US3489548A - Particulate powder of iron with copper contained therein - Google Patents

Description

A. ADLER 3,439,548

PARTICULATE POWDER OF IRON WITH COPPER CONTAINED THEREIN Jan. 13, 1970 2 Sheets-Sheet 1 FIG. 2

Filed July 13. 1965 FIG.

0 1 MICRON 0 1 MICRON FIG. 4

FIG. 3

1O 0 MICRONS INVENTOR A/QTI/MQ ADLEE' iii-1 ATTORNEY A. ADLER Jan. 13, 1970 PARTICULATE POWDER OF IRON WITH COPPER CONTAINED THEREIN Filed July 13, 1965 2 SheetsSheet 2 FIG. 5

1 nv v m ii wmm 0 MICRON INVENTOR %?7//l/Q A045? ATTORNEY United States Patent US. CI. 75-05 11 Claims ABSTRACT OF THE DISCLOSURE An alloy in powder form is disclosed comprising iron intimately infiltrated with from about 1 to 50% by weight of copper.'The particulate alloy is produced by mixing a reducible compound of iron with an appropriate proportion-of a copper compound selected from the group consisting of elemental copper and reducible compounds of copper, the mixture being heated under reducing conditions at a temperature of up to about 1150 C. and at least about 100 C. above the sintering temperature for copper for a time until the reducible compounds are substantially completely reduced to the metal state.

This invention is concerned with alloys of copper and iron, and more particularly with novel iron powders preinfiltrated with copper, and with processes for their preparation.

As employed herein and in the appended claims, an alloy is defined to be a substance having metallic properties and composed of two or more chemical elements of which at least one is elemental metal. It has in the past been recognized that the physical properties of iron are improved by alloying with copper. Since these metals are virtually insoluble in each other at room temperature, and sincetheir mutual solubility is quite limited even at elevated temperatures, various expedients have been employed in an attempt to bring them into intimate association. Thus, copper and iron powders have been blended and molded into finished objects by the techniques of powder metallurgy. In-addition, the infiltration process has been employed, i.e. filling the pores of a sintered powder metallurgy part, of iron or steel in this case, with a metal or alloy of lower melting point, e.g. copper.

-These prior methods for the preparation of copperiron alloys are characterized by important problems and disadvantages. Blended copper and iron powders are subject to segregation in storage and shipment. More important, even' very finely divided, blended powders do not provide the degree of homogeneity which affords optimum properties. In addition, sintering of compacted copper-iron powder blends results in expansion of the compact, representing a porosity increase which is a major factor in interior strength, molding flaws and high rejection rate. v A relatively simple procedure has now been discovered for the preparation of novel copper-iron alloys in powder form, offering substantial cost advantages over conventional infiltration techniques. This procedure. imparts to the new powders a unique microstructure, characterized by a more intimate admixture of the elements, to which 3,489,548 Patented Jan. 13, 1970 P CC the superior physical properties which result may be attributable. Upon simple pressing and sintering, the new particulate alloys shrink to high-density products of great strength.

The distinctive metallographic features of the new alloys will be better understood by reference to the accompanying illustrations, which are photographic reproductions of highly magnified electron microscope photomicrographs. Each photograph depicts a portion of a single particle of one of the new alloys, as etched in a 3% solution of nitric acid in alcohol in order to erode the copper-rich areas.

FIG. 1 illustrates an alloy of iron with 7% by weight of copper, prepared by the process of the present invention and enlarged approximately 100,000 diameters.

FIG. 2 shows the alloy of FIG. 1 after heat treatment as detailed hereinafter, also enlarged approximately 100,- 000 diameters.

FIG. 3 depicts an alloy of iron with 20% by weight of copper, prepared in accordance with the present invention and enlarged approximately 3600 diameters.

FIG. 4 shows the alloy of FIG. 3 after heat treatment, also enlarged approximately 3600 diameters.

FIG. 5 shows a portion of the particle depicted in FIG. 4, this time enlarged approximately 17,700 diameters.

The salient features of these illustrations will be referred to hereinafter, in connection with a discussion of the microstructure of the new products.

In essence, the process of the present invention entails blending a reducible iron compound with copper or with a reducible copper compound, and reducing these reactants to the metallic state at elevated temperature. The relative proportions are selected to yield a product containing from about 1 to about 50% by weight of copper.

Copper sinters at about 825-850 C., and it melts at about 1083 C. in the pure state and at about 1094 C. when it contains 3.2% or more of iron. In order to achieve the uniquely intimate consolidation of the iron and copper which characterizes the invention, it is essential that the temperature during the reduction step reach at least C. above the sintering temperature of copper, and it is ordinarily preferable that the reduction temperature be at least at the melting point of copper. However, for those alloys containing in excess of 20% by weight of copper, reduction temperatures at or above the copper melting temperature tend to cause agglomeration of the reduced product to a mass which can be broken down into smaller particles only with great difficulty. Accordingly, when alloys of such high copper content are prepared, it is best to keep the reduction temperature below the melting point of copper, but still at least 100 C. above the copper sintering temperature, preferably at about 950- 1050 C. For those alloys containing from about 1 to 20% copper, the fullest advantage is obtained by conducting the reduction at or above the copper melting temperature, preferably at about 11201135 C. In all cases, however, reduction temperatures above about 1150 C. are undesirable, since they favor extensive product agglomeration, producing a tough, hard mass which is impossible to grind to metal powder by any economic means.

Under the described conditions, the reactant mixture is reduced to a particulate alloy of iron intimately infiltra ed with copper, without the need for the copper to flow through the mass of iron to saturate the pores as 3 is the case in conventional infiltration of molded iron compacts. During the new process, the oxide or other reducible iron compound undergoes a solid state reduction. Where the reduction is conducted below 1094 C., but at least 100 above the copper sintering temperature, the copper does not liquify, but the reduced solids undergo grain boundary diffusion, with comparable results. These lower reduction temperatures are preferred in the production of alloys of high copper content, as previously discussed, and the high copper volume fractions are believed to favor products of infiltrated nature.

