EP1511870B1 - Hard metal substrate body and method for producing the same - Google Patents

Abstract

The combined dopant (Al, Cr, V, Nb, Ta, Ti, Zr, Hf) content in the substrate is limited to 4 weight % at most. The cubic phase content in the substrate is less than 4 vol%. The binder metal content (Fe, Co, and/or Ni) in an edge zone of the substrate is up to 1 microns, preferably up to 0.5 microns, falling to less than 0.5 times the binder content in the substrate interior An Independent claim is included for the method of manufacture

Description

The invention relates to a hard metal substrate body consisting of a WC hard material phase and a 3- to 25% by mass binder phase, which in addition to at least one of the binder metals Fe, Co and / or Ni still up to 15% by mass (based on the binder phase) contains dissolved dopants derived from the group Al, Cr, Mo, Ti, Zr, Hf, V, Nb, Ta.

The invention further relates to a method of such a hard metal substrate body, in which the starting mixture pretreated powder metallurgy, pre-pressed into a green compact and finally heated and sintered in an atmosphere of a furnace.

In the hard metal compositions mentioned, the dopants, which are usually added in the form of carbides, nitrides or carbonitrides of the elements Ti, Zr, Hf, V, Ta or alloys of these elements, in particular Ti ₂ AlN or Ti ₂ AlC in the starting powder mixture, act as Grain growth inhibitors that ensure that the produced WC-Co base alloy remains fine-grained and uniform to ensure optimum hardness and wear resistance.

It has also been known for a long time that the wear characteristics of cemented carbide bodies can be influenced by applying one or more surface layers of carbides, nitrides, carbonitrides, borides and / or oxides or diamonds. Early on, namely in DE-A 24 33 737 or DE-A-25 25 185, chemical or physical coating processes have been mentioned.

In DE 27 17 842 A1 it is stated that it is necessary to save the separate operation, the layer application by CVD or PVD it would be useful to suspend the cemented carbide body at a high pressure of between 2 bar (2 × 10 ⁶ Pa) and 5000 bar (5 × 10 ⁸ Pa) under nitrogen-containing atmosphere after the final sintering. The treatment temperature should be between 800 ° C and an upper limit that is at least 50 ° C below the maximum sintering temperature. With this "surface nitridation", which should be effective to a depth of 300 microns, an improved wear behavior and improved oxidation resistance and a reduction in the diffusion and tack of the cemented carbide should be ensured in its interaction with the wear partner. For many practical applications, however, a surface coating is still not dispensable. Especially with diamond coatings, but also coatings of other composition, the problem of poor adhesion of the coating on the substrate body. The reason for a defective adhesion is, for example, too high a binder content on the substrate body surface.

In DE 199 22 059 A1, a hard metal or cermet body having a hard material phase of WC and / or at least one carbide, nitride, carbonitride and / or oxicarbonitride at least one of the elements IVa, Va or VIa group of the Periodic Table and a binder metal phase of Fe, Co and / or Ni, the proportion of which is 3 to 25% by mass, proposed in which protrude from the body surface by 2 to 20 microns WC crystallites. This is to be achieved by either a nitrogen-free mixture of hard materials and binder metals is pre-pressed into a green compact and heated in a vacuum or inert gas atmosphere to a temperature between 1200 ° C and the sintering temperature, after which at the latest

Reaching the sintering temperature, at least temporarily, a nitrogen and optionally carbon-containing atmosphere with a pressure between 10 ³ and 10 ⁷ Pa is set, then optionally heated to sintering temperature and maintained over a holding time of at least 20 minutes or in this period of at least 20 min only a slight cooling of a maximum of 2 ° C / min performed and then cooled. When heating or at the latest from reaching the sintering temperature remains the set nitrogen atmosphere is maintained until at least 1000 ° C is reached in the cooling phase.

