WO1987006273A2 - Coating to protect against wear and fretting corrosion of, in particular, metal mechanical components held together by frictional adherence - Google Patents

Abstract

Coating to protect against wear and fretting corrosion of, in particular, metal mechanical components held together by frictional adherence, which are subjected to vibrations and made of the same material. Direct contact between the mating surfaces is prevented by the fact that a material coating of a different nature from that of the machine parts is applied to at least one of the mating surfaces.

Description

 Protective layer against wear and corrosion, especially of metallic, frictionally mated machine parts against fretting corrosion

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Technical field:

The invention relates to a protective layer against wear and corrosion, in particular metallic, kraftschlüs¬ sig paired machine parts before fretting corrosion, wherein a I _Q direct contact between the joining surfaces is avoided by uniform between the paired surfaces on at least one joining surface a layer of material with other Beschaffen¬ than that of the machine parts is attached.

20 ^{B (} ≥i metallic frictionally mated machine parts, such as in engines, occasionally, especially in the area of the blade roots, fatigue fractures occur even under stresses far below the fatigue strength, which result from surface areas with fretting corrosion damage

25 go. The reason for this is the so-called "frictional stress". This long-term frictional stress is composed of a surface pressure and an alternating shear stress due to the smallest abrasive movements (slip) of the paired surfaces. The resulting shear stresses are unexpectedly high.

35 The-. Frictional stress can damage the machine part in two ways. On the one hand, "fretting corrosion" can occur as surface damage, on the other hand there is a reduction in the fatigue strength of vibratingly loaded machine parts when two metals rub against one another.

If the frictional stress exceeds the strength of the material, micro-cracks occur in the surface. In this case, tribochemically activated particles can emerge from the surface, which react spontaneously with the oxygen in the ambient air or oxygen as the working medium.

The following can be determined about the extent of the surface destruction:

- the interface wear increases with the number of friction vibrations,

the interface wear increases with increasing surface pressure,

the initial state of the interface practically does not affect the extent of the destruction,

- Lubricants have only a minor influence on reducing fretting corrosion damage.

If an oscillatingly stressed machine part is additionally subjected to a frictional stress on the surface, the durability is reduced. In practice, the term "frictional fatigue fracture" is used for the fracture of a component which is subjected to vibrations and which emanates from such a surface subjected to frictional stress. The friction breakage is due to ^' oxidic abrasion products and a "nose" at the starting point to distinguish the break from other permanent breaks.

The "greatest vibrating load in the component" is referred to as the "friction durability" at which no friction fatigue fracture occurs yet.

There is always the risk of frictional fractures on machine parts or assemblies which are subjected to vibrations if they are designed in such a way that vibrating relative displacements (slip) of the paired surface become possible when subjected to load. Frictional breaks occur, among other things. also very often on sealing inserts for rotors of turbocompressors on and in particular in engines with titanium blades in the area of the blade roots.

State of the art:

Various steps have already been recommended in order to avoid the breaks (Research Booklet Research Curator Mechanical Engineering, Book 56, 1976: "Fretting Corrosion - Final Report"), such as

- Avoiding frictionally paired joining surfaces, e.g. by welding, soldering or adhesive connections instead of shrinking and tensioning connections,

- Reduction of the frictional stress through various measures, for example by minimizing the difference in elongation of the joined parts

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A known solution is contained in German Offenlegungsschrift 32 36 376. However, the solution described there is limited to galvanic protective layers for titanium materials.

Another solution is contained in German Offenlegungsschrift 33 27 346. It is a galvanically deposited dispersion layer with the cobalt system for the matrix and Cr-O _^ particles for the non-metallic disperse phase. Only electrodepositable metals can be used for the matrix for this process. The particles are limited to a certain particle size so that they can be kept in suspension.

The object of the present invention is to improve the properties and application of layers which protect against wear and corrosion on surfaces or surface areas of machine parts. It should not only be possible to coat titanium materials and the composition of the protective layer should be chosen so that a whole range of application methods can be used, and not just the galvanic deposition as described in the journal Metallfläche 11/1982, pages 557 to 560. The area of application of such protective layers should also be expanded beyond the general area of mechanical engineering whenever components or components are used. ■ ersel - -b.en d__er Rbeeiibuenrgh? Öuhntteerrl ^T ieemgpeenrawtiuer during the relative movement between components, in particular any type of storage, guidance, steering and the components are additionally exposed to chemically aggressive media such as the polluted industrial air or other fluids or media that are exposed have a corrosive effect, be it that corrosion damage can occur immediately or only as a result of friction or other wear. Invention:

This complex problem is solved by a protective layer according to the features of patent claim 1. Further embodiments of the invention as well as manufacturing methods and applications of the protective layer can be found in further claims.

The invention expressly includes all combinations and subcombinations of the claimed features both with one another and with those which are explained in the description with reference to exemplary embodiments. These exemplary embodiments can of course be modified without thereby leaving the scope of the invention.

