EP0881958B1 - Material for the powder-metallurgical production of shaped parts, in particular valve seat rings or valve guides with high resistance to wear - Google Patents

Description

The invention relates to a material for powder metallurgical production of molded parts with high thermal conductivity and high wear and tear Corrosion resistance through pressing, sintering and, if necessary, recompression a powder mixture with a copper content of at least about 50% by weight.

Such sintered materials are used for molded parts, the hot gases or Exposed to gas mixtures are required, for example for production of valve seat rings and valve guides for internal combustion engines, the on the one hand high mechanical loads and on the other hand at the same time are exposed to hot combustion gases. You need to therefore be made from materials that are not only wear and tear are corrosion-resistant, but also have a high thermal conductivity. Thermal conductivity is becoming increasingly important, as that Temperature level at the valves due to the emission reasons required expansion of the stoichiometric mixture increases and there is a continuing trend towards more powerful engines.

It is known the temperature difference between the head of the valve and the cylinder head, into which the valve seat ring is incorporated, by heat transfer decrease in the valve. For this purpose the valve stem provided with a hollow bore and cooled. For reasons of cost and weight have been the diameters of the valve stems in recent years so scaled down that it is no longer possible in most cases to be provided with a hollow hole so that the use of hollow holes and, for example, valves filled with sodium in the future will be possible. The endeavor therefore goes there, the thermal conductivity the material from which the valve seat, in particular the valve seat ring, is produced to improve the heat more quickly dissipate, lower the temperature level to the tribological Improve conditions and the system technologically and cost-effectively to improve.

There are molded parts made of sintered materials based on powder metallurgy Iron base with infiltrated copper known to be used as a Valve seat ring or valve guide have sufficient wear resistance, its thermal conductivity compared to sintered materials without Copper content is not high enough. For example, from the DE-PS 21 14 160 a sintered material is known, which is made of an iron-based material consists of carbon and lead, as well as other alloy components are clogged. Valve seat rings made from this material have sufficient heat and wear resistance, their However, thermal conductivity is not enough, especially around this upcoming problem in the outlet area of a modern Solve internal combustion engine.

PCT-EP 89/01343 describes a sintered material for powder metallurgy Manufacture of valve seat rings known to increase Should have thermal conductivity with high wear resistance. The Sintered material consists of a base metal powder with a Copper content of about 70 to 100 wt .-% copper and one Proportion of alloy. The alloy content can be, for example, from 1 to 3 % By weight of cobalt or a high-alloy additional metal powder, which the base metal powder is mixed as a hard phase, the proportion of which is then is a maximum of 30% by weight.

Experiments carried out with such a material have shown that the material has insufficient wear resistance for the manufacture of valve seat rings, in particular for the exhaust area of internal combustion engines. This is due to the fact that although the hardness of the material could be increased by the solidification of the matrix through the incorporation of hard materials with a maximum particle size of 150 μm and thus the wear resistance of the valve seat ring, it could be increased due to the relatively large and sharp-edged Deposits of the opposing body was worn out more. The wear on the valve seat ring was therefore low, while the overall wear, which is important for the permanent functioning of the system, was worsened.

A powder mixture consisting of copper powder solidified by 0.1-1.1% by weight of Al ₂ O ₃ with at least 50% by weight of Cu is generally known from EP-A-144959.

The invention has for its object a sintered material for the powder metallurgical production, in particular of valve seat rings or To create valve guides whose wear resistance is very high and at the same time a significantly high thermal conductivity compared to known sintered materials used for this purpose.

Starting from a material for powder metallurgical production of molded parts with high wear and corrosion resistance and high thermal conductivity, in particular for the production of valve seat rings or valve guides for internal combustion engines, by pressing, sintering and, if necessary, post-compression of an initial powder mixture with a copper content of at least about 50% by weight. %, the invention consists in that the starting powder mixture consists of a base powder containing the Cu content in an amount of 50 to 90% by weight and a powdery alloy additive containing molybdenum in an amount of 10 to 50% by weight and that the base powder is a dispersion-strengthened copper powder, the dispersion-strengthened copper powder being strengthened by Al ₂ O ₃ , containing 0.1 to 1.1% by weight of Al ₂ O ₃ and less than 0.5% by weight of impurities and by Spraying a Cu-Al melt and then heating it in an oxidizing atmosphere selective oxidation of the aluminum is made.

