 200˜500                                          0    0  6    6217 comparative      23 3  10 2  38  15 0.5˜200                                44 200˜500                                          0    0  3    3218 comparative      23 3  10 2  38  5  0.5˜200                                25 200˜500                                          0    0  32   32219 comparative      23 3  10 2  38  8  0.01˜0.4                                40 200˜500                                          0    0  14   14220 comparative      23 3  10 2  38  8  220˜400                                40 200˜500                                          0    0  14   14221 comparative      23 3  10 2  38  8  0.5˜200                                40 0.1˜8                                          0    0  14   14222 comparative      23 3  10 2  38  8  0.5˜200                                40 1200˜2000                                          0    0  14   14223 comparative      27 4  12 3  46  14 0.5˜200                                40 200˜500                                          0    0  0    0224 comparative      26 3.4            11.3               2.3                  43  14 0.5˜200                                43 200˜500                                          0    0  0    0225 comparative      24.8         3.2            10.8               2.2                  41  14 0.5˜200                                45 200˜500                                          0    0  0    0__________________________________________________________________________ 
    
     A general performance test was made on the samples in accordance with the JASO C406-82 passenger car braking device dynamometer test method. The ranges of friction coefficients were measured at initial braking speeds of 50 km/h and 100 km/h and deceleration of 0.1 to 0.9 G in a second effectiveness test. Abrasion loss values of the samples were measured before and after the general performance test. Further, bending test pieces were collected from the respective samples for performing a three-point bending test under conditions shown in Table 6. Table 7 shows the results. Referring to Tables 5 and 7, the samples Nos. 201 to 212 are inventive samples, and the samples Nos. 213 to 225 are comparative samples. In the columns of &#34;Classification&#34;, &#34;inventive&#34; and &#34;comparative&#34; indicate the inventive and comparative samples respectively. 
     
                       TABLE 6______________________________________               7 (width) by 5 (thickness)Dimensions of Test Piece (mm)               by 30 (length)______________________________________Distance between Support Points (mm)               20Load System         three-point bendingCrosshead Speed (mm/min.)                 0.5______________________________________ 
    
     
                       TABLE 7______________________________________                  Abra-                  sion                  Loss ofSam-          Friction Friction          Bendingple  Classi-  Coeffi-  Material                        Appearance after                                    StrengthNo.  fication cient    (mm)  Friction Test                                    (Mpa)______________________________________201  inventive         0.47˜0.54                  0.12  excellent with neither                                    at least                        chipping nor cracking                                    40202  inventive         0.44˜0.50                  0.09  excellent with neither                                    at least                        chipping nor cracking                                    40203  inventive         0.46˜0.53                  0.13  excellent with neither                                    at least                        chipping nor cracking                                    40204  inventive         0.48˜0.55                  0.14  excellent with neither                                    at least                        chipping nor cracking                                    40205  inventive         0.48˜0.55                  0.15  excellent with neither                                    at least                        chipping nor cracking                                    40206  inventive         0.48˜0.53                  0.10  excellent with neither                                    at least                        chipping nor cracking                                    40207  inventive         0.48˜0.53                  0.12  excellent with neither                                    at least                        chipping nor cracking                                    40208  inventive         0.46˜0.51                  0.10  excellent with neither                                    at least                        chipping nor cracking                                    40209  inventive         0.46˜0.51                  0.10  excellent with neither                                    at least                        chipping nor cracking                                    40210  inventive         0.46˜0.51                  0.10  excellent with neither                                    at least                        chipping nor cracking                                    40211  inventive         0.46˜0.51                  0.10  excellent with neither                                    at least                        chipping nor cracking                                    40212  inventive         0.46˜0.51                  0.10  excellent with neither                                    at least                        chipping nor cracking                                    40213  compar-  0.20˜0.27                  0.25  excellent with neither                                    at leastative                   chipping nor cracking                                    40214  compar-  0.45˜0.53                  0.22  corner chipped                                    15ative215  compar-  0.40˜0.47                  1.10  excellent with neither                                    at leastative                   chipping nor cracking                                    40216  compar-  0.30˜0.40                  0.95  corner chipped                                    10ative217  compar-  0.45˜0.50                  0.20  corner chipped                                    24ative218  compar-  0.46˜0.52                  0.80  corner chipped                                    26ative219  compar-  0.18˜0.25                  0.25  excellent with neither                                    at leastative                   chipping nor cracking                                    40220  compar-  0.45˜0.56                  0.20  corner chipped                                    10ative221  compar-  0.44˜0.52                  0.50  corner chipped                                     8ative222  compar-  0.33˜0.55                  0.60  corner chipped                                    10ative223  compar-  0.48˜0.56                  0.26  corner chipped                                    26ative224  compar-  0.48˜0.55                  0.24  corner chipped                                    24ative225  compar-  0.48˜0.53                  0.22  corner chipped                                    22ative______________________________________ 
    
