JP2819134B2 - Aluminum based oxide dispersion strengthened powder and its textureless extruded product - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an aluminum-based oxide dispersion-strengthened powder, a method for preparing the same, and an extruded product thereof having substantially no texture (preferred crystal orientation structure).

BACKGROUND OF THE INVENTION There is a strong need for high strength and good ductility metal alloys that can withstand adverse environments such as corrosion and carbonization under increasingly high temperatures and pressures. The upper limit operating temperature of conventional heat-resistant alloys is limited by the temperature at which the second phase particles substantially dissolve in the matrix or the temperature at which the second phase particles become excessive. Above this temperature limit, the alloy no longer exhibits useful strength. One exceptionally promising alloy for use in such applications is a dispersion strengthened alloy obtained by mechanical alloying techniques. These dispersion-strengthened alloys, particularly oxide dispersion-strengthened alloys, are a class of materials that contain fine, inert particles that are substantially homogeneously dispersed, and that exhibit useful strength up to temperatures near the melting point of the alloy material. .

The main requirement of the technology used to produce dispersion-strengthened metallic materials has been to be able to create a homogeneous dispersion of the second (hard) phase with the following properties: 1. Small grain size (<50 nm), preferably oxide particles; 2. Spacing between small particles (<200 nm); 3. Chemically stable second phase, (Negative free energy of formation as large as possible, and range of use conditions for alloys) Must not exhibit phase transformation within); 4. be substantially insoluble in the metallic matrix.

Prior Art Dispersion-strengthened alloys are generally prepared by conventional mechanical alloying methods in which a mixture of metal powder and second or hard phase particles is intimately dry mixed in a high energy mill (milling kneader) such as a Szeguari attritor. produced. Such a method is disclosed in U.S. Pat.
No. 1,362. High energy mills result in repetitive welding and breaking of the metallic phase, which is accompanied by refinement and dispersion of the hard phase particles. The resulting composite powder particles are generally
It consists of a substantially homogeneous mixture of a metallic component and a second (hard) phase well dispersed therein. The bulk material is then obtained by hot or cold compaction and extrusion to the final shape.

One reason industrial dispersion-strengthened alloys, such as oxide dispersion-strengthened alloys, have not gained widespread acceptance in the industry is that they contain microstructure defects and contain a composite matrix that can be formed into a desired form, such as a tube. This is because there was no technically and economically appropriate technique for obtaining a uniform dispersion of fine oxide particles. Although research and development on oxide dispersion strengthened materials has continued over the last two decades, these material products have not been able to reach satisfactory industrial standards. This is because the progress of the microstructure during the processing that allows control of the grain size and grain shape in the alloy product has not been understood so far. Furthermore, there was no explanation for the formation of inherent microstructural defects introduced during processing, such as vein oxides (stringers), grain boundary cavities, and micropores.

Vesicular oxide (stringers) consist of elongated pieces of oxides of the constituent metal components. These vein oxides act as weak surfaces across their length and act to prevent control of grain size and shape during subsequent recrystallization. Micropores, including cavities at grain boundaries, have an adverse effect on yield strength, tensile strength, ductility and creep rupture strength,
Harmful for dispersion strengthened alloys.

There is a great demand in various industries for lightweight and high strength metallic materials. Such materials are particularly useful in the manufacture of aircraft skins, aircraft interior structures, rifle components, automotive components, and drilled pipes for oil well exploration. The prime candidate for such a material is an aluminum-based material. Aluminum and aluminum-based alloys are generally selected for use in applications where high strength-to-weight ratio is a major consideration. However, such metals can only be used at relatively low temperatures because conventional aluminum-based alloys tend to lose strength at temperatures above half their absolute melting point (ie,> 200 ° C.). The demand for increased fuel efficiency and higher loading rates in the aviation industry has driven the demand for aluminum alloys as skin and frame materials instead of titanium alloys and high strength steels. More recently, the need for reduced torque and drag in inclined drilling has promoted the use of aluminum-based alloys as drill strings, but their use has been severely limited by the strength loss problem at elevated temperatures described above.

Early attempts to increase the strength of aluminum
The purpose was to hot-press the aluminum powder in an oxygen-containing atmosphere to form a thin film of aluminum oxide on the surface of the original aluminum powder particles in situ.
This dispersion strengthened aluminum material, commonly known as sintered aluminum product (SAP), has shown surprisingly high levels of hardness and tensile strength. A disadvantage with this method was that the aluminum oxide, although insoluble, was relatively coarsely dispersed. As a result, the alloys could not achieve very high strength at elevated temperatures and did not lead to practical use in industry.