The invention is based on the surprising finding that the use of a Cu-Al ₂ O ₃ powder which has been strengthened by means of Al ₂ O ₃ dispersion as a material for the powder-metallurgical production of molded parts leads to products which on the one hand have high wear and corrosion resistance and on the other hand have a high thermal conductivity, so that they are particularly suitable for the production of valve seat rings or valve guides for internal combustion engines.

Only those with Al ₂ O ₃ dispersion-strengthened Cu powder are suitable for the present purpose, which after the z. B. from US-PS 37 79 714 or DE-PS 23 55 122 known methods by internal oxidation and subsequent heating of Cu-Al alloy powder, made from atomizing a Cu-Al melt, are produced in an oxidizing atmosphere, while Dispersion-strengthened metal powders produced by another method according to GB-A-2 083 500, in which internal oxidation is expressly to be excluded, are unsuitable. The applicant attributes this to the fact that in the case of the Cu-Al ₂ O ₃ powder produced by means of internal oxidation, the distance between the dispersed Al ₂ O ₃ particles in the copper matrix is of the order of 3 to 12 nm, while in the case of the without inside oxidation produced powder is about 40 μ m. There is no reference in these publications to the use according to the invention of dispersion-strengthened metals as base powder for the powder-metallurgical production of molded parts, in particular valve seat rings or valve guides.

A preferred embodiment of the invention provides that the alloy surcharge from a powdered, preferably water atomized intermetallic hard phase from 28 to 32, preferably 30% by weight Molybdenum, 9 to 11, preferably 10% by weight of chromium, 2.5 to 3.5, preferably 3 wt .-% silicon, the rest of cobalt, the intermetallic Hard phase in the powder mixture in an amount of about 10% by weight and the base powder is present in an amount of about 90% by weight.

In another embodiment of the invention, there is the intermetallic Hard phase of 28 to 32, preferably 30% by weight of molybdenum, 9 to 11, preferably 10 wt .-% chromium, 2.5 to 3.5, preferably 3 wt .-% silicon, balance iron, the intermetallic phase in the Powder mixture in an amount of about 10 wt .-% and the base powder in an amount of about 90 wt .-% are present.

According to the invention, the alloy surcharge can also consist of a hard phase from a high-speed steel powder of about 6% by weight of tungsten, about 5% by weight Molybdenum, about 2 wt% vanadium, about 4 wt% chromium, balance Iron exist, the hard phase in the powder mixture in an amount up to about 30% by weight and the base powder in an amount of about 70 wt .-% or higher.

The alloy surcharge can also consist of a hard phase from a Mo-P-C powder of about 11% by weight molybdenum, about 0.6% by weight Phosphorus, about 1.2 wt .-% carbon, balance iron, the Hard phase and the base powder in the powder mixture in an amount of each about 50 wt .-% are present.

The invention also relates to a material which consists of a starting powder mixture from about 80% by weight of base powder, about 10% by weight Molybdenum powder and about 10% by weight copper powder or about 79% by weight Base powder, about 10% by weight molybdenum powder, about 10% by weight copper powder and about 1% by weight of powdered molybdenum trioxide.

The invention further provides that the base powder additionally molybdenum disulfide (MoS ₂ ) and / or manganese sulfide (MnS) and / or tungsten disulfide (WS ₂ ) and / or calcium fluoride (CaF ₂ ) and / or tellurium (Te) and / or calcium carbonate ( CaCO ₃ ) in a total amount of at least 1 wt .-% to a maximum of 3 wt .-% based on the amount of the base powder.