     As understood from Table 7, the samples Nos. 201 to 212 having matrices of copper, tin, nickel and aluminum exhibited high friction coefficients and had neither chipping nor cracking on the appearances after the test. It is also understood that the samples Nos. 201 to 212 maintained a bending strength of at least 40 MPa and had sufficient strength for serving as friction materials. 
     On the other hand, the samples Nos. 213 to 225, similarly having matrices of copper, tin, nickel and aluminum, were insufficient as friction materials as described below: 
     The sample No. 213 containing dolomite in a ratio smaller than those of the remaining samples exhibited an insufficient friction coefficient for serving as a friction material. The sample No. 214 containing dolomite in a high ratio was inhibited from sintering of the matrix and reduced in material strength. 
     The sample No. 215 containing graphite in a ratio smaller than those of the remaining samples exhibited high abrasion loss. The sample No. 216 containing graphite in a high ratio was remarkably reduced in material strength and increased in abrasion loss. 
     The sample No. 217 containing potassium titanate in a ratio smaller than those of the remaining samples was reduced in material strength with no effect of maintaining the material strength. The sample No. 218 containing potassium titanate in a ratio larger than those of the remaining samples was reduced in material strength and increased in abrasion loss. 
     The sample No. 219 containing dolomite in a grain size smaller than those of the remaining samples was incapable of removing an oxide film or the like adhering to the surface of the counterpart and exhibited an insufficient friction coefficient for serving as a friction material. The sample No. 220 containing dolomite in a grain size larger than those of the remaining samples was inhibited from sintering of the matrix and reduced in material strength. 
     The sample No. 221 containing graphite in a grain size smaller than those of the remaining samples was inhibited from sintering of the matrix, reduced in material strength and deteriorated in abrasion resistance. The sample No. 222 containing graphite in a grain size larger than those of the remaining samples was incapable of ensuring a homogeneous dispersed state due to remarkable segregation of the graphite, reduced in material strength and increased in abrasion loss. 
     The samples Nos. 223 to 225 of conventional sintered friction materials containing no potassium titanate exhibited did not exhibit an effect of maintaining material strength and were reduced in material strength and suffered increased abrasion loss due to the absence of potassium titanate. 
     (TEST EXAMPLE 4) 
     Mxed powder materials were prepared by blending matrices, orthoclase, graphite and potassium titanate in the ratios shown in Table 8, molded into green compacts under a pressure of 2 to 5 tons/cm 2  and thereafter sintered in an N 2  atmosphere at 750° C. for 20 to 90 minutes, thereby preparing samples Nos. 301 to 325 of sintered friction materials. 
     
                                           TABLE 8__________________________________________________________________________      Matrix                              Potassium Titanate                  Total                      Orthoclase                                Graphite               Total                  Ratio                      Ratio     Ratio                  RatioSample                 (Vol.                      (Vol.                         Grain Size                                (Vol.                                   Grain Size          (Vol.No. Classification      Cu Sn Ni Al %)  %) (μm)                                %) (μm)                                          Whiskery                                               Platy                                                  Spherical                                                       %)__________________________________________________________________________301 inventive      23 3  10 2  38  12 0.5˜180                                30 200˜600                                          0    0  20   20302 inventive      23 3  10 2  38  4  0.5˜180                                45 200˜600                                          0    0  13   13303 inventive      23 3  10 2  38  8  0.5˜180                                26 200˜600                                          0    0  28   28304 inventive      23 3  10 2  38  13 0.5˜180                                21 200˜600                                          0    0  28   28305 inventive      26 3.4            11.3               2.3                  43  13 0.5˜180                                16 200˜600                                          0    0  28   28306 inventive      24.8         3.2            10.8               2.2                  41  13 0.5˜180                                41 200˜600                                          0    0  5    5307 inventive      24.8         3.2            10.8               2.2                  41  13 0.5˜180                                31 200˜600                                          0    0  15   15308 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          0    0  14   14309 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          0    14 0    14310 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          14   0  0    14311 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          0    7  7    14312 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          7    0  7    14313 comparative      23 3  10 2  38  0.5                         0.5˜180                                43 200˜600                                          0    0  18.5 18.5314 comparative      23 3  10 2  38  18 0.5˜180                                33 200˜600                                          0    0  11   11315 comparative      33.3         4.3            14.5               2.9                  55  15 0.5˜180                                5  200˜600                                          0    0  25   25316 comparative      22.4         2.9            9.7               2.0                  37  2  0.5˜180                                55 200˜600                                          0    0  6    6317 comparative      23 3  10 2  38  15 0.5˜180                                44 200˜600                                          0    0  3    3318 comparative      23 3  10 2  38  5  0.5˜180                                25 200˜600                                          0    0  32   32319 comparative      23 3  10 2  38  8  0.01˜0.4                                40 200˜600                                          0    0  14   14320 comparative      23 3  10 2  38  8  220˜400                                40 200˜600                                          0    0  14   14321 comparative      23 3  10 2  38  8  0.5˜180                                40 0.1˜8                                          0    0  14   14322 comparative      23 3  10 2  38  8  0.5˜180                                40 1200˜2000                                          0    0  14   14323 comparative      27 4  12 3  46  14 0.5˜180                                40 200˜600                                          0    0  0    0324 comparative      26 3.4            11.3               2.3                  43  14 0.5˜180                                43 200˜600                                          0    0  0    0325 comparative      24.8         3.2            10.8               2.2                  41  14 0.5˜180                                45 200˜600                                          0    0  0    0__________________________________________________________________________ 
    
