AT10479U1 - FLUID-DENSITY SINTERED METAL PARTS AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Description

2 AT 010 479 U1

The invention relates to fluid-tight sintered metal parts of high mechanical strength, essentially non-ferrum metal powder mixtures, processes for their preparation and their use.

Here, the term non-ferrum is also understood to mean metal mixtures which contain iron in small amounts, up to about 8% by weight, smaller amounts of iron than alloying additives should be possible.

Under sintered parts of increased strength are understood in the context of this invention sintered parts of a higher hardness than (non-pressure) substantially solid phase sintered parts without costly pressing aid removal of the same chemical composition.

In the context of this application, fluid-tight parts are understood to mean a dense body with a dense surface which does not permit the entry of fluids, such as liquids or gases, under elevated pressure (between 0.1 and 100 bar). They are also called " pressure-tight " designated.

First, processes and terminology in the field of sintering, as known to those skilled in the art, will be explained.

By sintering is meant generally the processing of starting materials in powder form, which allows combinations with physical properties that are not economically producible by melt metallurgy. After compaction on green compacts, they are subjected to a process-controlled and controlled heat treatment in the sintering furnace. This treatment of a powder compact takes place at a temperature from about half the melting temperature to about the melting temperature. Sintering is extremely temperature dependent. After temperature and pressure shrinkage and decrease of the porosity takes place.

By default, sintering takes place without pressure in a sintering furnace under ambient pressure and inert gas atmosphere.

Sintered products are characterized by: * a high utilization of raw materials * a high geometric reproducibility of mass components * the possibility to combine different alloy components - even those that do not form a homogenous melt

There are different variants of sintering:

Liquid phase sinter (liquid phase sinterinq)

Particles of higher melting material are connected by the occurring during sintering liquid phase of another material and cause a strong shrinkage.

Solid phase sintering (solid state sintering)

The occurrence of a liquid phase is largely avoided, which leads to liquid phase sintering less distortion in the final component. Essentially, only diffusion occurs at the grain boundaries. Only during solid-phase sintering does recrystallization (grain regeneration) occur with compaction of the moldings. At the recrystallization temperature, grain structure reformation occurs in the furnace. It is known that this is temperature and pressure dependent (see above)

There is a fluid transition between solid and liquid phase sintering. 3 AT 010 479 U1

Pressure assisted sintering

Sintering under elevated pressure makes it easier and better to make contacts between adjacent grains where diffusion can take place. 5

Hot isostatic pressing

In hot isostatic pressing (HIP = hot isostatic pressing), the green parts are individually batch sintered in pressure chambers, which is acceptable for mass production only in exceptional cases.

Continuous isostatic pressing

Continuous isostatic pressing is described in EP-A-1412113. 15

During sintering phase sintering temperatures, pressure is continuously applied to a pressed bolt in an extrusion press, with sintering thereof.

Standard sintering 20

The standard sintering is carried out without pressure predominantly under protective gas in furnaces, since usually materials are sintered, which easily react at elevated temperatures with the gases, which are replaced by the inert gas. For example. is used without oxygen to prevent oxide formation or with dry gases to prevent hydroxide formation. In standard internal sintering powder, granules, grits or the like. Is pressed together with pressing aids in near final shape usually uniaxial and the green compact thus produced in a sintering furnace at temperatures at 1/2 - 4/5 of the melting or. Solidus temperature of the metal powder, possibly under protective atmosphere, sintered. 3o forms of repressing:

Calibrate

Calibration, in the context of sintered parts, is understood to mean the three-dimensional pressing of a part with low compression of the same in order to compensate for sintering distortions. There is only a slight change in geometry. There is a correction of any distortion occurring during sintering. There is no basic shaping, but a simple repressing. The minor shape changes by holding on the order of a few percent and there is no new shape. 40

Free drawing is a two-dimensional shaping and refers to the smoothening of sintered surfaces. 45 Faceting - edge breaking

This is understood in the context of sintered parts deburring sharp edges on a product without other dimensional change. so sinter powder preparation

Cold pressing:

It is compacted powder with or without pressing aids without heat. 55 4 AT 010 479 U1

hot pressing

The powder is hot-pressed without sintering, with less and thermally higher compressible pressing aids are used as in cold pressing.

Pressing aids Can be release agents or lubricants or else also adhesives, which lead to a higher green strength and also to a reduction of the pressing force necessary for compaction of the powder.

Under this term, both release agents, which promote the ejection of the compact from the mold as well as lubricants which promote the sliding of the individual powder particles in the powder against each other -. For example, waxes, graphite or silicone oils understood. Preferably, pressing aids are expelled during the sintering or chemically converted - for example, burned.

