Sliding element made of a copper alloy

Abstract

Sliding element made of a copper alloy containing the following components (in wt.%): 2.0 to 3.0% Ni, 0.45 to 1.0% Si, 0.45% to 0.95% Ti and / or Cr, optionally from 0.05 to 1.5% Co, optionally from 0.05 to 0.1% Mg, Al, Fe, optionally from 0.01 to 0.1% Pb, optionally from 0.002 to 0.01% P, Residual copper and unavoidable impurities, characterized by that at least one fraction of excretions is present, wherein the excretions have a volume-equivalent sphere diameter of at least 1.0 µm and a density of 5,000 to 20,000 particles per mm² 2 exhibit that the excretions are Cr-containing and / or Ti-containing silicides, that the ratio of the sum of the Ni content [Ni], Ti content [Ti] and Cr content [Cr] to the Si content [Si]: 4.3 ≤ ([Ni] + [Ti] + [Cr]) / [Si] ≤ 6.5.

Description

[0001] The invention relates to a sliding element made of a copper alloy according to the preamble of claim 1.

[0002] Sliding elements made of copper alloys are used, for example, in internal combustion engines in the connecting rod or crankshaft bearing eyes. The technical requirements for the sliding element material are becoming more stringent with the development of modern engines. Legal regulations also require the lead content in the material to be reduced to a minimum. At the same time, pressure is increasing to reduce the cost of sliding elements.

[0003] A well-known copper-zinc alloy for sliding elements is CuZn31Si1. Up to 0.8 wt.% lead can be added to the alloy to improve the material's machinability. The high copper content in this alloy makes the sliding element expensive. Furthermore, the bearing capacity of the wear-resistant structural components in this alloy is too low to withstand the stresses encountered in modern engines in the future.

[0004] EP 2 128 282 A1 discloses a copper alloy with excellent strength and formability for use in electrical and electronic components. The copper alloy contains 1.5 wt% to 4.5 wt% nickel (Ni) and 0.3 wt% to 1.0 wt% silicon (Si). Additionally optionally one or both of 0.01 wt% to 1.3 wt% tin (Sn) and 0.005 wt% to 0.2 wt% magnesium (Mg), 0.01 wt% to 5 wt% zinc (Zn), one or both of 0.01 wt% to 0.5 wt% manganese (Mn) and 0.001 wt% to 0.1 wt% chromium (Cr), a total of 0.1 wt% or less of at least one member selected from the first group of elements consisting of B, C, P, S, Ca, V, Ga, Ge, Nb, Mo, Hf, Ta, Bi, and Pb, each in an amount of 0.0001 wt% to 0.1 wt%, and a total of 1 wt%.-% or less of at least one member selected from the second group of elements consisting of Be, Al, Ti, Fe, Co, Zr, Ag, Cd, In, Sb, Te and Au, each in an amount of 0.001 wt% to 1 wt%, the total amount of the first and second groups of elements being 1 wt% or less, the balance being copper and unavoidable impurities.

[0005] Furthermore, EP 2 463 393 A1 discloses a copper alloy containing Ni: 1.5 wt.% to 3.6 wt.% and Si: 0.3 wt.% to 1.0 wt.%, with the remainder consisting of copper and unavoidable impurities. Furthermore, the copper alloy can optionally contain one or more elements selected from the group consisting of Fe, Mn, Mg, Co, Ti, Cr, and Zr in a total amount of 0.01 wt.% to 3.0 wt.%.

[0006] The copper alloy has crystal grains with an average crystal grain size of 5 µm to 30 µm. The area ratio of crystal grains with a crystal grain size not less than twice the average crystal grain size is not less than 3%; the area ratio of crystal grains with a cubic orientation to the area of ​​crystal grains with a crystal grain size not less than twice the average crystal grain size is not less than 50%.

[0007] Furthermore, WO 2009 / 082695 A1 discloses a copper-based alloy with an improved combination of yield strength and electrical conductivity for electronic applications. The copper alloy consists essentially of 1.0 wt% to 6.0 wt% Ni, up to about 3.0 wt% Co, 0.5 wt% to 2.0 wt% Si, 0.01 wt% to 0.5 wt% Mg, up to 1.0 wt% Cr, up to 1.0 wt% Sn, and up to 1.0 wt% Mn, with the remainder being copper and impurities. The alloy is processed to have a yield strength of at least about 945 MPa and an electrical conductivity of at least about 25% IACS.