     Test pieces were collected from the respective samples for performing a counterpart attackability test as a determination of judder resistance under a low surface pressure with a constant-speed frictional abrasion tester. Table 9 shows the test conditions. Table 10 shows counterpart attack quantities (abrasion depths from reference surfaces) and abrasion loss values of the friction materials. Referring to Tables 8 and 10, the samples Nos. 301 to 312 are inventive samples, and the samples Nos. 313 to 325 are comparative samples. In the columns of &#34;Classification&#34;, &#34;inventive&#34; and &#34;comparative&#34; indicate the inventive and comparative samples respectively. 
     
                       TABLE 9______________________________________Shape of Friction Surface (mm)               10 × 20______________________________________Counterpart         FC200Peripheral Speed (m/s)               10Surface Pressure (kgf/cm.sup.2)               1Friction Time (hr)  24Effective Radius of Friction (m)               0.1______________________________________ 
    
     
                       TABLE 10______________________________________              Counterpart Attack                           Abrasion Loss ofSample             Quantity     Friction MaterialNo.    Classification              (μm)      (mm)______________________________________301    inventive   not more than 10                           0.12302    inventive   not more than 10                           0.09303    inventive   not more than 10                           0.13304    inventive   not more than 10                           0.14305    inventive   not more than 10                           0.15306    inventive   not more than 10                           0.10307    inventive   not more than 10                           0.12308    inventive   not more than 10                           0.10309    inventive   not more than 10                           0.10310    inventive   not more than 10                           0.10311    inventive   not more than 10                           0.10312    inventive   not more than 10                           0.10313    comparative 55           0.19314    comparative not more than 10                           0.70315    comparative 15           1.10316    comparative 20           0.95317    comparative 14           0.50318    comparative 16           0.81319    comparative not more than 10                           0.75320    comparative 105          0.19321    comparative 20           0.50322    comparative 18           0.55323    comparative 20           0.50324    comparative 18           0.55325    comparative 16           0.60______________________________________ 
    
