Multilayer material for sliding elements and process for the production thereof

Abstract: A process for the production of sliding elements, is described in which an overlay of lead-tin-copper is applied by electroplating to the prefabricated semi-finished product, and in which a ternary, fluoroborate-free electroplating bath is used without brighteners and with the addition of non-ionic wetting agents and free alkyl sulfonic acid. After the deposition of the galvanic overlay a heat treatment is carried out in the temperature range of 150°C to 200°C for between 1 and 100 hours. The multilayer material for sliding elements comprises at least a backing and an overlay of 12 to 16 wt. % tin and 7 to 11 wt. % copper, the rest being lead. The overlay comprises 15 to 25 wt. % particles of intermetallic compound Cu6Sn5.

Description: The invention relates to a process according to the preamble of claim 1 and to a multilayer material according to the preamble of claim 8. Sliding elements should be understood to mean all types of bearing liners as well, inter alia, as pistons and piston rings. Overlays of multilayer materials for sliding elements are generally produced by electroplating in appropriate electrolyte baths. There have hitherto generally been used for this purpose fluoroborate-containing baths, which exhibit a number of disadvantages, however. Deposits from fluoroboric acid based baths are unstable at the temperature at which crankshaft bearings operate in internal combustion engines. The main alloying element in the lead based overlay, which may be tin or indium, diffuses at engine temperature into the underlying copper-lead lining, resulting in a loss of tin or indium from the overlay and a corresponding reduction in the resistance of the overlay to wear, fatigue cracking and corrosion. Diffusion into the copper-lead lining may be prevented by the incorporation of an electrodeposited nickel "dam" between the copper-lead lining and the overlay, but diffusion towards the nickel still occurs, resulting in the growth of a nickel tin compound such as NiSn on the surface of the nickel dam. A degree of loss of the alloying element from the overlay thus occurs in spite of the presence of the nickel dam, and a significant deterioration in the bearing performance of the overlay results. However, the extent of the deterioration is not as great when a nickel dam is present as when it is not, and for that reason a nickel dam is generally incorporated in overlay plated copper-lead crankshaft bearings. The significant discovery disclosed in DE 195 45 427 A1 is that lead-based overlays may be deposited from an alkylsulfonic bath which show the deleriorous diffusion behaviour described above to a much lesser extent than overlays from a fluoroboric acid bath. The reduction in diffusion is such that the nickel dam may be omitted, resulting in a simplification of the plating process, while at the same time an improvement in the bearing performance of the overlay is obtained. In particular the resistance of the overlay to corrosion is improved, and the wear incurred during engine operation is reduced. The experimental results demonstrating these advantages have been described in "New Bath Formulation for Electrodeposition of Improved Corrosion and Wear Resistant Sliding Layers for Engine Bearings" by Grünthaler, Huhn, Miiller, Staschko and Toth, SAE Paper 960964, Feb. 26-29, 1996. Although hardness was improved by 20 % compared to conventional sliding layers, wear resistance was not yet satisfactory. It is therefore the object of the invention to supplement the process known from DE 195 45 427 so as to further improve the wear resistance of the sliding layer. It is also an object of the invention to create an improved layer compound material. The problem is solved by a process whereby, after application of the galvanic running layer, a heat treatment is performed in the temperature range 150°C - 200°C for a period of 1 - 100 h. It was found that the heat treatment results in diffusion and coming-together of the copper and tin components, so that particles of the intermetallic phase Cu6Sn5 are generated. Due to these Cu6Sn5 particles the wear of the sliding layer is reduced by app. 50 %. The heat treatment is preferably executed in air. According to a further embodiment, the heat treatment may also be executed in oil, whereby paraffin oil and silicon oil are particularly suitable. The heat treatment is preferably performed in a temperature range between 170 - 185°C. The heat treatment is preferably performed for a period of 4 - 12 h. The process known from DE 195 45 427 is especially well suited to generate both tin and copper in high concentrations. It was found that the content of Cu6Sn5 particles is greater, the higher the tin and copper contents are. To further improve wear resistance, a running layer of 12 - 16 weight-% tin and 7 - 11 weight-% copper and remainder lead is preferably applied. The layer material for sliding members shows 15 - 25 weight-% Cu6Sn5 particles in the sliding layer. A lead-bronze layer and a nickel layer are preferably provided between the sliding layer and the support layer. Exemplary embodiments of the invention are discussed below by reference to the drawings. The figures show: Fig. 1a micro section of the layer material produced according to DE 195 45 427 A1, Figs. 1b and 1c detail views of the sliding layer with accentuation of copper and tin Figs. 2a-c presentations of the material corresponding to Figs. 1a - c after 8-hours heat treatment at 177°C. Fig. 1 a shows a micro section of a sample prior to heat treatment. A lead-bronze layer 1 and a nickel layer 2 as well as a sliding layer 3 are applied on a carrier material (not shown) by the process according to DE 195 45 427 A1, whereby the sliding layer consists of 7.8 weight-% Cu, 15.5 weight-% Sn and remainder copper. Figs. 1b and 1c show enlargements of the sliding layer 3, whereby the distribution of the individual components copper and tin are respectively shown in elemental maps obtained on an electron microscope. Fig. 1 b shows no copper particles at all, whereas Fig. 1c shows significant tin accumulations. After heat treatment for 8 h at 177°C the structure in sliding layer 3 has changed (Fig. 2a). The tin accumulations resp. tin particles 4 have increased (Fig. 2c) and there are now additional copper particles 5 which are visible in Fig. 2b. The presence of coincident concentrations of copper and tin shows that particles consisting of the intermetallic phase Cu6Sn5 must be present. The appearance of intermetallic particles in the overlay, harder than the surrounding matrix, would be expected to increase wear resistance and this has been demonstrated during engine tests. The table shows the results of comparison of heat treated and non-heat treated bearings plated according to DE 195 45 427 after being run in a Caterpillar 3126 heavy duty engine. Overlay composition was 7.8 % copper, 15.5 % tin and remainder lead, and the heat treatment was at 177°C for 8 hours. Heat treated Bearings Non-heat treated bearings Overlay thickness micron 23 23 Test hours 75 75 Average overlay wear micron 5.9 13.2 Average weight loss mg 68.2 100.5 The wear suffered by the heat treated bearings was 45 % of that suffered by the non-heat treated bearings.