Mechanical alloying methods have been used to produce aluminum dispersion strengthened materials that do not exhibit the disadvantages of sintered powder materials. This technique generally produces a more homogeneous material,
And it gave more precise and precise control over the chemical composition. Furthermore, these mechanical alloying techniques are suitable for producing multi-component materials in which one or more of the components are immiscible with one another. Examples are tungsten and copper or refractory substances in metals.

However, early attempts to produce dispersion strengthened aluminum materials by mechanical alloying techniques have been unsuccessful.
This is because the ductility of the aluminum resulted in the welding of the powder particles together and the welding to the process equipment parts, preventing the dispersion of the dispersed phase. One attempt to alleviate this problem is disclosed in U.S. Pat. No. 4,409,038, which discloses the use of a process control agent such as stearic acid to prevent such welding. Although this method has met with some success, it has not been possible to produce dispersion-enhanced materials in which the dispersoid is a high melting material that is insoluble in the matrix. For example, the above methods result in alloys reinforced with coarsely dispersed oxides and finely dispersed carbides. These coarsely dispersed oxides contribute little strength due to their relatively large spacing, and the carbides are relatively unstable and tend to coarsen at elevated temperatures, leading to rapid strength loss. . Therefore, these alloys are usually about 200 ° C
Limited to use at lower temperatures.

Thus, there is still a need in the art for a dispersion strengthened aluminum material having high temperature strength.

SUMMARY OF THE INVENTION According to the present invention, a machine comprising aluminum and aluminum oxynitride, wherein the individual powder particles are substantially uniformly dispersed throughout the aluminum matrix and the aluminum oxynitride dispersoid particles. An alloyed composite powder is provided. The present invention further provides an extruded mechanically alloyed article comprising an aluminum matrix having a substantially uniform distribution of oxynitride particles and substantially free of texture.

In a preferred embodiment of the present invention, the composite powder comprises 50
It contains more than weight percent of aluminum, oxynitride and one or more other metals, refractory materials or both.

In one preferred embodiment of the present invention, at least 0.1% by volume of the dispersoid particles is aluminum oxynitride and the one or more other refractory materials are oxides.

In another preferred embodiment of the present invention, at least 0.5% by volume of the dispersoid particles is aluminum oxynitride and the refractory material is alumina.

The aluminum-based material of the present invention comprises introducing a metal powder comprising aluminum alone or one or more other metals into a mill, and forming a powder mixture with a nitrogen-containing cryogenic liquid at a temperature below the boiling point of liquid oxygen. It is prepared by milling.

In another preferred embodiment of the present invention, a high melting point material is introduced with the metal powder. Preferably, the high melting point material is selected from oxides and oxynitrides, preferably oxynitrides.

A texture-free aluminum material article comprising the aluminum oxynitride dispersoid particles of the present invention comprises a billet of a mechanically alloyed aluminum powder material consisting of grains having an average grain size of less than about 5 microns. formula (Where R is the radius of the die contour at a given point x from its entrance plane along the major axis of the die orifice, _Ro is the radius of the billet and K is an arbitrary constant.) By extruding through an extrusion die having an internal profile substantially conforming to

DETAILED DESCRIPTION OF THE INVENTION The practice of the present invention results in an aluminum-based dispersion strengthening material having the following characteristics: 1. Aluminum oxynitride, which is substantially uniformly distributed throughout the matrix with an average spacing of less than about 20 nm. Comprising particles, thereby resulting in a material having excellent high temperature strength.

2. The energy stored in the low-temperature milling process
During subsequent reheating of the alloy powder, it is released and, when formed, results in fine grain size in the powder grains.

3. The composite powder surface has substantially no oxide scale.

The strength (σ) of the composite is related to the elastic modulus (E) of the matrix and the interparticle spacing (λ) of the dispersoid particles according to the following equation: σ = αE / λ, where α is a constant .) When the iron-based dispersion strengthening material is produced by low temperature milling, the distance between the particles of the dispersoid is on the order of about 60 nm. Since the elastic modulus of iron is 210 GPa, this interparticle distance is sufficient to give such materials the required strength. According to the above formula, the spacing between the particles of the dispersoid in the iron-based system can be realized only by refining the high melting point powder during low temperature milling. For metals such as aluminum, the elastic modulus is about one-third that of iron, so the spacing between particles must be one-third smaller to achieve comparable high-temperature strength (<20 nm) . The required intergranular distance is only achieved by setting the size of the dispersoid in the size range of about 2 to 6 nm, but this cannot be achieved by merely refining the high melting point phase as in the case of iron. Instead, fine dimensional dispersoids in aluminum systems are achieved through controlled chemical reactions on an atomic scale. By using a cryogenic milling process in a nitrogen-containing cryogenic liquid with up to 1% by weight of oxygen, an in situ surface reaction of reactive aluminum with nitrogen at a temperature of about 77 ° K. At this temperature, the situation is, from thermodynamics and kinetics,
It favors the formation of very fine oxy-nitride species through the reaction of aluminum, oxygen and nitrogen.