     As understood from Table 10, the samples Nos. 301 to 312 having matrices of copper, tin, nickel and aluminum were excellent in judder resistance with counterpart attack quantities of not more than 10 μm and exhibited small abrasion loss values of the friction materials. 
     On the other hand, the samples Nos. 313 to 325, similarly having matrices of copper, tin, nickel and aluminum, were insufficient as friction materials as described below: 
     The sample No. 313 containing orthoclase in a ratio smaller than those of the remaining samples was insufficient in judder resistance. The sample No. 314 containing orthoclase in a high ratio was inhibited from sintering of the matrix and reduced in material strength, and exhibited high abrasion loss. 
     The sample No. 315 containing graphite in a ratio smaller than those of the remaining samples exhibited high abrasion loss. The sample No. 316 containing graphite in a high ratio was remarkably reduced in material strength and increased in abrasion loss. 
     The sample No. 317 containing potassium titanate in a ratio smaller than those of the remaining samples was reduced in material strength and increased in abrasion loss. The sample No. 318 containing potassium titanate in a ratio larger than those of the remaining samples was reduced in material strength and increased in abrasion loss. 
     The sample No. 319 containing orthoclase in a grain size smaller than those of the remaining samples was inhibited from sintering of the matrix and reduced in material strength, and exhibited high abrasion loss. The sample No. 320 containing orthoclase in a grain size larger than those of the remaining samples was insufficiently improved in judder resistance. 
     The sample No. 321 containing graphite in a grain size smaller than those of the remaining samples was inhibited from sintering of the matrix, reduced in material strength and deteriorated in abrasion resistance. The sample No. 322 containing graphite in a grain size larger than those of the remaining samples was incapable of ensuring a homogeneous dispersed state due to remarkable segregation of graphite, reduced in material strength and increased in abrasion loss. 
     The samples Nos. 323 to 325 of conventional sintered friction materials containing no potassium titanate were reduced in material strength and increased in abrasion loss due to the absence of potassium titanate. 
     (TEST EXAMPLE 5) 
     Mixed powder materials were prepared by blending matrices, magnesium oxide, graphite and potassium titanate in the ratios shown in Table 11, molded into green compacts under a pressure of 2 to 5 tons/cm 2  and thereafter sintered in an N 2  atmosphere at 750° C. for 20 to 90 minutes, thereby preparing samples Nos. 401 to 425 of sintered friction materials. 
     
                                           TABLE 11__________________________________________________________________________      Matrix                              Potassium Titanate                  Total                      Magnesium Oxide                                Graphite               Total                  Ratio                      Ratio     Ratio                  RatioSample                 (Vol.                      (Vol.                         Grain Size                                (Vol.                                   Grain Size          (Vol.No. Classification      Cu Sn Ni Al %)  %) (μm)                                %) (μm)                                          Whiskery                                               Platy                                                  Spherical                                                       %)__________________________________________________________________________401 inventive      23 3  10 2  38  12 0.5˜180                                30 200˜600                                          0    0  20   20402 inventive      23 3  10 2  38  4  0.5˜180                                45 200˜600                                          0    0  13   13403 inventive      23 3  10 2  38  8  0.5˜180                                26 200˜600                                          0    0  28   28404 inventive      23 3  10 2  38  13 0.5˜180                                21 200˜600                                          0    0  28   28405 inventive      26 3.4            11.3               2.3                  43  13 0.5˜180                                16 200˜600                                          0    0  28   28406 inventive      24.8         3.2            10.8               2.2                  41  13 0.5˜180                                41 200˜600                                          0    0  5    5407 inventive      24.8         3.2            10.8               2.2                  41  13 0.5˜180                                31 200˜600                                          0    0  15   15408 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          0    0  14   14409 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          0    14 0    14410 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          14   0  0    14411 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          0    7  7    14412 inventive      23 3  10 2  38  8  0.5˜180                                40 200˜600                                          7    0  7    14413 comparative      23 3  10 2  38  0.5                         0.5˜180                                43 200˜600                                          0    0  18.5 18.5414 comparative      23 3  10 2  38  18 0.5˜180                                33 200˜600                                          0    0  11   11415 comparative      33.3         4.3            14.5               2.9                  55  15 0.5˜180                                5  200˜600                                          0    0  25   25416 comparative      22.4         2.9            9.7               2.0                  37  2  0.5˜180                                55 200˜600                                          0    0  6    6417 comparative      23 3  10 2  38  15 0.5˜180                                44 200˜600                                          0    0  3    3418 comparative      23 3  10 2  38  5  0.5˜180                                25 200˜600                                          0    0  32   32419 comparative      23 3  10 2  38  8  0.01˜0.4                                40 200˜600                                          0    0  14   14420 comparative      23 3  10 2  38  8  220˜400                                40 200˜600                                          0    0  14   14421 comparative      23 3  10 2  38  8  0.5˜180                                40 0.1˜8                                          0    0  14   14422 comparative      23 3  10 2  38  8  0.5˜180                                40 1200˜2000                                          0    0  14   14423 comparative      27 4  12 3  46  14 0.5˜180                                40 200˜600                                          0    0  0    0424 comparative      26 3.4            11.3               2.3                  43  14 0.5˜180                                43 200˜600                                          0    0  0    0425 comparative      24.8         3.2            10.8               2.2                  41  14 0.5˜180                                45 200˜600                                          0    0  0    0__________________________________________________________________________ 
    
     A creak test was carried out on the samples in accordance with the JASO C406-82 passenger car braking device dynamometer test method. Table 12 shows the test conditions. Abrasion loss values were measured before and after the creak test. Table 13 shows the ranges of friction coefficients, creak ratios (number of creaking times÷total number of braking times) and abrasion loss values in the creak test. Referring to Tables 11 and 13, the samples Nos. 401 to 412 are inventive samples, and the samples Nos. 413 to 425 are comparative samples. In the columns of &#34;Classification&#34;, &#34;inventive&#34; and &#34;comparative&#34; indicate the inventive and comparative samples respectively. 
     
