Mechanical Alloying And Interdispersion Cold Bonding Agents Therefor

Abstract

The invention involves mechanical alloying of powder wherein the formation of composite powder particles characteristic of mechanical alloying process is facilitated through the use of special interdispersion cold bonding agents such as a halide, e.g., a metal halide.

Description

The present invention relates to powder metallurgy, and is particularly directed to the "mechanical alloying" of powder.

As is known, the recently introduced concept of "mechanical alloying", described in U.S. Pat. No. 3,591,362 (incorporated herein by reference), involves a dry, intensive milling of powders in high energy machines, such as the Szegvari attritor. During this unique process, initial constituent powders are repeatedly fragmented and cold bonded by the continuous impacting action of attriting elements, usually metal balls, for a period such that composite product powder particles of substantial saturation hardness are formed, the composition of which correspond to the percentages of the respective constituents in the original charge. The constituent powders become most intimately interdispersed at close interparticle spacings, the composite particles being exceptionally dense and homogeneous, and characterized by cohesive internal structures.

For the most part "mechanical alloying" (often herein "MA") has been conducted in the presence of an atmosphere comprised of an oxygen-nitrogen mixture. However, such an environment can serve to introduce various problems. If present to the excess, comminution of the powders dominates to such an extent as to virtually preclude the critically necessary cold bonding. Moreover, oxygen, for example, is retained in the composite product particles formed. As a consequence and depending upon the alloy composition to be produced, this can subvert certain metallurgical properties, tensile and creep ductility of nickel-base superalloys being illustrative.

On the other hand, in the absence of such atmospheres the powders either fixedly adhere to the attriting elements and interior attritor surfaces (with subsequent buildup) or, depending upon the composition of the attriting elements and powder charge, cold bond in such manner as to form undesirably large particles. Whether by reason of the thickness of the adherent powder or of the excessive particle size, such powder cannot be satisfactorily deformed by the energy available in subsequent collision events. Processing therefore effectively ceases. Indeed, a point may be reached where there is such an overload on the attritor as to bring about a self induced shut-down. This, quite naturally, leads to considerable loss occasioned by down-time. In any case, powder recovery is extremely poor.

It is evident from the foregoing that an indispensibly necessary mechanical alloying "control balance" must be achieved, this "control balance" being defined as one in which the intimate interdispersion of constituent powders continues by means of the establishment of steady state processing (fragmentation and cold bonding reaching a virtual equilibrium), but without (i) the formation of appreciable quantities of detrimentally large composite product particles, or (ii) the deleterious adherence of powders to the attriting (milling) elements or other attritor surfaces, and (iii) without incurring serious impairment of the mechanical, physical or other properties of the alloy composition being produced.

It has now been discovered that the above drawbacks can be considerably minimized, if not virtually eliminated, that the desired "control balance" can be attained, through incorporating an effective percentage of at least one interdispersion, cold-bonding control agent (ICBCA), as herein detailed.

Generally speaking, and in accordance herewith, it has been found that an inorganic agent or gas capable of reacting with or of being adsorbed on a plurality of the powder (particle) surfaces of an initial powder charge and which is capable of residing thereon in reacted or adsorbed form during at least a significant part of the "mechanically alloying" process, is effective in achieving the aforedescribed "control balance." It has been further found that but a small quantity of such materials (ICBCAs) is required, though this is somewhat dependent upon the given conditions used in producing the desired mechanically alloyed composite product powder particles. But it is worthy of note that as little as 0.05 percent of certain ICBCAs (based upon the weight of the powder charge) has been found satisfactory.

In carrying the invention into practice it is most advantageous that the ICBCA be sublimable or decomposable, the sublimation or decomposition temperature exceeding the operating temperature of the attritor mill (or equivalent functioning high energy machine such as the planetary or vibratory ball mills) but preferably not exceeding about 2,000.degree. F. Halides, including the metal halides, are deemed quite advantageous, small amounts of, for example, nickelous chloride and bromide having given excellent results.