Alternatively, a mixture of hard materials and binder metals containing at least 0.2% by mass of nitrogen is pre-pressed and the green compact produced thereby is heated to sintering temperature, the inert gas or vacuum atmosphere set during heating at least temporarily starting from a temperature between 1200 ° C. and the sintering temperature is replaced by the entry of nitrogen-containing gases under a pressure of 10 ³ to 10 ⁷ Pa against this gas pressure atmosphere. The sintering holding time is at least 30 minutes; when heating from 1200 ° C or later, the nitrogen pressure should be maintained until at least 1000 ° C are reached in the furnace atmosphere during cooling.

However, the above method requires a hard material composition in which considerable amounts of other carbides, nitrides or carbonitrides must still be present in addition to WC and the binder to a considerable extent.

It is an object of the present invention to provide an improved, substantially biphasic hard metal body of the type mentioned above and a method for its production, which provides over the known in the prior art substrate bodies better adhesion for surface coatings, which are deposited from the gas phase , Such layers may e.g. consist of diamond, amorphous carbon, cubic boron nitride, carbon nitrides, oxides and metallic hard materials of carbides, nitrides, carbonitrides and oxicarbonitrides, in particular the elements of the IVa to VIa group of the Periodic Table.

This object is achieved by the hard metal substrate body according to claim 1, wherein according to the invention, the sum of the binding metals to the substrate body at a depth of 0 to 1 micron drops to less than half the concentration of binder metals in the substrate body interior. The percentage of dopants in the cemented carbide consisting of WC and a binder phase is according to the invention 4% limited by mass, likewise limited is the percentage of a possible third cubic phase to a maximum of 4% by volume.

In contrast to the carbide bodies created according to the prior art, not only a mere binder depletion in the near-surface edge zones is desired, but a marginal zone in which the "free spaces" created by binder depletion are "filled up" by dopants. However, the amount of the dopants should be limited to 15 mass% based on the binder metal phase, which in turn may be 3 mass% to 25 mass% of the total amount. The remainder, namely 75 to 97% by mass, consists of the pure WC hard material phase. Preferably, the concentration of the binder phase gradually decreases in said near-surface region, whereas the concentration of the dopants, the carbon and the nitrogen gradually increases.

According to a further embodiment of the invention, the grain size of the WC in the carbide substrate body is a maximum of 1.5 microns.

In particular, the hard metal substrate body described above is suitable for layers of diamond, but also of carbides, nitrides and / or carbonitrides of titanium, zirconium and / or hafnium or of Al ₂ O ₃ , HfO ₂ , ZrO ₂ , mixtures of oxides, amorphous Carbon, cubic boron nitride or carbon nitrides.

Preferably, in the near-surface edge zone, nitrides of the metallic dopant, e.g. TiN, CrN or VN, enriched.

For the production of the hard metal substrate body according to the invention, the method according to claim 5 or claim 6 is used.

In the first alternative embodiment, the starting powder mixture of the desired hard metal composition is pretreated by powder metallurgy in a manner known in the art, pre-pressed into a green body and until heated to the sintering temperature, wherein in the heating phase after reaching the eutectic, but at the latest after reaching the sintering temperature, the vacuum or inert gas atmosphere replaced by an N ₂ atmosphere with an N ₂ pressure ≤ 10 ⁵ Pa and at least until reaching the sintering temperature or until is maintained at the end of the holding time, in which the body is kept at sintering temperature.

Alternatively, it is also possible to carry out the nitrogen treatment after the final sintering, by subjecting the finished sintered body below the eutectic temperature to an N ₂ atmosphere under a pressure p of 10 ⁵ Pa <p <10 ⁷ Pa over at least 10 min becomes. This treatment can be connected either in the cooling phase after sintering or in a second step, possibly also following a grinding and / or blast treatment of the finished sintered body.

The nitrogen atmosphere may be introduced either by introducing nitrogen gas into the furnace atmosphere or by introducing precursors, i. N-containing gases are set, from which nitrogen forms at the corresponding temperature in the gas atmosphere in situ.

It is well known that with the length of time and with the gas composition in which the sintered body is above eutectic temperatures, the size of WC crystallites can be affected. Longer treatment times lead to larger WC crystallites.

