EP0659507B1 - Cobalt metal powder and composite sintered article made thereby - Google Patents

Abstract

The invention relates to cobalt metal powders as a binder metal for the production of diamond and/or hard-metal tools and/or wear-resistant coatings and to composite sintered articles produced therefrom.

Description

The present invention relates to cobalt metal powder as a binder metal for the Manufacture of diamond and / or hard metal tools and / or wear protection coatings and composite sintered bodies made therefrom.

It is known to powder cobalt metal by atomizing the molten metal to manufacture. JP-A 53-093 165 discloses the manufacture and use atomize Cobalt metal. Here, the raw product after the atomization Milling and shock annealing post-processed to a desired hexagonal / cubic To achieve phase relationship. The cobalt metal powder is produced by grinding processes not only more expensive, but also contaminated.

Cobalt metal powders can be produced quite cheaply by atomization from the melt are produced, but these powders are available as binder metals, e.g. for the Manufacture of diamond tools completely unsuitable because of the spheroidal grain shape and grain size at the usual sintering temperatures between 800-900 ° C no dense composite sintered parts from result in sufficient hardness.

The main reason for the inadequate performance properties of hot-pressed composite sintered bodies made of atomized cobalt metal powder is the lack of compressibility of the pre-pressed shaped bodies due to the spheroidal grain shape, the relatively narrow grain size distribution and the coarse primary particles (FIG. 2). The necessary density of at least 8.5 g / cm ^{3 is also} not achieved by hot pressing.

On the other hand, hydrogen reduction of oxygen-containing cobalt compounds suitable as matrix material at elevated temperature Cobalt metal powder with an FSSS value of 3 to 5 µm, so-called 400 mesh powder (Fig. 1) available. This designation is explained by the sieve passage this powder through a 400 mesh sieve. Such powders meet requirements that of the matrix metal for composite materials in terms of hardness and sintered density be put. However, the so-called 400-mesh powders are quite right high level of impurities. It is generally known that Aluminum, calcium, sodium, magnesium and silicon easily with the oxygen form stable oxides of the cobalt metal powder. These can be in diamond segments cause undesirable porosity.

Porosity can reduce the strength of hard metals, if the above impurities as well as sulfur in too high Amounts are included. Cobalt metal powder is therefore used in both applications low levels of impurities are desirable. Depending on the cleaning effort in the metallurgical precursors, the purity of the cobalt metal powder be adapted to requirements. The effort for the production Particularly pure cobalt metal powder is naturally expensive and such Powders are therefore very expensive.

It is an object of this invention to provide a cobalt metal powder make, which do not have the disadvantages of the powder described.

A cobalt metal powder was now found, which required this Properties This invention relates to a cobalt metal powder Binder metal for the production of diamond and / or hard metal tools and / or wear protection coatings, which is characterized by that it is 20 to 80 wt .-% of an atomized cobalt metal powder with optical determined grain sizes from 5 to 150 microns and the rest missing to 100 wt .-% from an optionally agglomerated cobalt metal powder optically determined primary size of less than 3 microns exists.

The cobalt metal powder according to the invention has the price advantage of Oxides or oxygen-containing compounds by reduction of cobalt metal powder obtained on, but contains significantly smaller amounts of the above critical contaminants. It preferably contains less than 20 ppm Al, 20 ppm Ca, 30 ppm Na, 20 ppm Mg, 30 ppm S and 75 ppm Si.

The cobalt metal powder according to the invention is a Mixing of atomized cobalt metal powder with fine cobalt powder from the Hydrogen reduction.

The good technical suitability of the cobalt metal powder according to the invention sets even with a mixture proportion of 20% by weight of atomized fine cobalt metal powder from the reduction of hydrogen, taking into account the price advantage however, an upper limit of this proportion up to 80% by weight is still acceptable. The Powder metallurgical behavior of the mixtures is within the above Limits are also very advantageous.

The amount of atomized cobalt metal powder is preferably 30 to 70% by weight. The atomized cobalt metal powder is both a water atomized cobalt metal powder with predominantly spheroidal habit as well as a gas atomized Cobalt metal powder with spheroidal habit suitable.

The cobalt metal powder with a crystalline structure preferably has BET surface areas, determined by the nitrogen 1-point method (DIN 66 131), of greater than 0.8 m ² / g. In a preferred embodiment, the cobalt metal powder according to the invention has a bulk density of less than 1.4 kg / cm ³ .

