WO1997034720A1 - Composite material and process for the preparation thereof - Google Patents

Abstract

The invention relates to composite materials substantially comprising: a cermet material with a binding metal phase of 3 to 30 mass %, with a rest formed from at least one carbonitride phase; or a hard metal with at least one hard material phase of 65 to 99 %, with a rest formed from the binding metal phase; or a steel produced by powder metallurgy; or a metal or ceramic magnetic material. The invention also relates to a process for preparing said composite material. To obtain composite materials and a process for the preparation thereof, which are economical to produce in the shape of geometrically complex moulded articles, and which have the lowest possible level of surface roughness, it is proposed that the composite material is prepared by hot casting and, subsequently sintering. The powdery starting materials are transformed, using a thermoplastic binder, into a stable, dispersive suspension with a viscosity between 100 mPa and 5 Pa. Said suspension is poured without pressure or at a maximum pressure of 5 MPa at a temperature between 70 DEG C to 120 DEG C, and subsequently heated, the thermoplastic binder being expelled before the binder-free structure is sintered.

Description

 description

Composite and process for its manufacture

The invention relates to composite materials, consisting essentially of a cermet material with a binder metal phase of

3 to 30 mass%, remainder at least one carbonitride phase or a hard metal with at least one hard material phase of

65 to 99%, the rest of the binder metal phase, a powder metallurgy steel or a metallic or ceramic magnetic material.

The invention further relates to a method for producing this composite material.

To produce the composite materials mentioned, the starting powders are mixed, homogenized and ground in accordance with the desired quantitative composition before they are subjected to a shaping for producing a green body, which is then sintered. The following variants of the shaping method are known from the prior art:

The compacted blank is shaped to the desired geometry in the green state or after its pre-sintering by means of mechanical turning, cutting, drilling and grinding operations. Alternatively, the mixed and ground starting powder is granulated and compressed with the aid of plastic binders by means of die presses to the desired final shape. In the metal powder injection molding process, the starting powder mixture is made flowable by adding a thermoplastic plastic binder and injection molded under high pressure in accordance with the injection molding process known for plastics. The necessary injection molding tools increase the manufacturing costs considerably. In addition, to remove the introduced Binder's process steps are necessary in which gaseous nitric acid or organic solvents are used, the handling and disposal of which, from an environmental point of view, is further cost-increasing.

Strand-shaped blanks can be formed using plasticizers such as wax using screw or piston extrusion presses.

It is an object of the present invention to provide composite materials and a method for their production which can be produced inexpensively in a complex geometric shape and which have the lowest possible surface roughness.

This object is achieved by the composite materials according to claim 1, which are characterized according to the invention in that the composite material has been produced by hot casting and subsequent sintering.

Developments of the composite materials are described in claims 2 to 16.

The qualitative and quantitative composition of the composite materials consisting of a cermet material, a hard metal or a powder-metallurgy steel is basically known in the prior art, for example from DE 43 40 652 A1. The respective base materials, namely cermets, hard metals or steels, can be in pure form or have additives of various types, namely metals, further hard materials, ceramic materials and single-crystal reinforcing materials in whisker or plate form. The fundamental difference between the composite materials claimed is that the starting materials are shaped into a non-porous green body by hot casting prior to sintering. Hot casting is basically for the production of ceramic moldings from cfi / Ber. DKG 72 (1995) No. 10, pages 640 to 642. The hot casting process, which is also referred to as low-pressure hot spraying or low-pressure injection molding, is based on the fact that the powdery starting mixtures are brought into a flowable state by adding a thermoplastic binder, essentially paraffins and / or liquid-melting waxes and surface-active substances - including surfactants or called detergents - are added. The surfactants serve as a connection between the solid particles, which they coat "in one layer" and the waxes and / or paraffins. In contrast to the production of ceramic green compacts, in which the density of the starting powder is a maximum of 6 g / cm ³ , cermet, hard metal or steel powder contain components that have much higher densities up to 16 g / cm ³ . Due to these high densities, there is a risk of segregation, with the result that the finished sintered bodies are prone to breakage and brittle, but surprisingly, through targeted selection of the thermoplastic binder, hot casting can also be used to shape the composite materials characterized in claim 1. The hot casting of the suspension consisting of the powdery starting materials and the thermoplastic binder enables the production of molded parts with a high degree of complexity, so undercuts, transverse bores and blind holes, large wall thickness differences, threads, grooves, surface structures, lettering and combinations of the aforementioned shapes can be cost-effectively , in particular by approximately 80% to 90% lower tool costs compared to high-pressure injection molding. Application products are, in particular, indexable inserts with complex chip form geometries, milling cutter blanks with a twisted chip chamber, rotor milling cutters, screws, micro-drills, drills and cutting inserts with flushing holes, guide fingers for cigarette manufacture, rotors, pump parts, such as bearing rings, shaft seals and shafts, gear wheels, complex nozzles, bearing shells, Watch case, scissors blanks, Cylinders for metering pumps, control pistons for paint spray guns, balls, work and transport rollers for the packaging industry, paddle wheels and the like.