The actual densification of the green part during sintering in the furnace is often followed by solution annealing, which improves the structure formed during sintering by recrystallization. Thereafter, other common processing steps, such as grinding, turning, coating, etc. of the sintered part can be done.

In general, sintered parts made of metal powder mixtures produced by known processes, in particular if sintered powder mixtures that do not melt homogeneously, frequently had porous or demixed regions due to the different diffusion rate of the sintered powder mixing components. This disturbs the sintered substructure and its mechanical technological properties insofar as a leaky porous surface or complete component arises. Accordingly, the properties of the powder sintered parts thus produced were deteriorated by these disturbing areas whose occurrence was unpredictable, and large differences in individually manufactured sintered parts occurred, resulting in, for example, an increased tendency for material breakage along the inhomogeneous areas, increased surface roughness and reduced surface roughness Surface hardness showed. This is especially when the sintered parts are exposed to high loads during operation - for example, as gears, impellers etc. disadvantageous and the conventional methods lead to high costs due to the high reject rate.

It is accordingly an object of the invention to produce sintered parts which exhibit a high surface hardness, high mechanical strength and are fluid-tight.

The object is achieved by a fluid-tight sintered metal part of high mechanical strength, essentially non-ferrum metal powder mixtures, producible by: presenting a substantially press-agent-free green compact; pressureless sintering of the green compact under protective gas at temperatures up to 70% of the molten metal temperature, preferably up to 60% of the molten metal temperature, optionally solution heat treatment, optionally calibrating and further processing.

Furthermore, the invention relates to a method for producing such a fluid-tight sintered metal part, comprising: presenting a substantially press-agent-free green compact; Sintering of the green body without pressure in a sintering furnace under protective gas, if appropriate, solution heat treatment of the sintered products; and possibly reworking the same.

Advantageous developments emerge from the dependent claims.

The fluid-tight sintered metal part produced according to the invention preferably has a density in the range from 95% to 97% of the theoretical density of the metal powder mixture. 5 AT010 479U1

The starting mixture of the material powder to be sintered is essentially metals and metal alloys, as well as smaller amounts of alloy constituents, hard materials, wear carriers, fibers and pressing aids.

For the purposes of this application, a green compact which is produced completely without pressing aids is one which has been produced with less than 5% by weight pressing assistant and one which, owing to a pressing aid removal step known per se, has a pressing aid content of less than 1% by weight. , preferably less than 0.5% by weight and very particularly preferably brought to a pressing aid content of less than 0.01% by weight, understood.

Preferably, sintered metal parts according to the invention are produced with a high to predominantly light metal content, the light metal being selected from Al, Mg, Be, Ti. Other constituents may be other metals or elements, such as Cu, Si, Zn, Ca, O, C, Fe, etc. ,

Preferably, the removal of the pressing aid and optionally the sintering in a sintering furnace under inert gas, such as noble gas, H2, N2, C02 or mixtures thereof, carried out in order to avoid oxidation and hydroxide formation during sintering.

Due to the fact that, according to the invention, a green compact with a very low or zero residual wax content is pressure-less sintered, metal powder can surprisingly be sintered to form a fluid-tight part while largely avoiding the liquid phase. It was completely unexpected that this classic non-pressure standard sintering of substantially green-free green compacts at these relatively low solid phase sintering temperatures (resulting in low energy costs) provides a high density product of great dimensional stability and low distortion.

It has been found that this process gives sintered parts having superior hardness and toughness, which have been manufactured in a fluid-tight manner by continuous isostatic pressing in an extrusion press according to the process of EP-A1-1412113, due to the high density and relatively spherical grain structure , harder and less ductile, which is desirable for highly stressed components (see Table I).

According to the invention, a powder compact produced by known pressing methods for powder compaction is preferably used as the starting material for the pressing aid removal step.

In another embodiment, this continuously produced sintered product formed by the die can be cooled by controlled cooling, for example by spraying with water, so that once a fine crystalline state is generated by quenching or that a defined heat treatment, for. B. in aluminum alloys solution annealing, can be done. The cooled part can be mechanically reworked. As finishing, surface coating or calibration - can be used. The sintered part can also be subjected to a heat treatment, if necessary, in order to modify or compensate the material structure.

Sintered parts of non-homogeneously melting metal mixtures produced in accordance with the invention also exhibit greater hardness and lower ductility at lower elongation than those produced by methods with continuous isostatic pressing which are capable of achieving similar degrees of density. For use as components, the mechanical, technological characteristics of the sintered parts, elasticity, tensile strength and elongation are very favorably influenced.

For example, a pressure-sintered aluminum alloy component with 13% by weight has 6 AT 010 479 U1

Silicon an elongation at break of less than 10% of a component made of the same alloy, which was continuously isostatically sintered.

