EP0213410B1 - Process for manufacturing a metallic work piece from an amorphous alloy with at least partly magnetic components - Google Patents

Description

• A) Ein Zwischenprodukt aus mindestens zwei pulverförmigen, zumindest teilweise magnetischen Komponenten der Legierung wird unter Vornahme eines Kompaktierungsschrittes so ausgebildet wird, daß die Legierungskomponenten in dem Zwischenprodukt jeweils in mindestens einer Dimension höchstens 1 _Jlm ausgedehnt sind.

The invention relates to a method for producing a metallic body from an amorphous or crystalline alloy, in which method the following method steps are to be carried out:

• A) An intermediate product from at least two powdery, at least partially magnetic components of the alloy is formed by performing a compacting step in such a way that the alloy components in the intermediate product are each expanded in at least one dimension by at most 1 _J lm.

• B) Das Zwischenprodukt wird in den metallischen Körper mit amorphem Legierungszustand mittels einer Diffusionsreaktion bei einer vorbestimmten erhöhten Temperatur, die unterhalb der Kristallisationstemperatur der amorphen Legierung liegt, umgewandelt.

Furthermore, in the case of the production of the amorphous alloy, a further process step must be provided:

• B) The intermediate product is converted into the metallic body with an amorphous alloy state by means of a diffusion reaction at a predetermined elevated temperature which is below the crystallization temperature of the amorphous alloy.

In the case of the production of a crystalline alloy, a further process step must be provided:

B ') The intermediate product is converted into the metallic body with a crystalline alloy state by means of a diffusion reaction at a predetermined elevated temperature.

Such a method for producing an amorphous or crystalline alloy is e.g. from WO-A-84/02926.

Amorphous materials referred to as "metallic glasses" are generally known (cf. for example "Zeitschrift für Metallkunde", volume 69, 1978, number 4, pages 212 to 220 or "Elektrotechnik und Maschinenbau", 97th year, September 1980, number 9, Pages 378 to 385). These materials are generally special alloys which are to be produced from at least two predetermined starting elements or compounds, also referred to as alloy components, by means of special processes. Often the material of at least one of the elements or one of the connections is magnetic. These special alloys have a glass-like, amorphous structure instead of a crystalline one and have a number of extraordinary properties or combinations of properties such as high wear and corrosion resistance, high hardness and tensile strength with good ductility as well as special magnetic properties. In addition, micro-crystalline materials with interesting properties can be produced via the detour of the amorphous state (see e.g. DE-C-28 34 425).

Up to now, metallic glasses have generally been produced by rapid quenching from the melt (cf. also DE-A-31 35 374 or DE-A-31 28 063). However, this method results in at least one dimension of the material produced being less than about 0.1 mm. For various applications, on the other hand, it would be desirable if metallic glasses of any shape and size were available.

It has also been proposed to produce metallic glasses by means of a special solid-state reaction instead of by rapid quenching. Here, one of the alloy components must diffuse rapidly into the other below the crystallization temperature of the metallic glass to be produced, the other component remaining practically immobile. Such a diffusion reaction is generally also referred to as anomalous, rapid diffusion. Certain energetic requirements must be met (cf., for example, "Physical Review Letters", Vol. 51, No. 5, August 1983, pages 415 to 418 or "Journal of Non-Crystalline Solids", Vol. 61 and 62, 1984, Pages 817 to 822). The alloy components must react exothermically with one another. Further, a certain microstructure is required by the alloy components involved are closely adjacent and have at least one dimension very small expansions below 1 _J lm respectively. Accordingly, layer structures are particularly suitable which can be produced, for example, by vapor deposition (cf., for example, the uterine site mentioned from "Phys.Rev.Letters", vol. 51). In addition, a layering of thin metal foils is also possible for this (cf., for example, "Proc. MRS Europe Meeting on Amorphous Metals and Non-Equilibrium Processing", ed. M. von Allmen, Strasbourg, 1984, pages 135 to 140).

A corresponding microstructure is also formed in the method according to WO-A-84/02926 mentioned at the outset. According to this method, metal alloys of the desired composition are first mixed as alloy components and then compacted to an intermediate product in such a way that the alloy components are each expanded in at least one dimension by at most 11 m. This intermediate product is then converted into the desired metallic body with an amorphous structure by anomalous rapid diffusion at a predetermined elevated temperature. This known method is also published in the "Frankfurter Zeitung: Blick durch die Wirtschaft" by: "Frankfurter Allgemeine Zeitung", 27th year, No. 23, 1.2.1984, page 5 and in "Machine Design", vol. 55 , No. 25, 10.10.1983, page 8 indicated.

