JPH0285301A - Aluminum base oxide dispersed reinforcing powder and extruded product having no texture thereof - Google Patents

Abstract

PURPOSE: To obtain composite powder capable of producing a dispersion strengthened Al material excellent in high temp. strength by forming powder from particles obtd. by mechanically alloying Al oxygen nitrides into an Al matrix and uniformly dispersing them therein. CONSTITUTION: This mechanically alloyed Al composite powder has an Al matrix and the dispersoid particles of Al oxide nitrides in which individual particles are substantially uniformly dispersed through the whole body of the matrix. The powder may contain metals other than Al such as Li, Cr, Si or the like or high m.p. compounds (oxides, oxygen nitrides, carbides or the like) other than Al oxygen nitrides. For producing the above powder, Al powder is subjected to milling for effective time for producing the composite powder substantially contg. no oxide steel in a nitrogen-contg. cryogenic liq. The mechanically alloyed powder material of the particulate Al is extrued, by which the product free from priority crystal orientation structure can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aluminum-based oxide dispersion strengthened powder, a method for its preparation, and an extruded product thereof that is substantially free of texture.

There is a strong need for metal alloys with high strength and good ductility that can withstand adverse environments such as corrosion and carburization at increasingly high temperatures and pressures. The upper limit service temperature of conventional heat resistant alloys has been limited by the temperature at which the second phase particles substantially dissolve in the matrix or by the temperature at which the second phase particles become too large. Beyond this temperature limit, the alloy no longer exhibits useful strength. One class of alloys that is exceptionally promising for use in such applications are dispersion strengthened alloys obtained by mechanical alloying techniques. These dispersion-strengthened alloys, particularly oxide dispersion-strengthened alloys, are a class of materials that contain a substantially homogeneous distribution of fine, inert particles, and these alloys exhibit useful strength up to temperatures near the melting point of the alloying 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 particle size. (<50 nm), preferably oxide particles; 2. Small interparticle spacing (<200 nm); 3. Chemically stable second phase, (large enough to have a negative free energy of formation); and the use of alloys. 4. It must be substantially insoluble in the metallic matrix.

Conventional dispersion-strengthened alloys are generally produced using traditional 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 such as a Szeguari attritor. Manufactured by. Such a method is disclosed in US Pat. No. 3,591,362 for producing oxide dispersion strengthened alloys. High energy mills result in repeated welding and fracture of the metallic phase, which is accompanied by refinement and dispersion of the hard phase particles. The resulting composite powder particles generally consist of a metallic component and a second well dispersed therein.
consisting of a substantially homogeneous mixture with a (hard) phase. after that,
The bulk material is obtained by hot or cold compaction and extrusion into the final shape.

One reason industrial dispersion-strengthened alloys, such as oxide dispersion-strengthened alloys, have not gained widespread acceptance in industry is that composites that do not contain microstructural defects and can be formed into desired shapes, such as tubes, This is because there was no technically and economically suitable technique to obtain a uniform dispersion of fine oxide particles in the matrix.Research and development of oxide dispersion reinforced materials has been carried out over the last 20 years. However, these materials products have not been able to reach a sufficient industrial level because, until now, it has not been possible to improve the microstructure during processing to allow control of grain size and shape in alloy products. Further, the formation of inherent microstructural defects introduced during processing such as stringers, grain boundary cavities, and micropores was not understood. It didn't exist.

Stringer stringers consist of elongated fragments of the oxides of the constituent metal components. These veinlet oxides act as weak surfaces across their length and serve to prevent control of grain size and shape during subsequent recrystallization. Micropores, including voids at grain boundaries, are detrimental to dispersion strengthened alloys because they adversely affect yield strength, tensile strength, ductility, and creep rupture strength.

There is a great need in various industries for lightweight, high strength metallic materials. These materials are particularly useful in the manufacture of aircraft skins, aircraft internals, rifle parts, automotive parts, and perforated pipe for oil well exploration. The best candidates for such materials are aluminum-based materials. Aluminum and aluminum-based alloys are commonly selected for use in applications where a high strength-to-weight ratio is a primary consideration. However, these metals
Conventional aluminum-based alloys tend to lose strength at temperatures above half their absolute melting point (i.e., >200° C.), so they can only be used at relatively low temperatures.

The desire for increased fuel efficiency and higher load factors in the aviation industry has driven the demand for aluminum alloys in place of titanium alloys and high strength steels as skin and frame materials.