When reference is made in this disclosure and in the appended claims to particulate alloys of iron infiltrated with copper, this expression is intended to describe individual particles containing both copper and iron in intimate mutual dispersion, as distinguished from mere blends of copper powder with iron powder, and as further distinguished from particles of the one element merely coated with the other.

By their nature, the new particulate alloys of the present invention are not subject to segregation into the individual elements in storage or shipment. They may be truly termed pre-infiltrated alloys, since they are directly moldable by conventional powder metallurgy techniques to useful parts, without the need for a separate penetration of liquid copper into a molded iron part as practiced in conventional infiltration.

Any reducible iron compound may be employed in the new process, including iron salts or any oxide of iron such as hematite, magnetite, beneficiated magnetite ores, fiue dusts, synthetic oxides or reducible mill scales, e.g. from rolling mill operations. By reducible mill scales is meant those which are reducible to the extent of about 99% or better, such as carbon steel mill scale and low alloy steel mill scales.

The source of copper may be elemental copper, such as reduced copper powder, atomized copper, electrolytic copper powder or hydrometallurgical copper powder. However, it will usually be less expensive to employ an oxide of copper, either precipitated or mechanically produced, such as cuprous oxide, cupric oxide, copper mill scale, or cement copper, a byproduct of mine waste water which typically contains about 50-98% cuprous oxide. Where copper oxides are employed, it is sometimes beneficial to incorporate nitric acid in the reaction charge, to promote a more intimate dispersion. Alternatively, cupric nitrate or other water-soluble copper salt, may be employed in water solution as the copper source.

In addition to copper and iron, nickel, cobalt, molybdenum or tungsten may be included, or reducible compounds of these elements, such as nickelous acetate, cobaltic oxide, molybdic oxide, or tungstic anhydride. Such elements will generally be employed in minor proportion, i.e. up to about 6% by weight of any one element or a total of up to about 12% by weight in the case of several in combination, in order to improve strength. Such elements may be added in the form of soluble salts such as nitrates or acetates, for optimum dispersion, or as compounds in combination with an acid or base solvent, such as ammonia water or nitric acid.

Those reactants are preferred which have particle sizes finer than 250 microns, and especially preferred are iron compounds finer than about 50 microns and copper compounds finer than about microns, since these favor the most intimate interdispersion of the elements.

While not essential, it is often advantageous to blend the reactants with an aqueous dispersion of an organic adhesive, to minimize dusting losses or segregation of the reactants during handling and subsequent processing. Suitable binders include animal protein glue, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and the like. Such compounds are readily decomposed at the reduction temperature and should preferably be low in ash content. Adhesive levels of about 0.5% of the total batch weight are usually entirely adequate, the proportion of water usually being up to about 18% of the total batch.

Where an adhesive is employed, the blending of reactants may be advantageously conducted in a mix muller or chaser, which will form the ingredients into hard pellets up to about an inch in diameter with little or no secondary grinding. These pellets may be charged to the reduction furnace without drying. If no adhesive is employed, the reactants are thoroughly blended before charging to the furnace.

Reducing conditions may be provided within the furnace in the form of a gaseous reducing atmosphere, e.g. hydrogen or carbon monoxide, or sources of such agents including dissociated ammonia, water gas, producer gas and the like. Alternatively, the reducing conditions may be provided by incorporating finely divided carbon within the reactant mixture. Suitable forms of carbon include lamp black, petroleum coke, anthracite fines, carbon black, bone black or graphite. The minimum-carbon levels, being dependent on the particular reactants and reactant proportions, may be estimated from the stoichiometry of the reaction, but optimum levels are best determined by experiment. Carbon levels of about 812% are typical. Even where a gaseous reducing atmosphere is provided, it is sometimes beneficial to incorporate a minor proportion of carbon, particularly in large batches, to insure effective reduction. As is well known in the reduction art, where carbon is the principal reducing agent it is ordinarily desirable to sweep the furnace with a carrier gas, to drive off the volatile reduction products and prevent re-oxidation. Suitable carrier gases include endothermic gases high in nitrogen, exothermic gases, methane, propane, natural gas, or the like. Manufactured gas, producer gas or hydrogen may, of course, also be used if desired.

The reduction is continued until the reducible compounds are substantially completely reduced, i.e. about 93-98% reduced. During reduction, the product particles usually form a lightly sintered sponge, which may readily be subdivided to final particle size specifications by milling. It has been found that a residual oxygen content of 2% or more yields a particularly friable sponge which is broken up more easily than sponges of lower oxygen content. The time required to carry the reduction to this level will vary with the reducing conditions and the particular reactants selected. Ordinarily, reduction is usually substantially complete in from about 30 minutes to two hours. It is undesirable to prolong the reduction unnecessarily, since reduction times longer than about two hours may lead to difiiculty in breaking up the sponge.

After cooling, the product may be g ound in a hammer mill or pulverizer to final particle size specifications, generally to pass 60 or mesh.

The resulting powders may be molded into useful shapes by conventional powder metallurgy techniques, i.e. by compacting at about 1060 tons per square inch and then sintering under non-oxidizing conditions at elevated temperature, preferably at or above the melting point of copper for optimum properties. It should be noted that where blended copper and iron powders are molded in this fashion, it is necessary at high copper content to sinter'below the melting point of copper, with attendant strength disadvantages, in order to avoid loss of copper by blistering. This is caused by agglomeration of the copper-rich masses in such blends'during sintering. It is also important to note that the sintering of premixed copper and iron powders results in an expansion of the compact as a reflection of the alloying process. In the new particulate alloys, on the other hand, any'expansion as a result of alloying occurs during the reduction step and not during the sintering of the compacted particles. The sinterin got these new alloys represents a consolidation of the pre-infiltrated or alloyed particles, with further alloying" occurring mainly at the particle mterfaces. This results in shrinkage of the sintered compact, which, as previously noted, is more desirable.

Sintered parts prepared from the particulate alloys of the described reduction process possess good physical properties even without further treatment. The degree of shrinkage and the resulting strength depend mainly on the copper content, with maximum shrinkage and maximum strength at about 30% copper.