By virtue of being sublimable or decomposable the interdispersion cold bonding agent can be appreciably removed during subsequent heat treatment of the mechanically alloyed composite product powder particles. As is known, the composite product powder particles produced by "MA" are hot consolidated, temperatures on the order of 1,600.degree. to 2,000.degree. F. being commonly used. Thus, an ICBCA with a sublimation or decomposition temperature below about 2,000.degree. F., and advantageously below 1,600.degree. F., lends itself to this treatment. This coupled with the fact that only a small amount of an ICBCA is required as a matter of first instance indicates that no particular problem need be experienced in achieving the necessary "control balance."

It should be mentioned, however, that not all of the ICBCA can be removed and this does focus attention on a major difference between the subject invention and conventional ball milling in which surfactants, lubricants and other grinding aids are used for various purposes, mainly for powder comminution. Generally, the latter are virtually completely removed from the powder by expedients such as leaching or burning off. In contrast, due to the necessary intimate interdispersion of constituent powders which occurs by reason of "mechanical alloying," removal techniques affecting only the composite particle powder surfaces are incapable of extricating all the ICBCA since an amount of it is occluded in interdispersed fashion.

In addition to the specific halides above mentioned, the following sublimable, interdispersion, cold bonding control halides can be used: aluminum chloride; nickelous iodide; cobaltous and cobaltic chloride; vanadium trifluoride; chromic chloride, zirconium tetrachloride, tetrabromide, tetraiodide and tetrafluoride; titanium trichloride; hafnium tetrachloride; hafnium tetrabromide; niobium oxychloride; cuprous fluoride; the trifluorides of aluminum, chromium and rhodium; ammonium bromide and iodide; rhodium trichloride; etc. Decomposable halide ICBCAs include cuprous chloride; ferrous chloride; iridium di and trichloride; palladium chloride; molybdenum di and trichloride; titanium trichloride and titanium dibromide; zirconium di and tribromide; iridium bromide and the iridium di and tribromides; ferric bromide; palladium fluoride; manganese di-iodide; palladium fluoride; palladium di-iodide; and the iodides of copper (cupric), rubidium, strontium and samarium. This list of halides is not intended to be exhaustive.

Apart from halides, appropriate nitrides, carbonates, nitrates, nitrites, chlorates, sulfates and borates, etc., can be utilized, including the nitrides of copper (Cu.sub.3 N), iron (Fe.sub.2 N) and chromium (CrN); the carbonates of magnesium, calcium, cesium, and nickel as well as cupric carbonate and ammonium carbonate; ammonium nitrate and nitrite; etc. Gases such as chlorine, bromine, iodine, fluorine and HC1, HBr, HI and HF also can be used.

The amount of an ICBCA employed will be largely influenced, inter alia, by the alloy composition to be produced, milling time, ball-to-powder ration, and the nature of the attriting elements, particularly the latter. Hardened steels, stainless steels, tungsten carbide, nickel and other metals as well as cermets may be used as the attriting media; however, considerably less ICBCA will usually be necessary in conjunction with the harder attriting elements such as 52100 steel as opposed to, say, nickel, The longer milling periods may require a slightly higher percentage of ICBCA than otherwise. Generally, not more than 2 or 3 percent of an effective ICBCA component need be employed, a range of 0.1 to 0.5 percent and up to 2 percent being deemed quite satisfactory. Excessive amounts can be detrimental. In terms of a metal halide, for example, a range of about 0.05 to 0.5 percent of halide as metal halide is of advantage, the halide serving as the ICBCA.

Due to the high energy milling of mechanical alloying, a part of the attriting composition may wear during processing and become a part of the composite product particles. This can be beneficial but if undesirable, recourse should be had to a more appropriate attriting composition.

The following illustrative data are given.

EXAMPLE I

NiC1.sub.2 and NiBr.sub.2 were used as ICBCAs to determine particle size results and ICBCA retention in processing commercial nickel 123 powder. 8 kg batches of the nickel powder were processed in a 4-gallon attritor for 5 hours at an impeller speed of 250 rpm using 3/8 inch diameter carbonyl nickel balls at a ball-to-powder ratio of about 11.4 to 1. Oxygen, about 0.05 percent of the charge weight, was added as air during processing. Nitrogen was also added and served to maintain the oxygen partial pressure at about 1 percent of the weight of gas in the attritor.