More recently, the need for reduced torque and drag in inclined drilling has encouraged the use of aluminum-based alloys as drill strings, but their use has been severely limited by the strength loss problems at elevated temperatures mentioned above.

An early attempt to increase the strength of aluminum was to hot press aluminum powder in an oxygen-containing atmosphere to form a thin film of aluminum oxide in situ on the surface of the original aluminum powder particles. This dispersion-strengthened aluminum material, commonly known as sintered aluminum products (S, A, P, ), exhibited surprisingly high levels of hardness and tensile strength. , although insoluble,
It was relatively coarsely dispersed. As a result, the alloys were unable to achieve very high strength at elevated temperatures and were not of practical use in industry.

Mechanical alloying methods were used to produce aluminum dispersion strengthened materials that do not exhibit the drawbacks of sintered powder materials. This technique generally produced -layer homogeneous materials and gave more precise and finer control over chemical composition. Furthermore, these mechanical alloying techniques are suitable for making multi-component materials where one or more of the components are immiscible with each other. Examples are tungsten and copper or high melting point materials in metals.

However, early attempts to produce dispersion-strengthened aluminum materials by mechanical alloying techniques were unsuccessful. This is because the malleability of aluminum led to welding of the powder particles to each other and to process equipment parts, which prevented the dispersion of the dispersed phase. One attempt to alleviate this problem is disclosed in US Pat. No. 4,409.038, which discloses the use of process control agents such as stearic acid to prevent such welding. Although this method has had some success, it has not been possible to produce dispersion-strengthened materials in which the dispersoid is a high melting point material that is insoluble in the matrix. For example, the above method results in alloys strengthened with coarsely dispersed oxides and finely dispersed carbides. These coarsely dispersed oxides contribute little to strength due to their relatively wide spacing, and the carbides are relatively unstable and tend to coarsen at elevated temperatures, leading to rapid strength loss. Therefore, such alloys are typically restricted to use at temperatures below 200°C.

Thus, there remains a need in the industry for dispersion strengthened aluminum materials that have high temperature strength.

According to the present invention, dispersoid particles of aluminum oxynitride are comprised of aluminum and aluminum oxynitride, wherein the individual powder particles are substantially uniformly dispersed throughout the aluminum matrix and the matrix. A mechanically alloyed composite powder is provided. The present invention further provides an extruded mechanically alloyed article comprising an aluminum matrix having substantially uniformly dispersed oxynitride particles with substantially no texture distortion.

In a preferred embodiment of the invention, the composite powder comprises 50
% by weight of aluminum, oxynitrides and one or more other metals, high melting point substances, or both.

In one preferred embodiment of the invention, at least 0.1% by volume of the dispersoid particles are aluminum oxynitride and the one or more other high melting point substances are oxides.

In another preferred embodiment of the invention, at least 0.5% by volume of the dispersoid particles are aluminum oxynitride and the high melting point material is alumina.

The aluminum-based material of the present invention may be aluminum alone or 11! ! It is prepared by introducing the metal powder with the addition of the other metals mentioned above into a mill and milling the powder mixture with a nitrogen-containing cryogenic liquid at a temperature below the boiling point of liquid oxygen.

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

Texture-free aluminum material articles containing aluminum oxynitride dispersoid particles of the present invention are prepared by forming a billet of mechanically alloyed aluminum powder material comprising grains having an average grain size of less than about 5 microns. Formula % Formula % (where R is the radius of the die profile at a given point X along the main axis of the goo orifice from its entrance face, Ro is the radius of the billet and K is an arbitrary constant. ) is made by extrusion through an extrusion die having an internal contour substantially conforming to .

The practice of the present invention provides an aluminum-based dispersion reinforced material having the following characteristics: 1. aluminum acid substantially uniformly distributed throughout the matrix with an average spacing of less than about 20 nm; nitride particles, resulting in a material with excellent high temperature strength.

2. The sufficient energy stored in the low temperature milling process is released during the subsequent reheating of the alloy powder, resulting in fine grain size in the resulting composite powder grains.

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

The strength (σ) of the composite material is related to the elastic modulus (E) of the matrix and the interparticle spacing (E) of the dispersoid particles according to the following formula: σ = αE/λ (where α is a constant ) When iron-based dispersion-strengthened materials are produced by cryogenic milling, the distance between 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 a material the required strength. According to the above formula, the spacing between particles of the dispersoid in iron-based systems can be achieved only by refining the high melting point powder during cold milling. For metals such as aluminum, the elastic modulus is approximately 1/3 that of iron, so to achieve the same high temperature strength, the spacing between particles must be 1/3 that of iron.
3 small (must be <20 nm).