Due to the favorable particle size distribution of the cobalt metal powder according to the invention, a density after hot pressing of at least 8.5 g / cm ^{3 is} achieved, which is associated with excellent compressibility of the powder. A further preferred embodiment of the cobalt metal powder of the invention is that the powder has a Rockwell hardness, as measured on hot-pressed test plates, of at least 98 HR _B has.

The cobalt metal powder according to the invention is outstandingly suitable for powder metallurgy Manufacture of diamond tools and / or hard metals, in which the cobalt - optionally together with other customary matrix metals - represents the binder phase.

This invention therefore also relates to composite sintered bodies produced from Hard material powder and / or diamond powder and binder metals, whereby as binder metal, optionally the cobalt metal powder according to the invention in addition to other metal powders is used.

In the following, the invention is explained by way of example, without any restriction you can see.

Example 1: (mixture 70/30)

0.7 kg of a fine cobalt metal powder from the reduction of cobalt oxide with hydrogen with an average grain size of 1.7 μm, was sieved through a 63 μm sieve with a bulk density of 1.2 g / cm ³ (FIG. 1) mixed with 0.3 kg of a water-atomized cobalt metal powder (11.7 μm FSSS), sieved through a 38 μm sieve with a bulk density of 3.3 g / cm ³ (FIG. 2), in a Turbula mixer. The product produced in this way had an FSSS value of 2.25 μm and a bulk density of 0.73 g / cm ³ . The content of critical impurities compared to a 400-mesh cobalt metal powder according to the prior art was significantly reduced (Table 2).

Sinter test:

Aufheizgradient:

180 K/min

Sintertemperatur:

830°C (in der Graphitform gemessen)

Sinterdruck:

350 N/mm²

Haltzeit:

3 min

The mixed powder was filled into a round graphite mold with a diameter of approx. 30 mm for the sintering test and hot pressed under the following conditions:

Heating gradient:

180 K / min

Sintering temperature:

830 ° C (measured in the graphite form)

Sinter printing:

350 N / mm ²

Stop time:

3 min

The test plate obtained in this way has a final density of 8.54 g / cm ³ and a hardness (Rockwell-B) of HR _B = 101.6.

Example 2: (Mix 60/40)

0.6 kg of a fine cobalt metal powder with a BET value of 1.11 m ² / g, an average grain size of 1.7 µm (FSSS), sieved through a 63 µm sieve with a bulk density of 1.2 g / cm ³ (Fig. 1), were with 0.4 kg of a water-atomized cobalt metal powder (11.7 µm FSSS) with a BET value of 0.73 m ² / g, determined by the N ₂ -1-point method (DIN 66 131), sieved through a 38-µm sieve with a bulk density of 3.3 g / cm ³ (Fig. 2) mixed in a ploughshare mixer for 60 minutes. The cobalt metal powder obtained in this way (FIG. 3) had an FSSS value of 2.6 μm, a BET value of 0.74 m ² / g and a bulk density of 0.8 g / cm ³ . The level of chemical impurities is significantly reduced compared to a conventional 400 mesh cobalt metal powder (Tab. 2).

A hot-pressed test plate as described in Example 1 had a density of 8.54 g / cm ³ and a hardness of HR _B = 101.2. Fig. 4 clearly shows that large round cobalt particles in addition to fine primary crystals have been preserved in the polished and etched sample.

Example 3: (Mix 50/50)

0.5 kg of a fine cobalt metal powder, obtained from the reduction of cobalt hydroxide with an average grain size of 0.9 μm, a BET value of 1.85 m ² / g, sieved through a 100 μm sieve (bulk density 0.8 g / cm ³ ), was sieved with 0.5 kg of a water-atomized cobalt metal powder (11.7 μm FSSS) with a BET value of 0.73 m ² / g, through a 38 μm sieve (bulk density 3.3 g / cm ³ ), mixed in a "Turbula mixer" for 15 minutes. The resulting mixture had an FSSS value of 1.5 µm FSSS, a BET value of 1.06 m ² / g with a bulk density of 0.8 g / cm ³ .

A hardness of HR _B 100.4 and a density of 8.5 g / cm ^{3 were} measured from a hot-pressed sample plate according to Example 1.

