SE460461B - PROCEDURE APPLY HOT ISOSTATIC COMPRESSION OF A METALLIC OR CERAMIC BODY IN A BOTTLE OF PRESSURE TRANSFERING PARTICLES - Google Patents

Description

460 461 --- = 2 'pressure vessel. The pressure vessel has internal heating elements for raising the temperature of the powder material to a suitable consolidation temperature. Internal temperatures of 1000 ° C to 2100 ° C are typically used depending on the material to be treated. Coinciding with the increase in the internal temperature of the HIP vessel, the internal pressure increases slowly and is maintained at from 1050 bar (15000 psi) to about 2100 bar (30000 psi) depending on the material to be treated. During the combined effects of temperature and isostatic pressure, the density of the powder is increased to the theoretical bulk density of the material.

A HIP vessel can receive more than one can during a given cycle and thus there is the possibility of increasing the density of several powdered metal articles per cycle. In addition, through the use of isostatic pressure, the increased density is more or less uniformly straight through the HU% ankle. Through the use of a suitable can design, it is possible to form abutments for transverse holes or slits in the compressed article. However, the time cycle for charging is slow, often requiring 8 hours or longer for a single cycle. In addition, upon completion of a cycle, the cans surrounding the powder metal article must be removed either mechanically or chemically.

The second general method of compressing powdered metal is a technique referred to as powder forging ("PF") .The powder forging process comprises the steps of: (a) cold compressing dissolved metal powder at room temperature in a closed mold at a pressure in the range of 0; L3, 5bar (10-50 psi) to a suitable geometry (often referred to as a "preform") for subsequent forging. At this stage, the earform is brittle and may comprise 20-30% porosity and its strength is derived from the mechanical co. the man-locking of the powdered particles i? -f = 3 460 461 (b) Sintering the preform (ie subjecting the preform to elevated temperature at atmospheric pressure) under a protected atmosphere The sintering causes a solid state "welding" of the mechanically interlocked powdered particles. (c) To reheat the preform to a suitable forging temperature (depending on the alloy) Alternatively, this reheating step can be incorporated into the sintering step. (d) Forging preform but in a closed form to the final form. The form is typically maintained at a temperature of about 149% (äocPF): ni 31s ° c <60 ° F).

The forging step eliminates the internal porosities from the preform and gives the final shape to the PF portion.

The advantages of powder forging include: Operating speed (up to 1000 bits per hour), ability to produce a final fl um, mechanical properties essentially the same as conventionally forged products and increased material use.

However, there are a number of disadvantages including non-uniformity in density due to the cooling of the preform when in contact with the relatively cold mold, and the inability to form countermeasures that can be made in the HIP. as regards the patents mentioned above above, they appear to show a combination of isothermal and isostatic conditions of HIP and HIP's ability to form counterclaims, with the high speed, low cost of continuous production normally associated with powder forging. U.S. Patent 3,356,496 discloses the use of a molded outer ceramic container as the primary heat barrier. In addition, this molded outer ceramic container, when deformed, causes an almost uniform distribution of pressure on the powdered material. U.S. Patent No. 3,689,259 discloses the use of granular refractory material. This U.S. Pat. No. 3,689,259 is intended to be an improvement on the previous patent 3,356,496 with respect to a faster heating of the core and a faster heating of the pressed part. Although the two U.S. patents represent advances in the art, significant problems remain with the use of a ceramic bed in which a preform is placed prior to consolidation. More specifically, it has been found that the use of crushed and ground ceramics or carbides results in a significantly uneven pressure distribution from the top of the charge (the surface facing the movable press member) to the bottom of the charge (the surface facing the fixed press bed). . This non-uniformity of the pressure distribution is easily demonstrated when a pre-pressed completely circular cylinder of powdered material is consolidated.

After the consolidation in a bed of crushed and ground or molten ceramic material to almost 100% bulk density, it was determined that the surface of the pre-pressed cylinder closest to the movable baler was smaller in diameter than the surface closest to the fixed bed. Sectioning of the consolidated cylinder along a diameter and examination of the sectioned surface indicated that it had a trapezoidal shape. The above phenomenon was observed in all consolidated articles when a crushed and ground or molten granulated ceramic matrix was used as the consolidation medium. The solution to the problems associated with such deformation and lack of dimensional dimensional stability has proved inaccessible especially when the solution must also be useful. in mass production. The present invention provides a solution adapted to mass production.

SUMMARY OF THE INVENTION The present invention is directed to a method of consolidating integer or ceramic bodies comprising the steps of: M9? * f * 5 460 461 (a) To form a manufactured article from powdered metal or ceramic material. Such a forming step is preferably done by compression in a manner well known in the art; (b) sintering the article of manufacture to increase the strength; (c) In the next step, a hot bed of substantially spheroidal ceramic particles to which graphite or a similar lubricant has been added is provided, into which bed the article of manufacture is embedded. This bed, preferably of a refractory material such as alumina (Al 2 O 3) and, optionally, a lubricant, is made of initially heated alumina particles (and the lubricant compound if present) in a fluidized bed or of other equivalent means. In addition, due to the frequent occurrence of times when the sintered article is cooled, the article can then be reheated and placed in the hot bed. Additional spheroidal ceramic particles (and the optional lubricant compound) are then added to cover the article.