Mechanical milling (milling and kneading) of one or more metals is a process in which the initial component powder is repeatedly milled and cold welded by the continuous impaction of the milling media, and therefore, a significant part of this operation. Strain energy is stored. During subsequent reheating before extrusion, recrystallization of the resulting composite powder occurs. It is well known that the grain size produced by recrystallization after cold working depends on the degree of cold working. However, there is a lower limit of the processing amount below which the recrystallization does not occur. Since the degree of cold working is a measure of the strain energy stored in the material, a decrease in the milling temperature leads to an increase in the amount of work that can be stored in the material over a given period and the amount of work that can be stored until saturation. . Thus, a reduction in the milling temperature results in an increase in the reduction rate of the powder particle size and a reduction in the particle size achieved at longer milling times.

It is also within the scope of the present invention to mechanically alloy the aluminum powder alone by low temperature milling in the substantial absence of oxygen to make the resulting powder very small in size. In this case, i.e., when it is not desired to produce aluminum oxynitride, the cryogenic material is about -240
It may be any liquid having a boiling point in the range of ℃ to -150 ℃.
Examples include liquefied gaseous nitrogen, methane, argon, krypton, and the like.

The formation of ultrafine grains during recrystallization prior to extrusion serves to reduce the tendency of the material to form grain boundary cavities during extrusion and subsequent processing. The reason for this is that as the grain size becomes finer,
It is believed that the slip deformation can be further absorbed by the diffusion process near the grain boundaries. As a result, the concentration of slip within the grains decreases and the grain boundary concentration of the slip band decreases proportionally.

As already discussed, vein oxides (stringers)
Are elongated pieces of oxides of constituent metal elements such as aluminum, chromium and iron. Surprisingly, the inventors have found that these oxide stringers are derived from oxide scale formed on the particles during ball milling in air. Even more surprisingly, this oxide scale is exposed to metal oxides such as aluminum, chromium and iron with trace amounts of oxygen during conventional milling using industrial-grade argon to form an external oxide scale on the particle surface. Occurs when forming These scales crush during subsequent compaction and elongate during extrusion to form oxide stringers. Stringers act as centers of weakening of the bulk material and act to prevent grain boundary migration during annealing. By doing so, the stringers hinder control of grain size and grain shape during the final thermomechanical processing stage. Although oxygen is used in the practice of the present invention, the temperature at which cryogenic milling is performed is low enough to prevent the formation of such oxide scale.

The properties of the materials produced according to the present invention include a substantially uniform fine dispersion of refractory particles (typically having an average diameter of about 3 nm and a spacing of about 20 nm), the absence of external oxide scale, and the A significant improvement in the ability to form extruded products with substantially no texture under typical operating conditions.

Suitable high melting compounds for use in the practice of the present invention include those having a negative free energy of oxide formation of at least about 90,000 calories per gram atom of oxygen at about 25 ° C and a melting point of at least about 1300 ° C. Some oxynitrides, oxides, carbides, nitrides, borides,
And carbonitrides. Preferred are oxynitrides and oxides. Examples of such oxynitrides and oxides are
Silicon, aluminum, yttrium, cerium, uranium, magnesium, calcium, beryllium, thorium, zirconium, hafnium, titanium and the like. Also included are mixed oxides of aluminum and yttrium, such as: Al ₂ O ₃ .2Y ₂ O ₃ (YAP), Al ₂ O ₃ .Y ₂ O
₃ (YAM) and 5Al ₂ O ₃ .3Y ₂ O ₃ (YAG). The preferred ones are
Aluminum oxynitride and oxide are more preferable, and aluminum oxynitride is more preferable.

The total amount of aluminum oxynitride present in the material of the present invention is at least an effective amount. Here, an effective amount means the minimum amount required to increase the strength of the aluminum matrix by at least about 10%, preferably by at least about 20%. Generally, this amount will range up to about 5% by volume, preferably up to about 2% by volume, more preferably up to about 1% by volume, and most preferably from about 0.1 to 0.5% by volume, based on the total volume of the material. When one or more other refractory compounds are present, the total volume of refractory material (addition + in situ production) may be about 0.5-25%, preferably about 0.5%, based on the total volume of the material. -10%, more preferably 0.5-5%.