The hot casting process according to the invention of cermet, hard metal, steel and / or metallic or ceramic magnet materials is characterized in accordance with claim 17, that the components of the composite materials in the desired quantitative mixing ratio as powdery starting materials after grinding with a thermoplastic binder, the proportion of which in the total amount is 20 to 50% by volume, preferably 30 to 40% by volume, and which has a viscosity between 3 to 6 mPa s, in a stable dispersive suspension with a viscosity between 100 mPa s and 5 Pa s is transferred, this suspension is cast into a shape corresponding to the desired contours of the composite component to be produced without pressure or under a pressure of at most 5 MPa, preferably 0.1 to 1 MPa, at 70 ° C. to 120 ° C. and at temperatures, which are above the evaporation temperatures of the thermoplastic binder, is heated and the thermoplastic B in which the stripped body is sintered. The form in which the dispersive suspension is made. The powder starting mixture and the thermoplastic binder by hot casting, i.e., above the melting temperature of the thermoplastic binder, has the true-to-shape negative contour of the finished component to be manufactured, taking into account the sintering shrinkage. The low pressures used do not place as high demands on the mold as in high-pressure injection molding. In particular, less expensive materials can be used as mold material.

Further preferred method steps are described in claims 18 to 29.

The average grain size of the powdered raw materials is less than 15 μm (for steel and magnetic Substances below 100 μm), it can be in particular ≤ 3 p and / or the viscosity of the suspension is between 100 mPa s and 2000 mPa s. Variations in the average grain size are included insofar as, for example, some of the powdered starting materials can have a coarser grain and the rest can have a finer grain.

According to a development of the invention, the thermoplastic binder consists of waxes and / or paraffins, to which 2 to 30% by volume of surface-active substances, preferably with an aliphatic hydrocarbon residue or alkylbenzene residue with 10 to 22 C atoms, are added. In individual cases, the selection of the surface-active substances must be adapted to the binder and powder properties and the grain size, so that all the starting powder grains are coated. The suspension is preferably cast in casting molds made of brass, copper, steel or plastic.

According to a further embodiment of the invention, the thermoplastic binder can be driven out in stages, namely in a first stage at temperatures up to 300 ° C. at which 50 to 80% by volume of the thermoplastic binder is expelled. be driven. The residual content of the thermoplastic binder remaining in the hot-cast molded body can then be used in the course of further treatment with a view to greater strength of the blank. The rest of the thermoplastic binder is then expelled at higher temperatures. The thermoplastic binder is preferably expelled in a protective gas atmosphere, as a result of which undesired reactions of the green body with the furnace atmosphere can be avoided.

In particular, in the first stage, the shaped body can be coated with an absorbent material (a powder bed), such as Al 2 O ₃ powder, or lie on a ceramic base, in particular A1 ₂ 0 ₃ , and the second stage can be carried out in a sintering furnace. The powder bed and the ceramic underlay serve as an aid for sucking up the liquefied binder. The residual content of thermoplastic binder in the molded body is preferably 20 to 30% by volume before being transferred to the sintering furnace, this residual content ensuring adequate stabilization of the molded body. The two-stage binder removal can optionally also be exploited to that targeted in the first stage at temperatures up to 300 ^* C acids present as surface-active substances, such as oleic acid, stearic acid, etc., are cracked, and the resulting cracking carbon for carburizing of Shaped body are used.

