Copper-based sliding surface

Details Copper-based sliding surface Copper-based sliding surface

1998-01-09

2000-02-08

Speer, Timothy M.

Stock material or miscellaneous articles

All metal or with adjacent metals

Having metal particles

428674, 428677, 384910, 384912, 420591, 75247, F16C 3312, C22C 2912, B22F 704

Patent

active

060226293

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a copper-based sliding layer, comprising a matrix of copper or a copper alloy with softer metallic inclusions of at least 10 wt-%, which form particles having sectional areas separate from each other with respect to an observation plane parallel to the layer.
Cast or sintered sliding layers of lead-containing bronzes, which usually have a tin content between 1 and 5 wt-% and a lead content of 10 to 30 wt-%, exhibit a heterogeneous structure characteristic of the respective production process and dependent on the tin and lead contents with a wide statistical scatter of the mean particle diameters related to the individual lead particles. During the casting process, lead accumulates in the interdendritic spaces of the solidifying bronze, where the size of the lead particles increases with decreasing rate of solidification, which leads to a correspondingly wide Gaussian distribution of the size of the lead precipitates. In the case of sintered lead bronzes, a similar random distribution of the lead particle sizes is observed, but for a different reason. Since the coagulation and growth processes taking place during sintering are not uniform, the originally very fine lead distribution in the sintering powder leads to different lead particle sizes, which lie in a wide range of scatter.
With increasing lead content, bronze-containing sliding layers made both by casting and by sintering include coarser and in part coherent lead phases, which provide lower strength values with good tribological properties of the sliding layer. For higher strength requirements, it was therefore necessary to restrict the lead content to e.g. 15 wt-% and accept the less favorable tribological properties of the sliding layer involved in such restriction. Attempts at making a sliding layer with a particularly fine lead distribution, for instance with mean particle diameters smaller than 1 .mu.m, by means of an electrodeposition or a physical deposition, have led to higher strength values as expected, but despite the increased lead content up to 35 wt-%, the tribological properties of the sliding layer have surprisingly hardly improved.
It is therefore the object underlying the invention to improve a copper-based sliding layer as described above such that good tribological properties corresponding to the higher contents of softer inclusions can be combined with advantageous strength values.
This object is solved by the invention in that when adding up the sectional areas of the particles starting with the smallest sectional area and proceeding according to ascending area size, the sectional area of that particle which completes the subtotal of the sectional areas up to its own area size to 50% of the final total corresponds to a maximum of ten times the sectional area of the particle completing the subtotal to 5% of the final total, but at least one fifth of the largest individual sectional area.
The invention is based on the knowledge that for the tribological properties of a copper-based sliding layer having for instance softer lead inclusions, not only the proportion of the lead inclusions, but also their size distribution is decisive, namely in particular in the sliding surface and/or in an observation plane parallel to the layer. When the sectional areas between the lead particles and the observation plane lie within a limited range of sizes, unexpectedly good tribological properties can surprisingly be achieved for the sliding layer. Although the causes therefor have not yet been clarified completely, it is assumed that due to the much more uniform structure of the inclusions as compared to the conventional wide random distribution of sizes of the lead phases neither the strength of the sliding layer is locally impaired by larger coherent lead phases nor is there obtained a significant content of lead inclusions, which as a result of the small particle size can hardly contribute to the tribological properties. As accordingly both the size of the sectional areas of the lead particles and their size distrib

REFERENCES:
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patent: 5004581 (1991-04-01), Takagi
patent: 5045405 (1991-09-01), Koroshetz
patent: 5242717 (1993-09-01), Tanaka
patent: 5346668 (1994-09-01), Tanaka
patent: 5413875 (1995-05-01), Tanaka
J.A. Thornton and A.S. Penfold: Thin Film Processes, pp. 103-105, 1978.

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