Prior to the present invention, mechanically alloying a ductile metal, such as aluminum, was not practical. this is,
This is because aluminum has a tendency to stick to the attritor and its parts. Using conventional process control agents during milling to substantially eliminate this problem only results in materials having insufficient high temperature strength for many industrial applications. By the practice of the present invention, aluminum and aluminum-based alloys can be successfully mechanically alloyed by cryogenic milling to provide dispersion-reinforced composite particles having a substantially uniform distribution of aluminum oxynitride particles throughout the matrix. Generate

The dispersion-strengthened mechanically alloyed aluminum of the present invention mainly comprises aluminum and a dispersoid. The material may also contain various additives that can, for example, solid-solution harden or age harden aluminum and provide certain specific properties. For example, magnesium, which forms a solid solution with aluminum,
Let's provide additional strength with corrosion resistance, good fatigue resistance and low density. Other additives that can provide additional strength include, for example, Li, Cr, Si, Zn, Ni, Ti, Zr, Co, Cu
And Mn. Additives and amounts to aluminum are well known in the art.

Generally, the dispersion strengthened mechanically alloyed aluminum material of the present invention has at least 50%, preferably at least about 80%, more preferably at least about 80%, based on the total weight of the material.
Composed of 90% aluminum.

The present invention is practiced by loading a nitrogen-containing cryogenic substance, such as liquid nitrogen, into a high energy mill containing aluminum powder. Other seed metal powders and / or high melting point (high melting point) materials may also be present. High energy mills also contain grinding media such as metal balls or ceramic balls that are maintained in a highly active relative motion state. The milling operation, carried out in the presence of an effective amount of oxygen, breaks the components of the mixture and binds or fuses them together and disperses each other throughout the metal matrix of the product powder, and is desirable during subsequent recrystallization by heating. For a time sufficient to make it possible to obtain a fine grain size and fine grain structure.

By an effective amount of oxygen is meant an amount that is less than that which results in the formation of oxide scale on the surface of the metal powder particles, but which produces the desired amount of aluminum oxynitride. This amount generally ranges up to about 1% by weight, preferably about 0.1 to 0.5% by weight. The material resulting from this milling operation is metallographically characterized by an agglomerated internal structure in which the components are tightly bound to provide an interdispersion of finely divided pieces of the starting components.

During the milling process, the initial aluminum powder particles collide with the grinding media and break. This break automatically creates a clean surface with highly reactive aluminum atoms. The nitrogen and oxygen atoms present adsorb on these clean surfaces and combine with the aluminum atoms, thereby forming a complex of aluminum, oxygen and nitrogen, referred to herein as aluminum oxynitride. The dimensions of these composites are very fine. That is, they are generally in the range of about 300-700 atoms (2-5 nm diameter). In addition to these in situ generated aluminum oxynitrides, the metal matrix may also contain other species refractory compounds introduced with the initial powder charge. After cryogenic milling, these high melting compounds have a size range of 30-50 nm. Thus, only by producing the aluminum oxynitride in situ, it is possible to obtain the ultrafine grain size which leads to the composite powder of the present invention having excellent properties.

As used herein, the term "cryogenic medium" means an oxygen-containing liquid material capable of producing aluminum oxynitride having an average diameter of 1 to 10 nm, with preference being given to liquid nitrogen.

The material of the present invention is extruded such that the extruded product has substantially no texture. As used herein, "substantially has no texture" means that it has substantially no preferred crystallographic orientation. Another way to express this is that when a pole figure is obtained from a material that has virtually no texture (preferred crystallographic orientation), any region of the pole figure will be about 10 times the pole density as would be obtained from a disordered orientation sample. It does not show a pole density exceeding, more preferably about 5 times or less, and most preferably about 3 times or less. This makes the material isotropic, ie, has substantially the same mechanical and physical properties in all directions. It is possible to obtain such materials by practicing the invention. This allows the material whose inner contour is being extruded through the die in the die zone to the following formula: (Where A is the cross-sectional area at a given point x from the die entry surface along the die orifice principal axis, A _o is the billet cross-sectional area, and is the true (or natural) strain rate. And v is the speed of the ram of the extrusion press) because it is made to vary continuously in a manner that conforms to

The mechanically alloyed powder material of the present invention is formed into billets by any suitable conventional means. Billet then
Prior to extrusion, the powder is hot worked to form a compaction by techniques such as forging, upsetting, rolling or hot isostatic pressing.