A further important feature of the present invention resides in the discovery of a novel heat-treatment process for the alloy powders, which leads to a striking and unprecedented increase in the density and physical strength of the final sintered compact. This heat treatment represents in effect a densification or pre-shrmkage, reducing the degree of shrinkage in the final smtermg step without, however, leading to the undeslrable expansion effect referred to previously.

The ot-'y transition temperature of iron lies at about 910 C., but in the case of iron containing over 3.5% copper this transition occurs at about 83 5-850 C. It has been found that heat treatment of the new alloy powders is most effective at a temperature between the oc-'y transition temperature of the iron-rich phase and a temperature about 150 C. lower. The best results are obtained by heat treating at a temperature less than 50 C. below the ot-'y transition, preferably at about 825-845 C. Such conditions lead to development of the highest density, strength and hardness, with minimum shrinkage, upon sintering. Properties begin to drop off abruptly from the optimum when the heat-treatment temperature exceeds 845-850 C.

For best results, the powder should be heat treated for at least about 30 minutes before cooling. The maximum time is not critical, and periods up to hours may be used. However, there is no advantage to heat treating for more than 4 hours, and the optimum results are generally achieved in about 1-2 hours.

If the reduced powder subjected to heat treatment contains over 2% oxygen, it is best to heat treat under reducing conditions, so as to further reduce oxygen content below 2% and preferably below 1% during this step. If however, the oxygen content is already 2% or less, an inert atmosphere may be employed if desired.

The powders are discharged from the furnace as loosely sintered masses, which quickly cool and may be reground to particles finer than 60-80 mesh in the same manner as after the primary reduction process.

Heat treatment as described greatly enhances the properties of the alloy powders of this invention. After compacting and sintering, the products exhibit outstanding tensile strength, as may be seen from the appended examples. It should be noted that those alloys containing about 16% copper have tensile strengths above 45,000 p.s.i. or more; 10-40% copper yields.75,000 p.s.i. or more; and 40-50% copper yields tensile strengths above 65,000 p.s.i. By way of comparison, sintered parts made from preblended powders have tensile strengths which level off at 40-45,000 p.s.i., and this is substantially unaffected by prior heat treatment of the powder blends.

In addition, sintering shrinkage is greatly reduced as a result of heat treatment of the new alloys, density is substantially increased, and porosity reduced. Each of these advantages is illustrated quantitatively in the examples. Such sintered properties are within the range of or superior to those of the conventional infiltrated part, yet they are obtained by the rather simple and cheap pressing and sintering process rather than by the more involved and costly infiltrating technique.

A'preliminary insight into the microstructures of the new alloys is provided by their X-ray diffraction patterns. An alloy containing 20% copper displays essentially the same pattern after primary reduction and after heat treatment: both an ot-iron-rich phase and an e-copperrich phase is detected. The diffraction pattern of a 7% copper alloy after heat treatment is substantially similar, except for the expected indication that a lower proportion of the copper-rich phase is present. However, the 7% alloy after primary reduction exhibits a pattern corresponding to a single a-iron-rich phase. In each of these diagrams, the iron peaks are relatively flattened, the copper peaks sharper.

The failure to resolve a second phase by this technique 1S rather surprising, indicating that alloys of copper content below the solubility limit in iron at the reduction temperature (about 8% at 1125 C.) retain the copper 1n extremely fine dispersion after primary reduction. This may be related to the rate of cooling upon removal from the furnace, the temperature dropping to about 490 C. 1n the first minute in the typical case, thereby quickly traversing the range of maximum solubility change. (The solubility of copper in iron at 500 C. is only about 0.25%.) On the other hand, the impression is gained that subsequent heat treatment within the specified temperature range for 30 minutes or more does permit separation of a resolvable copper-rich phase.

A more accurate insight into the microstructures is gamed by microscopic examination of the alloy particles, mounted, polished, and etched with nitric acid to erode copper-rich areas and thereby delineate the phases.

In those alloys containing from about 1 to 10% copper the microstructure is seen to be highly uniform, with the copper content up to about 8% dispersed within the Iron grams in the form of particles less than about 1000A. (0.1 ,u.) in diameter. At 250 power magnification, no clearcut grain boundaries can be seen, and it is necessary to turn to the higher magnification of the electron microscope for further delineation. In FIG. 1 is shown a 7% copper alloy of iron after primary reduction, and FIG. 2 shows the same alloy after heat treatment, both views enlarged about 100,000 diameters. The depressions represent areas where copper was removed by the etching acid, and the fineness of the dispersion is readily apparent. When the fields are surveyed further, it is found that the specimen after reduction displays dispersed copper-rich particles about 350 A. in diameter arranged in clustered bands, with an average distance of about A. between copper particles. The clusters are separated from each other by distances ranging from a little as 500 A. to as great as about 0.75 micron. Between the clusters, copper-rich particles also averaging about 350 A. in diameter are detected, but it is likely that particles smaller than the 50 A. resolution limit are also present. It is likewise possible to detect cracks in the microstructure, about 0.1-0.3 in length by 400-900 A. in width, as well as angular voids 0.1-0.9, in diameter. Upon heat treatment, the cracks are no longer visible, and the clusters now appear in bands or rings about IO tiS in length by 3 i1 in width. The copper particles in these rings are found to average about 400 A. in diameter, with an interparticle spacing of about 150 A. Those copper particles between clusters which are resolved average about A. in diameter, with an interparticle spacing of about 550 A.

Microscopic examination of those alloys of the present invention which contain in excess of 10 and up to about 50% by weight of copper reveals that they contain unusually fine and closely packed iron-rich grains, less than about 35 in their major or largest diameter, with an average separation between adjacent iron grain boundaries of less than about 5g. These iron-rich grains contain a highly uniform dispersion of finely divided copperrich particles.

FIG. 3 illustrates an alloy containing 20% copper, after primary reduction, and FIG. 4 depicts the same alloys after heat treatment, each enlarged about 3600 diameters. In these pictures, the prominent insular areas which occupy most of the field of view are plateau-like iron grains surrounded by copper-rich valleys eroded by the acid. There may be a tendency here for the iron grains to appear to the eye as depressions, but this apparent stereoscopic reversal is an optical illusion which can be attributed to the lighting. It will be noted that in the specimen after primary reduction, the iron grains are irregular in shape, whereas after heat treatment they have become rounded or spheroidized.