The required interparticle distance can only be achieved by setting the dispersoid to a size range of approximately 2 to 6 nm, but this cannot be achieved solely by refining the high melting point phase, as is the case with iron. Instead, microdimensional dispersoids in aluminum systems are achieved through controlled chemical reactions on the atomic scale. By using a cryogenic milling process in a nitrogen-containing cryogenic liquid with up to 1% oxygen by weight, the in situ surface reaction of reactive aluminum with nitrogen is approximately 7%
Bring vines at a temperature of 7°. At this temperature, the thermodynamics and kinetics dictate that through the reaction of aluminum, oxygen, and nitrogen, the situation is to form extremely fine oxynitrides.
-nitride) species formation.

Mechanical milling of one or more metals is a process in which initial component powders are repeatedly ground and cold welded by the continuous impact action of a milling medium.
Considerable strain energy is stored during this operation. During subsequent reheating prior to extrusion, recrystallization of the resulting composite powder occurs. It is known that the grain size produced by recrystallization after cold working depends on the degree of cold working.However, there is a lower limit to the working amount below which recrystallization does not occur. Since the degree of cold working is a measure of the strain energy stored in the material, the reduction in milling temperature increases the amount of work I that can be stored in the material over a given period of time and the amount of work that can be stored up to saturation. Therefore, a decrease in milling temperature leads to an increase in the rate of reduction in powder particle size and a decrease in particle size realized at longer milling times.

It is also within the scope of this invention to mechanically alloy the aluminum powder alone by cold milling in the substantial absence of oxygen to give the resulting powder a very small particle size. In this case, i.e. if it is not desired to produce aluminum oxynitride, the cryogenic material should be about -240
Any liquid having a boiling point in the range of -150°C may be used. Examples include liquefied gaseous nitrogen, methane, argon,
Such as krypton.

The production 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 believed to be that as the grain size becomes finer, more slip deformation can be absorbed by the diffusion process near the grain boundaries. The grain boundary concentration of the band also decreases proportionally.

As already discussed, veinlet oxides (stringers)
They are elongated fragments of oxides of metal elements such as aluminum, chromium, and iron. Surprisingly, the inventors have discovered that these oxide stringers originate from the oxide scale that forms on the particles during atmospheric ball milling.

More surprisingly, this oxide scale is produced even during conventional milling using industrial grade argon, where metals such as aluminum, chromium, and iron react with trace amounts of oxygen to form external oxide scales on the particle surfaces. Occurs when forming. These scales fracture during subsequent compaction and elongate during extrusion to form oxide stringers. The stringers serve as centers of weakness in the bulk material and act to prevent grain boundary movement during annealing. By doing so, the stringers interfere with particle size and shape control during the final thermomechanical processing step. Although oxygen is used in the practice of this invention, the temperature at which cryogenic milling is performed is low enough to prevent the formation of such oxide scale.

The properties of the material produced by the present invention include high melting point particles (
A substantially uniform fine dispersion of particles (typically particles having an average diameter of about 3 nm and a spacing of about 20 nm), the absence of external oxide scale, and the ability to form extruded products with substantially no texture under industrial practice conditions. Including significant improvements.

High melting point compounds suitable for use in the practice of the present invention include those having a negative free energy of oxide formation per duram atom of oxygen of at least about 90.0 at about 25°C.
00 calories and its melting point is at least about 13
Examples include oxynitrides, oxides, carbides, nitrides, borides, carbonitrides, etc. that have a temperature of 00°C. The preferred one is
Oxynitrides and oxides. Examples of such oxynitrides and oxides are those of silicon, aluminum, yttrium, cerium, uranium, magnesium, calcium, beryllium, thorium, zirconium, hafnium, titanium, and the like. Mixed oxides of aluminum and yttrium are also included, such as: AI□Os 2
Y203 (YAP), Al2O3・Y2oz
(YAM) and 5A1□0.・3Y, 0. (YA
G). Preferred are aluminum oxynitrides and oxides, and more preferred is aluminum oxynitride.

The total amount of aluminum oxynitride present in the materials of the invention is at least an effective amount. By effective amount is meant the minimum amount required to increase the strength of the aluminum matrix by at least about 10%, preferably at least about 20%.