The invention has many advantages: it allows the use and application of protective layers to be widened for the purposes mentioned above. The protective layers themselves have been improved and in part meet the opposite requirements for the abovementioned applications. The protective layers have a different structure and a different hardness than the base material or the base, in particular with regard to their crystal lattice and hardness.

With the invention, all of these requirements are met and can be used industrially and for the described applications. Technically reproducible, relatively simple economic manufacturing processes are shown which are such that the layers produced have measurable success in terms of their desired properties, compared to previous so-called composite layers made of superalloys (nickel-based), titanium alloys and high-alloy steels, in particular with regard to wear and corrosion or with coated machine parts which are exposed to this fretting corrosion. Only a few known layers were suitable for this combined load or permanent load. This applies even if metals form the matrix for the incorporation of particles made of metal oxides such as oxide ceramics or other metal compounds. The metallic matrix, especially when it comes to metals of the iron group, then tends to oxidize even at moderately high temperatures from about 500 ° C.

The invention is explained below on the basis of exemplary embodiments which have been selected to show which base materials are preferred for the components for coating with the combined composition of metal alloys and metal compound and preferred methods for applying such layers and their use. Of course, the base materials, the coating materials and processes for the components on the surface or surface areas of which they are to be used are interchangeable. Preferred embodiment:

1. Substrates: Co, Ni, Ti and their alloys

2. Matrix of the layer: Co

3. Additional alloying elements introduced into the matrix: Cr, Al, Si, Ta,

Met. -All of the platinum group,

4. Non-metallic particles. Metal connection: Cr 0, Cr.C,

Description of the figures:

1 shows a substrate coated with the composite material,

2 shows different steps of manufacturing processes for the coating.

10 Metallic materials such as alloys containing iron, cobalt or nickel, especially base alloys of these metals serve as substrates, here: machine parts, for protective layers against wear at elevated temperatures, where the wear protection effect is caused, among other things, by

1.5 Oxidation processes, such as hot gas corrosion, is affected, and particularly affects the surfaces of such substrates. In addition to non-metallic phases, such as Cr, particles, metallic elements are also used as alloys in a metallic cobalt matrix of the layer.

2.0 'built-in additives that increase the oxidation protection of the cobalt matrix. The cobalt matrix contains elements of the iron group of group VIII of the periodic system. The non-metallic phase consists of metal compounds such as nitrides, borides, suicides, carbides, oxides, in particular

25 special ones made of chrome oxide, chrome carbide, tungsten carbide or silicon carbide. This disperse phase can also consist of Cr ₂ 0- ,, Zn0 ₂ , BN, Si N, CoSi, CoSi, FeSi, ZnB ₂ . The phase has the shape of particles 4 and is said to be at the end of the deposition and / or heat treatment

30 at least superficially protected component according to FIG. 1 as evenly as possible in the matrix metal or the metal alloy of the composite material forming the layer.

35 In addition to the particles 4, the alloy additives 3 mentioned above are connected to the matrix material 2 of the layer 4 cobalt. In addition to the disperse phase, this cobalt matrix contains - particles 4 - elements which increase the oxidation resistance of the matrix, such as one of the elements from the group consisting of chromium, aluminum, silicon, tantalum, platinum, rhodium, palladium or a combination in which Additional elements such as yttrium and hafnium can be added to the cobalt matrix in order to increase the adhesion of the oxides, which are formed somewhat later.

In FIG. 2 different ways of manufacture of a protective layer provided with Su _^ bstrats of FIG. 1 are shown.

Variants i, ii, iii are shown one above the other. The following are shown side by side: a) the respective initial state b) the respective state after deposition of the matrix c) the application of oxidation-inhibiting, alloy-forming additional elements d) any subsequent diffusion heat treatment.

As shown in FIG. 2a, the invention in these exemplary embodiments always assumes that the cobalt, e.g. is applied in solution as a matrix for the layer and at the same time the disperse phase, for example Cr-O particles 4, are applied to the protective surface. Instead of the deposition from a suspension, the application can also be applied by thermal spraying.

In the process step as shown in FIG. 2 a, line £, the alloy-forming additional elements 3 are deposited simultaneously with the cobalt 2 and the particles 4 of the disperse phase. This then results in the state after deposition of the matrix as shown in FIG. 2b. Then, in Fig. 2 i, in step d, a diffusion heat treatment is carried out analogously to carburizing or nitriding or aluminizing (for example in the manner of the German published documents 27 34 529 and 28 30 851). This heat treatment is carried out under conditions such that the alloy-forming additional elements are distributed in the cobalt matrix in such a way that they form a suitable oxidation protection.

In addition to the diffusion through the heat treatment, a targeted oxidation of the cobalt matrix can take place, e.g. by treatment (reaction) in an oxidizing atmosphere according to a temperature-time program or simple air.