At high magnification, cracks are detected in the reduced specimen, about 2500 A. in length and 850 A. in Width. These may account at least in part for the higher shrinkage which occurs upon sintering, and they are absent in the particles after heat treatment.

The following are the average dimensions observed in the 20% copper alloy after primary reduction at 1125 C., as determined by Zeiss counter measurements:

Iron grains: Microns Length 17.50 Width 13.89 Intergranular spacing 1.76

Copper particles within iron grains:

Length 0.0423 Width 0.0371 Interparticle spacing 0.0352

Iron particles in copper-rich areas:

Length 0.0268 Width 0.0216 Interparticle spacing 0.0894

Upon close inspection, the iron grains of FIG. 4 present a much rougher texture than those of FIG. 3, the reason for which is revealed by greater magnification. FIG. 5 represents a portion of the field of view of FIG. 4, enlarged about 17,700 diameters. The most prominent feature of the illustration is an elongated valley or copperrich area separating portions of two adjacent iron grains. The pictured area within those iron grains is pitted by erosion of copper-rich particles through the acid treatment, and it is seen that the copper particles within the iron grains fall into two difiYerent size groups: primary particles having a diameter of about 0.1-0.5u, and secondary particles having a diameter less than about 0.05

This unexpected and unique structure only appears after heat treatment, and it seems likely that the larger primary particles represent agglomeration of the original copper particles in the reduced specimens, resulting from the difference in solubility of copper in iron at the reduction temperature (about 8% at 1125 C.) and at the heattreating temperature (about 3.5% at 835 C.). It may be theorized that the primary copper particles represent the copper in excess of solubility at the heat treating temperature, which agglomerates during such treatment step. It may further be theorized that the smaller secondary particles represent that copper which dissolved in the iron to saturation at the heat-treating temperature and subsequently separated during cooling to room temperature. The fact that these secondary particles are similar in size to the copper particles present within the iron grains after primary reduction lends credence to this hypothesis. Nevertheless, it should be understood that the present invention is not limited by any theory or hypothesis, however plausible.

The following are the average dimensions observed in the 20% copper alloy after heat treatment at 835 C.:

Iron grains: Microns Length 20.09 Width 16.39 Intergranular spacing 1.66

Primary copper particles within iron grains:

Length 0.2713 Width 0.2404 Interparticle spacing 0.2865

Microns The dispersion of more copper within the iron grains in the alloys of the present invention may account for their higher sintered strength relative to conventionally infiltrated alloys of equivalent density, whose copper content would appear to be more concentrated between the grains.

It may be noted here that when the primary reduction is conducted below the melting point of the copper-rich phase, but yet at least C. above the copper sintering temperature (e.g. reduction of a 40% copper alloy at 950 C.), microscopic examination reveals that the iron and copper-rich portions are nevertheless intimately associated, with fusion at the grain boundaries. This is true for the particle after primary reduction and also after heat treatment.

Microscopic examination of the novel alloys of this invention after compacting and sintering has also been conducted, and it is found that the alloys as sintered closely resemble the unsintered particles. The sintering process has merely consolidated the particles into massive form by grain-boundary diffusion. This can be seen by comparing the average iron grain sizes and intergranular distances in the heat-treated powders and the sintered parts which result, e.g. for the 20% copper alloy:

Distance Iron between grain iron width grains 16.39 1. ea 17. a9 1. as 27. 91 s. 33

Iron grain length Heat-treated powder, [1. Sintered part Conventional infiltration Distance Iron Iron between grain grain iron length width grains Sintered part from heat treated powder, [L 16. 28 14. 00 3. 41 Conventional infiltration 40. 01 22. 6G 12. 51

The porosity of sintered iron compacts is ordinarily such that it is necessary to introduce in excess of 10-15% copper for adequate infiltration by conventional technique. Accordingly, for a standard of comparison for the new alloys of low copper content, it is necessary to turn to sintered parts made from blended copper and iron powders. Sintered bars containing 7% copper and prepared from a blend of 100 mesh copper and iron powders, when microscopically examined, exhibit large angular pores and massive copper areas 30,11. and more in diameter. The sintered compact prepared from the new particulate alloy containing 7% copper, on the other hand, exhibits a very fine, uniform, close-packed structure.

The excellent physical properties provided by the new particulate copper-iron alloys can be even further enhanced by various techniques, providing tensile strengths as highas 150,000 p.s.i. For instance, the incorporation .of minor proportions of graphite before'molding and sintering affords increases of from 30,000 to 60,000 p.s.i. in tensile strength. Graphite levels of about 0.5-2% are usually adequate. Re-pressing and re-sintering (coining) operations are also beneficial for increasing density and strength, as are various post treatments, such as quenching, drawing and normalizing, as further illustrated in the examples which follow.

Provision of these examples for illustrative purposes is not intended to restrict the invention, the scope of which is defined by the appended claims.

EXAMPLE 1.7% COPPER ALLOY (A) Reduction Grams Iron mill scale 1247.1 Dried cement copper 77.0 Hydroxyethyl cellulose 5.3 Water 285.0

The iron mill scale of the above formulation is a byproduct of steel blooming or finishing mills, finer than 325 mesh with about 50% coarser than 20 microns. It has an apparent density of 1.8-2.2 grams per cubic centimeter and an analysis as follows:

The cement cop per of the above formulation is a byproduct of mine waste water, finer than 20 microns with about 85% finer than 10 microns. It has an apparent. density of 0.8-1.5 grams per cubic centimeter and an analysis as follows:

- Percent Cu (as Cu, 2.91; as Cu O, 96.72; as CuO, 2.61) 90.80 0 8.03 Zn 0.22 Fe 0.47 SiO 0.03 Other metals 0.26 Soluble nitrates 0.01 Soluble chlorides 0.08

Soluble sulfates 0.10

The ingredients are combined and milled into pellets in amix muller or chaser, which permits intimate admixture with a minimum of grinding action. The resulting pell'ets are charged to a reduction furnace at about 1120- ll35' C. and held atthat temperature in hydrogen or dissociated ammonia-for 45 minutes. After reduction the pellets are removed from'the furnace and broken up, first in a hammer mill to /s inch and smaller, and then in a micropulverizer so that all particles are finer than 80 mesh. The product has an apparent density of 2.3-2.5 .grams per cubic centimeter and an oxygen content of about 1.6% (obtained by reduction in hydrogen at 1050 C. for 30 minutes) or 2.37% (obtained by Leco methodmelting in vacuum at 3500 F.). The hydrogen weight loss reflects only reducible oxygen content.