While only very thin structures can be obtained in the evaporation process mentioned, the two deformation processes mentioned assume good ductility of the alloy components involved. In addition, in the known method, which starts with powdery alloy components, there arises the difficulty that the oxide layers on the surface of the metal powder have to be removed by the deformation and that the structure resulting from the compacting and deformation is very irregular. If you also consider technically interesting alloys, you will find that often one of the alloy components is poorly or practically not deformable, such as boron for FeNiB or cobalt for CoZr. Also, some components are not available as a film, or only at a high price, such as rare earth metals for amorphous transition metal / rare earth compounds.

A method which is proposed with the older European patent application according to the unpublished EP-A-0 200 079 can be used for the large-scale production of metallic bodies with a relatively extensive shape and dimension from amorphous alloys, in particular using hard-to-deform or brittle alloy components has been. According to this method, a mixed powder is first produced by means of a grinding process known per se from the mostly crystalline powders of the starting elements or compounds representing the alloy components, the individual particles of which are built up approximately in layers from the starting elements or compounds. The point in time at the end of the grinding process at which this structure of the mixed powder particles is present can easily be determined and thus determined, for example by experimental examination of the particles. This mixed powder produced in this way is then compacted and / or deformed in a further working step to form a compact intermediate product with the desired shape and size adapted to the body. This compact intermediate product still consists of crystalline parts of the starting elements or compounds, the respective dimensions of which in at least one dimension are less than 1 _{1 1} m or even less than 0.2 _{1 1} m. In a subsequent diffusion annealing, the intermediate product is then converted in a manner known per se into the desired metallic body made from the amorphous alloy or from the metallic glass.

In this proposed method, the powder is compacted either by extrusion or by other shaping methods such as e.g. Hammer. This deformation causes a reduction in the individual layer thicknesses if the layers are parallel to the direction of deformation. Although powder particles with largely parallel layers are obtained by the grinding process, the particles are not aligned during the compacting, so that the arrangement of the individual layers is statistically distributed with respect to the direction of deformation. For layers that are perpendicular to the direction of deformation, the layer thickness can even increase during the deformation, whereas layers that are predominantly parallel to the direction of deformation become thinner during the deformation. The statistically oriented alignment of the layers before the compacting may therefore lead to an increase in the range of layer thicknesses after the deformation; i.e. the deformation during the compacting is not used.

The object of the present invention is to design the processes of the type mentioned at the outset such that they can be used to produce large-scale metallic bodies with a relatively extensive shape and dimension from an amorphous or also from a non-amorphous, crystalline alloy, using at least one magnetic component, whereby, in particular, hard-to-deform and brittle alloy components are to be used, and in the compacting step the individual layers are arranged parallel to a predetermined preferred direction, the later direction of deformation.

This object is achieved both in the case of the production of an amorphous alloy and in the case of the production of a crystalline alloy according to the invention in that for carrying out process step A) from the powdery alloy components by means of a grinding process to be ended at a predetermined point in time with a crystalline mixed powder Particles are produced in such a way that they each have at least largely a layer-like structure made of the alloy components, then the powder particles of this mixed powder are aligned at least in the state of their mobility in a magnetic field, and finally this mixed powder is compacted in this direction to form the intermediate product of the desired shape and size and possibly deformed further.

The advantages associated with this embodiment of the method can be seen in particular in the fact that the particles of the mixed powder align themselves in an applied magnetic field of sufficient strength such that their layer-like structures lie approximately parallel to the magnetic field. The magnetic field is applied during the manufacturing process at least at a time when the individual particles are still mobile, i.e. generally at least before the actual compacting step. Due to the special orientation of the individual layer-like structures of the mixed powder in the magnetic field, it is achieved that they then become even thinner during the deformation, i.e. that is, the deformation process for compacting is also used to further reduce the layer thicknesses. It is known that diffusion reactions between the particles are favored by correspondingly small layer thicknesses. This is particularly advantageous if an amorphous material is to be produced with the alloy components.

Advantageous embodiments of the method according to the invention emerge from the dependent claims.

The invention is further explained below on the basis of the production of a body from a special metallic glass. The at least two powdered alloy components do not necessarily all have to be metallic, but some of them can also be metalloids. However, at least one of these components must have magnetic properties. Generally the components will be crystalline; in special cases, however, the use of metalloids can also amorphous powders such as boron can be provided.

The metallic glass of the body to be produced should have an average, for example binary, composition A _x By, where A and B mean the metallic starting elements or alloy components as well as x and y atom% (with x + y = 100). One of the alloy components A or B should consist of a magnetic material. According to a specific exemplary embodiment, A can be, for example, magnetic Co and B can be non-magnetic Zr. In addition, appropriate other components for the formation of known two- or multi-component amorphous or non-amorphous alloys can also be assumed. According to the assumed embodiment of a binary alloy, powders of the two components A and B are first placed in a suitable grinding bowl together with hardened steel balls. The size of the powder can be of any size, but a similar size distribution of both components involved is advantageous. The resulting atomic concentration of the body to be produced from these powders is determined by the quantitative ratio of the two types of powder.

