WO2004108632A1

WO2004108632A1 - Sintered part and the method for the production thereof

Info

Publication number: WO2004108632A1
Application number: PCT/DE2004/000901
Authority: WO
Inventors: Walter Lengauer; Klaus Dreyer; Klaus RÖDIGER
Original assignee: Kennametal Widia Produktions Gmbh & Co. Kg
Priority date: 2003-05-21
Filing date: 2004-04-29
Publication date: 2004-12-16
Also published as: US20060280639A1; EP1625102A1; CN100398497C; CN1842508A; JP2007511665A; DE10322871A1

Abstract

The invention relates to a sintered part consisting of a hard metal, in particular WC with Co, Ni and/or Fe binders-based hard metal, or cermet, in particular on the base of composition consisting of (Ti, W) (C, N) or (Ti, Mo) (C, N) with Co, Ni and/or Fe binders and to a method for producing such a sintered part. The inventive method consists in exposing a sintered part totally or partially to an active plasma gaseous phase at a maximum pressure of 3x104 Pa during heating, sintering or after sintering, at least during a certain time preferably during a time period ranging from 10 to 100 min.

Description

description

Sintered body and process for its production

The invention relates to a sintered body consisting of a hard metal, in particular a hard metal based on WC with Co, Ni and / or Fe binder proportions, or a cermet, in particular based on a (Ti, W) (C, N) or (Ti, Mo) (C, N) with binder components composed of Co, Ni and / or Fe.

The invention further relates to a method for producing such a sintered body.

Sintered bodies of the type mentioned are used in particular as cutting inserts in machining operations.

It is an object of the present invention to provide a sintered body which has improved cutting properties. Furthermore, a method for producing such a sintered body is to be specified, which enables shorter process times and allows the structure to be influenced in the deepest possible penetration zones.

This object is achieved by the sintered body according to claim 1 or by the method according to claim 6.

Developments of the invention are described in the subclaims.

Basically, plasma diffusion treatment, in particular in the form of nitriding or nitriding or nitrocarburizing, has long been a method of refining steel surfaces in order to increase the wear and corrosion resistance of the steels. More recently, titanium alloys and stones have also been subjected to a plasma diffusion treatment in order to diffuse the structure of the edge zones of such bodies in such a way that a diffusion zone or one or more connecting layers are formed. the. The species diffused in can be, for example, nitrogen or carbon, which do not change the crystallographic structure of the base material, with the exception of any changes in the spacing of the crystal lattice. On such a diffusion layer or near-surface zone, some or more connecting layers can be formed, which represent a further phase, such as a connection of an element of the base material with the diffused species.

A cermet is known from the abstract under the publication number JP 05302140 A, which consists of a hard phase such as TiCN and a binding metal such as Co and Ni and which is exposed to a gaseous nitrogen-plasma atmosphere, the plasma being generated by high frequency or microwave discharge becomes. A nitride zone with a thickness of 10 to 500 μm should be formed, in which TiN particles with a grain size <0.1 μm are contained in a homogeneous distribution. In contrast, in the sintered body of the present invention in the near-surface zones by the plasma-activated gas phase additional structural components are contained, the grain sizes of which are of the order of magnitude of the structural components that the hard material portions of hard metals and cermets usually have. The substances contained in the plasma-activated gas phase that diffuse into the surface can be nitrogen, carbon, boron, metals that can be excited to a plasma state. Compared to purely thermally activated gas phases, the sintered body, which has been subjected to a plasma-activated gas phase, has a surface zone that is influenced down to much deeper areas. Depending on the gas composition of the plasma, the plasma-activated gas phase also enables cleaning and / or reduction of the zones near the surface, an improvement in the surface roughness in terms of smoothing and the formation of new structural components (phases) and their arrangement. According to the invention, the composition of the edge zone near the surface can also improve the adhesion of subsequently applied layers of carbides, nitrides, oxides, borides or carbon or combinations of these materials. The plasma-activated treatment also makes it possible to influence the binder phase, for example plasma-activated nitrogen can lead to the formation of cobalt-nickel or iron nitrides, which is not possible with thermally-activated nitrogen. The sintered body according to the invention preferably has edge zones in which substances from the plasma-activated gas phase or compounds formed therefrom are contained by migration and / or by diffusion. The depth of the affected edge zones can be controlled up to 1200 μm via the choice of the process parameters temperature, pressure and treatment time as well as the structural inhomogeneity of these edge zones.

In particular, additional nitride particles with a grain size> 0.2 μm are contained in the edge zone due to the plasma-activated gas phase.