The hot casting according to the invention is not only limited to the production of moldings of homogeneous composition. Inhomogeneities in the form of changing substance compositions can be achieved by casting molds with two different pouring channels, into which suspensions of different compositions are poured. In particular, different compositions can be cast on top of one another or next to one another, which merge into one another at the respective interfaces and also make it possible to set radial composition gradients if the cast core material is encapsulated by a material of a different composition. As an alternative to the simultaneous casting of two hot casting slurries in a single mold, a core can first be produced in a first mold by hot or injection molding, which is then transferred to a second mold and encased in a shell made of hot-moldable material. In this way, abrasion-resistant wear protection layers can preferably be cast around a tough core, wherein the wear protection layers can consist of one or more layers of the same or different material composition. With the hot-casting method according to the invention, drill blanks with helical cooling channels can also be produced, a placeholder which can later be melted out having to be placed in the place of the later helical cooling channels during hot-casting. This can be accomplished by having a core A strand of plastic, preferably polyethylene or wax or another material that can be melted out at the sintering temperature, is firmly adhered as a placeholder for a later channel and that the molded body consisting of the strand and the core is then extrusion-coated in a casting mold by hot casting and the one thus produced Composite body is sintered, the strand thermally decomposing. The strand can be formed in a linear form, for example in the case of piercing tools, or in a spiral form in the case of drill blanks. In the case of screw-shaped cast parts, such as drills, it is advisable to use an elastic plastic mold as the casting mold, which has been produced by casting around a sample body and then separating the plastic mold along a helical surface. The separated plastic mold enables easy removal of drill blanks cast with molded chip chambers or spiral bars.

Exemplary embodiments of the invention are described below.

In a first exemplary embodiment, a hard material powder mixture of 94% by mass of WC and 6% by mass of Co is mixed, ground and then with a thermoplastic binder, which is 45% by volume based on the total mixture, to give a 75 ° C. warm suspension been melted. 70% by volume of the thermoplastic binder consisted of a low-chain paraffin, 20% by volume of wax and 10% by volume of oleic acid. The hot slip suspension has a viscosity that is greater than 100 mPas. If smaller viscosity values were reached, powdery WC / Co was refilled in an amount until the desired minimum viscosity was reached and the dispersion was stable. The slip is put into a casting mold without pressure or at a maximum of 1 MPa via sprue channels, the inner contours of which correspond to the molded component to be produced, taking into account the sintering shrinkage. The casting mold is then cooled to room temperature, the molding is removed and under protective gas in a powder bed up to 300 ° C. heated, except for a residual content of thermoplastic binder between 20 and 30% of the binder is driven off. Then the molded body is placed on a graphite base in a sintering furnace and sintered at approx. 1450'C. In the warm-up phase up to 500 ° C, the residual binder is driven out into the gas phase.

In a second exemplary embodiment, 5175 g of hard metal powder with the composition 87.77 mass% WC (grain size 0.9 μm), 10.6 mass% Co, 1.5 mass% TaC / NbC and 0.13 mass% VC are ver¬ been mixed. 270.4 g of a thermoplastic binder composed of a paraffin-wax-oleic acid mixture of the composition given in exemplary embodiment 1 were melted at 70 ° C., after which the carbide powder mentioned was added in portions while stirring the slip. The slip viscosity is here has been monitored and adjusted to a value of about 200 mPas. under a pressure of 3 x IO ⁵ Pa (3 bar), the slurry prepared is injected into a mold, ^β under a controlled atmosphere to 300 C and then ent at Bindert Sintered at 1450 ° C.

In a third embodiment is made of a soft magma. table Fe-Co powder with 80 mass% Fe and 20 mass% Co and an average particle size of 25 microns and a based on the total mixture of 5.5 mass% thermoplastic binder a suspension was prepared. The thermoplastic binder consisted of 70% by volume of a low-chain paraffin, 24% by volume of wax and 6% by volume of stearic acid. The thermoplastic binder was heated to 80 ° C. in a heatable mixing device and 2/3 of the powder mixture was added and mixed until the viscosity of the suspension decreased. The rest of the powder is then added and again mixed intensively. The suspension has a viscosity above 100 mPas. The slip thus produced is poured into a mold for a coil core under a pressure of 1 MPa and cooled. After cooling, the green compact is removed removed from the divisible casting mold and thermally debindered in an alumina powder bed in a push-through furnace under a hydrogen stream and sintered at 1350 ° C. for 4 hours.