Comparative Example 1 (100% water-atomized cobalt metal powder <63 µm):

Pure water atomized cobalt metal powder, sieved through a 63 µm sieve, With an FSSS value of 12 μm was hot-pressed according to Example 1, the Hot pressing temperature was varied. On the test slides thus obtained following hardness values determined:

Sintering test using hot pressing:

Heating gradient:

180 K / min

Sinter printing:

350 N / mm ²

Holding time:

3 min

Results:

Sintering temperature Hardness values (HR _B ) density 800 ° C Press body disintegrates, hardness cannot be determined n.b. 850 ° C 25th 7.0 900 ° C 40 7.5 950 ° C 47 7.8

In no case did the atomized cobalt metal powder achieve the required minimum density of 8.5 g / cm ³ and the minimum hardness of 98 HRB.

Example 5 (100% water-atomized cobalt metal powder <38 µm):

Pure water-atomized cobalt metal powder, sieved through a 38 μm sieve (FIG. 2), with an FSSS value of 11.8 μm, was hot-pressed according to the conditions described in Example 1, the hardness of HR _B 80 being measured on the test platelets .

Even with this even finer screening, it was not possible to to achieve the required minimum density and minimum hardness.

Table 1 summarizes the data from Examples 1 to 3 and the comparative data for the 400-mesh cobalt powder and the atomized powder (according to the prior art). (Test results from the endurance test): Hot pressing temperature Sintered densities / Rockwell hardness (HR _B ) (° C) Atomized co-powder Example 5 Mixture from example 1 (70/30) Mixture from example 2 (60/40) Mixture from example 3 (50/50) Co 400 mesh St.dT 830 8.1 g / cm ³ 8.54 g / cm ³ 8.54 g / cm ³ 8.5 g / cm ³ 8.45 80 HR _B 101.6 HR _B 101.2 HR _B 100 HR _B 97.7 HR _B

Comparative example (400 mesh powder) Table 2: Comparative data of critical impurities in cobalt metal powders

The level of critical contaminants was compared to one usual 400-mesh cobalt metal powder significantly reduced (Tab. 2)

Impurities 400-mesh cobalt (400-mesh cobalt metal powder ("Cobalt Powder 400-mesh" from Hoboken Overpelt, Belgium)) and mixtures according to Examples 1, 2 and 3 according to the invention: Impurities 400 mesh-Co (100/0) Mixture example 1 (70/30) Mixture example 2 (60/40) Mixture example 3 (50/50) Al (ppm) 180 6 7 6 Ca (ppm) 320 12th 12th 13 Na (ppm) 55 25th 22 9 Mg (ppm) 150 8th 8th 3rd S (ppm) 140 13 14 15 Si (ppm) 310 34 36 41

Claims (9)

1. A cobalt metal powder as binder metal for the production of diamond tools and/or hard metal tools and/or wear-resistant coatings, characterised in that 20 to 80 wt.% of the powder consists of an atomised cobalt metal powder having optically determined particle sizes of from 5 to 150 µm and the balance to 100 wt.% consists of an optionally agglomerated cobalt powder having an optically determined primary particle size of less than 3 µm.
2. A cobalt metal powder according to claim 1, characterised in that the quantity of atomised cobalt metal powder is from 30 to 70 wt.%.
3. A cobalt metal powder according to one of claims 1 or 2, characterised in that the cobalt metal powder of crystalline structure has BET surface areas, as measured by the nitrogen one-point method (DIN 66131), of greater than 0.8 m²/g.
4. A cobalt metal powder according to one or more of claims 1 to 3, characterised in that the atomised cobalt metal powder is a water-atomised cobalt metal powder having a predominantly spheroidal habit.
5. A cobalt metal powder according to one or more of claims 1 to 3, characterised in that the atomised cobalt metal powder is a gas-atomised cobalt metal powder having a spheroidal habit.
6. A cobalt metal powder according to one or more of claims 1 to 5, characterised in that it has a bulk density of less than 1.4 g/cm³.
7. A cobalt metal powder according to one or more of claims 1 to 6, characterised in that it contains less than 20 ppm of aluminium, 20 ppm of calcium, 30 ppm of sodium, 20 ppm of magnesium, 30 ppm of sulphur, 75 ppm of silicon.
8. A cobalt metal powder according to one or more of claims 1 to 7, characterised in that it has a Rockwell hardness, as measured on hot-pressed test plates, of at least 98 HR_B.
9. Composite sintered articles produced from hard material powders and/or diamond powder and from binder metals, wherein the cobalt metal powder according to one or more of claims 1 to 6 is used as binder metal, optionally together with other metal powders.

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