DE102011013894A1 - Final shape production of components made of material comprising intermetallic phases of trimolybdenum silicide and molybdenum borosilicide distributed in matrix, comprises e.g. subjecting powder mixture to grinding and producing suspension - Google Patents

Abstract

Final shape production of components made of a material comprising intermetallic phases of trimolybdenum silicide and molybdenum borosilicide homogeneously distributed in a molybdenum matrix, comprises: (a) subjecting a starting powder mixture to a grinding process; (b) producing a suspension with the ground starting powder mixture; (c) introducing the resulting suspension into a metal powder injection molding tool or constructing a green body in layers by screen printing; (d) subjecting the placed green body to thermal and/or chemical treatment; and (e) performing an unpressurized sintering. Final shape production of components made of a material comprising intermetallic phases of trimolybdenum silicide and molybdenum borosilicide homogeneously distributed in a molybdenum matrix, comprises: (a) subjecting a starting powder mixture to a grinding process that comprises at least molybdenum (80 mass), and additionally silicon nitride and boron nitride; (b) producing a suspension with the ground starting powder mixture that comprises at least an organic binder, and exhibits a suitable viscosity for screen printing or for metal powder injection molding; (c) introducing the resulting suspension into a metal powder injection molding tool or constructing a green body in layers by screen printing; (d) subjecting the placed green body to a thermal and/or chemical treatment for expelling the organic components; and (e) performing an unpressurized sintering in a non-oxidizing atmosphere or in high-vacuum conditions at 1600[deg] C.

Description

The invention relates to a method for near net shape production of components made of a material in which intermetallic phases of Mo ₃ Si and Mo ₅ SiB _{2 are} homogeneously distributed in a molybdenum matrix. Such a material is suitable for high temperature applications and can withstand corrosion attack as well as mechanical loads.

For example, single-crystal nickel-base alloys are used for components used in aircraft turbines. Their maximum operating temperature is limited to approx. 1150 ° C. Use at higher temperatures can only be done by additional application of thermal barrier layers, which increases the cost of manufacturing and the cost and the intrinsic mass of such components. In addition, mechanical stresses in thermal cycling can be detrimental.

It is therefore desirable to provide materials for components that can be used at higher temperatures above 1300 ° C, even at high mechanical stress.

Such materials also include those formed with a molybdenum matrix containing intermetallic phases of Mo ₃ Si and Mo ₅ SiB ₂ . They can have high fracture toughness and withstand mechanical stresses at high temperatures. They also have a high corrosion resistance at temperatures above 1300 ° C.

That's the way it is US 2009/001266 A1 in principle known how such materials can be produced. During production, a powder mixture consisting of Mo, Si ₃ N ₄ and BN should first be ground and processed into a suspension. From the suspension containing an organic binder, a homogeneous powder mixture should be obtained by spray-drying. This powder mixture can be shaped into a green body by cold isostatic pressing and then sintered. The sintering should take place in an atmosphere in which hydrogen and an inert gas are contained. To increase the density and the achievement of the final shape, a hot isostatic pressing is to be carried out after sintering.

In the case of materials produced by this method, it can not be ensured that the intermetallic phases of Mo with Si are homogeneously distributed in the molybdenum matrix, since this is impaired in particular by the treatment in the spray drying and the further processing of the powder mixture obtained thereafter. In addition, the spray drying process is energy intensive and therefore the cost is increased. In addition, the poor flow behavior of the resulting powder mixture has a detrimental effect on shaping by cold isostatic pressing. Components produced in this way must be reworked to obtain the final shape. This is costly. Because of the hardness and brittleness at room temperature many processing methods, eg. As a machining, not be used.

It is therefore an object of the invention to provide components that can be used in the high temperature range, which are resistant to corrosion at the same time and can be manufactured close to the final form.

According to the invention, this object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments of the invention can be achieved with features described in the subordinate claims.

In the method according to the invention, a starting powder mixture in which at least 80 mass is preferably at least 90 mass Mo and additionally Si ₃ N ₄ and BN are used. This starting powder mixture is subjected to a grinding process. The ground and homogeneously mixed starting powder mixture is used to prepare a suspension in which at least one organic binder is present. The suspension should have a suitable for screen printing or metal powder injection molding viscosity.