                       TABLE 12______________________________________Car Speed (km/h)        30Braking Start       50→80→120→160→200→160.fwdar       w.120→80→50Temperature (°C.)Brake Fluid Pressure       5→10→15→20(kgf/cm.sup.2)Number of Cycles       4 cycles of above combinationTotal Number of       144Braking Times______________________________________ 
    
     
                       TABLE 13______________________________________                       Abrasion                       Loss of                       FrictionSample           Friction   MaterialNo.   Classification            Coefficient                       (mm)   Creak Ratio______________________________________401   inventive  0.47˜0.54                       0.12   not more than 1%402   inventive  0.44˜0.50                       0.09   not more than 1%403   inventive  0.46˜0.53                       0.13   not more than 1%404   inventive  0.48˜0.55                       0.14   not more than 1%405   inventive  0.48˜0.55                       0.15   not more than 1%406   inventive  0.48˜0.53                       0.10   not more than 1%407   inventive  0.48˜0.53                       0.12   not more than 1%408   inventive  0.46˜0.51                       0.10   not more than 1%409   inventive  0.46˜0.51                       0.10   not more than 1%410   inventive  0.46˜0.51                       0.10   not more than 1%411   inventive  0.46˜0.51                       0.10   not more than 1%412   inventive  0.46˜0.51                       0.10   not more than 1%413   comparative            0.35˜0.42                       0.19   30%414   comparative            0.45˜0.53                       0.62   not more than 1%415   comparative            0.40˜0.47                       1.10   10%416   comparative            0.30˜0.40                       0.95   5%417   comparative            0.45˜0.50                       0.50   5%418   comparative            0.46˜0.52                       0.81   4%419   comparative            0.33˜0.40                       0.65   not more than 1%420   comparative            0.45˜0.56                       0.19   21%421   comparative            0.44˜0.52                       0.50   2%422   comparative            0.33˜0.55                       0.55   6%423   comparative            0.48˜0.56                       0.70   10%424   comparative            0.48˜0.55                       0.65   6%425   comparative            0.48˜0.53                       0.60   5%______________________________________ 
    
     As understood from Table 13, the samples Nos. 401 to 412 having matrices of copper, tin, nickel and aluminum exhibited high friction coefficients and small abrasion loss. It is also understood that the samples Nos. 401 to 412 had sufficient creak resistance for serving as friction materials with creak ratios of not more than 1%. 
     On the other hand, the samples Nos. 413 to 425, similarly having matrices of copper, tin, nickel and aluminum, were insufficient as friction materials as described below: 
     The sample No. 413 containing magnesium oxide in a ratio smaller than those of the remaining samples was insufficiently improved in creak resistance. The sample No. 414 containing magnesium oxide in a high ratio was inhibited from sintering of the matrix, reduced in material strength and increased in abrasion loss. 
     The sample No. 415 containing graphite in a ratio smaller than those of the remaining samples exhibited high abrasion loss. The sample No. 416 containing graphite in a high ratio was remarkably reduced in material strength and increased in abrasion loss. 
     The sample No. 417 containing potassium titanate in a ratio smaller than those of the remaining samples was reduced in material strength and increased in abrasion loss. The sample No.418 containing potassium titanate in a ratio larger than those of the remaining samples was reduced in material strength and increased in abrasion loss. 
     The sample No. 419 containing magnesium oxide in a grain size smaller than those of the remaining samples was inhibited from sintering of the matrix, reduced in material strength and increased in abrasion loss. The sample No. 420 containing magnesium oxide in a grain size larger than those of the remaining samples was insufficiently improved in creak resistance. 
     The sample No. 421 containing graphite in a grain size smaller than those of the remaining samples was inhibited from sintering of the matrix, reduced in material strength and deteriorated in abrasion resistance. The sample No. 422 containing graphite in a grain size larger than those of the remaining samples was incapable of ensuring a homogeneous dispersed state due to remarkable segregation of graphite, reduced in material strength and increased in abrasion loss. 
     The samples Nos. 423 to 425 of conventional sintered friction materials containing no potassium titanate were reduced in material strength and exhibited remarkable abrasion loss due to the absence of potassium titanate. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.