The invention further relates to a method for the powder metallurgical production of molded parts with high wear and corrosion resistance and high thermal conductivity, in particular for the production of valve seat rings or valve guides for internal combustion engines, in which a starting powder mixture with one of the compositions described above with about 0.3 wt .-% of a pressure-relieving agent, e.g. B. wax, mixed, molded and pressed into a molded part with a density of about 8.0 g / cm ³ and subjected to a subsequent sintering under protective gas; the sintering is preferably carried out under a protective gas atmosphere of about 80% by weight of nitrogen and about 20% by weight of hydrogen for a period of about 45 minutes at a temperature of about 1,040 ° C. If necessary, the sintered molded part can be subjected to post-compression to a density of approximately 8.8 g / cm ³ .

An alternative embodiment of the invention provides that the starting powder according to claim 1 contains one or more of the substances or substance mixtures listed below: a) 5 - 30% by weight tool steel type M35 or type T15, Ni-Cr-Si-Fe-B-Cu-Mo; b) 5-10% by weight of W, Mo, Nb, WC, TiC, B ₄ C, TiN, c-BN, TiB ₂ ; c) 0.5-5% by weight of Ti, Cr, Zr, Cr + Zr, Be, Ni + P.

The materials of group a) alloy with the copper matrix of the dispersion hardened Copper by diffusing these additives into the copper and thereby significantly reducing the electrical and thermal conductivity. Around The proportion should keep the thermal conductivity above 100 W / m · k Do not exceed 5-20% by weight, typically 10% by weight.

The materials of group b) do not alloy with the copper matrix and have therefore no noticeable influence on the thermal conductivity. they are however relatively expensive. However, it has been found that a Share of 5 - 10 wt .-% is sufficient.

The additions of group c) cause the intermetallic constituents to be excreted and in this way superimpose the hardness effect in addition to the hardening by the Al ₂ O ₃ particles in the dispersion-strengthened copper. While the aluminum oxide particles effectively harden the copper matrix at high temperatures (> 500 ° C), the precipitation phases result in more effective hardening in the medium temperature range (200 - 500 ° C), which are the typical operating temperatures to which the valve seat rings are concerned are exposed. The higher warm hardness generally leads to higher wear resistance.

The wear of the valve seat rings is also caused by the addition of solid lubricants such as graphite, MoS ₂ , MnS, h-BN, CaF ₂ and the like, as well as metal additives such as Mo, Co, W or the like, which form oxide skins at operating temperatures that have a lubricating effect .

The fact that the starting powder according to one or more of the substances listed below:
5-20% by weight of Zn, 0.1-5% by weight of one of the elements Al, Be, Si, Mg, Sn
contains, the oxidation resistance, ie corrosion resistance during operation, is increased considerably. With a view to reducing the thermal conductivity as little as possible, Zn is the preferred alloy component. In this regard, an addition of 5-30% by weight is not critical.

The starting powder preferably contains one or more of the following powdery substances with an irregular particle shape:
5 - 25 wt .-% Cu high green strength, electrolyte Cu, oxide-reduced Cu, Mo, or the like.

Because the dispersion-strengthened copper used is round, smooth Has particles, the green parts made of this material only have green low strength. The green strength can be achieved by adding the aforementioned Components can be increased significantly. With the "Cu high green strength" are powders with fibrous, long, thin particles, which intertwine with each other when pressed together in this way cause a high strength of the green body. The Thermal conductivity is not affected by the addition of pure Cu, so that 5-25% by weight can be added, the preferred one Range is 10-15% by weight.

The machinability, in particular the machinability, of dispersion-strengthened copper is improved by adding one or more of the substances mentioned below: a). 0.2-2% by weight of chemical elements such as C (graphite), Te, Se; b). 0.5-5% by weight sulfides such as MoS ₂ , MnS, etc .; c). 0.5-5 wt% oxides such as MoO ₃ , WO ₃ , Co ₃ O _4, etc .; d). 0.5 - 5% by weight of compounds such as hexagonal BN, CaF ₂ .