As shown in FIG. 2 in line ii, Cr_0, particles 4 can be embedded in a cobalt matrix 2, so that a state according to FIG. 2b results in line 2i. Then, according to step c of line 2i, the alloy-forming additional elements 3 are applied to the cobalt matrix 2 with embedded particles 4. The additional elements 3 can be applied to the matrix 2 with embedded particles 4 by electrolytic deposition, chemical or physical deposition from the gas phase (CVD, BVD); alloying surfaces by remelting or treatment by means of high-energy beams can also be used.

. 2, line iii In the production process according to Fig, starting from a substrate, in which at the same time a cobalt matrix 2 and particles 4 were deposited, so that the particles 4, shows, in the matrix 2 as shown in Fig. 2b in line ^~ iii, are distributed. In step c of line iii, that the alloy-forming elements 3 are added to the matrix 2 with an embedded particle 4 by means of a coating from the gas phase or in the powder pack process introduced into the matrix.

The coating can be carried out analogously to carburizing or nitriding or aluminizing as in the production of an aluminite layer, for example in the manner of German laid-open publications 27 34 529 and 28 30 851.

The cobalt matrix and the disperse phase of chromium 2 or particles of another metal compound, as listed above, are brought into a powder or gaseous environment which contains the additional elements 3 individually or in groups and releases them at elevated temperature, i.e. to the cobalt matrix. Then the additional elements are deposited on the surface, but because of the high process temperature (see the German published documents mentioned in the previous paragraph), they immediately enter the cobalt matrix.

At the end of treatment steps d of all three production processes according to line i or ii or iii, the final state (protected substrate) according to FIG. 1 is reached.

Claims

P a t e n t a n s r u c h e l. Protection layer against wear at elevated temperatures at which the Verschleißs _^ phutzwirkung inter alia influenced by oxidation processes, to protect surfaces or surface regions of metallic machine parts which are coupled frictionally, data characterized by that (dispersed) in a metallic matrix in addition to non-metallic phases additional metallic elements are installed which increase the oxidation protection of the metallic matrix. "" 2. Layer according to claim 1, characterized in that the metallic matrix contains elements of the iron group (group VIII of the periodic system). 3. Layer according to claim 2, characterized in that the metallic matrix consists of cobalt. 4. Layer according to one of claims 1, 2 or 3, characterized in that the disperse phase consists of metal oxides, carbides, nitrides, borides, suicides or a mixture of such components. 5. Layer according to claim 4, characterized in that the disperse phase consists of chromium carbide, tungsten carbide ^'' or silicon carbide. 6. Layer according to claim 4, characterized in that the disperse phase consists of Cr 0, ^Zr0 2 ^BN ' ^Si 3 ^N 4 * (B Si, B _έ Si), CoSi, CoSi ₂ , TaSi, ZrB_. 7. Layer according to claim 4, 5 or 6, characterized in that the metallic matrix contains, in addition to the disperse non-metallic phase, elements which increase the oxidation resistance of the matrix. 8. Layer according to claim 7, characterized in that the metallic matrix contains one of the elements Cr, Al, Si, Pt, Eh, Pd, Ta additionally or a combination thereof. 9. Layer according to claim 8, characterized in that additional elements are contained which increase the adhesion of the oxides (formed during operation). 10. Schich according to claim 9, characterized in that the metallic matrix contains one of the elements Y, Hf or a combination thereof. 11. The method for producing the layer according to one or more of claims 1-10, characterized in that metallic matrix, non-metallic particles and anti-oxidation elements are applied simultaneously to the surface to be protected 12. The method according to claim 11, characterized in that the components of the layer are deposited from a suspension 13. The method according to claim 11, characterized in that the components of the layer are applied by thermal ^S spraying 14. A method for producing the layer according to one or more of claims 1-10, characterized in that ^" the oxidation-inhibiting elements are subsequently introduced into a wear protection layer consisting of a metallic matrix and non-metallic particles (claims 1-6). 15. The method according to claim 14, characterized in that the oxidation-inhibiting elements are applied to the existing layer (claims 1-6) by electrolytic deposition, electroless deposition or chemical or physical deposition from the gas phase (CVD, PVD) 16. The method according to claim 14, characterized in that the oxidation-inhibiting elements are introduced by a diffusion coating in the gas phase or in the powder pack in the existing layer (claims 1-6) 17. The method one of claims 11 to 16, characterized in that after the application of the layer, a heat treatment is carried out in order to distribute the oxidation-inhibiting elements in a suitable manner in the metallic matrix 18. Heat treatment according to claim 17, characterized in that in addition a targeted oxidation of the matrix _{^ is} effected 19. The method according to claim 14, characterized in that the antioxidant elements (in the form of particles) by heating, e.g. can be thermally introduced into the matrix by means of high-energy radiation or laser beams.