10 Hematite (Fe O or magnetite (Fe O -FeO) in sufficient quantity to provide the same iron content may be substituted for the iron mill scale in the above formulation. In the same way, pure cuprous oxide may be substituted for the cement copper.

For the reduction step, carbon monoxide may be substituted for hydrogen, or gases rich in carbon monoxide or hydrogen, such as producer gas, may be used.

(B) Heat treatment 150 grams of the reduced powder is charged to the reduction furnace, maintained at 825-845 C. for one hour, and cooled. The powder is discharged from the furnace as a loosely sintered mass and reground to powder finer than mesh in the same manner as after the primary reduction. The annealed powder has an oxygen content of 0.3% (by weight loss in hydrogen) or 1.14% (Leco method).

EXAMPLE 2.-1 AND 2% COPPER ALLOYS Grams Iron mill scale 1314.2 Cupric nitrate trihydrate 37.5 or 76.0 Carboxymethyl cellulose 6.2 Water 300.0

The above formulations are reduced at 1150 C. and heat-treated in the same manner as is described in Example 1. Hematite (Fe O or magnetite (Fe O -FeO) in sufficient quantity to provide the same iron content may be substituted for the iron mill scale.

The cupric nitrate may be replaced by equivalent proportions of cupric oxide and nitric acid, or by an equivalent proportion of cupric acetate.

EXAMPLE 3.-14% COPPER ALLOY WITH 1% NICKEL Grams Iron mill scale n 1153.3 Dried cement copper 154.0 Animal protein glue 6.0 Water 270.0 Nickel nitrate (20.3% Ni) 49.5

This formulation is pelletized, reduced at 1110 C. and heat-treated as described in Example 1. Equivalent quantities of hematite (Fe O and nickelous acetate tetrahydrate may be substituted for the iron mill scale and nickel nitrate. An equivalent proportion of pure cuprous oxide may be substituted for the cement copper.

EXAMPLE 4.20% COPPER ALLOY Grams Iron mill scale 1072 ;Dried cement copper 205.2 Cupric nitrate trihydrate 37.1 Lampblack' .'.....2 105.1 Methyl cellulose 7.9

These ingredients are pelletized, charged to a reduction furnace, and maintained at 1095 C. for 75 minutes while sweeping with a lean endothermic carrier gas (approx.

84% nitrogen, 10% carbon monoxide, 6%v hydrogen).

After reduction, the charge is processed by milling and heat-treating as detailed in Example 1.

A 20% copper alloy containing 1% molybdenum is prepared from the following ingredients by the reduction and heat treatment procedure of Example 1:

Grams Iron mill scale 1072.8 Dried cement copper 220.5 Molybdic oxide 15.0 Ammonia water (26 Be) 34.0 Carboxymethyl cellulose 6.0 Water 275 12 EXAMPLE 6.-BINDER EFFECT 7% Cu Cu With Binder Dry Mix With Binder Dry Mix Tensile strength, p.s.i 39, 600 33, 200 60, 500 51, 000 sintered density, gJcc 5. 96 5. 67 6. 87 6. 54 Elongation, percent 1. 0 0. 5 3. 0 2. 0 Linear shrinkage, percent 1. 81 1 (0.25) 3.68 2. 65 Hardness B 32.3 B 28. 0 B 69. 6 B 51. 2

1 Expansion.

A similar alloy containing 1% tungsten is prepared in the same manner, by substituting 12.6 grams of tungstic anhydride. (W0 for the molybdic oxide in the above formulation. An equivalent cobalt content is provided by substituting 14.1 grams of cobaltic oxide (C0 0 for the molybdic oxide. Hematite (Fe O may also be substituted for the iron mill scale by appropriate adjustment in the quantity added.

EXAMPLE 7.REDUCTION TEMPERATURE EFFECT The procedure of Example 1A is repeated in a series of batches with the single exception that some of these are reduced at 1000 C. instead of 1120-1135 C. Each of the reduced powders is then compacted at 50 t.s.i. sintered in hydrogen at 1120 C. for minutes, and subjected to physical testing, with results as follows:

Reduction temp.

Batch 1 Batch 2 Batch 3 Batch 1 Batch 2 Batch 3 Reduced Powder:

Apparent density, g./cc 2.15 1. 83 1. 73 2. 35 2. 39 2. 44

Flow rate, see/ g 3. 54 40. 0 None 30. 7 29. 3 29. 9

325 Mesh, percent. 42. 2 59. 8 67. 9 32. 8 36. 7 42.8

H; Wgt. loss, percent 2 1. 70 1. 93 2.07 1. 21 1. 22 1.29 Compact, Green density, g./cc 6.40 6. 29 6.33 5. 76 5.67 5. 73 Sintered Compact:

Sintered density, g./cc 6. 31 6. 20 6.09 5. 96 6. 02 6. 04

Tensile strength, p.S.i. 40, 900 32, 200 40, 000 39, 600 40, 100 39, 500

Elongation, percent-.. 1. 3 1. 4 1.0 1.0 1. 1 1. 3

Linear shrinkage, percen 1 (0.90) 1 (0.13) l (0.1 1.81 1. 75 1.82

Hardness B 55. 3 B 50. 7 B 48.0 B 32. 3 B 30. 7 B 34.0

1 Expansion. 1 1,100 C. for 30 minutes.

EXAMPLE 5.PARTICLE SIZE EFFECT The procedure of Example 1A is repeated with iron mill scales of varying particle size. The resulting reduced powders are compacted at 50 tons per square inch, sintered in hydrogen at 1120 C. for 45 minutes, and subjected to physical testing, with results as follows:

EXAMPLE 8 .HEAT-TREATMENT EFFECT A quantity of the reduced 7% copper alloy powder prepared in Eaxmple 1A is divided into a number of 150 gram batches for heat treatment as described in Example 13, but the temperatures and periods of heat treatment are varied as outlined below. Each heat-treated powder is compacted and sintered as described in Example 7, and tested with results as follows:

1 hour 2 hours 3 hours Heat-treated at 900 C.:

Apparent powder density, g./cc 2. 39 2. 41 2. 39 Sintered density, g./cc .33 6. 34 6. 29 Tensile strength, p.s.i 42, 300 41, 600 39, 100 Elongation, percent 1. 1 1. 1 1. 0 Linear shrinkage, percent 0. 83 0. 0. 71 Hardness B 42. 4 B 43. 1 B 40. 7

Heat-treated at 850 C.:

Apparent powder density, g /ee 2. 44 2. 45 2. 46 Sintered density, gJcc- 1 6. 52 6. 5'.) 6. 50 Tensile strength, p.s 47, 800 49, 000 40, 900 Elongation, percent .2. 0 2. 0 1. 9

The apparent powder densities range from 2.44 to 2.58 g./ cc. and the sintered densities from 6.52 to 6.84 g./cc.,

1 hour 2 hours 3 hours Linear shrinkage, percent 0.80 0. 62 0. 54 ardness B 52.7 B 53.1 B 49.2 for thls Senes of tests Heatitreatedtat; 835; t 2 58 2 56 2 50 pparen pow er ensi y g. cc Sintered density, g./cc 6. 83 6. 89 6. 70 5 EXAMPLE 10.HEAT-TREATMENT EFFECT giansiletstrength, ps.i 63, 200 65, 58,

on a ion ercen .1 meg, shrnfia e, percent 7 Q62 053 The procedure of Examples 8 and 9 is repeated, this Hardness B B B 5942 time subjecting a 7% copper alloy powder to heat treat- Heat-treated at 800 0.: o

. gppareitpowtder d/ensity,g./cc 2. 52 g, 51 $7 ment at 835 C. for periods of 30, 45 and 60 minutes,

intere ensi y, g. cc .80 .80 8 Tensile strength, p.s.i.. 58,300 00,000 51,000 10 Wlth the followmg results Elongation, percent 2.9 3.0 2.9 Linear shrinkage, percent 0. 77 0.70 0. 55 Hardness B 61.0 B 61. 9 B 58. 8 Heat-treated at 700 6.: Heat treatment for Apparent powder density, g./cc 2. 36 2. 48 2. 47 sintelrled densitly, g./cc. 506683 6. 88 4 6. 1111115- 60 1111115 t 2 5, 5 fifi hioifi fiergefiifu 2, 0 2,1 1, Cp p green e y,g-/cc 5. 91 6.40 6. 65 Linear shrinkage, percent 0.71 0. 09 0. 51 smtered COmPaCtI Hardness B 60 1 B 1 2 B 5g 1 11111081 shrinkage, percent 1. 21 0. 97 0. 79 Heabtmated at C Tensile strength, p.s.i 56, 700 58, 100 63, 300

Apparent powder density, g./cc 2. 25 2. 23 2. 21 Sintered density, g./cc 6. 30 6.30 6. 21 Tensile strength, p.s. 46, 200 44, 300 38, 800 20 il g ign gercent "t 1 1 0. 3 EXAMPLE l1.-REDUCTION TEMPERAI URE AND H e t r?iie ssf i jffif j: n 542 n 50.2 B 49.1 HEAT-TREATMENT EFFECTS HeaKtreatedtat l 2 15 2 n aren pow er ens1 y .00 gg density 609 610 M2 Samples of each of the reduced powders prepared in Tensile strength, p.s.i-. 34,500 32,000 30,000 25 Example 7 are heat-treated for one hour at 835 C. The ggggf gfig gj g 3 3 3 heat-treated powders are then compacted and sintered Hardness 1338.0 B 33.2 B 34 5 as before, and Subjected to phySlCal testing, w1th results as follows:

Reduction temp.

Batch 1 Batch 2 Batch 3 Batch 1 Batch 2 Batch 3 Heat-Treated Powder:

Apparent density, g./ec 2. 44 2. 12 2.10 2. 69 2. 58 2. 57 Flow rate, sec g 33. 3 38. 6 None 25. 3 25. 7 25.0 325 mesh, percent 40. 5 53. 9 60. 0 34.1 40. 2 45. 0 H2 wgt. loss, percent 0.51 0.52 0.67 0.30 0.22 0.20 Compact, green density, g./cc 6. 48 6.37 6.30 6. 65 6.73 0. 66 Sintered Compact:

sintered density, g./c c 6. 68 6. .52 6. 83 6. 80 6. 76 ITBHSIIB strength, p.s.i.. 53,500 49,000 47, 500 63,300 61,100 62,600 Elongation, percent 1. 9 2. 0 1. 8 3.1 3. 2 2. 9 Linear shrinkage, percent- 1. 49 1. 31 1. 53 0. 79 0. 77 0.64 Hardness B 60.9 B 59.4 B 63.0 B 63 3 B 58.9 B 60.4

1 1,100 O. for 30 minutes.

EXAMPLE 9.--HEAT-TREATMENT EFFECT EXAMPLE 12.EFFECT OF OTHER METALS The procedure of Eaxmple 8 is repeated, this time confining each heat treatment to a -minute period while more closely exploring the temperature range between 810 and 850 C., with temperatures controlled 50 to :2 C. Six testspecimens are molded from each batch, with average test results as follows.