Claims: A process for the production of sliding elements, in which an overlay of lead-tin-copper is applied by electroplating to the prefabricated semi-finished product, and in which a ternary, fluoroborate-free electroplating bath is used without brighteners and with the addition of non-ionic wetting agents and free alkyl sulfonic acid, characterized in that after the deposition of the galvanic overlay a heat treatment is carried out in the temperature range of 150°C to 200°C for between 1 and 100 hours. A process according to claim 1, characterized in that the heat treatment is carried out in air. A process according to claim 1, characterized in that the heat treatment is carried out in oil. A process according to claim 3, characterized in that the heat treatment is carried out in paraffin oil or silicone oil. A process according to one of the claims 1 to 4, characterized in that the heat treatment is carried out between 170 and 185°C. A process according to one of the claims 1 to 5, characterized in that the heat treatment is carried out for between 4 - 12 hours. A process according to one of the claims 1 to 6, characterized in that an overlay comprising 12 - 16 wt.% tin, 7 - 11 wt.% copper and remainder being lead is deposited by electroplating. A multilayer material for sliding elements, which comprises at least a backing and an overlay of 12 to 16 wt.% tin and 7 to 11 wt.% copper, the rest being lead, characterized in that the overlay comprises 15 to 25 wt.% particles of intermetallic compound Cu6Sn5.

Inventors: PRATT GEORGE, PRATT, GEORGE
Applicants: FEDERAL MOGUL WIESBADEN GMBH
Application year: 1999
Main classification: C25D3
IPC codes: F16C33, C25D5, C25D7, C25D3, C22C11