By avoiding the occurrence of melt phases, immiscible components, such as hard phases, can be incorporated homogeneously distributed. It can be used as a material powder, a powder mixture consisting essentially of metals or their alloys and other materials such as hard parts, fibers, or wear carriers such as boron carbide, BN and non-metals. In this way one can produce metal-matrix composite materials, whereby another component can be fibrous or else particulate.

As fibers short or long fibers or particles may be added in proportions between 5-30 vol%. Short fibers or whiskers have a length that wstl. is less than 100 times the fiber diameter 15. Long, continuous or continuous fibers are those whose fiber length is greater than 100 times their diameter. Fibers can serve to improve the strength of the sintered parts.

Particle-reinforced materials typically have an admixture of SiC, boron carbide, Al 2 O 3, etc.

Due to the high degree of homogeneity ensured by the process, other typical sintered alloys, such as Ti alloys, in particular Ti / Nb alloys, TiAl, TiAINb and Co-Ti-B, Mg with SiC, boron carbide, Al 2 O 3 or AIPb alloys high heat storage capacity, which can not be produced by melt metallurgy, or beryllium parts - magnesium parts, etc. Typical compositions are, for example, aluminum with Si, Mg, Cu, Zn and possibly Fe, for example with 10 - 40% Si, Mg 0 -. 3%, Cu 0 - 5%, Zn and Fe 0 - 7% and other light metal alloys, such as magnesium, calcium, beryllium etc. Aluminum sintered parts include alumina sintered materials: 30 AlSi, AlSiCu, AICuMg with: Cu 3.8 - 4.4, Mg 0.5 - 1.0, balance Al: AlMgSi with AlSi 0.4 - 0.8 Mg 0.5 - 1.0, AIZnMgCu with 0.05 - 0.6 Cu 0.25 - 1.6 Mg 0.1 - 1.5 Zn 1.5 - 8.0, AlSi with more than about 7% Si, on. In particular, the invention relates to light metal sintered parts made of difficult to machine light metal alloys. Hypereutectic alloys can also be produced, with other advantages evident to the person skilled in the art on account of his specialist knowledge. 35

Among the advantages of the sintered parts according to the invention are to be listed, inter alia: The structure is distinguished from conventional sintered parts, in which a substantially press agent-freed green compact is sintered, by a significantly greater density than those of the same material composition obtained by standard sintering of powder compacts 40 with Wax contents are made, from.

Typical is the incorporation of wear carriers. It can be a fine and uniform grain size of the wear carrier and a much finer distribution of the same over other methods can be achieved. There are no segregations and segregations and a homogenous structure is obtained. It is an extremely simple process for producing highly wear-resistant sintered metal components with high dimensional accuracy. Hypereutectic alloys can also be made.

By sintering in fibers such as ceramic fibers, carbon fibers or hard material fibers, higher strengths-increase in tensile strength, increase in yield strength, increase in modulus of elasticity, better heat resistance and creep resistance-a reduction in the coefficient of thermal expansion are obtained. Typically, SiC particles, AIN, BN, TiB2, boron carbide, SiO 2, WC: fibers, such as carbon fibers, metal fibers, ceramic or glass fibers are wear-resistant or hard materials. 55 7 AT010 479 U1

Suitable metal phases may be selected from aluminum, titanium, copper, beryllium, magnesium, calcium, nickel, lithium, chromium, molybdenum, tungsten, bronzes, niobium, lead, zinc and cobalt.

It is useful to carry out sintering at temperatures up to about 70% of the melting point of the main component of the metal powder starting mixture under an inert gas such as a noble gas, nitrogen, carbon dioxide.

Other objects, features and advantages will be apparent from a consideration of the following description and claims taken in conjunction with the accompanying drawings. For a fuller understanding of the nature and objects of the invention, reference is made to the drawings, in which:

Fig. 1 is a micrograph of solid sections of AISiCuMg alloy prepared by conventional sintering.

FIG. 2: a micrograph of the surface area of a solid-state cut of a sintered part made of the AISiCuMg alloy according to the invention and of FIG. 1. FIG.

Fig. 3: a sintered product with denser surface area and less compressed inner area - shown schematically; and

4 shows a schematic process sequence of the production of the sintered products according to the invention.

Hereinafter, a preferred embodiment of the invention will be described with reference to the production of AISiCuMg molded parts, but it is by no means limited to this application. Other sinterable metallic powder, such as Ti, Ta, Mg, Be, Cs, Cu, can also be processed by this process ,

EXAMPLES

Example 1 :

Production of Inventive AISiCuMg Sinterscheiben

A substantially press-aid-free disc-shaped green compact having a diameter of 10 cm and a thickness of 10 mm of an aluminum powder mixture AISiCuMg was sintered at 590 ° C under argon for 30 min and then solution-annealed at 400 ° C for 30 min.