In accordance with the procedures of Examples 3 and 4, 7% copper alloy powders are prepared, each containing 1% cobalt, nickel or molybdenum. These are compacted and sintered as in the previous examples, in both the as-reduced and as-heat-treated forms, with results as follows:

Tensile sintered Linear strength, Elongation, density, shrinkage,

p.s.i. percent g./ce. percent Hardness 1% cobalt:

Reduced 31, 800 1. 9 5. 97 1. 43 B 29. 1 Heat-treated 55, 200 4. 0 6. 79 0. 72 B 59. 7 1% nickel:

Reduced 32,400 1. 9 5. 94 1. 54 B 33. 0 Heat-treated 65, 100 2. 3 6. 77 0. 90 B 70. 9 1% molybdenum:

Redu ed 35,300 1.3 5. 00 1.73 B 28.1 Heat-treated 65, 500 1. 9 6. 90 0. 69 B 74. 5

Tensile Linear strength, Elong., shrinkage,

p.s.i. percent percent Hardness 2 O 0 73 B 60 2 EXAMPLE l3.USE OF ELEMENTAL COPPER 3:8 813 323-3 The procedure of Example 1 is repeated, this time sub- 1 1 B stituting for the cement copper an equivalent proportion 2 8-32 figs- (70 grams) of atomized copper powder finer than 100 2 B5217 mesh. The reduction is conducted at 1000 C. for 45 minutes, with heat treatment at 835 C. for one hour.

After compacting and sintering as before, the reduced and heat-treated powders provide the following properties:

EXAMPLE 15. EFFECT OF COMPACTING PRESSURE Heat- Reduced treated A 7% copper alloy powder, prepared by reduction and Tensilemngthyp si 52,400 65,800 e treatment s descrlbed 111 E p l combined Elongation, percent 0.8 1.0 With 0.75% stear1c acid, compacted at various pressures,

Sintered density g./ce 6.39 6. 70 a Linear Shrinkage, percen 0'85 Q09 and each compact 1s sintered at 1120 C. for 45 minutes Hardness 1361.3 1368.4 in hydrogen. The physical properties, as a function of compacting pressure, are found to be as follows:

Compacting pressure t.s.i. t.s.i. 50 t.s.i. 60 t.s.i.

Compact:

Green density, g./cc 5. 94 6. 29 6. 65 6. 76 4 Green strength, p.s.i 2, 058 2, 501 3, 591 4, 829 Smtered Compact:

Tensile strength, p.s.i 43, 400 52, 90 63,300 75, 200 Elongation, percent 2. 9 3.1 3.0 1. 8 Sintered density, g./cc 6. 09 6. 46 6. 83 6. 95 Linear shrinkage, percent. 0. 83 0.80 0. 79 0. 75 Hardness B 46. 0 B 61.3 B 63.3 B 69.2

EXAMPLE 14.OTHER COPPER SOURCES The procedure of Example 1 is repeated, substituting for the cement copper equivalent quantities in proportion to their copper content of various other copper sources. After reduction at 1125 C. for minutes and heat treatment EXAMPLE 16.GRAPHITE EFFECT WITH VARYING COMPACTING PRESSURES 30 Example 15 is repeated, this time incorporating 1% graphite in each heat-treated powder prior to compacting and sintering, with results as follows:

Compacting pressure 30 t.s.i. 40 t.s.i. t.s.i. 60 t.s.i.

Compact, green density, g./ec 5. 96 6. 33 6. 68 6. 78 Sintered Compact:

sintered density, g./cc 6. 07 6. 43 6. 80 6. 91 Tensile strength, p.s.i 72, 700 91, 500 109, 100 137, 000 Elongation, percent... 1. 9 2.0 2. 0 0.9 Linear shrinkage, percent. 0. 86 0. 84 0.81 0.80 Hardness B 72.3 B 83. 2 B 86.9 B 100. 2

at 825845 C. for one hour, the powders are pressed and sintered as before to yield the following properties:

Sintered Tensile density, strength, Copper Source glee. p.s.i.

Cupric oxide (83.02% Cu) 6. 81 50, 100 Copper mill scale (88.64% Cu) 6. 80 51, 200 Cement Copper No. 1 (90.80% Cu 6.85 63,300 Cement Copper No. 2 (93.04% Cu) 6.88 68, 000 Reduced copper powder (99.52% Cu) 6. 75 69, 200

EXAMPLE 17.COINING EFFECT The procedures of Examples 15 and 16 are repeated,

this time subjecting the final sintered piece to re-pressing and re-sintering under the same conditions used in the first pressing-sintering cycle. The properties achieved are summarized below:

Compacting pressure 50 t.s.i. 50 t.s.i. t.s.i. 60 t.s.i.

Additive 1% graphite 1% graphite Compact, green density, g./cc 6. 6. 63 6. 76 6. 74 Sintered Compact:

sintered density, g./ee 6. 83 6. 79 6. 92 6. 90 6. S6 6. 81 7. 13 7. 05 6. 93 6. 85 7. 20 7. 11 77,200 111, 800 82, 900 123, 600 Final elongation, percen 3. 0 2.0 5. 1 3.0 Final Hardness B 77. 8 B 94. 2 B 85. 3 B 99. 7 Linear shrinkage, pere After 1st sintering 0. 0. 91 0. 0. 78 After 2nd compaction 0. 08 0. 01 0. 06 0. 01 After 2nd sintcring 0. 07 0. 01 O. 05 0. 0]

17 EXAMPLE 18.-GIU\PHITE EFFECT WITH VARYING COPPER CONTENT A series of ferrous allow powders of varying copper content are prepared by the procedures of Examples 1 and 2, with reduction at 1125 C. for 45 minutes followed by heat treatment at 835 C. for one hour in-hydrogen. Each powder is combined with 1% graphite. After press- Perce nt copper:

BBBBBBBBBBBBBB rrrizaaaeasae 99 00 80 00980 LL LLILZZZQMKQM LL1LL1LLLLLLL 050 C. for 30 minutes; sintered at 1,120 0. for 10 minutes.

0. for minutes; sintered at 1,120" O. for 10 minutes.

ing at 50 t.s.i. and sintering at 1120 C. forj minutes 25 in hydrogen, physical properties are as follows:

Copper content 4% Cu 7% Cu 14% Cu 20% Cu EXAMPLE 2l.-EFFECT OF COPPER CONTENT IN HEAT-TREATED POWDERS Reduced powders prepared as described in Example 20 are heat-treated at 835 C. for 60 minutes in hydrogen, before compacting at 50 t.s.i. and sintering at 1120 C.