[0008] Also known from DE 10 2009 017 362 A1 is a multilayer plain bearing and a copper-based alloy for a multilayer plain bearing. The multilayer plain bearing comprises a support metal layer, a bearing metal layer, and a sliding layer, wherein the bearing metal layer comprises a copper alloy. It is proposed that the copper alloy be a copper-based alloy containing at least one transition element from the group consisting of Cr, Fe, Co, Ni, Mn, Zr, Si, Zn, and Cu, in particular in a proportion of 0.1 to 3.0 wt.%.

[0009] The invention is based on the object of providing a sliding element which is resistant to wear caused by friction against steel and, in addition, of developing a copper alloy.

[0010] The invention is defined by the features of claim 1. The further dependent claims relate to advantageous embodiments and developments of the invention.

[0011] The invention includes a sliding element made of a copper alloy containing the following components (in wt%): 2.0 to 3.0% Ni, 0.45 to 1.0% Si, up to 1.5% Ti and / or Cr, where the sum of the Ni content [Ni] and the Ti content [Ti]: [Ni] + [Ti] ≥ 0.2%, optionally from 0.05 to 1.5% Co, optionally from 0.05 to 0.1% Mg, Al, Fe, optionally from 0.01 to 0.8% Pb, optionally from 0.002 to 0.01% P, Rest Cu and unavoidable impurities, where the ratio of the sum of the Ni content [Ni], Ti content [Ti] and Cr content [Cr] to the Si content [Si]: 4.3 ≤ ([Ni] + [Ti] + [Cr]) / [Si] ≤ 6.5.

[0012] The copper alloy preferably contains a Ti and / or Cr content of at least 0.2 wt.%.

[0013] The alloy of the sliding element according to the invention contains hard phases embedded in the alloy matrix. Such hard phases provide a significant support component in a friction pair. Several hard phase fractions can also form, which differ in their particle size.

[0014] The hard phases formed by at least one fraction of the above-disclosed precipitates provide a contact area of ​​up to approximately 3% of the surface area of ​​a friction pair. Surface areas of up to 5% still provide particularly preferred contact areas. This also results in a significant reduction in the coefficients of friction or sliding friction.

[0015] The optionally added elements magnesium, aluminum and iron further improve the mechanical properties and resistance to corrosive influences.

[0016] In principle, the lead content in the alloy can be up to 0.8 wt.%. If legal regulations permit, up to 0.25 wt.% lead can be added to the alloy as a chip breaker if necessary. The lead content is preferably a maximum of 0.1 wt.%. However, the alloy particularly preferably has a lead content that lies within the range of unavoidable impurities. The function of a sliding element according to the invention is not impaired by the absence of lead.

[0017] Optionally, up to 0.08 wt.% phosphorus can be added to the sliding element alloy. Phosphorus serves to deoxidize the melt and, together with nickel, forms nickel phosphides, which also contribute to wear resistance.

[0018] A special type of sliding element is plain bearing bushings. Due to the different manufacturing processes, a distinction is made between rolled and turned bushings.

[0019] Rolled bushings are manufactured from strip-shaped semi-finished products made of the copper alloy according to the invention by forming an appropriately dimensioned strip section into a hollow cylinder and joining the abutting strip edges. Preferably, the material is used from strip and plate casting. In strip casting, a relatively thin strip is cast as the casting format. Unlike thin cast strip, cast slabs are hot-formed. Cooling from the hot-forming stage can already lead to the formation of particles containing Cr, Ti, and Si. To influence the final strength of the subsequent process steps of cold forming and annealing, rapid cooling from the hot-forming stage is used.

[0020] Turned bushings are manufactured by machining from a rod- or tubular semi-finished product made of the copper alloy according to the invention. To produce the semi-finished product, a bolt-shaped casting format is cast, from which a press tube or rod is pressed through a hot pressing process. The semi-finished product from which the plain bearing bush is made is obtained from the respective pressed product through a series of drawing processes. For this production method, the alloy used must be readily hot- and cold-formable. Furthermore, the alloy must be machinable.