The so non-pressure sintered parts were then heat treated at 250 ° C for 6 hours. The sintered parts resulting from the heat treatment are then calibrated in a sizing press with a force of 150 KN and the final, dimensionally very tight toleranced shape is achieved. They can then be used as finished parts without further post-processing.

The product had a dense hard surface and a density of 2.67 g / cm 3 (96% of the theoretical density) as shown in FIG.

Example 2 (comparative experiment):

It disc-shaped AISiCuMg% sintered parts of the same dimensions as in Example 1 were conventionally prepared by sintering by pressing from the powder mixture as a comparison product a green compact with 3 wt.% Wax to a disc, then this disc in a Ent-wachungsanlage 20 min with 400 ° C, subsequently sintered in a sintering oven at 590 ° C for 30 min under argon and then solution-annealed again at 400 ° C over 35 min. 8 AT010 479 U1

Clearly visible porous surface areas (Fig. 1). Example 3:

Production of a sintered disc with hard outer material and easily machinable interior area.

It is a powder mixture of AISiCuMg pressed into a disc with a diameter of 10 cm and a height of 4 cm and this green compact substantially completely press adjuvant. The substantially press-auxiliaries-free green compact is sintered in a sintering oven at 590 ° C under dry nitrogen for 30 min. The result is a sintered part that is not completely sealed inside. Such sintered parts are suitable as pump wheels for oil and water pumps, which have an easily editable interior for the introduction of bores, while the densely sintered outer area is resistant to abrasion.

In Figs. 1 and 2 is a comparison of the microstructures of the sintered aluminum discs of AISiCuMg, prepared with conventional hot sintering according to comparative experiment and those after hot sintering of the invention in WSTL. shown to be free of green resources. It is clearly evident that the part produced according to the invention (FIG. 2) is significantly denser. TABLE 1

Material index ranges for AISiCuMg (Al based Si 16%, Cu 2.8%, Mg 0.8%) (at room temperature unless otherwise specified)

Measurement class Class..Sintert..Part EP1412113 Fluid-tight part Density g / cm3 2.65 2.77 2.67 Hardness HB 120 95 145 Tensile strength N / mm2 280 340

It can be clearly seen from Table 1 that the sintered bodies produced by the continuous isostatic pressing method are leakproof - that is, they are more precisely adjustable and thus also provide fewer defective parts. The continuously isostatically pressed sintered parts according to the method of EP 1412113 are more elastic, resulting in a significantly more elastic behavior and lower hardness, as required in particular by mechanical parts such as rotors and stators in a camshaft adjuster system or oil pump parts, bearing parts, pump wheels, etc. ,

The parts according to the invention are in contrast u.a. for sprockets (against steel chains), toothed belt wheels u. Like. Used, which require a hard surface and low abrasion. It turns out that the surface hardness of the part according to the invention is greater than that of those parts of the same composition, which were produced by the other two methods.

FIG. 3 shows the result of the production of a sintered part according to the invention with different structural areas in a sectional view. Here, the surface area is denser than the interior area. These parts can be made by sintering with a shorter sintering time than is necessary to completely sinter the part. This leaves a less dense core, which ensures a much less hard and dense and thus easier machinable area.

Of course, the invention is not limited to the exact construction or the embodiments listed or described, but there are different modifications.

Claims (5)

9 AT010 479U1 without departing from the core and scope of the invention obvious to those skilled in the art. Claims: 1. Fluid-tight sintered metal part of high mechanical strength consisting essentially of non-ferrum metal powder mixtures, producible by: - presenting a wstl in the. press-free green goods; pressure-free sintering of the green compact under protective gas at temperatures of up to 70% of the molten metal temperature, preferably up to 60% of the molten metal temperature, if appropriate solution heat treatment, and optionally calibrating and further processing. 2. Sintered metal part according to claim 1, characterized by a density in the range of 95-96% of the theoretical density of the sintered metal powder mixture. 3. sintered metal part according to claim 1, characterized in that the starting mixture of the material powder to be sintered essentially metals and metal alloys, and lower amounts of alloying constituents, hard materials, wear carriers, fibers. 4. sintered metal parts according to one of the preceding claims, characterized in that at least one metal is selected from Al, Ca, Ti, Cu, Mg, Be, Ni, Cr, bronzes, Nb, Pb, Co, Zn. 5. A process for producing a fluid-tight sintered metal part according to one of the preceding claims, characterized by: - presenting a Wstl in the. greenware free of sintering - sintering of the green body without pressure in a sintering furnace under protective gas, if appropriate, solution heat treatment of the sintered products; and possibly reworking the same. For this purpose 3 sheets of drawings