Corresponding exemplary embodiments have been carried out using starting powder powders in which the following materials have been used instead of the iron-cobalt powder:

pure iron,

2.5 to 5% by mass Si, Reεt Fe,

10 to 50 mass% Co, Reεt Fe,

45 to 55% by mass of Ni, Fe and Fe

6 to 13 mass% AI, 10 to 18 mass% Ni,

0 to 42 mass% Co, 2 to 6 mass% Cu,

0 to 3 mass% Nb, 0 to 9 mass% Ti, balance Fe (AlNiCo-

Material).

In a corresponding manner, cermets and powder-metallurgical steel starting grades of the type mentioned have been processed. The starting grain sizes of the powder metallurgical materials were either on average below 1 μm (so-called fine grain). or below 2 μm.

Claims

Patent claims 1. Composite materials, essentially consisting of a cermet material with a binding metal phase of 3 to 30% by mass, the remainder at least one carbonitride phase or a hard metal with at least one hard material phase of 65 to 99%, the remainder binding metal phase or a powder metallurgically produced steel or a metallic or ceramic magnetic material, which indicates that the composite material was produced by hot casting and subsequent sintering. 2. Composite material according to claim 1, characterized in that the composite material has also been subjected to a final hot isostatic pressing (HIP) for post-compaction, preferably under a pressure between 0.5 MPa and 300 MPa (5 bar and 3000 bar), where Cermet or hard metal composite bodies have been post-compacted at temperatures from 1200°C to 1750°C and steel composite bodies at temperatures from 1000°C to 1600°C. 3. Composite material according to one of claims 1 or 2, characterized in that the cermet has a carbonitride phase based on Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and / or W and a binding metal phase made of Co and / or Ni has. 4. Composite material according to claim 1 or 2, characterized in that the hard material phase has oxicarbides, oxynitrides, oxycarbonitrides or borides. 5. Composite material according to claim 1, 2 or 4, characterized in that the hard metal is hexagonal WC as 1st phase and cubic carbide of the mixed crystal made of W, Ti, Ta and / or Nb as the 2nd phase and a binding metal phase made of Co, Ni, Fe or mixtures thereof. 6. Composite material according to one of claims 1, 2, 4 or 5, characterized in that the hard metal consists of hexagonal mixed carbides WC with MoC and / or cubic mixed carbides of the elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and/or W with a binding metal phase made of Co, Fe and/or Ni. 7. Composite material according to one of claims 1 to 6, characterized in that the binding metal phase has up to 15% by mass of Mo, W, Ti, Mn and/or Al - based on the total mass of the binding metal phase. 8. Composite material according to claim 7, characterized in that the binding metal phase consists of a Ni-Al alloy with a Ni-Al ratio of 90: 10 to 70: 30. 9. Composite material according to claim 8, characterized in that the binding metal phase contains up to 1 mass% boron (based on the total mass of the binding metal phase). 10. Composite material according to one of claims 1 to 6, characterized in that the binding metal phase consists of Ni ₃ Al, Tisi ₃ , Ti2Si ₃ , Ti ₃ Al, TisSi ₃ , TiAl, Ni2TiAl, TiSi ₂ , NiSi, MoSi ₂ , MoSiθ2 or mixtures consists of this. 11. Composite material according to claim 10, characterized by additions of 0 to 16 mass% of Co, Ni, Fe and / or rare earth metals. 12. Composite material according to one of claims 1, 2 or 4, characterized by a heat-resistant binding metal phase, consisting of high-speed steel produced by powder metallurgy and / or a superalloy. 13. Composite material according to one of claims l, 2 or 4, characterized by a binding metal phase made of Ni and Cr. 14. Composite material according to claim 13, characterized by additions of Mo, Mn, Al, Si and Cu in amounts of 0.01 up to 5% by mass. 15. Composite material according to one of claims 1 to 14, characterized by one or more layers applied using PVD, CVD and / or PCVD. 16. Composite material according to one of claims 1 to 15, characterized by additives up to 25% by mass consisting of single-crystalline reinforcing materials in platelet and/or whisker form and/or powdered ceramic materials added to the starting mixture, preferably from the group of borides and/or carbides and/or nitrides and/or carbonitrides of the elements of groups IVa (Ti, Zr, Hf), Va (V, Nb, Ta) or Via (Cr, Mo, W) or