Alternating layers of hot particles and hot articles are also within the scope of the invention; and (d) compressing the article of manufacture in the hot bed under a high pressure to thereby consolidate the article into a desired solid configuration.

By using the methodology of the present invention, substantially improved constructions of articles of manufacture can be achieved with minimal deformation. The new features which we consider to be the characteristic of this invention, both for its organization and functional procedure, together with further objects and advantages, will be better understood from the following description taken in conjunction with the appended claims. the drawings in which a presently preferred embodiment of the invention is illustrated by way of example. However, it should be clearly understood that the drawings are for illustrative and descriptive purposes only and are not intended as a definition of the limitation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow chart showing the process steps of the present invention.

Fig. 2 is a sectional plan view showing the consolidation step of the present invention.

Fig. 3 is a plan view showing a consolidated article of manufacture which has been consolidated in a bed of alumina particles of non-spheroidal shape.

Fig. 4 is a plan view showing a consolidated article of manufacture which has been consolidated in a bed of spheroidal alumina particles.

Fig. 5 is a plan view showing a consolidated article of manufacture which has been consolidated in a bed of spheroidal alumina particles coated with graphite.

BRIEF DETAILED DESCRIPTION OF THE INVENTION In Fig. 1, a flow chart is shown illustrating the process steps of the present invention. As can be seen from number 10, an article of manufacture of metal or preform is initially made, for example in the form of a key. Although the preferred embodiment intends to use a metal preform made of powdered steel particles, other metal and ceramic materials such as alumina, silica and other similar materials may also be used within the scope of the invention. A preform is typically about 85% of the theoretical density. After the powder has been formed into a preformed shape, it is then sintered to increase the holding property. In the preferred embodiment, the sintering of the metal preform (steel) requires temperatures in the range of 1093 ° C at 120 DEG-20 DEG-230 DEG C. for a period of about 2-30 minutes in a uniform atmosphere. In the preferred embodiment, such a protective, non-oxidizing inert atmosphere is nitrogen-based.

After the sintering illustrated at 12, the sintered preforms can be stored for later processing. Should this be the case, as illustrated at 14, the preform is then heated to approximately 1066 ° C (190 ° F) in a protective atmosphere.

The consolidation process, illustrated at 16, picks up after the hot coated preform has been placed in a bed of ceramic particles as will be described in more detail below. To produce the desired high production quantity, alternating layers of hot ceramic particles and hot coated preforms can be used. To further increase the production rate, the consolidation can be performed after sintering as long as the preform is not allowed to cool. The consolidation is performed by exposing the embedded coated preform to high temperatures and pressures.

For metal objects (steel) temperatures in the range possibly around 1o93 ° C (2ooo ° F) are used. frame. The coated preform has now been compressed and can be separated, as shown at 18, where the ceramic particles easily separate from the preform and can be reused. If necessary, any particle adhering to the preform can be removed and the final product can be further machined.

As discussed above, a problem associated with the use of an ordinary ceramic bed was that the final product suffered from deformation. Microscopic examination of such crushed and ground or molten granulated ceramic materials indicates a highly irregular shape, with many individual particles having either a rectangular or triangular cross-sectional appearance. However, by using the substantially spherical ceramic particles according to the invention, in particular in combination with a lubricant, a substantially minor change in shape is achieved. .460 461- = ß More specifically, it was determined that by using a bed of spheroidal ceramic particles, preferably alumina, without a lubricant, certain minor deformations remained. Although the use of such a bed produced articles of superior dimensional stability over the prior art, the need to improve such dimensional stability remains. The present invention addresses this problem by incorporating a specific lubricant in an amount of about 1 to 2% by weight of the spheroidal ceramic particles into the bed of the spherodial ceramic.

In the preferred embodiment, carbon in the form of graphite with a particle size smaller than own (325 mesh) is mixed with and adheres to the ceramic particles much like a coating. The addition of graphite acts as a lubricant between the ceramic particles and increases the consolidation. Other similar thermally stable, substantially non-reactive lubricants, such as molybdenum disulfide, mica, and the like are also included within the scope of the invention.

In the preferred embodiment, the lubricant is mixed with alumina particles prior to forming the hot bed.

The mixing can be accomplished in a V-mixer or double cone, or other conventional systems to ensure an intimate mixing of the lubricant and the ceramic particles.