To produce such a sintered body, a method is used in which the hard metal or the cermet is pretreated by powder metallurgy and pressed to form a green body, which is then at least temporarily, preferably over a period of at least, during heating to the sintering temperature, during sintering or after finished sintering 10 to 100 minutes has been completely or only partially exposed to a plasma-activated gas phase under a pressure of maximum 3 x 10 ⁴ Pa. The plasma activation can be generated by microwaves or by a glow discharge, the glow discharge preferably being generated by means of a pulsed method in which the sintered body is switched as a cathode to which a pulsed DC voltage is applied. Preferred DC voltages are between 200 to 900 V. In the pulse pauses, the DC voltage can either be reduced to 0 V or a residual DC voltage which is equal to or greater than the lowest ionization potential of the gases involved, but a maximum of 50% of the maximum value of the pulsed DC voltage. If a residual DC voltage is maintained in the pulse pauses, its ratio to the maximum pulsed DC voltage is 0.02 to 0.5. The period of the pulsed DC voltage is between 20 μs and 20 ms. The ratio of the pulse length to the pulse pause is between 0.1 to 0.6.

As already mentioned, nitrogen, carbon, boron or even plasma-activatable metals, compounds or mixtures of the aforementioned substances or also precursors should be contained in the plasma-activated gas phase. According to a further development of the method according to the invention, the treatment body is exposed to an inert gas atmosphere, in particular a noble gas and / or a chemical reducing agent, preferably hydrogen, before the inlet of a reactive gas or a reactive gas mixture. Chemically non-reactive substances, such as argon, are used to clean the surface, after which the plasma-activated gas phase is let in in a further process step, through which specific migration and diffusion processes are triggered into the layers near the surface. Hydrogen contained in the gas phase serves to stimulate reduction processes on the surface, in particular to break down oxide deposits.

Temperatures above 900 ° C. to 1350 ° C. are preferably selected for the treatment of the sintered body in the plasma-activated gas phase.

Further advantages of the invention are explained on the basis of the exemplary embodiments discussed below and the drawings. Show it

1 to 4 are micrographs of sintered bodies which have been subjected to a plasma-activated gas phase (in each case _a ) in contrast to comparative samples (in each case b).

Example 1:

First, there are two sintered hard metal bodies of the type WC-Ti (C, N) -Co with identical chemical composition (40 mass% W, 25.5 mass% Ti, 9 mass% Ta, 0.5 mass% Nb, 7 mass% C, 3 mass% N and 15 mass% Co) were treated at a hypereutectic temperature of 1350 ° C at 300 mbar for 20 min in a nitrogen atmosphere, the first hard metal body having been exposed to plasma, but not the second. A so-called graded layer was formed in both samples, which shows an accumulation of titanium carbonitrides with simultaneous displacement of WC components into the interior of the sample. As can be seen from FIG. 1 a in contrast to FIG. 1 b, however, the is The nitrogen-affected zone in the sample exposed to nitrogen plasma (FIG. 1a) is significantly larger than the zone of the sample which was exposed to a gas phase which was only thermally activated but not plasma-activated.

Example 2:

A sintered WC-Ti (C, N) -co-hard metal body with the composition 60.5 mass% W, 16 mass% Ti, 5 mass% Ta, 0.3 mass% Nb, 7 mass% C and 1, 2 mass% N and 10% by mass of Co were exposed to a nitrogen plasma at a temperature of 1350 ° C. at 300 mbar on the side surfaces and the top, whereas the underside was not exposed to this plasma. 2a, which shows a micrograph of the top of the hard metal body, it can be seen that an approximately 25 μm thick Ti (C, N) -rich layer without WC particles, which appear bright in the image, was formed, while the micrograph of the bottom 2b shows practically no influence of the here only thermally activated attacking nitrogen.

Example 3:

Two sintered hard metal bodies of the composition 40% by mass W, 25.5% by mass Ti, 9% by mass Ta, 0.5% by mass Nb, 7% by mass C, 3% by mass N and 15% by mass Co were produced at a hypereutectic temperature of 1250 ° C annealed at 150 mbar N ₂ for 60 min, the first hard metal body having been subjected to the plasma-activated nitrogen and the second only thermally-activated nitrogen in the gas atmosphere. The sample exposed to plasma shows a clear displacement of the toilet down to a depth of 1200 μm in FIG. 3a. Up to a depth of approximately 20 μm, a Ti (C, N) enrichment can be seen in FIG. 3a. In contrast, the hard metal body, which is only exposed to a thermal nitrogen atmosphere, only shows an edge zone influence of up to 5 μm deep according to FIG. 3b. Example 4:

Two sintered hard metal bodies of the composition 60.5 mass% W, 16 mass% Ti, 5 mass% Ta, 0.3 mass% Nb, 7 mass% C and 1, 2 mass% N and 10 mass% Co were at a hypoeutectic temperature annealed from 1250 ° C at 150 mbar N ₂ for 60 min, the first body again being annealed in a plasma-activated gas phase, the second under a purely thermally activated gas phase. While the plasma-exposed sample shows a nitride layer with a thickness of 50 μm and an approximately 40 μm thick zone underneath with reduced WC proportions (see FIG. 4a), the body which has only been exposed to a thermally activated nitrogen gas phase is only a 5 μm thick nitride layer and a less than 5 μm thick zone underneath.