In a preferred embodiment, the body is heated to 1250 ° C and held this temperature for a period of at least 20 min, before proceeding with the heating to the sintering temperature. Further preferably, the body is heated in the warm-up first in a vacuum and only from about 1250 ° C in an inert gas atmosphere, for example of argon, to the sintering temperature, upon reaching the nitrogen atmosphere is set at a pressure of at least 10 ⁴ Pa. Preferably, the heating and cooling rates are a maximum of 10 ° C / min, preferably, the corresponding rate is between 2 ° C / min and 5 ° C / min.

According to a further embodiment of the invention, in the starting mixture additionally up to 15% by weight, based on the binder phase, of carbides, nitrides, carbonitrides of the elements of the IVA, VA and VLA group of the Periodic Table or of Al or complexed carbides, complex nitrides and / or complex carbonitrides of the form Ti ₂ AlC, Ti ₂ AlN, Cr ₂ AlN, contain Cr ₂ AlC, but preferably only in each case in an amount as maximum in the binder phase can be solved. This solubility limit is determined in each case by the sum of the dissolved elements and can change for each element by adding other soluble elements.

In the above-described treatment of the sintered body in a nitrogen atmosphere under a pressure of 10 ² Pa to 10 ⁷ Pa diffuse the dopants or their carbides, nitrides or carbonitrides in the direction of the substrate surface and displace by enrichment of corresponding hard particles, which additionally by the combination of existing nitrogen and at least one of the metals can be amplified, the binder phase into deeper regions, which thereby depleted at the surface. However, the nitrogen treatment also acts on the carbon activity due to the fact that nitrogen is dissolved in the binder phase, which in turn affects the precipitation of hard material phases. This also allows a hard material phase enrichment in the surface to be controlled.

The invention will be explained below with reference to exemplary embodiments.

Fig. 1

ein Sinterprofil für die Behandlung einer Probe,

Fig. 2a, b

jeweils ein halbquantitatives GDOS-Tiefenprofil der Probe A,

Fig. 3a, b

jeweils ein halbquantitatives GDOS-Tiefenprofil der Probe C,

Fig. 4

weitere Sinterprofile und

Fig. 5a, b

jeweils ein halbquantitatives GDOS-Tiefenprofil der Probe C, die gemäß einem Sinterprofil nach Fig. 4 unterzogen worden ist.

Show it

Fig. 1

a sintered profile for the treatment of a sample,

Fig. 2a, b

each a semiquantitative GDOS depth profile of the sample A,

Fig. 3a, b

each a semiquantitative GDOS depth profile of the sample C,

Fig. 4

further sintered profiles and

Fig. 5a, b

each a semiquantitative GDOS depth profile of the sample C, which has been subjected according to a sintered profile of Fig. 4.

Five alloys according to the composition shown in the following table were ground in a conventional manner, mixed and pre-pressed into a green compact and then subjected to a sintering treatment, the sintered profile of FIG. 1 can be seen. Table 1 sample composition sintered body Composition (mass%) A 92% WC, 7.5 Co, 0.5 Ti ₂ AlC B 91.75% WC, 0.75% Cr ₃ C ₂ , 3.75% Co, 3.75% Ni C 91.75% WC, 0.75% Cr ₃ C ₂ , 4.5% Co, 1.5% Ni, 1.5% Fe D 91.75% WC, 0.75% Cr ₃ C ₂ , 7.5% Co e 91.4% WC, 0.75% Cr ₃ C ₂ , 0.35% Mo ₂ C, 7.5% Co

The aforementioned alloy A was first heated to 1250 ° C at a heating rate of 5 ° C / min. This temperature was maintained for about 30 minutes, after which an argon gas atmosphere was set at a pressure of 5 × 10 ³ Pa. At the same time, the heating of the sintered body has been continued at a heating rate of 5 ° C / min, wherein when reaching 1480 ° C, an N ₂ pressure of 7 x 10 ⁴ Pa was set, which maintained even after reaching the sintering temperature of 1480 ° C. remained. The sintering time was about 1 hour, after which the oven has been switched off.

