BEARING ELEMENT FOR A PLAIN OR ANTIFRICTION BEARING

Abstract

A bearing element (1) for a plain or antifriction bearing is provided, the bearing element (1) being formed of or including at least sectionally a powder-metallurgical composite material which includes a metallic binder phase and a hard material phase, wherein the metallic binder phase is based on at least one element from the following group: chromium, cobalt, molybdenum, nickel, titanium.

Claims

1-10. (canceled)

11. A bearing element for a plain or antifriction bearing, the bearing element comprising: at least sectionally a powder-metallurgical composite material including a metallic binder phase and a hard material phase, wherein the metallic binder phase is based on at least one element from the group consisting of chromium, cobalt, molybdenum, nickel, and titanium.

12. The bearing element as recited in claim 11 wherein the metallic binder phase further comprises fractions of iron or carbon or nitrogen or of at least one iron or carbon or nitrogen containing compound.

13. The bearing element as recited in claim 12 wherein the metallic binder phase comprises chromium carbide or molybdenum carbide or titanium carbide as carbon containing compound.

14. The bearing element as recited in claim 11 wherein the hard material phase includes individual hard material phase grains, and the composite material includes an intermediate phase formed around the hard material phase grains, attachment of the hard material phase grains to the metallic binder phase is realized via the intermediate phase.

15. The bearing element as recited in claim 11 wherein the hard material phase is includes at least one of the following hard material compounds: borides, carbides, carbonitrides, and silicides.

16. The bearing element as recited in claim 15 wherein the hard material phase includes titanium carbide or tungsten carbide.

17. The bearing element as recited in claim 15 wherein the hard material phase includes titanium carbonitride or titanium nitride.

18. The bearing element as recited in claim 11 wherein the hard material phase in the composite material has a fraction of 50-99 vol % and the metallic binder phase has a fraction of 1-50 vol %.

19. The bearing element as recited in claim 18 wherein the hard material phase in the composite material has a fraction of between 85 and 95 vol %, and the metallic binder phase has fraction of between 5 and 15 vol %.

20. The bearing element as recited in claim 11 wherein, at least in the region of the surface, the bearing element has a hardness of 1000-2000 HV.

21. The bearing element as recited in claim 11 wherein, at least in the region of the surface, the bearing element has a hardness above 1100 HV.

22. The bearing element as recited in claim 11 wherein the bearing element has an average roughness value R.sub.a of between 0.02 and 1.0 m.

23. The bearing element as recited in claim 11 wherein the bearing element is a bearing ring or a sliding or rolling body or a rolling body cage for accommodating rolling bodies.

24. A bearing comprising the bearing element as recited in claim 11.

25. A plain or antifriction bearing comprising the bearing as recited in claim 24.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] An exemplary embodiment of the invention is shown in the drawing and is described in more detail below. In the drawing:

[0028] FIG. 1 shows a schematic representation of an antifriction bearing comprising a bearing element according to one exemplary embodiment of the invention;

[0029] FIG. 2 shows a segment from a microstructure of a powder-metallurgical composite material for forming a bearing element according to one exemplary embodiment of the invention; and

[0030] FIG. 3 shows a diagram for illustrating the corrosion resistance of a bearing element of the invention in comparison to a bearing element formed from a conventional corrosion-resistant antifriction bearing steel.

DETAILED DESCRIPTION

[0031] FIG. 1 shows a schematic representation of a bearing element 1 according to one exemplary embodiment of the invention. The bearing element 1 is part of an antifriction bearing 2. The bearing element 1 is the outer ring 3 of the antifriction bearing 2. The inner ring 4 of the antifriction bearing 2 could equally be formed as a corresponding bearing element 1 in accordance with one exemplary embodiment of the invention. The same is true of the rolling bodies 5 which roll between the outer ring 3 and the inner ring 4, and also of the rolling body cage 6 which guides and/or accommodates the rolling bodies 5.

[0032] The bearing element 1 could also constitute corresponding components of a plain bearing.

[0033] The bearing element 1 is formed from a powder-metallurgical composite material, this being a composite material produced by powder-metallurgical means. The powder-metallurgical composite material comprises a metallic binder phase, and a hard substance phase, which is formed of at least one hard substance. The powder-metallurgical composite material may accordingly also be thought of and termed as a Metal Matrix Composite.

[0034] The metallic binder phase is based in general on at least one element from the following group: chromium, cobalt, molybdenum, nickel, titanium. This means that the metallic binder phase is formed of at least one element from the following group: chromium, cobalt, molybdenum, nickel, titanium, or comprises as principal constituent at least one element from the following group: chromium, cobalt, molybdenum, nickel, titanium. This also means that the metallic binder phase is formed of or comprises a metallic compound containing chromium and/or cobalt and/or molybdenum and/or nickel and/or titanium. The stated elements may therefore be present in elemental form or in (chemically) bonded form.

[0035] The metallic binder phase may further comprise fractions of iron and/or carbon and/or nitrogen and/or of at least one iron and/or carbon and/or nitrogen containing compound. Contemplated in particular as carbon containing compound are chromium carbide and/or molybdenum carbide and/or titanium carbide.

[0036] The hard substance phase is generally formed of at least one of the following hard substance compounds, or comprises at least one of the following hard substance compounds: borides, carbides, more particularly titanium carbide and/or tungsten carbide, carbonitrides, more particularly titanium carbonitride, nitrides, more particularly titanium nitride, silicides. The hard substance phase is present typically in the form of individual or a plurality of connected hard substance phase grains. The hard substance phase grains typically have a grain size of approximately 0.5-10 m, more particularly 0.9-6 m.