FIG. 10 is a perspective view of one half of a rod extrusion die and FIG. 11 shows a cross-sectional view of the same die. The contour of the internal passage 14 substantially follows the formula: i) For a given desired extrusion ratio E (where E is equal to the ratio of the cross-sectional area of the billet to the cross-sectional area of the extruded rod), the length of the converging die channel is Given by; ii) given for the ram speed one, the true strain rate to be imposed on the material passing through the die is given by = Kvr _o.

The radius R of the die orifice or passage is indicated at a given point x along the main axis 12 from the inlet face Y along the die orifice. The die includes an inlet orifice at the inlet face Y, where the radius of the die orifice is greatest.
The die contour 14, referred to herein as the die internal contour, converges according to the above equation and terminates at a distance along the major axis as shown at 16. Thereafter, the die orifice may include a small parallel section between 16 and 18, which section, if present, has a minimum length to minimize friction of the extruded material along the inner wall of the die orifice. Should be maintained. From 18 to the exit face Y ', the radius of the inner contour 20 of the die increases slightly to allow the extruded product to leave the die. The die separation section of the die is conventional and its upper limit is usually set by the die support system. The actual stall angle is conventional and can be readily determined by one skilled in the art for a given die system, but will typically have a lower limit of about 3 degrees.

Generally, the practice of the present invention is accomplished by placing a billet of fine aluminum-based powder contained in a can (coated container can) in a container of an extrusion press. Billet
It can be made by first filling a can with a fine powder material. The can can be composed of any suitable aluminum-based material. The billet is coated with a conventional lubricant such as graphite or molybdenum disulfide, which is also applied to the container walls and die. To prevent loss of lubricant prior to extrusion, the billet preferably has an elongated portion at its forward end so that it fits snugly into the die orifice. Thereafter, the billet is extruded by moving the ram forward at a predetermined speed, whereby the billet is extruded through the die into the rod at a constant natural strain rate. The exit surface of the die is open against the shear plate of the extrusion press. The specific temperatures and strain rates required for a given material to be extruded with improved plasticity to produce a substantially textureless product are:
It is determined by first measuring the strain rate sensitivity of the material by conventional techniques such as tensile, compression or torsion tests. A combination of temperature and strain rate that provides a strain rate sensitivity of greater than about 0.4 is then calculated. The techniques used herein to determine the criteria for a given dispersion strengthened material are discussed in detail in the next section.

The die used to extrude the finely divided composite material into a tube must have an internal profile substantially according to the following formula: (Where R is the radius of the die profile at a given point x from its entrance plane along the major axis of the die orifice, _Ro is the radius of the billet, R _m is the radius of the mandrel, and K is an arbitrary constant.) = Kv (each factor is defined) The following example illustrates the invention in more detail for illustrative purposes.

Comparative Example A 585 g of 567.5 g aluminum and 17.5 alumina
Metal mixture from Union Process Inc. Laboratory model I
High-speed attritor (ball mill) manufactured by -S
Was charged inside. The attritor has a charge ratio of 18: 1
Stored 6mm diameter stainless steel balls.

Milling is performed at room temperature (about 25 ° C) at a mill rotation speed of 180 rpm.
In argon.

The test was stopped after 28 minutes because the mill stalled. Inspection of the mill revealed that the alloy powders welded together and partially to the mill, forming a horseshoe-shaped fragment on the inner circumference of the mill. This result indicates that dry milling without the aid of an anti-deposition agent is not feasible with aluminum-based systems due to the extremely high ductility of the metal phase and the ease with which newly created aluminum surfaces are cold welded. Indicates that

Comparative Example B Sample from Novamet Inc. Novamet IN9052-F, Novamet
met IN9021-FT-651 and Novamet IN905 XL were purchased. These alloys are, according to maximum information, U.S. Pat.
It was made by the mechanical alloying technique taught in US Pat. No. 4,297,136. That is, the patent discloses a method of preparing a mechanically alloyed powder by ball milling the component metal powder at room temperature in the presence of argon and a milling aid.

A test sample with a diameter of 7.2 x 5.6 mm was prepared using alloy IN9021-F
Made as compression specimen from T-651 and 25 x 8.1 mm
Other test samples of the diameter dimensions were prepared as IN9021-FT-651 and IN
A creep test piece was prepared from both 9052-F. The creep specimens were then subjected to constant stress creep tests at various applied stress levels ranging from 51 to 103 MPa and at temperatures of 177, 232 and 275 degrees. Table I and Table I show the relationship between time to failure and applied stress and temperature obtained from these tests.
This is shown in FIG. II and plotted in FIG. 1 as a stress-rupture curve. The compression test samples were subjected to unidirectional compression at a strain rate of 3 × s ⁻¹ . The force and sample shrinkage were measured and the stress-strain response of the material was obtained. Compression tests were performed at 25, 125, 175, 225, 275, 325, 375 and 425 degrees. The 0.2% offset proof stress was measured for each test sample and these data are shown in Table III and plotted in FIG. 2 against test temperature.