[0021] A particular advantage of a sliding element constructed from the copper alloy according to the invention is a low coefficient of friction compared to alternative solutions available on the market. Furthermore, the sliding element according to the invention exhibits good resistance to stress relaxation and the associated stable settling behavior, for example in bearing bushings [H.-A. Kuhn, M. Knab, R. Koch: Thermal Stability of Lead-free Wrought Cu-Based Alloys for Automotive Bushings, World of Metallurgy - ERZMETALL 60 (2007), 199]. The high thermal conductivity of the sliding element according to the invention also exhibits a low tendency toward thermally induced stresses in the material. Overall, the solution according to the invention is a sliding element made of a copper alloy in the form of a wear-resistant ductile material with high thermal conductivity, suitability for good settling behavior, and an improved coefficient of friction under oil lubrication, especially with steel friction partners.Overall, the tribological system underlying the plain bearing, with its hard phase precipitates, exhibits further advantageous properties by allowing dirt particles to be embedded on the tribosurface. These wear-resistant precipitates significantly increase the contact area of ​​the tribosurface.

[0022] Advantageously, the ratio can be: 5.1 ≤ ([Ni] + [Ti] + [Cr]) / [Si] ≤ 6.2. With element ratios within the specified range, distributions of hard phases form in the alloy matrix, whose contact area leads to a particularly low tendency to wear in a friction pair. The particle number and size lie within a particularly preferred range.

[0023] In a preferred embodiment of the invention, 2.3 to 2.7% Ni and / or 0.45 to 0.65% Si may be present. The selected interval of the elements nickel and silicon, along with the additional elements titanium and chromium, represents a particularly suitable selection in terms of particle size and distribution.

[0024] In a preferred embodiment of the invention, at least one fraction of precipitates may be present, the precipitates having a volume-equivalent spherical diameter of at least 1.0 µm and a density of 5,000 to 20,000 particles per mm 2The precipitates can be round or ellipsoidally elongated particles with a stoichiometric composition, as well as non-stoichiometric precipitates of the Cr-Ni-Si, TiSi, or Cr-Si systems. Furthermore, the precipitates can be round or ellipsoidally elongated particles with a stoichiometric composition, as well as non-stoichiometric precipitates of the Ti-Ni-Si system. The Ni content can advantageously be greater than or equal to the Ti content. Non-rounded particles with a more angular or angular appearance can also be embedded in the alloy matrix.

[0025] In this embodiment, the alloy of the sliding element according to the invention can also contain multiple populations of precipitates. For example, a first population with relatively small precipitates and at least one second population with relatively large precipitates. The large precipitates act as a particularly wear-resistant load-bearing portion. Their volume fraction in the structure can be comparatively small, amounting to between 1 and 2%. Due to the low density of the second population, relatively large gaps remain between them. These gaps are stabilized by the first population with smaller precipitates. By stabilizing the matrix in the gaps, the first population prevents the large precipitates of the second population from breaking out.

[0026] The precipitates are a hard phase embedded in an alloy matrix, which can contribute significantly to the bearing capacity of a friction pair.

[0027] In a further advantageous embodiment, at least one fraction of precipitates may be present, wherein the precipitates with a volume-equivalent spherical diameter of at least 1.0 µm have a density of 10,000 to 20,000 particles per mm 2 The hard phase content, which determines the positive sliding properties, is ensured by a high particle density.

[0028] Advantageously, at least one fraction of precipitates may be present, the precipitates having a volume-equivalent spherical diameter of at least 1.0 µm and at most 3.0 µm having a density of 10,000 to 18,000 particles per mm 2The majority of the precipitates are in the size range between 1.0 µm and 3.0 µm. Larger precipitates occur only rarely.

[0029] In a preferred embodiment of the invention, the precipitates can be Cr-containing and / or Ti-containing silicides. The precipitates can be round or ellipsoidally elongated particles of the composition (Cr,Ni)2Si, (Cr,Ni)3Si, Cr3Si, as well as non-stoichiometric precipitates of the Cr-Ni-Si or Cr-Si systems. Furthermore, the precipitates can be round or ellipsoidally elongated particles of the composition (Ti,Ni)2Si, (Ti,Ni)3Si, Ti5Si3, as well as non-stoichiometric precipitates of the Ti-Ni-Si system. The Ni content can advantageously be greater than or equal to the Ti content.