In the case of the sintered body according to sample A, it was found that the N ₂ treatment influenced the near-surface regions at a depth of up to 1 μm such that there the binder phase, ie the sum of the binder metals, depleted and a marked accumulation of the hard material phase at the surface and in the near-surface regions (see Fig. 2a). This could both be detected in the metallographic cross section as well as purely optically by a color change. 2b shows the ratio of the dopant Ti to the binder metal Co. It can be seen that the doping element in relation to the binder metal accumulates strongly towards the surface of the substrate body and a very thin Ti (C, N) layer is present on the surface.

As another example of the effect of modification of the edge zone, Fig. 3a shows a semi-quantitative GDOS depth profile. It can be clearly seen that the sum of the binder metals (Fe, Co, Ni) on the outer surface decreases. FIG. 3b shows a ratio Cr / (Co + Fe + Ni) which increases significantly to the surface at lower penetration depths (about 0.1 μm). This means that in the binder in the graded edge zone, which is affected by nitrogen, the Cr content in the binder phase is increased relative to the other elements of the binder phase over the non-nitrogen affected inner regions of the alloy. The nitrogen content increases strongly in the peripheral zone and the carbon and tungsten content increases slightly toward the surface.

Samples A to F of Table 1 were subjected to various annealing and sintering at elevated nitrogen pressure as shown in Table 2. Table 2 Sintered profiles for Samples A to F of Table 1 sample sintering profile B Cycle 7 C Cycle 7 A Cycle 7 C php_1 A php_1 D php_2 e php_2 C php_2 e php_2 B php_2 D php_2a F php_2a D php_2b F php_2b.

The sintered profiles are shown in Table 3 and FIG. 4. Table 3 Tabular description of the sintered profiles preparation p (N ₂ ) bar Max. temperature Holding time at max. Temperature h the cooling conditions Cycle 8 dynamic vacuum up to max. temperature 5 1200 ° C 10 Allow to cool = 250 ° C / min Cycle 7 dynamic vacuum up to max. temperature 25 1280 ° C 10 Allow to cool = 250 ° C / min php_1 dynamic vacuum up to max. temperature 25 1400 ° C 1 then allow to cool to 1200 ° C at 5 ° / min = 250 ° C / min php_2 dynamic vacuum up to 1200 ° C 25 at 1200 ° C 1400 ° C 1 then allow to cool to 1200 ° C at 5 ° / min = 250 ° C / min php_2a dynamic vacuum up to 1200 ° C 25 at 1200 ° C 1400 ° C 2 then allow to cool to 1200 ° C at 5 ° / min = 250 ° C / min php_2b dynamic vacuum up to 1200 ° C 25 at 1200 ° C 1400 ° C 4 then allow to cool to 1200 ° C at 5 ° / min = 250 ° C / min

A semiquantitative GDOS depth profile of Sample C is shown in Figure 5, which shows the decrease in the sum of the binding metals in near-surface regions. The sum of the binding metals again shows the same characteristics as in the case of the same vacuum-sintered variety. Also, the N and C contents are increased toward the surface as in the case of the reduced-pressure sintered alloy C. Fig. 5b shows a marked increase in the Cr / (Co + Ni + Fe) concentration ratio to near-edge zones.

By choosing the doping elements or their compounds and also by selecting the nitrogen pressure, the edge zone of the finished cemented carbide sintered body can be adjusted so that not only an accumulation of dopants, but even the formation of a diffusion layer of nitrides is promoted. If, for example, Cr or a Cr compound is used as a doping, then no vacuum sintering with subsequent N ₂ gas phase adjustment under small pressures (<105 Pa) results in no chromium nitride layer or enrichment because chromium nitrides do not form at low nitrogen pressures. On the other hand, by doping a V- or Ti-containing phase, the formation of TiN or VN or of Ti (C, N) or V (C, N) can be induced under the same conditions, because vanadium nitrides or carbonitrides already at low nitrogen pressures be formed.