The radial breaking strength of the valve seat rings, which must be given in particular when pressed into the cylinder head, is increased by adding one or more of the following substances: a) 5-20% by weight of Zn, 0.1-5% by weight of Al or Sn, etc .; b) 5 - 30% by weight tool steel type M35 or type T15, Ni-Cr-Si-Fe-B-Cu-Mo

By a corresponding combination of the above Alloy additives can be the starting powder mixture in terms of Optimally match the properties required for each valve seat ring.

The main advantage in terms of valve seat ring manufacturing lies in all of the aforementioned starting powder mixtures according to the invention in that the thermal conductivity is particularly high, d. H. at least 100 W / m · k.

Embodiments example 1

A Cu-Al ₂ O ₃ powder which had been dispersion-strengthened by means of internal oxidation and had a content of 0.5% by weight of Al ₂ O ₃ was mixed with 0.3% by weight of a customary pressure-relieving agent and at a pressure of 800 MN / mm ² pressed into valve seat rings with the dimensions 36.6 x 30.1 x 9 mm. The green compacts, which had a compression density of 8.4 g / cm ³ , were then sintered for 45 minutes at a temperature of 1,040 ° C. under a protective gas atmosphere of 80% N ₂ and 20% hydrogen. The sintered density was 8.4 g / cm ³ . The sintered rings were then subjected to post-compression to a density of 8.8 g / cm ³ at a pressure of 1,600 MN / mm ² .

Table 1 shows the measured densities and hardness values, Table 2 the thermal conductivity values, which were determined by the laser flash method. Procedural steps Density [g / cm ³ ] Hardness HB Press 8.41 - Sintering 8.41 89 - 99 - X = 93 Recompression 8.83 111 - 129 - X = 121 Temperature [° C] Thermal conductivity [W / m · k] RT 276 100 300 200 310 300 308 400 311 500 307 600 313 700 311

Example 2

90% by weight of a dispersion-strengthened Cu-Al ₂ O ₃ powder produced by means of internal oxidation with a content of 0.5% by weight of Al ₂ O ₃ were mixed with 10% by weight of a water-atomized, powdery, intermetallic hard phase and 3 wt .-% of a conventional pressure-relieving agent mixed. The intermetallic hard phase consisted of 60% by weight of cobalt, 30% by weight of molybdenum, 10% by weight of chromium and 3% by weight of silicon. The powder mixture was pressed at a pressure of 800 MN / mm ² into molds to form valve seat rings with the dimensions 36.6 x 30.1 x 9 mm. The green compacts had a compression density of 8.2 g / cm ³ . The rings were then sintered for 45 minutes at a temperature of 1,040 ° C. in a protective gas atmosphere composed of 80% N ₂ and 20% H ₂ ; the sintered density was 8.2 g / cm ³ . The densification to a density of 8.7 g / cm ^{3 was} carried out with a pressure of 1,600 MN / mm ² .

Table 3 shows the density and hardness values, Table 4 the thermal conductivity values determined by the laser flash method. Procedural steps Density [g / cm ³ ] Hardness HB Press 8.20 - Sintering 8.20 88 - 101 - X = 94 Recompression 8.73 124 - 142 - X = 133 Temperature [° C] Thermal conductivity [W / m · k] RT 95 100 102 200 117 300 129 400 139 500 150 600 157 700 155

The valve seat rings manufactured according to Examples 1 and 2 had one compared to unexpected improvement in thermal conductivity commercially available valve seat rings based on Fe with and without Copper infiltration. This results from Figure 1. Curve 1 shows the Thermal conductivity values of a valve seat ring according to example 1, curve 2 the values for a ring according to Example 2, curve 3 the values of a Valve seat ring based on Fe with copper infiltration and curve 4 die Values of a commercially available valve seat ring from the applicant.