Copper content 14% Cu 20% Cu 2 after sintering, then furnace-cooled to quenched from this temperature in for 45 minutes in hydrogen. The effect of the heat treatment on physical properties is summarized in the table below:

Sintered Tensile Linear density, Percent X10- Elongation, shrinkage, Percent O g./cc. porosity p.s.i. percent percent Hardness 1 As indicated by percent weight loss in hydrogen at 1,100 O. for 30 minutes. 1 Reduced at 1,

a Reduced at 950 4 Reduced at 950 C. for 30 minutes; sintered at 1,095 C. for 10 minutes.

t Linear shrinkage as aged, percent.

With 1% Graphite:

""tiIiir'ee'rit'j-..... Hardness..,

,000 C. for minutes ydrogen ior 10-minute soak d finally aged at 260 C. for one hour in air.

Percent copper:

g./cc Tensile strength, p.s.i

.lcc.- d tensile strength, p.s.i

./cc Aged tensile strength, p.s.i Elongation, p'ercent .IN REDUCED POWDERS A series of ferrous alloy powders of varying copper Sintered density Elongation, percent Linear shrinkage, percent. Hardness-.

Sintered compacts prepared as in Example 18 are subted to various additional treatments to further enhance 40 physical properties, with results as follows Aged density, g

Age

Elongation, percen Aged density, g

Linear shrinkage as age Quenched in water from sintering and aged at 485 Olin hydrogen for 30 minutes.

EXAMPLE 20.EFFECT OF COPPER CONTENT Compact, green density, g./cc.--- Sintered Compact:

EXAMPLE l9.POST-SINTERING TREATMENTS jec Without Graphite:

l 1 Normalized in nitrogen at 1 370 0., held M815 C. in h water, an

0 0 0 00 L1 LL2 2 L 2 1 As indicated by percent weight loss in hydrogen at 1,100 O. for 30 minutes.

2 Reduced at 1,050 O. for 30 minutes; Sintered at 1,120 C. for 10 minutes. I Reduced at 950 C. for 30 minutes; sintered at 1,120 O. for 10 minutes. 4 Reduced at 950 C. for 30 minutes; sintered at 1,0 C. for 10 minutes.

- 19 20 EXAMPLE 22.COPPER-IRON POWDER BLENDS the iron powder has in excess of about 10 and up to bout 40% by weight of copper said particles providing For purposes of comparlson, a series of copper alloys a is prepared by prior art procedures, by blending approa tensll? f of i leasts about 7500O poqnds g priate proportions of 100 mesh reduced elemental copper square Inc upon pressmg at tons per square Inch an sintering at 1120 C. in hydrogen.

and iron powders for 30 minutes, compacting at 50 t.s.i. 5. A Particulate alloy as claimed in claim 1 wherein and sintering at 1120 C. for 45 minutes in hydrogen.

The propertles Obtained are Summanzed below: the iron powder has in excess of about 40 and up to about Sintered Linear Percent density, Percent Tensile Elongation, shrinkage, copper g./cc. porosity X- ,p.s.i. percent percent Hardness 6. 28 20. 4 35. 6 4. 9 50.01) B 25. 5 6 3O 20. 7 0 2. 9 0. 92) B 21. 4 6. 37 20.7 42 1 1.6 (1.88) B 39.3 6. 40 20. 2 45 2 2. 3 (2. 04) B 20. 2 6 49 19.8 44 3 2.3 (2.24) B 19. 7 7 02 16.6 26 6 4.5 (0.99) B 3.2

1 All samples expand on sintering. 2 Sintered at 1,000 C. for 30 minutes.

Heat treatment of the powder blends by the procedure 50% by weight of copper, Said particles providing a of Example 21 prior to compacting has no significant tensile strength of at least about 65,000 pounds per square eifect on the results. inch upon pressing at 50 tons per square inch and sintering at 1095 C. in hydrogen. EXAMPLE 23 IMPACT STRENGTH 25 6. A particulate alloy as claimed in claim 1 wherein The impact strengths of the novel alloys of Example 21 said copper-rich particles are less than about 1,000 A. in are compared with the values for conventional alloys diameter. prepared from blended copper-iron powders as in Ex- 7. An alloy as claimed in claim 6 having a particle ample 22, and with iron compacts infiltrated with copper size finer than about 60 mesh. in the conventional manner, with results as follows: 8. The alloy of claim 1 wherein said copper-rich parti- Impact Strength, ft./lb.

What is claimed is: 45 cles comprise primary particles having an average diame- 1. An alloy in powder form consisting essentially of ter between about 0.1 and 0.5 micron and secondary pariron and 150% by weight of copper characterized by ticles having an average diameter less than about 0.05 iron-rich phase having a highly uniform dispersion of micron. sub-micron copper-rich particles therein, and such that 9. The alloy of claim 8 having a copper content of for copper contents in excess of 10% the micro-structure 50 about 4%. is characterized by iron grains whose average particle 10. The alloy of claim 8 having a copper content of size is less than about 35 microns. about 12%.

2. A particulate alloy as claimed in claim 1 wherein 11. The alloy of claim 8 having a copper content of the iron powder has from about 1 up to about 6% by about 20%. Weight of copper, said particles providing a tensile References Cited strength of at least about 45,000 pounds per square inch UNITED STATES PATENTS upon pressing at 50 tons per square inch and sintering at 1120 C i h d 2,042,635 6/1936 Schellens 75125 XR 3. A particulate alloy as claimed in claim 1 wherein 2,754,194 7/1956 Gr h m 75-55 the iron powder has in excess of about 6 a d up t b t 3,049,421 8/ 1962 en 55 10% by weight of copper, said particles providing a ten- 3,085,376 963 Alexander.

sile strength of at least about 60,000 pounds per square inch upon pressing at 50 tons per square inch and sinter- HYLAND BIZOT Pnmary Exammel ing at 1120 C. in hydrogen. U.S. Cl. X.R,

4. A particulate alloy as claimed in claim 1 wherein g9 1 91,g

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