The choice of ceramic material for the bed is also acceptable for another reason in the consolidation process. If a particle is selected which shows a tendency for sintering at the consolidation temperature, the applied pressure will be absorbed in both the compression of the prepressed powder metal and the compression of the medium. For example, the use of silica at a consolidation temperature of approximately 1093 ° C (ZOOOOF) will require a higher pressure to achieve the concentration than compared to the use of alumina at the same temperature. The use of zirconia, silica or mullite at a temperature above 927qC (1700OF) reflects a higher compression pressure due to the fact that the ceramics themselves begin to sinter at a temperature above 927oC U700oFy .lä eel / ha, to clarify the sintering and the resulting higher pressures required for certain ceramic materials, spherodial alumina is preferred as the consolidation medium up to temperatures of 150 ° C <22 ° C 1 =). In addition, the epharyngeal fluid has good flow characteristics, heat transfer and a minimal amount of self-bonding during consolidation. An additional advantage of the spheroidal shape is the greatly reduced self-bonding of the particles after consolidation. The spheroidal particles of the present invention have a size in the range of preferably llšll to * IfQ-Ióum (100 tilllll fi ø mesh). In the preferred embodiment, the preform 20 has been completely embedded in a bed of substantially spheroidal alumina particles 22 which have been coated with a graphite lubricant, and which in turn have been placed in a consolidation mold 24. The press bed 26 forms a bottom, while the hydraulic press heater 28 defines a top and is used to press down on the particles 22 and the preform 20. The coated preform 20 of metal powder is rapidly compressed under high uniaxial pressure by actuation of a pressure member 28 in the mold 24. The mold 24 has no defined shape (such as the shape of a key), and there is negligible lateral flow from the preform 20. As a consequence, the consolidation occurs almost exclusively in the direction of movement of the pressure member 28.

As discussed above, the use of non-spheroidal particles produces a non-uniform pressure distribution so that after consolidation, a plan view of the cylinder 30a sectioned along a diameter would be in the shape of a trapezoid as illustrated in Fig. 3 and would approach 100% of full density. In Fig. 4 it can be seen that the same pre-pressed fully circular cylinder 30, when consolidated in the form of uncoated spheroidal alumina particles, has an equal diameter at the top and bottom with a slightly larger diameter at the average height. Why the larger diameters occur at average height is not known; the difference in diameter was | s ~ 1a ~ 460 4611 -., - = 10 however so significantly reduced that it constitutes a distinct improvement over the prior art. To compensate for this minor deformation, minor changes to the preform may be made prior to consolidation or the article may be machined. In addition, the use of spherodial particles also greatly reduces the self-bonding of the particles to the preform during consolidation. Thus, the spheroidal ceramic particles 22 serve three primary functions: (1) to transfer the consolidation pressure to the preform 20; (2) serving as a semifluid mold to maintain the shape of the preform during consolidation; and (3) delaying the heat loss in the preform during transfer and consolidation. To further compensate for this deformation in the article in connection with the use of spheroidal alumina, and to avoid most if not all machining and / or deformations of the preform as mentioned above, a lubricant may be used. . Fig. 5 illustrates a further straight cylinder 30b. In this embodiment, graphite has been coated on the spheroidal alumina. As can be seen, the cylinder 30b is retained in its original shape, i.e. the diameter remains substantially uniform from top to bottom. Thus, by using a lubricant, the need for further machining and / or the transformation of the preform is substantially eliminated.

Although the present invention has been described, it should be understood by those skilled in the art that other embodiments are clearly within the scope of the present invention. For example, the preform may be a key or other similar object. In addition, other substantially spheroidal particles such as silica, zirconia and similar ceramics can be used for the bed. This invention is therefore not intended to be limited to the particular embodiments described hereinabove. 'year

Claims (6)

-a = H 460 461 Patent claim'_ A method of consolidating a metallic or ceramic body, characterized by the steps of: (a) forming a article of manufacture (30b) from powdered metal or ceramic material, (b) sintering the article of manufacture (30b) to increase the strength , (c) providing a bed of heated, substantially spheroidal ceramic particles (22), which have been coated with a thermally stable, substantially non-reactive lubricant, (d) heating said article of manufacture to a predetermined temperature, and (e) compressing said article of manufacture (30b) in said heated bed of the substantially spheroidally coated ceramic particles (22) under high pressure to thereby consolidate the article of manufacture into a dense, desired shape. A method of consolidating a metallic or ceramic body according to claim 1, characterized in that the manufacturing article (30b) is formed of compressed powdered metal. A method of consolidating a metallic or ceramic body according to claim 1, characterized in that the spheroidal ceramic particles (22) are of alumina. A method of consolidating a metallic or ceramic body according to claim 1 or 2, characterized in that the substantially spheroidal ceramic particles (22) have a particle size smaller than Um L (140 mesh). 460 461 ..,, / 2 A method of consolidating a metallic or "ceramic body" according to claim 1, characterized in that steps (b) and (d) are performed in a protective atmosphere. 6. A method according to any one of claims 1-S, characterized in that the lubricant is graphite.