Generally, this amount will be up to about 5% by volume, preferably up to about 2% by volume, and more preferably up to about 1% by volume, based on the total volume of the material.
and most preferably in the range of about 0.1-0.5% by volume. When one or more other high melting point compounds are present, the total volume of high melting point substances (addition amount + in situ generation M) is about 0.5 to 25%, preferably about 0.5 to 25%, based on the total volume of the material. It ranges from about 0.5 to 10%, preferably 0.5 to 5%.

Prior to this invention, it was not practical to mechanically alloy malleable metals such as aluminum. This is because aluminum has a tendency to stick to the attritor and its parts. The use of conventional process control agents during milling to virtually eliminate this problem only results in materials with insufficient high temperature strength for many industrial applications. Aluminum and aluminum-based alloys can be successfully mechanically alloyed by cryogenic milling to produce dispersion-strengthened composite particles having a substantially uniform distribution of aluminum oxynitride particles throughout the matrix.

The dispersion-strengthened mechanically alloyed aluminum of the present invention mainly consists of aluminum and dispersoids. The material also contains various additives that can provide certain properties to the aluminum, such as solid solution hardening or age hardening. For example, magnesium forming a solid solution with aluminum would provide additional strength with corrosion resistance, good fatigue resistance and low density. Other additives that can provide additional strength include, for example, Li, Cr, SL, Zn, Ni, Ti,
Examples include Zr, Co, Cu and Mn.

Additives and amounts added to aluminum are well known in the art.

Generally, the dispersion strengthened mechanically alloyed aluminum materials of the present invention are comprised of at least 50%, preferably at least about 80%, -layers preferably at least about 90% aluminum based on the total weight of the material.

The invention is practiced by loading a nitrogen-containing cryogenic material, 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 or ceramic balls that are maintained in a state of highly active relative motion.

The milling operation, carried out in the presence of an effective amount of oxygen, breaks up the mixture components and binds or welds them together and disperses them with each other throughout the metal matrix of the product powder and upon subsequent recrystallization by heating. grain size and fine grain structure can be obtained.

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

During the milling process, the initial aluminum powder particles collide with the grinding media and break up. This fracture automatically creates a clean surface with highly reactive aluminum atoms. The nitrogen and oxygen atoms present adsorb onto these clean surfaces and combine with the aluminum atoms, thereby forming a composite of aluminum, oxygen and nitrogen, referred to herein as aluminum oxynitride. The dimensions of these composites are ultrafine. That is, they generally range from about 300 to 700
atomic (2-5 nm diameter). In addition to these in-situ produced aluminum oxynitrides, the metal matrix may also contain other species high melting compounds introduced with the initial powder charge.

After cryogenic milling, these high melting point compounds
The size range is m. Thus, only by in-situ production of aluminum oxynitride can one obtain the ultra-fine grain size that leads to the superior properties of the composite powder of the present invention.

The term "cryogenic medium" used here means 1 to 10n+
means an oxygen-containing liquid material capable of forming aluminum oxynitrides with an average diameter of n, preferred is liquid nitrogen.

The materials of the present invention are extruded such that the extruded product has substantially no texture. As used here,
"Substantially no texture" means substantially no preferred crystal orientation. Another way to express this is that when a polar figure is obtained from a material with virtually no texture (preferred crystallographic orientation), no region of that polar figure has a polar density approximately 10 times greater than that obtained from a disorderly oriented sample. It is preferable that the polar density is not more than 5 times, 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 present invention. This indicates that the internal contour of the die defines the material being extruded through the die in the die zone by the following equation: (where A is the cross section at a given point where 80 is the cross-sectional area of the billet, L is the true strain rate and V is the speed of the ram of the extrusion press. ) is made to change continuously in such a manner as to match the .

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

FIG. 1O is a perspective view of the hand portion of a rod extrusion die, and FIG. 11 shows a cross-sectional view of the same die. Internal passage 1
The profile of 4 substantially follows the following formula: 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 (E-1) Ro2; ii) For a given ram speed λ, the true strain rate imposed on the material passing through the die is L = K vR.

is given by

The radius R of the die orifice or passageway is indicated at a given point X along the principal axis 12 of the die orifice from the entrance face Y. The die includes an entrance orifice at the entrance face Y, where the radius of the die orifice is at its maximum.