[0037] The microstructure of the composite material therefore consists in particular of individual or a plurality of interconnected hard substance phase grains which are surrounded by the metallic binding phase. Accordingly, the metallic binding phase extends between the hard substance phase grains and binds them in the microstructure. The microstructure of the composite material may be compared to a wall structure comprising a plurality of bricks connected by a mortar, with the hard substance phase grains representing the bricks, and the metallic binder phase the mortar.

[0038] The hard substance phase in the composite material has a fraction of 50-99 vol %, more particularly a fraction of between 85 and 95 vol %. The metallic binder phase has a fraction of 1-50 vol %, more particularly a fraction of between 15 and 5 vol %.

[0039] In one specific exemplary embodiment, the composite material may comprise, as metallic binder phase, nickel and bonded chromium. In this specific exemplary embodiment, the hard substance phase consists of tungsten carbide. The fraction of the hard substance phase is between 85 and 95 vol %. The high fraction of the hard substance phase ensures very high hardness, typically 1150-1750 HV1, on the part of the composite material and therefore on the part of the bearing element 1. The toughness of the metallic binder phase compensates the brittleness of the hard substance phase and ensures good impact strength, typically K.sub.1c 7-19 MN/mm.sup.3/2, on the part of the composite material and hence on the part of the bearing element 1. The compressive strength of the composite material and hence of the bearing element 1 is between 3500 and 6300 MPa, the modulus of elasticity is in a range between 500 and 650 GPa, the Poisson number is between 0.21 and 0.22, and the density is in a range of between 13.0 and 15.0 g/cm.sup.3. The grain size of the hard substance phase grains is between 0.5 and 5 m.

[0040] Similar properties can also be achieved in a further specific exemplary embodiment of the composite material which differs from the above specific exemplary embodiment essentially in that the metallic binder phase consists of cobalt as principal constituent.

[0041] In another specific working example of the composite material, this material may comprise, as metallic binder phase, primarily nickel and cobalt. The metallic binder phase here further comprises carbon compounds and/or carbide compounds, such as, in particular, nickel carbide or cobalt carbide compounds. The hard substance phase here is formed of titanium carbide and/or titanium carbonitride. In the composite material here, there is an intermediate phase formed around the hard substance phase grains, this intermediate phase realizing a strong attachment of the hard substance phase grains to the metallic binder phase. The intermediate phase is what is called a phase, i.e., a complex carbide structure. The hardness of the composite material and hence of the bearing element 1 is between 1100 and 1650 HV, the impact strength is about K.sub.1c 8-14 MN/mm.sup.3/2, the modulus of elasticity is between 370 and 450 GPa, the density is between 5.8 and 6.9 g/cm.sup.3. It should be emphasized that the comparatively low density of the composite material results in a comparatively low component weight.

[0042] FIG. 2 shows a detail of a microstructure of a powder-metallurgical composite material, similar to the exemplary embodiment described above, for forming a bearing element 1 according to one exemplary embodiment of the invention. The metallic binder phase, which here comprises primarily nickel and molybdenum, is indicated by reference 7; the hard substance phase grains, which here consist of titanium carbonitride, are indicated by reference symbol 8; and the phase is indicated by reference symbol 9. The attachment of the hard substance phase grains 8 to the metallic binder phase 7 is accomplished via the intermediate phase 9 which immediately surrounds the hard substance phase grains 8.

[0043] With all of the exemplary embodiments of the composite material it is possible, depending on external diameter, to realize bearing elements 1 having average roughness values R.sub.a of between 0.02 and 1.0 m, which signifies coherent and homogeneous distribution of the hard substance phase grains in the metallic binder phase and also high surface quality on the part of the bearing elements 1, as a result in particular of the selection of appropriate fabrication parameters.

[0044] Viewed overall, the composite material forming the bearing element 1, and hence the bearing element 1 as well, are notable for high strength, high toughness, high hardness, high overrolling resistance and wear resistance, high thermal conductivity, and high corrosion resistance.

[0045] FIG. 3 shows a diagram for illustrating the corrosion resistance of a bearing element 1 of the invention in comparison to a bearing element formed from a conventional corrosion-resistant antifriction bearing steel. From FIG. 3 it is possible to illustrate the improved corrosion resistance of the composite material forming the bearing element 1 of the invention, in comparison to one comprising a conventional antifriction bearing steel.

[0046] The diagram shown in FIG. 3 plots the electrical current (y-axis) against the electrical potential (x-axis). The diagram shows experimental results from electrochemical investigations of the pitting potential or repassivation potential (Ag/AgCl, 3.5% NaCl, 20 C.). The curve 10 represents the results of measurement for a bearing element 1 of the invention; the curve 11 represents the results of measurement for a noninventive bearing element formed of a conventional antifriction bearing steel.

[0047] As can be seen, the breakdown of material, indicated by the rise in the curve 10, begins significantly later for the bearing element 1 of the invention than for the noninventive bearing element. The repassivation potential, i.e., the potential at which the curves meet the x-axis again after having risen, is much higher for the bearing element 1 of the invention, in comparison to the noninventive bearing element. The investigations demonstrate the very good corrosion resistance of the bearing element 1 of the invention.

LIST OF REFERENCE NUMERALS

[0048] 1 Bearing element [0049] 2 Antifriction bearing [0050] 3 Outer ring [0051] 4 Inner ring [0052] 5 Rolling body [0053] 6 Rolling body cage [0054] 7 Metallic binder phase containing nickel and molybdenum [0055] 8 Hard substance phase grains [0056] 9 phase [0057] 10 Curve [0058] 11 Curve