In addition, the as-received bars were sectioned, fixed and polished as samples for light microscopy. Also alloy
Thin sections were taken from the IN 905XL bar and used to prepare thin foil samples for transmission electron microscopy. An example of a transmission electron micrograph taken from this material is shown in FIG.

Discussion of Comparative Examples Electron micrographs of samples of Novamet IN 905XL show that the average grain size ranges from 0.5 μm to over 2 μm (see FIG. 3). This relatively large particle size distribution is the result of the lack of a uniform distribution of ultrafine particle dispersoids. Similar observations were made for the microstructures of the other two Novamet alloys studied.

The data obtained from the uniaxial compression test show that, as can be seen in FIG. 2, the alloy exhibits high strength near room temperature, ie, up to 175 ° C., but the strength decreases rapidly with increasing temperature. Show.

Example 1 Comparative Example A, except that five 585 g metal / oxide powder mixtures were milled in a liquid nitrogen slurry and the attritor was modified to allow a continuous flow of liquid nitrogen to maintain a liquid. Prepared according to the procedure described in 4 batches of metal / oxide powder mixture at 3%, 7
%, 10% and 15% (by weight) prepared using alumina. This is 17.5g, 40g, 58.5g and 87.
Equivalent to 8 g of alumina.

In each case, milling was performed for 15 hours. Upon completion of the milling, the powder was allowed to warm to room temperature under a continuous stream of dry argon and was subsequently removed from the mill. 25 powder
After sieving to remove particles exceeding 0 μm, the mixture was placed in an aluminum can (cylindrical container having an end cover and an exhaust port). Evacuate can and 250 under vacuum for 24 hours
Heated to ° C. After that, seal the can and ASEA Model
The SL-1 Mini-Hipper Laboratory was charged to a high temperature isostatic press. The can-filled powder was placed at a temperature of 510 ° C. under an enclosure pressure of 2000 bar (206.7 MPa) for 5 hours. The compacted powder samples thus produced were prepared for metallurgical and mechanical tests.

A sample of each cryogenically milled powder was fixed in a transparent fixing medium, polished and optically examined for grain size and grain shape. The samples were also examined by scanning electron microscopy. The grain size and aspect ratio for the four alloys are listed in Table IV.

Samples of the compacted powder containing 3%, 7% and 15% alumina were cut into pieces, fixed on bakelite, polished and examined by light and scanning electron microscopy.

Compressed by hot isostatic press (HIP) and 3%,
6m compressed powder sample containing 7% and 15% alumina
It was cut into cylinders of m diameter and 9 mm length. These samples were uniaxially compressed at a strain rate of 3 × 10 ⁻³ s ⁻¹ . Force and sample shrinkage were measured and the stress-strain response of the material was derived. Compression tests were performed at 25, 125, 175, 225, 325, 375 and 425 ° C. The 0.2% offset proof stress was measured for each test sample. These data are given in Tables V, VI and VI
Listed in I and plotted against test temperature in FIGS. In addition, a hot isostatically pressed aluminum-3% alumina alloy sample was swaged to 70% area reduction and cut into 25 x 8.1 mm diameter samples as creep specimens. These latter samples were subjected to a constant stress creep test at temperatures ranging from 232 to 275 ° C and at stress levels of 34 to 103 MPa. These data are summarized in Table VIII and are shown graphically in FIG.

Additional 585g containing 3% and 7% alumina by weight
A metal / oxide powder mixture batch was prepared as described above. The alloyed powder batch was placed in a 75 mm diameter aluminum extrusion can and evacuated as a hot isobar press can in the manner described above. These extruded billets were subsequently extruded as 18 mm diameter bars at 450 ° C. at a ram speed of 5 mm / s. Material samples cut from these bars are 7.2 x 5.1 mm
A compression test sample of diameter was made and tested in the manner described above. These data are shown in Table IX and the 0.2% proof stress as a function of temperature is shown in FIG.