The die profile 14, referred to herein as the internal die profile, converges according to the above formula and terminates at a distance along the major axis as shown at 16. The die orifice can then 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 walls of the die orifice. should be maintained. The radius of the internal contour 20 of the die from 18 to the exit face Y" increases slightly to allow for separation of the extruded product from the die. The die separation section of the die is conventional and its upper limit is normally determined by the die support system. The actual separation angle is conventional and 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 invention is carried out by placing a billet of finely divided aluminum-based powder in a can (coated container can) into the container of an extrusion press. The can can be constructed from 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 before extrusion, the billet preferably has an elongated section at its front end so that it fits snugly into the die orifice.The billet then moves forward through the ram at a predetermined speed. The billet is extruded by moving the billet through the die into the rod at a constant natural strain rate.The exit face of the die is open against the shear plate of the extrusion press.It is substantially texture-free. The specific temperature and strain rate required for a given material to be extruded with enhanced plasticity to produce a product can be determined by conventional techniques such as tensile, compression or torsion testing. The sensitivity is determined by first measuring the temperature and strain rate combinations that give a strain rate sensitivity of greater than about 0.04 cm. The techniques used in are discussed in detail in the next section.

The die used to extrude the particulate composite material into a tube must have an internal contour that substantially conforms to the formula = 1 = (
1-,) R2(R,"+Rffi"K,) (where R is the radius of the die profile at a given point X from its entrance face along the main axis of the die orifice and Ro is (where R□ is the radius of the mandrel and K is an arbitrary constant.) L=Kv (factors defined) The following example further describes the invention for illustrative purposes. be.

Ratio jd"Δ 567, 585 g of a metal mixture consisting of 5 g of aluminum and 175 g of alumina was poured into the mouth.
sInc, Laboratory model I-3
The sample was charged into a high-speed attritor (ball mill) manufactured by. The attritor contained 6 mm diameter stainless steel balls at a charging ratio of 18:1.

Milling was carried out in argon at room temperature (approximately 25° C.) with a mill rotation speed of 180 rpm.

The test was stopped after 28 minutes because the mill stalled. Inspection of the mill revealed that the alloy powders were welded to each other and partially to the mill, forming horseshoe-shaped fragments on the inner circumference of the mill. This result shows that dry milling without the aid of anti-welding agents is not possible on aluminum-based systems due to the extremely malleable nature of the metallic phase and the susceptibility of the newly created aluminum surface to cold welding. Show that something is true.

Sample of Novamet Inc. Novamet
lN9052-F, Novamet lN9021-
F T-651 and Novamet IN905 XL
I bought it. These alloys, to the best of our knowledge, were made by mechanical alloying techniques taught in US Pat. No. 4,297,136. That is, the patent discloses a method for preparing mechanically alloyed powders by ball milling component metal powders in the presence of argon and milling aids at room temperature.

7, 2 test samples with diameter dimensions of 2 x 5.6 mm were prepared as compression specimens from the alloy lN9021-F T-651, and other test samples with diameter dimensions of 25 x 8.1 mm were made from lN9021-F T-651. and lN
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 L 03 MPa and at temperatures of 177,232 and 275 degrees. The relationship between time to failure versus applied stress and temperature obtained from these tests is shown in Table II and plotted as a stress-to-break curve in FIG. Compression test samples were subjected to unidirectional compression at a strain rate of 3×s−′. The force and sample shrinkage were measured and the stress-strain response of the material was obtained. Compression test is 25.125
．． 175.225.275.325:, 375 and 42
It was performed at 5 degrees.

The 0.2% offset yield strength was measured for each test sample and these data are shown in Table IN and plotted against test temperature in FIG.

Table ■ Creep rupture data for Novamet lN9052-F Temperature Applied stress Time to rupture 'C
M P a h 177 68.9 332+Table II Stress rupture data for Novamet lN9021-F T-651 Temperature Applied stress Time to rupture'CM P a h 177 103.4 600+232
51.8 2592+232
68.9 242232
103.4 0.723
2 68.9 3264232
86.1 4642232
102.4 13.251.8 68.9 6.4 51.8 68.9 75.8 86.1 5230+ 3 77, 8 0.5 Novamet lN9021-F Temperature C Table III Compression test data distortion for T-651 Speed Yield stress/s MPa 3X10-3 412 3XIO-410 3X10-" 340 3X10-3 176 3X10-3 113 3X10-' 72 3X10-3 52 3X10-" 34 In addition, the bar with the bridge still attached was examined under an optical microscope. A piece was taken as a specimen, fixed and polished. Also, alloy I
Thin sections were taken from the N 905XL bars and used to prepare thin foil samples for transmission electron microscopy. An example of a transmission electron micrograph obtained from this material is shown in FIG.