The suspension obtained in this way is then introduced into a metal powder injection molding tool in an alternative according to the invention or, in a second alternative, a green body is built up in layers by means of screen printing. The thus formed green body is then subjected to a thermal and / or chemical treatment to drive off the organic components. Subsequently, a pressureless sintering in a non-oxidizing atmosphere or under high vacuum conditions at a temperature of at least 1600 ° C is performed. The material of the component produced in this way has a homogeneous distribution of the two intermetallic phases Mo ₃ Si and Mo ₅ SiB ₂ in the molybdenum matrix of the material. This also applies to any residues of Si and boron which may still be present in the material and which have not been converted into intermetallic phases during the heat treatment and the sintering. The proportion of Si and B should be kept in the material after sintering less than 10 mass%, preferably less than 5 mass%.

For a homogenization of the starting powder mixture, milling has proved to be advantageous. The grinding technique used may be any of the mills usually suitable for homogenization. For example, the planetary ball mill or an attritor have proven to be particularly suitable. In this case, a mass ratio of starting powder to grinding balls of at least 1 to 10 should be maintained. The grinding process should be carried out over a period of up to 30 minutes, preferably up to 20 minutes, at a revolution number of a planetary ball mill of at least 100 rpm, preferably at least 200 rpm.

In the starting powder mixture Mo should have a mean particle size d ₅₀ of 10 microns to 15 microns, preferably 12 microns with a specific surface area of 1 m ² / g to 2 m ² / g and an elliptical to blocky particle shape, Si ₃ N ₄ with a mean particle size d ₅₀ of 0.3 μm to 5 μm, preferably 0.6 μm to 2.5 μm with a specific surface area of at least 3 m ² / g and a non-uniform particle shape and BN with a specific surface area of at least 3 m ² / g and a needle-shaped and / or particulate form in the form of flakes.

When preparing the suspension with the ground and thus mixed starting powder mixture, the starting powder mixture should be present in a proportion of at least 70 mass. In this case, the suspension can be prepared with at least one binder or a binder formed from a plurality of components. The desired viscosity can be adjusted with the binder content, it should be between 0.1 Pas and 200 Pas in the temperature range in which the actual shaping and the production of a green body takes place. In particular, in a shaping by metal powder injection molding should be maintained at a shear rate of 100 s ^-1, a viscosity of 2 Pas to 200 Pas or a shear rate independent viscosity in the range 0.4 Pas to 4 Pas. When adjusting the viscosity, the complexity of the final shape of the component to be produced can be taken into account. For example, the viscosity of filigree geometries or contours as well as components with undercuts in metal powder injection molding can be lower, but higher in screen printing.

Polyethylene, polypropylene, polyvinyl chloride, polyvinyl acetate, wax-based binders (eg beeswax or paraffin) or combinations of these substances, even with a suitable solvent, may be used as binders.

The material of the component achieved with the performed pressure-free sintering a physical density which corresponds to about 95 of the theoretical density. Densities of at least 99% theoretical density can be achieved with hot isostatic pressing performed subsequent to sintering. During sintering silicidation occurs.

If the shaping is carried out by screen printing, drying should be carried out at least after the application of every other layer. This can be z. B. be achieved by a suitable irradiation. In this case, alone or in addition, a layer thickness for the individual layers applied one above the other in the range of 5 μm to 75 μm, preferably in the range of 5 μm to 50 μm, can be maintained. By using different screens can be in the layer structure by changing the layer contour of layers three-dimensional components, eg. B. with cavities, channels, perforations or undercuts produce. In this case, layers having different layer thicknesses can also be applied in the layer structure produced by screen printing, if this is advantageous, for example, for the geometry of the component to be produced.

If the metal powder injection molding used for shaping, a three-dimensional design of the component can be achieved by the mold used. In addition, at least one core element made of an organic material may be used in the injection molding tool, but its organic components can also be expelled from the green body during the thermal treatment.

Depending on the binder (system) used, debinding can also be carried out with a solvent (eg water, acetone, alcohol), with catalyst (eg nitric acid), with sublimation and / or with a thermal treatment (eg successive evaporation of at least one or more components). The detachment / removal can take place in one or more process steps. The result is an open porosity in the material, through which then the last remaining binder components can be removed by evaporation immediately before sintering.

When binder component (s) are dissolved out, the greenest component can be dipped or sprayed into a solvent or solvent mixture after shaping and demolding. The respective binder component (s) is then progressively released progressively into the component interior starting from the surface of the component. The dissolution increases the porosity, which, however, can be reduced again during sintering and in particular during hot isostatic pressing (HIP).

The thermal treatment for expelling the organic components should be carried out in a protective gas atmosphere and / or up to a maximum temperature of 900 ° C. The protective gas atmosphere can be formed with at least one of the following gases, namely argon, hydrogen or nitrogen.

