Bearings having an overlay coating containing dispersed phase of

Details Bearings having an overlay coating containing dispersed phase of Bearings having an overlay coating containing dispersed phase of

1991-01-30

1993-05-11

Hannon, Thomas R.

Bearings

Rotary bearing

Plain bearing

384912, F16C 3312, F16C 3324

Patent

active

052095789

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to journal bearings and to coatings known as overlays deposited on such bearings particularly by the technique of cathodic sputtering.
It is known to deposit soft overlay alloy compositions onto the running surface of a journal bearing by cathodic sputtering. An example of this is described in European patent application 0 300 993 of Koroschetz et al. An overlay based on copper, aluminium or silver is described having colummar crystal grains with a major axis normal to the sliding direction and an embedded phase of particles which are softer than the matrix and also insoluble in the matrix metal. Examples are given of overlay compositions of aluminium-20 vol. % tin and copper-30 vol. % lead. Such alloy compositions were, until relatively recently used as wrought or cast materials as the main bearing material having an overlay running coating based on alloys of lead or tin. The use of such two-phase alloys as the overlay is attributable to the search for materials having both improved wear resistance and improved fatigue strength over conventional electro-deposited lead and tin based alloys whilst retaining good comformability and anti-seizure properties.
However, in the initial stages of running of a new shaft in an engine it is desirable to have a higher degree of conformability than is readily provided from known two-phase alloys such as are described in EP 0 300 993. Furthermore, as the overlay wears and the running clearance between shaft journal and bearing increases it is desirable to provide an increasing degree of wear resistance in the overlay material. With increasing overlay wear, conformability becomes less important and wear resistance becomes more important.
According to the present invention there is provided a journal bearing including a strong backing material having thereon a relatively thick layer of a bearing material, and having a relatively thin overlay coating, the overlay coating comprising a first material constituting the coating matrix and having therein a dispersed phase of a second material wherein the dispersed phase of the second material has a relatively low content adjacent the bearing material layer and has a relatively high content at the coating surface, the total thickness of said overlay coating being in the range from 10 to 50 micrometers.
The bearing material, interposed between the strong backing material which may, for example, be steel, and the coating may be a copper based alloy such as a leaded-bronze, an aluminium alloy such as an aluminium-copper-silicon-tin alloy or a silver alloy.
Where diffusion between the dispersed phase in the coating may occur into the bearing material at the bearing operating temperature, it is desirable for the coating at the interface to consist essentially of the matrix metal without dispersed second material therein. The thickness of the coating matrix material at the interface may be less than 3 micrometers and preferably be between 0.1 and 2 micrometers to serve as a diffusion barrier.
In some instances where there is a layer of a bearing material it may be desirable to provide a coating of a further material of, for example, nickel or cobalt prior to deposition of the overlay itself. This further material may be deposited by electro-plating or by sputtering.
The use of a relatively pure interlayer is also beneficial in that it enhances adhesion to the substrate on which the coating is deposited.
The total thickness of the coating may be between 10 and 50 micrometers and preferably between 15 and 40 micrometers depending upon the application.
At the running surface of the coating there may be a layer comprising virtually the pure second material to provide what is known as a sacrificial overlay. The thickness of this surface layer may be between 0.1 and 5 micrometers and preferrably be between 1 and 3 micrometers.
The purpose of the surface layer is to provide a high degree of conformability and compatibility in the initial running-in stage of an engine. The second material, constituting the disperse

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patent: 4973523 (1990-11-01), Neuhaus et al.
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