mixtures thereof and/or from Sie, Si ₃ N4 , Si2N2θ, A1 ₂ 0 ₃ , Zr0 ₂ , A1N and/or BN. 17. Process for hot casting of cermet, hard metal, steel and / or metallic or ceramic magnetic materials, characterized in that the components of the composite materials in the desired quantitative mixing ratio as powdery starting materials after grinding with a thermoplastic binder, the proportion of the total amount is 20 to 50% by volume, preferably 30 to 40% by volume, and which has a viscosity between 3 to 6 mPa s, is transferred into a stable dispersive suspension with a viscosity between 100 mPa ε and 5 Pa ε, this suspension is converted into one of the desired contours Composite material components to be produced in the corresponding form are cast without pressure or under a pressure of a maximum of 5 MPa, preferably 0.1 to 1 MPa, at at least 70 ° C to 120 ° C and at temperatures above the Evaporation temperatures of the thermoplastic binder are heated and the thermoplastic binder is expelled and the debinded body is sintered. 18. The method according to claim 17, characterized in that the average grain size of the ground powdery starting materials is below 15 μm, for steel and magnetic materials below 100 μm, preferably <3 μm, and / or the viscosity of the suspension is between 100 mPa s and 2000 mPa s. 19. Process according to claim 17 or 18, characterized in that the thermoplastic binder contains 2 to 30% by volume of surface-active substances (detergents, surfactants), preferably with an aliphatic hydrocarbon residue or alkylbenzene residue with 10 to 22 C atoms and a hydrophilic group such as -COOH, in particular oleic or stearic acid, residual waxes and / or paraffins. 20. The method according to any one of claims 17 to 19, characterized in that the casting mold consists of brass, copper, steel or plastic. 21. The method according to one of claims 17 to 20, characterized in that the expulsion of the thermoplastic binder takes place in stages, namely in a first stage at temperatures up to 300 "C 50 to 80% by volume of the thermoplastic binder and in a In the second stage, the remainder of the binder is expelled at a higher temperature, preferably under a protective gas atmosphere. 22. The method according to claim 21, characterized in that in the first stage the shaped body is covered with an absorbent material (powder bed), such as Al ₂ 0 ₃ powder, or on an absorbent ceramic base, preferably made of Al ₂ 0 ₃ , and / or the second stage is carried out in a sintering furnace. 23. The method according to any one of claims 21 or 22, characterized in that the shaped body has a residual content of thermoplastic binder of 20 to 30% by volume before being transferred to the sintering furnace. 24. Method according to one of claims 17 to 23, characterized in that different suspensions are poured into a casting mold via two different casting channels, as a result of which the shaped body produced has a radially or linearly inhomogeneous composition. 25. The method according to any one of claims 17 to 24, characterized in that a core is first produced in a first mold or by injection molding, which is then transferred to a second mold before the core is encased in a shell. 26. The method according to claim 25, characterized in that abrasion-resistant wear protection layers are cast around a core. 27. The method according to one of claims 24 to 26, characterized in that a strand made of plastic, preferably polyethylene or waxes, or another material that can be melted out at the sintering temperature is firmly attached to a core as a placeholder for a later channel and that the The shaped body consisting of strand and core is then encapsulated in a further mold by hot casting and the composite body produced in this way is sintered, with the strand thermally decomposing. 28. The method according to claim 27, characterized in that a cylindrical core is first produced by extrusion, die pressing or cold isostatic pressing, which is then helically wrapped with a strand of plastic, preferably polyethylene or wax, as a placeholder for a later drilling, that the wrapped core is overmolded in a casting mold and sintered after removal from the casting mold, whereby the strand decomposes thermally. 29. The method according to claim 28, characterized in that an elastic plastic mold is used as the casting mold, which was produced by casting around a sample body and then separating the plastic mold along a helical surface.