In addition to the improved material structure with the achievable homogeneous distribution of silicides, the achievable close to final production is advantageous because dispensed with a very expensive finishing, at least the required effort can be significantly reduced.

The invention will be further explained by way of examples.

example 1

A starting powder mixture containing 93 mass% Mo, 4.8 mass% Si ₃ N ₄ and 2.2 mass% BN was used. In this case, the powdery Mo (particle shape: elliptical-blocky) had an average particle size d ₅₀ = 12 microns and a specific surface area 1-2 m ² / g), the powdery Si ₃ N ₄ (particle shape: irregular) has an average particle size d ₅₀ = 0.6 - 2.5 μm and a specific surface area> 3 m ² / g) and the powdery BN (particle shape: acicular and flakes) has a specific surface area> 4 m ² / g).

When grinding in a planetary ball mill, which also leads to the mixing of the powders of the starting powder mixture, a mass ratio of powder to grinding balls of 1:10 and a grinding time of up to 20 minutes at a speed of 200 rpm were observed. Milling in the planetary ball mill was carried out under protective gas (eg nitrogen).

With the thus ground and mixed starting powder mixture, a powder-binder suspension was prepared in which a ratio of powder to organic binder of at least 70 percent by mass was maintained. With the binder, in this example, a thixotropic suspension having a load-dependent viscosity between 0.1 Pas and 200 Pas was prepared using a DECOFLUX WB 17 based pasting agent which is commercially available from Zschimmer + Schwarz DE. The suspension is preferably formed with water-soluble binder (s) and binder additives.

For the production of a near-net shape component ("green body") via the screen-printing process, the green body is built up in layers, wherein the suspension is pressed by a sieve which predetermines the contour of the respective layer. The layer thickness is between 5 microns and 50 microns. Depending on the layer thickness of the individual layers and the number of layers between 5 μm and 20 cm, the overall height of the green body can be achieved without any problems and according to the predetermined contour without any problems. Drying can be carried out between the application of the individual layers. Layer by layer, different screens can be used, so that a three-dimensional designed green body, with z. B. closed channels, undercuts or perforation can be made.

The thermal debindering of the green body is carried out under a suitable atmosphere, preferably under protective gas (argon, hydrogen, nitrogen or mixtures of these gases) by heating to a maximum temperature of 900 ° C. For complete removal of the binder, hold times up to 2 hours may be required.

After the organic components have been driven off, pressureless sintering of the green body into the desired shape is carried out under a non-oxidizing atmosphere, preferably under argon, hydrogen or high vacuum, at a heating rate of 5-10 K / min and a maximum temperature of> 1600 ° C and a holding time of more than 4 hours, preferably 6 hours, to achieve a physical density of> 94% of the theoretical density.

Optionally (for sinter densities above 94% of the theoretical density), there is the possibility of densification by means of hot isostatic pressing to produce a dense near-net shape molded article (that is, density ≥ 99% of the theoretical density).

The resulting material of the component had three phases: Mo, Mo ₅ SiB ₂ and Mo ₃ Si, the latter two phases being homogeneously distributed in a continuous Mo matrix. The phase proportions given below are for the composition obtained 96% by mass of molybdenum, 3% by mass of silicon and 1% by mass of boron. In the phases, 50-60% Mo were area / volume fractions and the remainder Mo ₅ SiB ₂ + Mo ₃ Si available.

Example 2

A starting powder mixture containing 92% Mo and Si ₃ N ₄ and BN having a mass ratio of 2.5 to 3: 1 was used. In this case, the powdery Mo (particle shape: elliptical-blocky) had an average particle size d ₅₀ = 12 microns and a specific surface 1-2 m ² / g), the powdery Si ₃ N ₄ (particle shape: irregular) has an average particle size d ₅₀ = 0.6-2.5 μm and a specific surface area> 3 m ² / g) and the powdery BN (particle shape: acicular and flakes) has a specific surface area> 4 m ² / g).

When grinding in a planetary ball mill, which also leads to the mixing of the powders of the starting powder mixture, a mass ratio of powder to grinding balls of 1:10 and a grinding time of up to 20 minutes at a speed of 200 U / min was maintained. Milling in the planetary ball mill was carried out under protective gas (eg nitrogen).