[0030] In a preferred embodiment of the invention, the Ti and / or Cr content can amount to a maximum of 1.0 wt.%. In a further advantageous embodiment, the Ti and / or Cr content can amount to at least 0.45 wt.% and a maximum of 0.95 wt.%. This results in a particularly favorable contact ratio for the hard phases embedded in the alloy matrix in a friction pairing. Furthermore, this leads to good resistance to stress relaxation and the associated good settling behavior of the material. Thus, a sliding element with a copper alloy in the form of a wear-resistant ductile material with high thermal conductivity, suitability for good settling behavior, and an improved coefficient of friction with oil lubrication is specified.

[0031] Advantageously, the electrical conductivity after a thermal treatment between 300°C and 600°C can be at least 25 MS / m. Furthermore, the final thermal treatment can preferably be at a temperature between 400°C and 500°C. This thermal treatment can be the final, final thermal process step. The electrical conductivity is directly related to the thermal conductivity. The aforementioned thermal treatment, for example, with durations of 1 to 3 hours, also finally establishes the preferred mechanical properties of the alloy.

[0032] In a preferred embodiment of the invention, the ratio of thermal expansion α in the temperature range 20°C to 300°C and thermal conductivity λ at room temperature can be: α / λ = 0.09 to 0.20 µm / W. A thermal conductivity λ is also associated with a comparatively high electrical conductivity of up to 29.5 MS / m. This electrical conductivity is significantly higher than that of the Cr- or Ti-free comparison samples.

[0033] In a preferred embodiment of the invention, the hardness after a final thermal treatment between 300°C and 600°C can be at least 150 HBW 2.5 / 62.5. Furthermore, the final thermal treatment can preferably be at a temperature between 400°C and 500°C.

[0034] The invention is explained in more detail using exemplary embodiments.

[0035] Various samples of sliding element copper alloys were melted and cast into cast sections. After milling off the casting skin, the thickness d of the samples was approximately 20 mm. This was followed by a hot rolling process with a rolling depth of 8 mm, combined with water quenching. This was followed by a cold rolling depth of 2 mm. A final age-hardening treatment was carried out at a temperature of 300 to 600 °C for approximately 2 hours. Table 1 shows examples of the composition of individual samples that were aged at 450 °C. Table 1: Composition of alloy variants [wt.%]: Sample No. Cu Ni Si Ti Cr (Ni+Ti+Cr) / Si Ni / Si fitness 1 rest 2,35 0,61 0,83 - 5,21 3,85 excellent 2 rest 2,4 0,6 0,5 - 4,83 4,00 excellent 3 rest 2,4 0,6 0,2 - 4,33 4,00 good 4 rest 2,41 0,58 - 1,14 6,12 4,16 excellent 5 rest 2,4 0,6 - 0,7 5,16 4,00 excellent 6 rest 2,4 0,6 - 0,46 4,76 4,00 good 7 rest 2,4 0,6 - 0,22 4,36 4,00 good 8 rest 2,4 0,6 0,5 0,2 5,17 4,00 good 9 rest 2,4 0,6 0,2 0,46 5,10 4,00 good 10 rest 2,4 0,6 0,048 - 4,08 4,00 Not sufficient! 11 rest 2,36 0,58 - - 4,07 4,07 Not sufficient!

[0036] Samples Nos. 1 and 4 have particularly preferred properties for suitability for plain bearings according to the invention.

[0037] Sliding elements, especially bushings, are exposed to thermally induced stresses and distortions during engine operation. Such thermally induced distortions depend on the material-specific ratio of the average thermal expansion coefficient α and the thermal conductivity λ. Due to the comparatively low thermal expansion coefficient α and the significantly higher thermal conductivity λ (data in Table 2 refer to room temperature RT), the thermally induced distortions in bearing bushes, especially in the low-alloy copper materials of samples 1 and 4 listed in Table 2, are advantageously minimal. Table 2: Physical properties of samples No. 1 and 4 after final heat treatment with other reference samples: Sample No. / Alloy Hardness HB Electrical conductivity (MS / m) Thermal conductivity λ (W / mK) at RT thermal expansion coefficient α × 10 6 K (20°C to 300°C) α / λ (µm / W) at RT 1 159 21,1 140 17,5 0,125 4 198 25,4 160 18 0,113 CuNi6Sn6 240 8,5 55 18 0,327 CuZn31Mn2Si1Al1NiFe 190 11,5 75 19,6 0,261 CuZn37Mn3Al2PbSi 165 7,8 63 20,4 0,324

