JP2007511665A - Sintered body and manufacturing method thereof - Google Patents

Abstract

The present invention relates to hard alloys, in particular hard alloys or cermets based on WC with Co, Ni and / or Fe binder moieties, in particular (Ti, W) (C, N) or (Ti, Mo) (C, N ) And a cermet based on a composition comprising a Co, Ni and / or Fe binder part and a method for producing these sintered bodies. According to the invention, the maximum pressure of 3 × 10 ⁴ Pa is fully or partly at least for a certain time, preferably for 10 to 100 minutes, during heating, sintering or after finish sintering of the sintered body. Underneath the plasma activated gas phase.

Description

  The present invention relates to hard alloys, particularly hard alloys or cermets based on WC with Co, Ni and / or Fe binder moieties, in particular (Ti, W) (C, N) or (Ti, Mo) (C, N ) And a cermet based on a composition comprising a Co, Ni and / or Fe binder part.

  The invention further relates to a method for producing these sintered bodies.

  Sintered bodies of the type described are used in particular as cutting material for cutting operations.

  The object of the present invention is to provide a sintered body with improved cutting properties. A method of manufacturing these sintered bodies should be provided that allows for shorter processing times and allows the influence of the tissue in the deepest possible penetration zone.

  The object is solved by the sintered body described in claim 1 or the method described in claim 6.

  Other configurations of the invention are described in the dependent claims.

  In particular, plasma diffusion treatment in the form of nitriding or nitration or carbonitriding is a method that has been used for a long time to improve the surface of steel and increases the wear and corrosion stability of the steel. In recent years, titanium alloys and stellite have also been subjected to plasma diffusion treatment, and the diffusion infiltration changes the texture of the surrounding zone of these objects, forming a diffusion zone or one or more coupling zones. The diffusion infiltrated material may be, for example, nitrogen or carbon, and these do not change the crystallographic structure of the base material except for the variation in spacing due to the case of the crystal lattice. Some or many bonding layers are formed over these diffusion layers or zones close to the surface, these layers forming other layers, for example bonding of the elements of the base material with the diffusion-infiltrated substances.

  JP-A-5-302140 discloses a cermet comprising a hard phase such as TiCN and a binding metal such as Co and Ni, exposed to a gaseous nitrogen plasma atmosphere, and the plasma is formed by high frequency or microwave discharge. is there. In this case, a nitride zone having a thickness of 10 to 500 μm is formed, and TiN particles having a particle size of 0.1 μm or less should be contained in the nitride zone in a uniform distribution. On the other hand, in the sintered body of the present invention, an additional structure component generated by the plasma activated gas phase is contained in a zone close to the surface, and the grain size is generally a structure having a hard material portion of a hard alloy and a cermet. The magnitude of the component. The substance contained in the plasma activated gas phase that diffuses and penetrates the surface may be nitrogen, carbon, boron, or a metal that can be excited to a plasma state. A sintered body treated with a plasma activated gas phase versus a purely heat activated gas phase has a surface zone that is affected to a much deeper region. The plasma activated gas phase can be used to purify and / or reduce a zone close to the surface, improve surface roughness in the sense of smoothness, and form new tissue components (phases) and their arrangement, depending on the gas composition of the plasma. enable. The composition of the peripheral zone close to the surface can improve the adhesion of layers consisting of carbides, nitrides, oxides, borides or carbon or combinations of these materials that are subsequently coated according to the invention. The plasma activation process also allows for the influence of the binder phase, for example plasma activated nitrogen can form cobalt-nickel nitride or iron nitride, which is not possible with thermally activated nitrogen.

  The sintered body according to the invention preferably has a peripheral zone, which contains substances from the plasma activated gas phase or compounds formed therefrom by migration and / or diffusion. The depth of the affected peripheral zone can be controlled to 1200 μm as well as the tissue uniformity of this peripheral zone by selection of processing parameters, temperature, pressure and processing time.

  Particularly in the peripheral zone, nitride particles having a particle size of 0.2 μm or more are additionally contained due to the plasma activated gas phase.

In order to produce these sintered bodies, the hard metal or cermet is pre-treated by powder metallurgy and compressed into a green product, and subsequently during the sintering, the green product is heated to the sintering temperature. Or after finish sintering, the plasma activated gas phase is completely or partially exposed under a pressure of at most 3 × 10 ⁴ Pa for at least a certain time, preferably for a time of at least 10 to 100 minutes Use the method. The plasma activation can be formed by microwave or glow discharge, in which case the glow discharge is advantageously formed using a pulsed method of connecting the sintered body as a cathode and applying a pulsed DC voltage to the cathode. Is done. The advantageous DC voltage is 200-900V, the DC voltage may drop to 0V or to the residual DC voltage during pulse pause, the residual DC voltage being the same as the lowest ionization potential of the gas phase involved or Greater than this, but the maximum value is 50% of the maximum value of the pulsed DC voltage. As long as the residual DC voltage during the pulse pause is maintained, the ratio of the residual DC voltage to the maximum pulsed DC voltage is 0.02 to 0.5. The cycle time of the pulsed DC voltage is 20 μs to 20 ms. The ratio of pulse length to pulse pause is 0.1-0.6.