For each extrusion rod, samples were cut perpendicular to the extrusion axis and combined with an automatic polar device
Texture was analyzed using a Rigaku DMAX-II-4 diffractometer. Data was collected for <200> reflections. The Decker method was used in transmission and the Schultz method was used in reflection to obtain all-pole diagrams (Elements of X-ray Diffraction by RD Cullity).
reference). The sample had virtually no texture, as shown in FIG. 12, which is a pole figure obtained for an aluminum / aluminum oxynitride alloy containing 3% alumina.

Additionally, alloy samples were cut into thin plates and made as thin foils for observation by transmission electron microscopy.
Examples of transmission electron micrographs obtained from these samples are shown in FIGS. 9a and 9b.

Discussion of the results From a comparison of the data in Tables V-VII and the data shown in FIGS. 4-6, an alloy made in accordance with the present invention was identified as Comparative Example B
Exhibit superior strength properties as compared to conventional mechanically alloyed aluminum materials such as those shown in US Pat. This alloy has a higher strength at room temperature compared to about 180 ° C for Novamet alloy
Only begin to lose above 250 ° C. Therefore, the alloy of the present invention increases the temperature resistance by about 50 ° C. Furthermore, at elevated temperatures above 400 ° C., the strength level is about three times higher than that of the comparative material.

The strength observed at high temperatures is due to the presence of ultrafine dispersoids of aluminum oxynitride introduced as a result of the in situ surface reaction of the cryogenic milling process. These fine dispersoids are indicated by bright arrows in FIG. 9b as bright contrast areas. These dispersoids strongly fix grain boundaries and control recrystallization and grain growth at elevated temperatures, resulting in very uniform grain size, typically 0.05 μm diameter. This is symmetric to the conventional mechanically alloyed material of Comparative Example B, which shows no sign of such fine dispersoids and is non-uniform in size and has an average particle diameter of typically 0.5 μm. It is.

In particular, the fact that high temperature strength is imparted by long fine aluminum oxynitride particles is due to the observation that the 0.2% proof stress vs. temperature curves for alloys with 3%, 7% and 15% alumina addition overlap almost exactly. Supported by the results. In other words, the yield strength of the alloy prepared according to the present invention shows the same strength at all temperatures regardless of the amount of alumina initially added to the mill. This result indicates that the strength level provided by the alumina particles formed by repeated milling of the added alumina was relatively large (0.
02 μm) and their spacing is also large (0.1 μm), which is explained by recognizing that they are small. In contrast, aluminum oxynitride particles formed in situ during cryogenic milling are much smaller (about 3 nm diameter) and dispersed at about 0.02 μm intervals, thus producing much higher strength levels. Therefore, the alloy strength is independent of the added alumina content, since most of the strength is due to the presence of ultrafine oxynitrides and their volume fraction does not depend on the amount of added alumina.

Further, extruding the composition through a die as shown in FIGS. 10 and 11 results in a texture-free product. This is a result of the ultrafine grain size of the powder produced by the cryogenic milling disclosed herein.

Effect of the Invention Cryogenic Milling Process Due to the presence of ultrafine dispersoids of aluminum oxynitride introduced as a result of an in-situ surface reaction, an aluminum-based alloy having excellent high-temperature strength was successfully developed for the first time in the art. A textureless isotropic extruded product is obtained.

[Brief description of the drawings]

FIG. 1 is a graph of creep rupture data obtained for two commercially available mechanically alloyed aluminum alloys. FIG. 2 is a graph showing the relationship between 0.2% proof stress and temperature obtained in a compression test for a commercially available alloy. FIG. 3 is an electron micrograph showing the metal structure of the commercially available alloy of Comparative Example B. FIG. 4 shows the 0.2% obtained in the compression test on a hot isostatically pressed aluminum-aluminum oxynitride material sample having 3% alumina as described in Example 1.
5 is a graph of proof stress versus temperature data. FIG. 5 shows the 0.2% obtained in the compression test for a hot isostatically pressed aluminum-aluminum oxynitride material sample having 7% alumina as described in Example 1.
5 is a graph of proof stress versus temperature data. FIG. 6 shows the 0.2% obtained in the compression test for a hot isostatically pressed aluminum-aluminum oxynitride material sample having 15% alumina as described in Example 1.
5 is a graph of proof stress versus temperature data. FIG. 7 is a graph of creep rupture data obtained for a hot isostatically pressed and swaged aluminum-aluminum oxynitride material having 3% alumina as described in Example 1. FIG. 8 is a graph of 0.2% proof stress versus temperature data obtained in a compression test for an extruded aluminum-aluminum oxynitride material having 3% alumina as described in Example 1. FIG. 9a is a transmission electron micrograph showing the metallographic structure of an aluminum-based material according to Example 1 and subjected to extrusion. FIG. 9b is a transmission electron micrograph showing the metallographic structure of an aluminum-based material, particularly 3 nm diameter oxynitride particles, according to Example 1 and extruded. FIG. 10 is a perspective view of one half of a die used to extrude a rod according to the present invention. FIG. 11 is a cross-sectional view of a die used to extrude a rod illustrating the internal contour of the die. FIG. 12 is a standard <200> polar diagram of an aluminum-aluminum oxynitride material with 3% alumina, presented in Table IX and obtained from a section cut perpendicular to the extrusion axis. 10: Die 12: Main axis 14: Internal contour 16: Convergent end point Y: Inlet surface Y ': Outlet surface