[0038] Since plain bearing bushings, for example, are usually embedded in high-strength connecting rod material, thermally induced distortions would cause additional mechanical stresses. Lower thermally induced distortions are therefore also beneficial for resistance to undesirable stress relaxation. This also results in favorable temperature- and time-dependent settling behavior of plain bearings, especially bushings.

[0039] The wear resistance of a sliding element according to the invention is determined using suitable tests and compared to the wear resistance of sliding elements made of known materials. Wear tests show no pronounced run-in phases, particularly for samples 1 and 4 listed in Table 2.

[0040] The invention is further explained using the following diagrams: Diagram 1: Friction values ​​µ (samples no. 1 and 4 with reference samples) Diagram 2: Wear (samples no. 1 and 4 with reference samples)

[0041] The friction coefficients µ in Diagram 1 and the wear rates in Diagram 2 of samples 1 and 4, as well as samples made of comparison alloys, were determined during a continuous test using a tribometer. The friction pair consists of a flat disc of the alloy and ring-shaped segments of 100Cr6 steel. The steel rotates at a sliding speed of 1 m / sec on the copper sheet. The friction partners are lubricated in a commercially available motor oil at a temperature of 120 °C. After a two-stage run-in phase, a constant load of 600 N is applied for 5.5 hours. The surface pressure is 9 N / mm 2 .

[0042] Compared to copper-based bearing materials already in use today, the alloys according to the invention are characterized by a lower average coefficient of friction. Both examples 1 and 4 wear significantly less than the tin-nickel bronze and a proven ferrous special brass with mixed silicides.

Claims

[1] Sliding element made of a copper alloy containing the following components (in wt%): 2.0 to 3.0% Ni, 0.45 to 1.0% Si, 0.45% to 0.95% Ti and / or Cr, optionally from 0.05 to 1.5% Co, optionally from 0.05 to 0.1% Mg, Al, Fe, optionally from 0.01 to 0.1% Pb, optionally from 0.002 to 0.01% P, Rest Cu and unavoidable impurities, characterized by , that at least one fraction of precipitates is present, the precipitates having a volume-equivalent spherical diameter of at least 1.0 µm and a density of 5,000 to 20,000 particles per mm 2 have, that the precipitates are Cr-containing and / or Ti-containing silicides, that the ratio of the sum of the Ni content [Ni], Ti content [Ti] and Cr content [Cr] to the Si content [Si]: 4.3 ≤ ([Ni] + [Ti] + [Cr]) / [Si] ≤ 6.

5. [2] Sliding element according to claim 1, characterized by that the ratio: 5.1 ≤ ([Ni] + [Ti] + [Cr]) / [Si] ≤ 6.

2. [3] Sliding element according to claim 1 or 2, characterized by , 2.3 to 2.7% Ni and / or 0.45 to 0.65% Si. [4] Sliding element according to one of claims 1 to 3, characterized by that at least one fraction of precipitates is present, the precipitates having a volume-equivalent spherical diameter of at least 1.0 µm and a density of 10,000 to 20,000 particles per mm 2 have. [5] Sliding element according to claim 4, characterized by that at least one fraction of precipitates is present, the precipitates having a volume-equivalent spherical diameter of at least 1.0 µm and at most 3.0 µm and a density of 10,000 to 18,000 particles per mm 2 have. [6] Sliding element according to one of claims 1 to 5, characterized bythat the electrical conductivity after thermal treatment between 300°C and 600°C is at least 25 MS / m. [7] Sliding element according to one of claims 1 to 6, characterized by that the ratio of the thermal expansion coefficient α in the temperature range 20°C to 300°C and the thermal conductivity λ at room temperature: α / λ = 0.09 to 0.20 µm / W. [8] Sliding element according to one of claims 1 to 7, characterized by that the hardness after a final thermal treatment between 300°C and 600°C is at least 150 HBW 2.5 / 62.5.

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