Electron micrographs of samples of Novamet IN 905XL show that the average grain size ranges from 0.5 μm to over 2 μm (see Figure 3). This relatively large particle size distribution is a result of the lack of a uniform distribution of ultrafine dispersoids. Similar observations were made in the other two Novamet studies investigated.
The microstructure of the alloy was also investigated.

- The data obtained from the axial compression test shows that, as seen in Figure 2, the alloy exhibits high strength near room temperature, i.e. up to 175°C, but the strength decreases rapidly as the temperature increases beyond that point. shows.

Comparative Example: Five 585 g mg/oxide powder mixtures were modified with the exception that the milling was done in a liquid nitrogen slurry and the atrique was modified to allow a continuous flow of liquid nitrogen to keep it liquid. Prepared by the process described in A. four batches of metal/oxide powder mixture at 3%;
7%, 10% and 15% (by weight) alumina were prepared using 17.5g, 40g, respectively.
, 585 g and 87.8 g of alumina.

In each case milling was carried out for 15 hours. Upon completion of milling, the powder was allowed to warm to room temperature under a continuous flow of dry argon and then removed from the mill. powder is 2
After sieving to remove particles larger than 50 μm, it was loaded into an aluminum can (cylindrical container with end cap and exhaust port). The can was evacuated and heated to 250° C. for 24 hours under vacuum. , seal the can and AS
EAModel 5L-I Mini-Hipper
It was loaded into a Laboratory high temperature isostatic press. The can-filled powder was placed at a temperature of 510° C. for 5 hours under a containment pressure of 2000 bar (206.7 MPa).

The compacted powder samples thus produced were prepared for metallurgical and mechanical tests.

Samples of each cryogenically milled powder were fixed in transparent fixing media, polished, and optically examined for particle size and shape. The samples were also examined by scanning electron microscopy.

The grain sizes and aspect ratios for the four alloys are listed in Table IV.

Table IV Particle Size and Shape Alumina for Cryogenically Milled Powders
Particle size Standard deviation Aspect ratio 1 and 1 - 2 - 314,612,70,612 715,513,00,591 1019,615,90,565 1517,914,90,617 3%, 7% and 15% Samples of compressed powder containing alumina were cut into pieces, fixed in Bakelite, polished and examined by optical microscopy and scanning electron microscopy.

compressed by hot isostatic pressing (HIP) and 3%;
Compressed powder samples containing 7% and 15% alumina were cut into cylinders of 6 mm diameter and 9 mm length dimensions. These samples were subjected to uniaxial compression at a strain rate of 3 x 10-'s-'. The force and sample shrinkage were measured and the stress strain response of the material was derived. Compression test 25.125.1
75.225.325.375 and 425°C. 0.2% offset yield strength was measured for each test sample. These data are listed in Tables v, 1 and VII and plotted against test temperature in Figures 4-6.

In addition, hot isostatically pressed samples of aluminum-3% alumina alloy were swaged to a 70% area reduction and cut into samples measuring 25 x 8.1 mm diameter as creep specimens. 232 for these latter samples.
at temperatures ranging from ~275 °C and from 34 to 103 MPa
A constant stress creep test was conducted at a stress level of . These data are summarized in Table VIII and shown graphically in FIG.

Table V As-HIP processed aluminum/oxynitride-3
Compression test data for % alumina Temperature Strain rate
Yield strength 'C/s M Pa 25 3X10"" 450125 3x
lO-3443 1753xlO-3373 2253xlO-3223 2753X10-3 206 325 3xlO-3163 3753X10 Bow 110 425 3xlO-3105 Table VI Old P As Processed Aluminum/Oxynitride - 7%
Compression test data for alumina Temperature Strain rate
Yield strength 'C/s M Pa 25 3xlCM" 51112c3 3X
IO-” 493175 3X10-3
443 225 3xlO-” 283275 3
X10-” 196325 3X10-3
146 375 3X10-3 104 425 3X10-3 105 Table VII As-HIP processed aluminum/oxynitride-1
Compression test data for 5% alumina Temperature °C Strain rate/S 3×1 3×1 3×1 3×1 3×1 3×1 3×1 X1 Yield strength Pa Table VIII As-HIP processed aluminum/acid Nitride-3
% Creep rupture data for alumina Temperature Applied stress 'CM P a 232 34.5 232 68.9 232 103.4 275 51.8 275 68.9 275 103.4 *Test completed - no damage + test still in progress until rupture Time 10.986” 5.491+ 215+ 10.773.