Accordingly, pure Co and Zr powders, each with powder particle sizes of, for example, an average of about 40 μm in each case, can first be introduced into a planetary ball mill (Fritsch brand: type "Pulverisette-5"), the steel balls of which each have a diameter of 10 mm. Varying the ball diameter and the number of balls causes any change in the grinding intensity. In order to prevent surface oxidation of the particles, the steel container of the mill is sealed under protective gas, for example under argon, and only opened again after the grinding process has ended. During the grinding process, the powders are then flattened, welded and divided again. A predetermined temperature level below the crystallization temperature of the amorphous material to be formed can advantageously be maintained. If necessary, several temperature levels can also be provided or a corresponding temperature program can be run through. As the grinding time progresses, larger powder particles are then formed which at least largely have a layer-like structure, ie consist of a multiplicity of alternating layer-like regions of the alloy components involved. This is a microstructure of the type that also arises, for example, in the initial phase of a known method for mechanical alloying (cf., for example, "Scientific American", vol. 234, 1976, pages 40 to 48). According to this known method, amorphous alloys can also be produced per se (see, for example, "Applied Physics Letters", Vol. 43, No. 11, Dec. 1, 1973, pages 1017 to 1019). However, while grinding in the known method of mechanical alloying until the aforementioned layer-like structure dissolves again and a real alloy is formed, on the other hand, in the method according to the invention, the grinding process is achieved when the desired layer-like structure is reached, in which the layer-like areas in the generally about 0.01 to 0.9 ₁ 1m, preferably between 0.05 and 0.5 Jlm thick, stopped. The size of the powder particles themselves is approximately 10 to 200 ₁₁ m in diameter. The predetermined point in time at which this desired structure of the powder particles is present can be determined, for example, by section examinations of the particles. At the end of the grinding process to be terminated at this point in time, there is a mixed powder, the particles of which consist of alternating thin, crystalline, layer-like areas, and which therefore still has sufficient mobility of the powder particles in a magnetic field and sufficient ductility for a compacting step that is finally to be carried out.

As long as the powder particles are still mobile, they are exposed to a constant magnetic field according to the invention. They then align themselves in such a way that their layer-like structures lie parallel to the magnetic field. The direction of the magnetic field is set so that it coincides with a later compaction direction.

The way in which the powder particles are magnetically aligned depends on the respective compaction method. E.g. If a so-called isostatic pressing is used, either in connection with simultaneous diffusion annealing as hot isostatic pressing or to form a shaped body for further deformation by extrusion, hammering or the like, the mixed powder is first filled into a deformable form. Then, with shaking and tapping, the magnetic field is then applied parallel to the longitudinal axis of the mold. The field strength for this can be in the range between 0.1 and 1 T. After the powder particles are aligned with their individual layers parallel to the field direction, the magnetic field can be switched off, the mold closed and the isostatic pressing process started. Care should be taken to ensure that the compact is handled carefully so that the powder does not rearrange itself.

Another possibility is to first compress the powder in a uniaxial press to form a compact intermediate product or several tablet-like shaped pieces. After the preliminary product or the shaped pieces have been or have been sheathed, a further deformation step, such as Extrusion or hammering. The magnetic field must be applied after filling the mixed powder into the press die before pressing. In addition, the mixed powder can also be poured directly into a jacket, magnetically aligned and then extruded, hammered or otherwise deformed in the jacket to form a good compaction.

In the selected embodiment, it was assumed that only one of the two alloys tion components A or B consists of a magnetic material. However, both components can equally well be magnetic. However, this means that there are generally different Curie temperatures T _c ^A and T _c ^B of components A and B. In this case, the inventive alignment of the powder particles produced is carried out in a magnetic field at a temperature T which lies between the two Curie temperatures, ie that: T _c ^A <T <T _c ^B if T _c A <T _C B is (otherwise vice versa).

At the end of a possibly further shaping step, there is then an intermediate product of the body to be produced with the desired shape and dimension. This is followed by a heat treatment in which the interdiffusion of the alloy components involved, which is responsible for the amorphization, takes place as a solid-state reaction. This reaction can, if appropriate, take place as an anomalous, rapid diffusion in a known manner, one alloy component diffusing into the other. However, other diffusion reactions with e.g. mutual diffusion of the components possible. In all of these reactions it should be noted that the finer the structure, the lower the temperatures and the shorter the annealing times are sufficient for the complete conversion of the intermediate into the desired body. For this solid-state diffusion reaction, the annealing temperature must in any case be below the crystallization temperature of the metallic glass in a known manner. The metallic body which is present as the end product at the end of this process thus consists of an amorphous alloy with a thickness and shape which is predetermined by the compacting process and can therefore be chosen as desired.