The above exemplary embodiments show that by treating the sintered body in a plasma-activated gas phase, a targeted structural inhomogeneity can be set and / or a connection layer can be produced which improves the usage properties of the body, such as its edge retention, service life and reduced reaction behavior compared to other bodies in machining processes. The plasma activation is preferably generated by a glow discharge, in particular by means of a pulsed method which avoids the occurrence of arcs. Plasma activation need not be maintained throughout the treatment period. The gas pressure is kept in a range up to 300 mbar, in which the plasma state can be reached, ie the plasma can be ignited and maintained. By choosing the treatment temperature or its limitation, it can be achieved that areas further inside the body are not subject to any recognizable heat influence, so that the structure inside the body remains in its original form and only the areas near the surface are influenced. By partially covering surfaces of the sintered body or their mutual abutment or support, it can be achieved that no plasma can attack there or the so-called plasma seam does not form. Any structural modifications are announced These points are only influenced by the gas atmosphere and the set process parameters, but not by the plasma, which has a different structural modification in the edge regions near the surface.

If necessary or desired, the treatment under a plasma-activated gas phase can be preceded by an annealing treatment with which the surface is cleaned. Alternatively or additionally, treatment in a gas phase consisting of a chemical reducing agent can also be carried out before the plasma-activated gas phase treatment.

Due to the influence of the plasma, new phases can be generated in the near-surface marginal zones, which cannot form without plasma activation. Thus, with the method according to the invention, both a changed phase composition in the surface layers near the surface and a deeper penetration zone of the structural influence and a desired structural homogeneity can be set by selecting the method parameters. This, as well as the smoothing or roughening of the surface produced in the same way, the latter with regard to any desired coatings, create clear advantages over comparable sintered bodies which are known from the prior art.

Claims

Expectations

1. Sintered body consisting of a hard metal, in particular a hard metal based on WC with Co, Ni and / or Fe binder proportions, or a cermet, in particular based on a (Ti, W) (C, N) or (Ti, Mo) (C, N) with binder components composed of Co, Ni and / or Fe, characterized in that the sintered body during the heating, during the sintering or after the finished sintering has been carried out completely or at least temporarily, preferably over a period of at least 10 min to 100 min has only been partially exposed to a plasma-activated gas phase at a maximum pressure of 3 x 10 ⁴ Pa.

2. Sintered body according to claim 1, characterized in that substances from the plasma-activated gas phase or compounds formed therefrom are contained in the near-surface edge zones by migration and / or diffusion.

3. Sintered body according to claim 1 or 2, characterized in that the sintered body has been treated in a plasma-activated gas phase which has contained nitrogen, carbon, boron, metals, compounds or mixtures thereof or corresponding precursors.

4. Sintered body according to one of claims 1 to 3, characterized in that nitride particles with a grain size> 0.2 μm are contained in the zones near the surface of the sintered body.

5. Sintered body according to one of claims 1 to 4, characterized by a structural gradient of the sintered body from the surface to the inside of the body.

6. A method for producing a sintered body made of a hard metal or a cermet according to one of claims 1 to 5, characterized in that that the body pretreated by powder metallurgy and pressed into a green body during the heating to the sintering temperature, during the sintering or after the finished sintering has been carried out at least temporarily, preferably over a period of at least 10 min to 100 min, completely or only partially in a plasma-activated gas phase under a Pressure of maximum 3 x 10 ⁴ Pa has been exposed, preferably at temperatures between 900 ° C to 1350 ° C.

7. The method according to claim 6, characterized in that the plasma activation is generated by microwaves or by a glow discharge, preferably by means of a pulsed method in which the sintered body is switched as a cathode to which a pulsed DC voltage is applied.

8. The method according to claim 6 or 7, characterized in that nitrogen, carbon, boron, metals, compounds or mixtures thereof are contained in the plasma-activated gas phase.

9. The method according to any one of claims 6 to 8, characterized in that before the inlet of a reactive gas or a reactive gas mixture, the gas phase consists of an inert gas, in particular a noble gas, and / or contains a chemical reducing agent, preferably hydrogen.

10. The method according to any one of claims 6 to 9, characterized in that parts of the surface of the substrate body are covered during the treatment in the plasma-activated gas phase.