452 + 310 + additional 585 containing 3 wt% and 7 wt% alumina
A metal/oxide powder mixture batch was prepared using the procedure described above. The alloyed powder batch was placed in a 75 mm diameter aluminum extrusion can and evacuated in the manner described above as a hot isobaric breath can.

These extruded billets were subsequently extruded as 18 mm diameter bars at 450° C. with a ram speed of 5 non/s. Material samples cut from these bars were
5.1 mm diameter compression test samples were prepared and tested in the manner described above. These data are shown in Table IX and the 0.2% yield strength as a function of temperature is shown in FIG.

For each extrusion rod, a sample was cut perpendicular to the extrusion axis and R
The texture was analyzed using an igaku DMAX-ll-4 diffractometer. data (200
>Collected against reflection. The Detzker method was used in transmission and the Schierz method was used in reflection so that all-pole figures were obtained (R,D).

Elements of X-ra by Cu1lity
y Diffraction). The sample had virtually no texture, as shown in FIG. 12, which is a polar diagram obtained for an aluminum/aluminum oxynitride alloy containing 3% alumina.

Additionally, alloy samples were cut into thin plates and prepared as thin foils for transmission electron microscopy observation. Examples of transmission electron micrographs obtained from these samples are shown in Figures 98 and 9b.

Table IX Compression test data for as-extruded and swaged aluminum/oxynitride-3% alumina Temperature °C Strain rate/S 3×1 3×1 3×1 3×1 X1 3×1 3×1 3×1 From a comparison of the yield strength Pa and the data shown in Tables ① to VII and the data shown in Figures 4 to 6, the alloy prepared in accordance with the present invention was compared to Comparative Example B.
It exhibits superior strength properties compared to conventional mechanically alloyed aluminum materials such as those shown in The alloy only begins to lose its room temperature strength above 250°C, which is high compared to about 180°C for the Novamet alloy. Therefore, the alloy according to the invention extends the temperature resistance by about 50°C. Furthermore, 4
At high temperatures above 00° C., the strength level is approximately three times higher than that of the comparative material.

The strength observed at elevated temperatures is due to the presence of ultrafine dispersoids of aluminum oxynitrides that are introduced as a result of in situ surface reactions during the cryogenic milling process.

and controls recrystallization and grain growth at high temperatures, resulting in highly uniform grain sizes, typically 0.05 μm in diameter. This is in contrast to the conventional mechanically alloyed material of Comparative Example B, where there is no sign of such fine dispersoids and where the grain size is non-uniform and the average grain diameter is typically 0.5 μm. It is.

In particular, the fact that high temperature strength is imparted by long fine aluminum oxynitride particles means that the 0.2% proof stress vs. temperature curves for alloys with 3%, 7% and 15% alumina overlap almost exactly. This is supported by the following observation. In other words, the yield strength of the alloy prepared according to the present invention is independent of the amount of alumina initially added to the mill (same strength at all temperatures.
The level of strength provided by alumina particles formed by repeated grinding of added alumina is significantly reduced by the fact that the particles are relatively thick (
0.02μm) and their spacing is also large (0.1μm)
m), it is explained by recognizing that it is small. In contrast, aluminum oxynitride particles formed in situ during cryogenic milling are much smaller (approximately 3 nm diameter) and dispersed with spacing of approximately 0.002 μm, thus producing much higher strength levels. Therefore, alloy strength is independent of added alumina content since most of the strength is due to the presence of ultrafine oxynitrides and their volume fraction is independent of the amount of added alumina.

Additionally, by extruding the composition through a die such as that shown in Figures 10 and 11, a texture-free product is obtained. This is a result of the ultrafine grain size of the powders produced by cryogenic milling as disclosed herein.

[1] Due to the presence of ultrafine dispersoids of aluminum oxynitride introduced as a result of in-situ surface reactions during the cryogenic milling process, we succeeded for the first time in the world in developing an aluminum-based alloy with excellent high-temperature strength. . Texture-free isotropic extruded products are obtained.

4. Figure 1 is a graph of creep rupture data obtained for two commercially available mechanically alloyed aluminum alloys.