  As already mentioned, the plasma activated gas phase may contain nitrogen, carbon, boron, or plasma activated metals, compounds or mixtures or precursors of said substances.

  Prior to the introduction of the reactive gas or reactive gas mixture according to another configuration of the method of the invention, the treated object is exposed to an inert gas atmosphere, in particular consisting of a noble gas and / or a chemical reducing agent, preferably hydrogen. Non-chemically reactive materials, such as argon, are used for surface purification, followed by the introduction of a plasma activated gas phase in other processing steps, thereby intentionally moving and diffusing to layers close to the surface. Arise. Hydrogen contained in the gas phase is used for activating the reduction process on the surface, in particular for decomposing oxide deposits.

  For the treatment of the sintered body in the plasma activated gas phase, a temperature of preferably higher than 900 and up to 1350 ° C. is selected.

  Other advantages of the present invention are illustrated in the examples and figures shown below.

  1-4 are photomicrographs of sintered bodies (each a) treated with a plasma activated gas phase, unlike the comparative samples (each b).

Example 1
First, WC-Ti (C, N)-having the same chemical composition (W 40% by mass, Ti 25.5% by mass, Ta 9% by mass, Nb 0.5% by mass, C7% by mass, N3% by mass and Co 15% by mass, respectively) Two sintered hard alloy bodies of type Co are treated at a temperature higher than the eutectic temperature of 1350 ° C. at 300 mbar for 20 minutes in a nitrogen atmosphere, with the first hard alloy body impinging on the plasma, The second sintered body does not collide with plasma. A so-called concentrated layer was formed in the two samples, which showed the accumulation of titanium carbonitride and at the same time the WC portion was excluded inside the sample. However, as can be understood from FIG. 1a compared to FIG. 1b, the zone affected by nitrogen in the sample impinged on the nitrogen plasma (FIG. 1a) is exposed only to heat and not exposed to the plasma activated gas layer. Obviously larger than the bandwidth.

Example 2
Sintered WC-Ti (C, N) -Co hard having a composition of W60.5% by mass, Ti16% by mass, Ta5% by mass, Nb0.3% by mass, C7% by mass, N1.2% by mass and Co10% by mass The side and upper side of the alloy body were exposed to a nitrogen plasma at a temperature of 1350 ° C. and 300 mbar, whereas the lower side was not exposed to this plasma. FIG. 2a, which shows a micrograph of the upper side of the hard alloy body, can be understood that a Ti (C, N) -rich layer of about 25 μm thickness without WC particles, which is brightly shown in the drawing, was formed, according to FIG. 2b. The lower micrograph here is activated only by heat and shows little effect of the attacked nitrogen.

Example 3
Two sintered hard alloy bodies having a composition of W 40% by mass, Ti 25.5% by mass, Ta 9% by mass, Nb 0.5% by mass, C7% by mass, N3% by mass, and Co15% by mass are obtained at an eutectic temperature of 1250 ° C. Heat treatment at 150 ° C. for ₂ minutes at a lower temperature, with the first hard alloy body treated with plasma activated nitrogen and the second hard alloy body with nitrogen activated only by heat in a gas atmosphere Process. The sample bombarded with plasma shows a clear exclusion of WC up to a depth of 1200 μm in FIG. 3a. In FIG. 3a, accumulation of Ti (C, N) is observed up to a depth of about 20 μm. In contrast, a hard alloy body exposed only to a hot nitrogen atmosphere shows the effect of a deep peripheral zone of only 5 μm according to FIG. 3b.

Example 4
Two sintered hard alloy bodies having a composition of W 60.5% by mass, Ti 16% by mass, Ta 5% by mass, Nb 0.3% by mass, C7% by mass, N1.2% by mass, and Co 10% by mass were combined at 1250 ° C. The first hard alloy body is again heat treated in the plasma activated gas phase at a temperature lower than the crystallization temperature at 150 mbar of N ₂ for 60 minutes, and the second hard alloy body is activated only by heat. Heat treatment in the gas phase The sample bombarded with the plasma shows a band of about 40 μm thickness with a 50 μm thick nitride layer and a reduced WC portion below this (FIG. 4 a), but in a nitrogen gas phase activated only by heat. In the exposed hard alloy body, it is possible to find a nitride layer with a thickness of only 5 μm and an underlying zone with a thickness of less than 5 μm.