The results of a sieve analysis to determine size distribution of the processed powders are given in FIGS. 1 and 2. It is evident that a very fine particle size distribution could be attained with both halides, approximately 90 percent of the processed powder being finer than about 105 microns in diameter at a halide content of 0.5 percent. The curves reflect that a "control balance" could be achieved.

The attrited powders were then placed in metal steel cans (31/2 inch diam.) and evacuated at 750.degree. F. to 20 hours. The cans were sealed, heated for 1 hour at 1,800.degree. F. and extruded thereat to 1 inch diameter rods.

Chemical analyses were made to determine retained chlorine and bromine content of the extruded rods, the results appearing below.

______________________________________ Chlorine Bromine Added Retained Added Retained % % % % ______________________________________ 0.02 0.012 0.02 0.021 0.05 0.018 0.08 0.031 0.10 0.039 0.41 0.022 0.50 0.37 ______________________________________

If the extrusion treatment had been carried out at a higher temperature, say 2,00.degree. F., it is considered that a greater amount of halide would have been removed. It is to advantage that the sublimation (or decomposition) temperature be at least 200.degree. to 300.degree. F. below the temperature of hot consolidation.

EXAMPLE II

The superalloy known as IN-792 (approximately 12.7% Cr, 9% Co, 2%Mo, 3.9%W 3.9%, Ta, 4.2%Ti, 3.2%A1, 0.21%C, balance Ni) was mechanically alloyed in a 1-gallon attritor at 340 rpm for 20 hours under argon, using 16 kg of +6.3 mm nickel pellets as the attriting media, the ball-to-power ratio being 16:1. Several runs were made using different percentages of Cl and NiCl.sub.2. The powder recovery (draining was for 1 hour) was as follows: ICBCA Powder Recovery ______________________________________ None 12.8% 0.05% Cl 25.6% 0.2% Cl 85.1% 0.5% Cl 102.0% ______________________________________

In this instance the 0.05 percent Cl addition was rather inadequate. On the other hand, 0.5 percent was a little high, the processed powders being too fine accompanied by excessive wear of the processing media. The 0.2 percent chlorine batch gave an 85 percent recovery within the experimental draining period. From a commercial production basis, if the recovery is virtually 100 percent for a practical draining period, this quantity, 0.2 percent, of Cl.sub.2 will be about optimum. Should the recovery be below 100 percent for the same draining period, a slightly higher amount of Cl.sub.2, e.g., 0.25 percent, would be in order. This is not to suggest that the 0.2 percent chloride was insufficient within the purview of the invention. Indeed, the recovery of the 0.05 percent Cl run would be markedly improved using steel attriting elements and/or a higher rate of energy input. This is reflected in Example III.

EXAMPLE III

Composite product powder particles of IN-792 were also produced using various halide ICBCAs and either nickel or steel attriting elements. Powder blends were used, each being comprised of carbonyl nickel powder (99.1 percent nickel approximately 4 microns in size), 0.15 percent Asbury flake graphite to raise the carbon content to nominal and a low oxygen omnibus master alloy (-100 mesh of 30 percent Ni, Cr, Mo, Co, A1, Ti, W, Ta, B, Zr and C) prepared by vacuum induction melting and grinding in cold nitrogen. Each run consisted of 5 grams of the blended powder plus the particular ICBCA used as given in Table II.

A Spex mill was employed in each case, the respective runs being conducted for 30 minutes under argon. The Spex mill jar was cooled prior to opening, emptied and the balls replaced in the jar and processed for an additional 30 seconds in air to remove any loosely adherent powder. The total amount of drained powder was weighed to ascertain the percentage of powder recovered. An oxygen analysis was also made and retained ICBCA was determined. Runs Nos. 1 and 2 are included for purposes of comparison.

TABLE III __________________________________________________________________________ Attriting Powder Oxygen Run ICBCA Element Recovery Analysis ICBCA No. (%) (%) Retained __________________________________________________________________________ 1 None Nickel(100 gm) 32 0.30 -- 2 None Steel (100 gm) 57 0.27 -- 3 0.05% Cl Steel (100 gm) 83 0.20 0.023% Cl as NiCl.sub.2 4 0.1% Cl Steel (100 gm) 86 0.33 0.072% Cl as NiCl.sub.2 5 0.25% Br Steel (100 gm) 86 0.20 0.20% Br as NiBr.sub.2 6 0.1% F Steel (100 gm) 88 0.24 0.008% F as NaF __________________________________________________________________________

The low recovery of Run No. 1 reflects the detrimental adherence of the IN-792 powder to the milling elements and to the interior surfaces of the mill. This was reduced somewhat by using the harder steel impacting elements in Run No. 2.