The rings produced according to Example 1 have a hardness which permits their use in the inlet area of an internal combustion engine, while the valve seat rings according to Example 2 can be used in the outlet area and have excellent running behavior here. This was determined by tests, the conditions of which are summarized in Table 5. Test duration 125 h Number of cylinders 4th Number of valves / cylinders 4th Displacement 1998 cm ³ power 100 kW at 5500 rpm Torque 190 Nm at 4000 rpm fuel Super lead-free - RON 95 Engine oil Shell Super 3 - 10 W 40 Valve disc, inlet
Valve disc, outlet uncoated
Armored stellite

The results of the engine test are summarized in Table 6 and shown graphically in Figure 2. The sinking depth is the sum of the wear of the valve and the valve seat ring. The valve seat ring according to Example 2 according to the invention was compared with the series material Como12 from the applicant, which is used on a large scale. Sinking depth [mm] Valve Outlet b) Cu-Al ₂ O ₃ with 10% intermetallic hard phase 0 0.02 Series material COMO 12 0.02 0.07 0.04 0

It can be seen that the sinking depth of the valve seat ring according to the invention with significantly increased thermal conductivity of the material is less than that of a commercially available valve seat ring.

Claims (25)

1. A material for powder-metallurgy production of shaped portions with a high level of resistance to wear and corrosion and a high level of thermal conductivity, in particular for the production of valve seat rings or valve guides for internal combustion engines, by pressing, sintering and possibly post-densification of an initial powder mixture containing at least 50% by weight of copper

   with a proportion of at least 50 to 90% by weight of dispersion-hardened copper powder which forms the base powder containing the proportion of copper, and

   with a proportion of 10 to 50% by weight of a molybdenum-bearing alloying additive in powder form,

   wherein the dispersion-hardened copper powder is hardened by Al₂O₃, contains from 0.1 to 1.1% by weight of Al₂O₃ and less than 0.5% by weight of impurities and is produced by atomisation of a Cu-AI-molten material and subsequent heating in an oxidising atmosphere for the selective oxidation of the aluminium.
2. A material according to claim 1 characterised in that the alloying additive comprises a preferably water-atomised intermetallic hard phase in powder form.
3. A material according to claims 1 and 2 characterised in that the intermetallic hard phase is of the following composition:

   28 to 32, preferably 30% by weight of molybdenum,

   9 to 11, preferably 10% by weight of chromium,

   2.5 to 3.5, preferably 3% by weight of silicon, and

   balance cobalt.
4. A material according to claim 3 characterised in that the intermetallic hard phase is present in the powder mixture in an amount of about 10% by weight and the base powder in an amount of about 90% by weight.
5. A material according to claims 1 and 2 characterised in that the intermetallic hard phase is of the following composition:

   28 to 32, preferably 30% by weight of molybdenum,

   9 to 11, preferably 10% by weight of chromium,

   2.5 to 3.5, preferably 3% by weight of silicon, and

   balance iron.
6. A material according to claim 5 characterised in that the intermetallic hard phase is present in the powder mixture in an amount of about 10% by weight and the base powder in an amount of about 90% by weight.
7. A material according to claim 1 characterised in that the alloying additive comprises a hard phase of a high-speed steel powder (AISI-type M2; DIN S-6-5-2) of the following composition:

   about 6% by weight of tungsten,

   about 5% by weight of molybdenum,

   about 2% by weight of vanadium,

   about 4% by weight of chromium, and

   balance iron.
8. A material according to claim 7 characterised in that the hard phase is present in the powder mixture in an amount of up to 30% by weight and the base powder in an amount of about 70% by weight or higher.
9. A material according to claim 1 characterised in that the alloying additive comprises a hard phase of an Mo-P-C-powder of the following composition:

   about 11% by weight of molybdenum,

   about 0.6% by weight of phosphorus,

   about 1.2% by weight of carbon, and

   balance iron.
10. A material according to claim 9 characterised in that the hard phase and the base powder are present in the powder mixture in an amount in each case of about 50%.
11. A material according to claim 1 characterised by the following composition of the initial powder mixture:

    about 80% by weight of base powder,

    about 10% by weight of molybdenum powder, and

    about 10% by weight of copper powder.
12. A material according to claim 1 characterised by the following composition of the initial powder mixture:

    about 79% by weight of base powder,

    about 10% by weight of molybdenum powder,

    about 10% by weight of copper powder, and

    about 1% by weight of molybdenum trioxide.
13. A material according to one of the preceding claims characterised in that the base powder additionally contains molybdenum disulphide (MoS₂) and/or manganese sulphide (MnS) and/or tungsten disulphide (WS₂) and/or calcium fluoride (CaF₂) and/or tellurium (Te) and/or calcium carbonate (CoCO₃) in a total amount of at least 1% by weight to a maximum of 3% by weight with respect to the amount of the base powder.
14. A process for powder-metallurgy production of shaped portions with a high level of resistance to wear and corrosion and a high level of thermal conductivity, in particular for the production of valve seat rings or valve guides for internal combustion engines, characterised in that an initial powder mixture according to one of the preceding claims is mixed with about 0.3% by weight of a pressing-facilitating agent, for example wax, shaped, and pressed to form a shaped portion of a density of about 8.0 g/cm³ and subjected to subsequent sintering under a protective gas.
15. A process according to claim 14 characterised in that the sintering operation is effected under a protective gas atmosphere comprising about 80% by weight of nitrogen and about 20% by weight of hydrogen for a period of about 45 minutes at a temperature of about 1040°C.
16. A process according to claims 14 and 15 characterised in that the sintered shaped body is subjected to a post-densification operation to a density of about 8.8 g/cm³.
17. Use of a Cu-Al₂O₃-Powder which is dispersion-hardened by means of Al₂O₃, according to claim 1, with a content of Al₂O₃ of between 0.3 and 1.1% by weight, which is produced by atomisation of a Cu-Al-molten material and subsequent heating in oxidising atmosphere, for the powder-metallurgy production of shaped portions which are resistant to wear and corrosion with a high level of thermal conductivity for the production of valve seat rings or valve guides.
18. A material according to claim 1 characterised in that the initial powder mixture contains one or more of the substances or substance mixtures listed below:

    a) 5 - 30% by weight of tool steel type M35 or type T15,
       Ni-Cr-Si-Fe-B-Cu-Mo;

    b) 5 - 10% by weight of W. Mo, Nb, WC, TiC, B₄C, TiN, c-BN, TiB₂; and

    c) 0.5 - 5% by weight of Ti, Cr, Zr, Cr+Zr, Be, Ni+P.
19. A material according to claim 1 characterised in that the initial powder mixture contains one or more of the substances listed below:
    5 - 10% by weight of Co, W.
20. A material according to claim 1 characterised in that the initial powder mixture contains one or more of the substances listed below:
    5 - 20% by weight of Zn, 0.1 - 5% by weight of one of the elements Al, Be, Si, Mg and Sn.
21. A material according to claim 1 characterised in that the initial powder mixture contains one or more of the substances in powder form listed below, with an irregular particle form:
    5 - 25% by weight of Cu of high green strength, electrolytic Cu, oxide-reduced Cu and Mo.
22. A material according to claim 1 characterised in that the initial powder mixture contains one or more of the substances listed below in a) to d):

    a) 0.2 - 2% by weight of chemical elements such as C (graphite), Te, Se;

    b) 0.5 - 5% by weight of sulphides such as MoS₂, MnS, etc;

    c) 0.5 - 5% by weight of oxides such as MoO₃, WO₃, Co₃O₄ etc; and

    d) 0.5 - 5% by weight of compounds such as hexagonal BN and CaF₂.
23. A material according to claim 1 characterised in that the initial powder mixture contains one or more of the substances listed below:

    a) 5 - 20% by weight of Zn, 0.1 - 5% by weight of Al or Sn, etc; and

    b) 5 - 30% by weight of tool steel type M35 or type T15,
    Ni-Cr-Si-Fe-B-Cu-Mo.
24. A material according to claim 1 and one or more of claims 18 to 23 characterised in that the initial powder mixture contains combinations of the substances or the substance mixtures of claims 18 to 23.
25. Use of a material according to claim 1 and one or more of claims 19 to 24 for the production of a valve seat ring or valve guides, the thermal conductivity thereof being at least 100 W/m • k.

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