  The above examples show that treatment of the sintered body in the plasma activated gas phase can adjust the intentional tissue non-uniformity and / or form a tie layer, the tie layer being a hard alloy body. Improves usage characteristics, such as blade fit, service life, and reduced response characteristics compared to other objects in the cutting process. In particular, the plasma method is preferably formed by glow discharge using the pulse method, which avoids the formation of arc discharge. Plasma activation may not be maintained over the entire processing time. The gas pressure is maintained in the range up to 300 mbar, in which the plasma state can be achieved, i.e. the plasma can be ignited and maintained. By selecting the processing temperature or its limit, it is not affected by the heat that can be recognized by other regions inside the sintered body, the structure inside the sintered body is maintained in its original form, and only the zone close to the surface is affected. receive. By partial coating of the deposited layer or coating layer on the surface of the sintered body or on the opposite side, it is achieved that no plasma is attacked or so-called plasma edges are not formed. The optional tissue deformation is only affected by the gas atmosphere and the processing parameters set at this location, but is not affected by the plasma, and the plasma acquires a different tissue deformation relative to it in the peripheral region close to the surface.

  If necessary or desired, heat treatment can be continued to purify the surface prior to treatment under the plasma activated gas phase. Alternatively or additionally, a treatment in the gas phase consisting of a chemical reducing agent can be performed before the plasma activated gas phase treatment.

  A new phase that cannot be formed without plasma activation can be formed in the peripheral zone near the surface by the action of plasma. Thus, the method according to the present invention can be used to adjust the desired tissue heterogeneity by selection of the phase composition varied in the peripheral layer near the surface and the deeper penetration zone of tissue effects and processing parameters. This provides a clear advantage over comparable sintered bodies known from the state of the art, for example with regard to the desired coating, as well as smoothing or roughening of the surface which is formed uniformly.

2 is a photomicrograph of a sintered body plasma-treated according to Example 1. FIG. 2 is a photomicrograph of a sintered body not subjected to plasma treatment according to Example 1. FIG. 3 is a micrograph of a sintered body that has been plasma-treated according to Example 2. FIG. 4 is a photomicrograph of a sintered body not subjected to plasma treatment according to Example 2. 4 is a photomicrograph of a sintered body plasma-treated according to Example 3. 4 is a micrograph of a sintered body that is not plasma-treated according to Example 3. FIG. 5 is a micrograph of a sintered body that has been plasma-treated according to Example 4. FIG. 6 is a micrograph of a sintered body that is not plasma-treated according to Example 4. FIG.

Claims (10)

Hard alloys, especially hard alloys or cermets based on WC with Co, Ni and / or Fe binder parts, in particular (Ti, W) (C, N) or (Ti, Mo) (C, N) and Co , A sintered body comprising a cermet based on a composition comprising Ni and / or Fe binder parts, wherein the sintered body is advantageously at least for a certain time during heating, during sintering or after finish sintering A sintered body characterized in that it is exposed to the plasma activated gas phase under a maximum pressure of 3 × 10 ⁴ Pa for a period of 10 to 100 minutes.   2. The sintered body according to claim 1, wherein the peripheral zone close to the surface contains a substance comprising a plasma activated gas phase by migration and / or diffusion or a compound formed therefrom.   The sintered body according to claim 1 or 2, wherein the sintered body is treated in a plasma activated gas phase containing nitrogen, carbon, boron, metal, a compound or mixture thereof or a corresponding precursor.   The sintered body according to any one of claims 1 to 3, wherein nitride particles having a particle size of 0.2 µm or more are contained in a zone near the surface of the sintered body.   The sintered body according to any one of claims 1 to 4, wherein the sintered body has a gradient of the structure of the sintered body from the surface toward the inside of the sintered body. 6. A method for producing a sintered body comprising a hard alloy or cermet according to claim 1, wherein a sintered body that has been pretreated by a powder metallurgy method and compressed into a green product is sintered. During heating to temperature, during sintering or after finish sintering, preferably for a period of at least a certain time, preferably for 10 to 100 minutes, completely or partly under a maximum pressure of 3 × 10 ⁴ Pa The manufacturing method of a sintered compact characterized by exposing to a plasma activated gas phase at the temperature of 900-1350 degreeC.   7. A method according to claim 6, wherein the plasma activation is formed by microwave or glow discharge, preferably using a pulse method in which the sintered body is connected as a cathode and a pulsed DC voltage is applied to the cathode.   The method according to claim 6 or 7, wherein the plasma activated gas phase contains nitrogen, carbon, boron, metal, a compound or a mixture thereof.   Before introducing the reactive gas or reactive gas mixture, the gas phase consists of an inert gas, in particular a noble gas, and / or the chemical reducing agent preferably contains hydrogen. The method according to claim 1.   10. A method according to any one of claims 6 to 9, wherein a portion of the surface of the substrate sintered body is coated during processing in the plasma activated gas phase.

Images