In the exemplary embodiment of the method according to the invention described above, it was assumed that a body should be made from a metallic glass. However, this process can also be used to produce bodies from crystalline mixed powder which are still crystalline after diffusion annealing. If necessary, the crystalline state of these materials can also be achieved via a detour of a non-crystalline, amorphous structure (see, for example, "Applied Physics Letters", Vol. 44, No. 1, January 1984, pages 148 and 149).

Claims (18)

1. Process for the production of a metallic part formed from an amorphous alloy, in which process the following process steps are to be carried out:

A) An intermediate product formed from at least two, at least partially magnetic, powdery components of the alloy is formed by carrying out a compacting step so that the alloy components in the intermediate product are, in at least one dimension, at the most 1 11m in extent and

B) the intermediate product is converted into the metallic part having an amorphous alloy state by means of a diffusion reaction at a predetermined high temperature which is below the crystallisation temperature of the amorphous alloy,
characterised in that to carry out the process step A)

- from the powdery alloy components a crystalline mixed powder with particles is produced, by means of a milling process which is terminated at a predetermined time, in such a way that the particles each have at least substantially a layer-like structure made from the alloy components,

- then the powder particles of this mixed powder at least in their mobile state are aligned in a magnetic field, and

- finally this mixed powder is compacted in this direction to form the intermediate product of the desired shape and dimensions and is still further deformed if necessary.

2. Process according to claim 1, characterised in that the amorphous structure of the intermediate product is converted into a micro-crystalline structure by a predetermined annealing treatment.

3. Process for the production of a metallic part from a crystalline alloy, in which process the following process steps are to be carried out:

A) An intermediate product from at least two, at least partially magnetic, powdery components of the alloy is formed by carrying out a compacting step so that the alloy components in the intermediate product are, in at least one dimension, at the most 1 11m in extent, and

B') the intermediate product is converted into the metallic part with a crystalline alloy state by means of a diffusion reaction at a predetermined high temperature,
characterised in that to carry out the process step A)

- from the powdery alloy components a crystalline mixed powder with particles is produced, by means of a milling process which is terminated at a predetermined time, in such a way that the particles each have at least substantially a layer-like structure made from the alloy components,

- then the powder particles of this mixed powder at least in their mobile state are aligned in a magnetic field, and

- finally this mixed powder is compacted in this direction to form the intermediate product of the desired shape and dimensions and is still further deformed if necessary.

4. Process according to one of claims 1 to 3, characterised in that the termination of the milling process is determined experimentally by examining the mixed powder particles.

5. Process according to one of claims 1 to 4, characterised in that the powdery alloy components are milled under protective gas to form the mixed powder.

6. Process according to one of claims 1 to 5, characterised in that the alloy components are milled at at least one predetermined temperature to form the mixed powder.

7. Process according to one of claims 1 to 6, characterised in that the powdery alloy components are milled until approximately alternating, layer-like areas are produced in the mixed powder particles with thicknesses of between 0.01 11m and 0.9 ₁1m, preferably between 0.05 11m and 0.5 µm.

8. Process according to one of claims 1 to 7, characterised in that the powdery alloy components are milled to form mixed powder particles with particle diameters of between approximately 10 and 200 µm, preferably approximately 20 and 100 µm.

9. Process according to one of claims 1 to 8, characterised in that the mixed powder particles are exposed to a magnetic field with a strength of between 0.1 and 1 Tesla.

10. Process according to one of claims 1 to 9, characterised in that the mixed powder is subjected to a shaking or knocking treatment when a magnetic field is applied.

11. Process according to one of claims 1 to 10, characterised in that the mixed powder is deformed into the intermediate product by hammering or extrusion.

12. Process according to one of claims 1 to 11, characterised in that the diffusion reaction is carried out after the last compacting or deformation step.

13. Process according to one of claims 1 to 11, characterised in that the diffusion reaction is carried out simultaneously with the last compacting or deformation step.

14. Process according to one of claims 1 to 13, characterised in that two magnetic alloy components (A and B) having different Curie temperatures (Te^A or T_CB) are provided and in that the aligning of the powder particles in the magnetic field is carried out at a temperature (T) which is between the two Curie temperatures (T_c ^A and T_cB).

15. Process according to one of claims 1 to 14, characterised in that the intermediate product is formed from at least two crystalline alloy components.

16. Process according to one of claims 1 to 14, characterised in that apart from at least one metallic starting element or one metallic starting compound being provided as one alloy component, at least a further starting element or a further starting compound is provided as a further alloy component, which is a metalloid.

17. Process according to claim 16, characterised in that amorphous boron is provided as the metalloid.

18. Process according to one of claims 1 to 17, characterised in that a compound or alloy comprising several elements is provided as at least one starting component.