Conventionally known as wear-resistant copper-based alloys are beryllium-added copper alloys, copper-nickel-silicon alloys known as Corson alloys, and dispersion-strengthened alloys in which hard oxide particles such as SiO2, Cr2O3 and BeO particles are dispersed in a copper-based matrix. These alloys, however, have a problem of adhesion and do not always possess sufficient wear resistance.
In this connection, the present applicants have developed a wear-resistant copper-based alloy containing zinc and/or tin, which are more easily oxidized than copper. This copper-based alloy has upgraded in adhesion resistance because of generation of oxides of zinc and/or tin, and accordingly has improved in wear resistance. However, since zinc and tin have considerably lower melting points than that of copper, this alloy is not always satisfactory. Particularly when a cladding layer of the abovementioned copper-based alloy is formed by using such a high-density energy heat source as a laser beam, zinc and/or tin tend to evaporate during the cladding operation and it is not easy to maintain target concentrations of alloying elements. In this connection, recently the present applicants have developed wear-resistant copper-based alloys having a composition comprising, by weight, 10.0 to 30.0% nickel, 0.5 to 5.0% silicon, 2.0 to 15.0% iron, 1.0 to 10.0% chromium, 2.0 to 15.0% cobalt, and 2.0 to 15.0% one or more of molybdenum, tungsten, niobium and vanadium. (Patent Document No. 1: Japanese Unexamined Patent Publication No. H08-225,868 and Patent Document No. 2: Japanese Examined Patent Publication No. H07-17,978). These alloys mainly comprise hard particles including silicide of Co—Mo, and a Cu—Ni based matrix. These wear-resistant copper-based alloys secure their wear resistance primarily by the hard particles including silicide of Co—Mo, while these wear-resistant copper-based alloys secure their crack resistance primarily by the Cu—Ni based matrix. These alloys exhibit high wear resistance even when used under severe conditions. Moreover, since neither zinc nor tin is used as a positive element, even if these alloys are used for cladding, there are little inconveniences caused by evaporation of alloying elements and fumes generate in a smaller amount. Consequently, these alloys are especially suitable for forming a cladding layer by using a high-density energy heat source such as a laser beam.
As mentioned above, the alloys according to Patent Document No. 3 (Japanese Unexamined Patent Publication No. H08-225,868) and Patent Document No. 4 (Japanese Examined Patent Publication No. H07-17,978) exhibit excellent wear resistance even when used under severe conditions. Particularly in an oxidizing atmosphere or in the air these alloys exhibit excellent wear resistance because of generation of an oxide which shows favorable solid lubrication.
However, although having an effect of improving wear resistance, the above silicide of Co—Mo is so hard and brittle that when the composition of these alloys is controlled to increase the area ratio of the hard particles, the wear-resistant copper-based alloys deteriorate in terms of crack resistance. Especially when these wear-resistant copper-based alloys are used for cladding, the cladding layer sometimes cracks and the cladding yield rate deteriorates. In contrast, when the composition of these alloys is controlled to decrease the area ratio of the hard particles in the wear-resistant copper-based alloys, these wear-resistant copper-based alloys deteriorate in terms of wear resistance.
In recent years, the above wear-resistant copper-based alloys have been used under a variety of environments and their service conditions are getting severer. Therefore, wear-resistant copper-based alloys have been requested to be capable of exhibiting excellent wear resistance under various environments. In the industrial world, there is demand for an alloy which has good wear resistance, crack resistance and machinability in a balanced manner when compared with those of the alloys according to the above publications.
[Patent Document No. 1] Japanese Unexamined Patent Publication No. H08-225,868
[Patent Document No. 2] Japanese Examined Patent Publication No. H07-17,978
[Patent Document No. 3] Japanese Unexamined Patent Publication No. H08-225,868
[Patent Document No. 4] Japanese Examined Patent Publication No. H07-17,978