Claims (11)

1. Hard metal substrate body comprised of a WC hard material phase and a binder phase of 3 to 25 mass % which apart from at least one of the binder metals Fe, Co and/or Ni contains up to 15 mass % (of the binder phase) dissolved doping agents selected from the group comprised of Al, Cr, V, Nb, Ta, Ti, Zr, Hf, characterized in that the percentage proportion of all doping agents in the hard metal is limited to a maximum of 4 mass % in that the proportion of a cubic phase in the hard metal is less that 4 volume % and in that the binder metal content in a hard metal-substrate body boundary zone falls from up to 1µm, preferably up to 0,5µm to less that 0,5 times the binder content in the substrate body interior, whereby the concentration of the binder phase falls gradually toward the substrate body surface and the concentration of the doping agents gradually increases in a corresponding manner.
2. Hard metal substrate body according to claim 1 characterized in that the grain size of the WC is ≤1,5µm whereby the WC fine hard metal (grain size ≤0,8µm) and/or with WC ultrafine grain hard metal (grain size ≤0,5µm), preferably contain Cr, V and/or Ta as doping agent.
3. Hard metal substrate body according to one of claims 1 or 2 characterized in that at least one layer is applied to the substrate body surface, the layer being comprised of a carbide, nitride and/or carbonitride of Ti, Zr and/or Hf and/or of Al₂O₃, HfO₂, ZrO₂, oxides, amorphous carbon, diamond, cubic boron nitride, carbon nitride (CN_x) or another compound of at least one of the elements B, C, N and/or O.
4. Hard metal substrate body according to one of claims 1 to 3 characterized in that in the boundary zone close to the surface there is an enrichment with nitride or carbonitride of the metal doping agents.
5. Method of producing a hard metal substrate body according to one of claims 1 to 4 in which the starting mixture is pre-treated powder metallurgically, is prepressed to a green body and then in an atmosphere of a furnace is heated and sintered, characterized in that in the heating phase, after reaching the eutectic, but not later that reaching the sintering temperature the vaccum or inert gas atmosphere is replaced with a N₂ atmosphere with a N₂ pressure of ≤10⁵ Pa and is maintained at least until the sintering temperature is reached.
6. Method of making a hard metal substrate body according to one of claims 1 to 4 in which the starting mixture is powder metallurgically pre-treated, is pressed to a green body and finally heated in an atmosphere of a furnace and sintered, characterized in that after finish sintering or optionally in a final treatment below the eutectic temperature, the sintered body is maintained in a N₂ atmosphere under a pressure (p) of 10⁵ Pa < p < 10⁷ Pa for at least 10 minutes.
7. Method according to claim 5 or 6 characterized in that the nitrogen atmosphere is established by introducing precursors that is N-containing gases whereby the nitrogen is formed in situ in the gas atmosphere.
8. Method according to one of claims 5 to 7 characterized in that the body is heated up to 1.250°C during the heating phase and this temperature is held for at least 20 minutes, preferably more than 1 hour, before the heating up is continued to the sintering temperature.
9. Method according to one of claims 5, 7 or 8 characterized in that initially in the heating up phase at about 1.200°C the previously existing vaccum is replaced by an inert gas atmosphere, preferably with a pressure of 10³ Pa to 10⁴ Pa and only upon reaching the sintering temperature is a nitrogen containing atmosphere established with a higher pressure, preferably ≥ 10⁴ Pa.
10. Method according to one of claims 5 to 9 characterized in that the heating up rate and the cooling down rate amounts to up to 10°C/min, preferably between 2°C/min and 5°C/min.
11. Method according to one of claims 5 to 10 characterized in that the starting mixture contains up to 15 mass % of the binder phase additional carbides, nitrides, carbonitrides of the elements of Group IVa or VIa of the periodic system or Al or complex carbides, complex nitrides and/or complex carbonitrides of the form Ti₂AlC, Ti₂AlN, Cr₂AlN, Cr₂AlC.

Images