Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2000-03-23
2001-05-22
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S645000, C428S935000, C428S923000, C384S912000, C205S109000
Reexamination Certificate
active
06235405
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electrodeposited alloy layer, in particular an overlay of a plain bearing, comprising a layered alloy having at least one alloying element in addition to a base metal, in whose matrix containing the alloying element in a finely crystalline form inorganic particles with a diameter smaller than 2 &mgr;m are incorporated finely divided.
DESCRIPTION OF THE PRIOR ART
To increase the hardness and the wear resistance of multilayer plain bearings with an electrodeposited lead-based overlay with the addition of tin, inorganic hard particles are embedded in the overlay matrix, which hard particles should rather be finely divided in individual particles in the overlay. For this purpose it is known (DE 196 22 166 A1) to use an electroplating bath free from fluoroborate with the addition of a non-ionic wetting agent for isolating the hard particles already in the electroplating bath, so that these hard particles with a diameter smaller than 2 &mgr;m are deposited finely divided together with the alloying constituents. By using an organic grain diminution agent in the electroplating bath there should also be achieved a finely crystalline deposition of the tin in the alloy matrix. Under thermal loads as they occur in plain bearings for internal combustion engines, a coarsening of the tin deposits occurs despite these measures, namely as a result of the temperature-dependent solubility of tin in the lead matrix. When the tin dissolved in the lead upon heating cools down, a coarser-grained tin phase occurs due to its tendency to reduce its surface as compared to the lead, where smaller deposits preferably attach to already existing larger deposits. The hard particles incorporated in the alloy matrix, which include carbides, oxides, nitrides, borides or silicides, have an influence on the diffusion of tin particles, but not on their tendency to coarsen, so that a corresponding ageing of the overlay due to a coarsening of its structure must be expected.
Since the electrodeposition of an alloy from an electroplating bath usually occurs in a temperature range below the melting and softening points of the alloying constituents, electrodeposited alloy layers generally represent metastable, supersaturated, solid solutions. When the heat cycles occurring during the operation of the engine fall below the solubility limit, alloying elements are deposited from the alloy matrix in elementary form or as intermetallic compounds, where this deposition largely takes place uncontrolled, but with a tendency to form larger deposits at the expense of the smaller deposits, so that this ageing behavior is not restricted to overlays of plain bearings, although the same are particularly important for such bearings.
SUMMARY OF THE INVENTION
It is therefore the object underlying the invention to provide an electrodeposited alloy layer, in particular an overlay of a plain bearing, wherein ageing due to a heat-related coarsening of the structure can be largely be prevented.
Proceeding from an electrodeposited alloy layer as described above, this object is solved by the invention in that the inorganic particles used as nucleating agents with a diameter of 0.01 to 1 &mgr;m have a crystal form at least substantially corresponding to the form of crystallization of the alloying element.
On the condition that their crystal form at least substantially corresponds to the form of crystallization of the alloying element whose finely crystalline deposition in the alloy matrix should be ensured, the inorganic particles, which have so far only been used for dispersion hardening, may surprisingly be used as nuclei for this alloying element, which due to the small diameters of these nuclei and the large enough number of nucleating agents crystallizes at many points at the same time, which first of all leads to a particularly fine distribution of this alloying element in the alloy matrix. Since the nucleating agents, which at the occurring treatment temperatures are insoluble in the alloy matrix, are fixed in the matrix and in the case of a temperature-related local dissolution of the alloying element are liberated in the base metal, the liberated inorganic particles are again available as nucleating agents when the solubility limit of the alloying element is not reached, so that the deposited alloying element preferably again crystallizes at these nuclei.
To be able to form a nucleus, the diameter of the nucleating agents must have a certain minimum magnitude, which is about 0.01 &mgr;m. To be able to ensure the finely crystalline structure of the alloying element deposited in the alloy matrix, the nucleating agents themselves should not be chosen too coarse-grained. An upper diameter of
1
pm is still acceptable in this connection, altough with an upper particle size of 0.5 &mgr;m better crystallization conditions can be created. A particle diameter between 0.03 and 0.5 &mgr;m turned out to be useful for most applications. Probably due to their small size, the inorganic particles used as nucleating agents do not effect a relevant dispersion hardening of the alloy layer.
As explained already, it is of major importance for a finely crystalline deposition of the alloying element in the alloy matrix to provide a sufficient number of nuclei. The concentration of the nuclei should be adapted to the concentration of the alloying element such that in essence for each deposited particle of the alloy phase an inorganic particle is available as nucleus. To satisfy this request, the total surface of the inorganic particles in a volume unit of the overlay may be ten to ten thousand times, preferably hundred to thousand times as large as the surface unit associated to the volume unit. In this connection it should be noted that to perform their function, the inorganic particles should preferably have a spherical structure, but not an acicular structure.
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patent: 5185216 (1993-02-01), Tanaka et al.
patent: 5266181 (1993-11-01), Matsumura et al.
patent: 6022629 (2000-02-01), Rumpf et al.
patent: 196 22 166 (1997-12-01), None
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Collard & Roe P.C.
Miba Gleitlager Aktiengesellschaft
Zimmerman John J.
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