With the thus ground and mixed starting powder mixture, a powder-binder suspension was prepared. A binder in the form of a wax or a combination of wax, which is commercially available under the trade name Siliplast TP 6000 from Zschimmer and Schwarz, DE, was prepared in a proportion of between 6 and 8 mass in the suspension. A viscosity was set at a temperature of 80 ° C. between 2 Pas and 100 Pas, at a shear rate of 100 s ^-1 and a shear rate-independent viscosity in the range from 0.4 Pas to 4 Pas.

The suspension thus obtained was introduced into an injection mold to achieve the molding of the component. After demolding, debindering was performed with a thermal treatment to expel the organic components from the three-dimensional green body obtained after the metal powder injection molding. This was achieved in a protective gas atmosphere (argon, hydrogen, nitrogen or a gas mixture thereof) at a maximum temperature of 500 ° C to be achieved, which has been maintained for up to 2 hours.

Following this process step, pressureless sintering was carried out in a non-oxidizing atmosphere (argon, hydrogen) or under high vacuum conditions. It was heated at a heating rate of 5 K / min to 10 K / min to a temperature of 1750 ° C and held this temperature for 6 h. After cooling, a physical density equal to 94.5% of the theoretical density was reached.

In a densification by hot isostatic pressing at a pressure of 280 MPa and a maximum temperature of 1600 ° C, a density that corresponds to above 99% of the theoretical density, achieved.

In the material of the component produced in this way, 50% to 55% area fraction of Mo and the remainder were formed with the two intermetallic phases Mo ₃ Si and MO ₅ SiB ₂ . The intermetallic phases were homogeneously distributed in the molybdenum matrix. What could be proven with a ground sample.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2009/001266 A1 [0005]

Claims (11)

Process for the near-net-shape production of components from a material in which intermetallic phases of Mo ₃ Si and Mo ₅ SiB _{2 are} homogeneously distributed in a molybdenum matrix, in which a starting powder mixture in which at least 80 mass Mo and additionally Si ₃ N ₄ and BN is subjected to a grinding process, is prepared with the ground starting powder mixture, a suspension in which at least one organic binder is contained and which has a viscosity suitable for screen printing or metal powder injection molding; the suspension thus obtained is introduced into a metal powder injection molding tool or screen-printed green body is subjected to a thermal and / or chemical treatment for expelling the organic components and then pressureless sintering in a non-oxidizing atmosphere or high vacuum conditions at a Temperature of at least 1600 ° C is performed. A method according to claim 1, characterized in that the suspension with a viscosity in the range 0.1 Pas to 200 Pas in the temperature range, which is maintained during the molding to obtain the green body is prepared, and / or the proportion of starting powder in the suspension at at least 70 mass is maintained. A method according to claim 1 or 2, characterized in that the grinding process is carried out with grinding balls while maintaining a mass ratio of starting powder to grinding balls of at least 1 to 10 and the grinding process over a period of up to 30 min at a rotational speed of a planetary ball mill of at least 100 RPM is performed. Method according to one of the preceding claims, characterized in that a starting powder mixture in the Mo having a mean particle size d ₅₀ of 10 microns to 15 microns with a specific surface area of 1 m ² / g to 2 m ² / g and an elliptical bis block particulate form, Si ₃ N ₄ having an average particle size d ₅₀ of 0.3 microns to 5 microns with a specific surface area of at least 3 m ² / g and a non-uniform particle shape and BN with a specific surface area of at least 3 m ² / g and a needle-shaped and / or particulate form in the form of flakes are used. Method according to one of the preceding claims, characterized in that subsequent to the pressureless sintering a densification is carried out by means of hot isostatic pressing to obtain a physical density corresponding to at least 99% of the theoretical density of the material. Method according to one of the preceding claims, characterized in that a component is produced from a material in which Mo ₃ Si and Mo ₅ SiB ₂ and residues of Si and B are homogeneously distributed in the Mo matrix and the proportion of Si and B less than 10 measures. Method according to one of the preceding claims, characterized in that in the shaping by screen printing, at least after the application of each second layer, a drying is carried out and / or a layer thickness for the individual layers in the range 5 microns to 75 microns is maintained. Method according to one of the preceding claims, characterized in that during screen printing, the shaping is achieved by using different screens. Method according to one of the preceding claims, characterized in that during metal powder injection molding for shaping in the injection molding tool at least one core element is used made of an organic material whose organic components are expelled during the thermal treatment of the green body. Method according to one of the preceding claims, characterized in that the thermal treatment for removing the organic components in a protective gas atmosphere and / or up to a maximum temperature of 900 ° C is performed. Method according to one of the preceding claims, characterized in that organic components are removed with a solvent.