2 is a graph showing the relationship between 0 and 2% proof stress versus temperature obtained by

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 a compression test for the hot isostatically pressed aluminum-aluminum oxynitride material sample with 3% alumina described in Example 1.
2 is a graph of % proof stress versus temperature data.

FIG. 5 shows the 0,
2 is a graph of 2% proof stress versus temperature data.

FIG. 6 shows the 0,
2 is a graph of 2% proof stress versus temperature data.

FIG. 2 shows the compression test for a commercially available alloy. FIG. Fig. 2 is a graph of creep rupture data.

FIG. 8 is a graph of 0.2% proof stress vs. temperature data obtained in a compression test for an aluminum-aluminum oxynitride material extrusion sample with 3% alumina as described in Example 1.

FIG. 9a is a transmission electron micrograph showing the metallography 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 according to Example 1 and subjected to extrusion, in particular 3 nm diameter oxynitride particles.

FIG. 10 is a perspective view of one half of a die used to extrude rods in accordance with the present invention.

FIG. 11 is a cross-sectional view of the die used to extrude the rod illustrating the internal profile of the die.

FIG. 12 shows the standard <200 aluminum-aluminum oxynitride material with 3% alumina presented in Table IX and obtained from sections cut at right angles to the extrusion axis.
＞It is extreme.

10: Die 12: Main axis line 14: Internal contour 16: Convergence section terminal point Y two person b side Y: Exit surface

Claims (1)

Claims: 1) A mechanically alloyed aluminum composite characterized in that the individual powder particles have an aluminum matrix and dispersoid particles of aluminum oxynitride substantially uniformly distributed throughout the matrix. body powder. 2) The composite powder of claim 1, wherein the concentration of aluminum oxynitride is up to about 5% by volume. 3) The composite powder according to claim 2, wherein the concentration of aluminum oxynitride is about 0.1 to 0.5% by volume. 4) Composite powder according to any of claims 1 to 3, in which one or more other metals are present and the aluminum metal content is at least 50% by weight, based on the total powder weight. 5) Other metals include Li, Cr, Si, Zn, Ni, Ti,
Composite powder according to claim 4, selected from the group consisting of Zr, Co, Cu, Mg, Mn and mixtures thereof. 6) A composite powder according to any one of claims 1 to 6, wherein the powder contains up to about 25% by volume of a high melting point compound consisting of aluminum oxynitride and at least one other high melting point compound. 7) The composite 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. powder. 8) The high melting point compound is Al_2O_3, Al_2O_3.
2Y_2O_3, Al_2O_3・Y_2O_3 and 5
The composite powder according to claim 7, which is an oxide selected from the group consisting of Al_2O_3.3Y_2O_3. 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 a nitrogen-containing cryogenic liquid containing an effective amount of oxygen and substantially free of oxide scale. A method for producing a dispersion-strengthened aluminum composite powder, comprising milling for an effective time to produce the composite powder. 10) The method according to claim 8, wherein the nitrogen-containing cryogenic liquid is liquid nitrogen. 11) A method according to claim 9 or 10, wherein up to 1% by weight of oxygen is present. 12) A method according to any of claims 9 to 11, wherein the aluminum powder comprises at least 50% by weight aluminum, one or more other metals or additives and one or more high melting point substances. 13) One or more other metals include Li, Cr, Si, Zn,
selected from the group consisting of Ni, Ti, Zr, Co, Cu, Mg, Mn and mixtures thereof, and the high melting point material consists of oxides, oxynitrides, carbides, nitrides, borides, carbonitrides and mixtures thereof 13. The method of claim 12, wherein: 14) A method of extruding a fine-grained aluminum mechanically alloyed powder material according to any of claims 1 to 8 into a substantially texture-free rod, the powder material having an average particle size of less than about 5 microns. A billet of , R_o is the radius of the billet and K is an arbitrary constant. 15) A method of extruding a mechanically alloyed fine-grained aluminum powder material according to any of claims 1-8 into a substantially texture-free tube, the powder material having an average particle size of less than about 5 microns. The billet is calculated using the following formula 1/R^2=(1-K_x)/(R_o^2+R_m^
2K_x) (where R is the radius of the die profile at a given point x from its entrance face along the major axis of the die orifice, R_o is the radius of the billet, and R
_m is the radius of the mandrel and K is an arbitrary constant. ) an extrusion method characterized by extrusion through a die having an internal contour substantially according to