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Joseph Barone West Sixth Avenue, Roselle, New Jersey 513 56) References JP-A-62-238344 (JP, A) JP-A-62-290840 (JP, A) JP-A-48-17461 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , (DB name) B22F 1 / 00,3 / 20 C22C 1/04-1/05 C22C 21 / 00,32 / 00

Claims (15)

(57) [Claims] A mechanically alloyed aluminum composite powder characterized in that the individual powder particles comprise an aluminum matrix and aluminum oxynitride dispersoid particles substantially uniformly dispersed throughout the matrix. 2. Composite powder according to claim 1, wherein the concentration of aluminum oxynitride is up to 5% by volume. 3. The composite powder according to claim 2, wherein the concentration of aluminum oxynitride is 0.1 to 0.5% by volume. 4. One or more other metals are present and the aluminum metal content is at least based on the total powder weight.
The composite powder according to any one of claims 1 to 3, which is 50% by weight. 5. The method according to claim 1, wherein the other metal is Li, Cr, Si, Zn, Ni, Ti, Zr,
The composite powder according to claim 4, wherein the composite powder is selected from the group consisting of Co, Cu, Mg, Mn and a mixture thereof. 6. A composite powder according to claim 1, wherein the powder contains up to 25% by volume of a high melting point compound comprising aluminum oxynitride and at least one other high melting point compound. 7. The method according to claim 6, wherein the at least one other high melting point compound is selected from the group consisting of oxides, oxynitrides, carbides, nitrides, borides, carbonitrides and mixtures thereof. A composite powder as described. 8. The high melting point compound is Al ₂ O ₃ , Al ₂ O ₃ .2Y ₂ O ₃ , Al ₂ O ₃
· Y ₂ O ₃ and 5Al ₂ O ₃ · 3Y ₂ composite powder of O ₃ claims is an oxide selected from the group consisting of paragraph 7, wherein. 9. A method for producing a dispersion-strengthened aluminum composite powder according to any one of claims 1 to 8, wherein the aluminum powder is substantially reduced in oxide scale with a nitrogen-containing cryogenic liquid containing an effective amount of oxygen. A method for producing a dispersion-strengthened aluminum composite powder, which comprises milling for an effective time to produce the above-mentioned composite powder which is not included. 10. The method according to claim 9, wherein the nitrogen-containing cryogenic liquid is liquid nitrogen. 11. The method according to claim 9, wherein up to 1% by weight of oxygen is present. 12. An aluminum powder containing at least 50% by weight.
Claims 9 to 11 comprising aluminum, one or more other metals or additives and one or more refractory substances.
The method described in any of the items. 13. The method of claim 1, wherein the at least one other metal is Li, Cr, Si, Zn,
Selected from the group consisting of Ni, Ti, Zr, Co, Cu, Mg, Mn and mixtures thereof, and wherein the refractory material is oxide, oxynitride,
13. The method of claim 12, wherein the method is selected from the group consisting of carbides, nitrides, borides, carbonitrides, and mixtures thereof. 14. A method of extruding a mechanically alloyed powder material of finely divided aluminum according to any one of claims 1 to 8 into a rod substantially free of texture, having an average particle size of less than 5 microns. The billet of the powder material is (Where R is the radius of the die contour at a given point x from its entrance plane along the major axis of the die orifice, _Ro is the radius of the billet and K is an arbitrary constant.) Extruding through a die having an internal profile substantially conforming to 15. A method for extruding a mechanically alloyed powdered material of finely divided aluminum according to any one of claims 1 to 8 into a tube substantially free of texture.
A billet of powdered material having an average particle size smaller than a micron is given by the following formula: (Where R is the radius of the die profile at a given point x from its entrance plane along the principal axis of the die orifice, R _o is the radius of the billet, R _m is the radius of the mandrel And K is an arbitrary constant.) An extrusion method characterized by extruding through a die having an internal contour substantially according to