In above describing the subject invention, reference has been made to the well-known commercial alloy IN-792. However, the invention is obviously not restricted to this particular composition, since it can be utilized in mechanical alloying whatever be the desired composition. It is particularly applicable to the production of superalloys including those containing up to 65 percent, e.g., up to 25 or 35 percent, chromium; up to 30 percent, e.g., 5 to 25 percent, cobalt; up to 10 percent, e.g., 1 to 9 percent, aluminum and up to 8 percent, e.g., 1 to 7 percent, titanium; including those alloys containing 4 or 5 percent or more of aluminum plus titanium; up to 30 percent, e.g., 1 to 8 percent, molybdenum; up to 25 percent, e.g., 2 to 20 percent, tungsten; up to 10 percent columbium; up to 10 percent tantalum; up to 7 percent zirconium, up to 0.5 percent boron; up to 5 percent hafnium; up to 2 percent vanadium; up to 6 percent copper; up to 5 percent manganese; up to 70 percent iron; up to 4 percent silicon, and the balance essentially nickel. Cobalt-base alloys of similar composition can be treated. Among the specific superalloys might be listed IN-738; Rene alloys 41 and 95, Alloys 500, 700, 713 and 718, Waspaloy, Astroloy, Mar-M alloys 200 and 246, A-286, B-1900, etc. The superalloys and other contemplated alloys can also contain up to, say, 10 percent by volume of a refractory dispersoid material including the oxides, carbides, nitrides and borides. Such refractory dispersoids can be of various elements including yttrium, lanthanum, thorium, zirconium, hafnium, titanium, silicon, aluminum, cerium, uranium, magnesium, calcium, beryllium and the like. As a practical matter, only a very small amount of such dispersoids need be employed, e.g., up to 2 percent by volume. Other base alloys such as titanium and copper can be processed as well as refractory alloys such as SU-16, TZM, Zircaloy, etc.

Finally, it will be understood that modifications and variations of the invention may be resorted to without departing from the spirit and scope thereof as those skilled in the art will readily understand. Such are considered to be within the purview and scope of the invention and appended claims.

Claims

We claim:

1. In the process of producing mechanically alloyed composite product powder particles, the improvement which comprises conducting the mechanical alloying operation in the presence of an inorganic interdispersion cold bonding agent (ICBCA) formed of a halide, the halide being in contact with the powder particles to be mechanically alloyed and being present in an amount effective to provide the necessary control balance during the course of the operation with the upper limit being about 3% by weight of the powder charge, the control balance being such that an intimate interdispersion of constituent powders is achieved without either the formation of an appreciable amount of detrimentally large composite particles or the deleterious adherence of powders to the milling elements or mill interior surfaces and without incurring serious impairment of the mechanical properties of the composition to be produced.

2. A process as set forth in claim 1 in which the halide is from the group consisting of HCl, HBr, HI and HF.

3. A process as set forth in claim 1 in which the halide is a gas from the group consisting of chlorine, bromine, iodine and fluorine.

4. In the process of producing mechanically alloyed composite product powder particles, the improvement which comprises conducting the mechanical alloying operation in the presence of an inorganic interdispersion cold bonding agent (ICBCA) formed of a metal halide, the metal halide being in contact with the powder particles to be mechanically alloyed and being present in an amount effective to provide the necessary control balance during the course of the operation with the upper limit being about 3 percent by weight of the powder charge, the control balance being such that an intimate interdispersion of constituent powders is achieved without either the formation of an appreciable amount of detrimentally large composite particles or the deleterious adherence of powders to the milling elements or mill interior surfaces and without incurring serious impairment of the mechanical properties of the composition to be produced.

5. A process as set forth in claim 4, in which the halide is a nickel halide selected from the group consisting of nickelous chloride, bromide and fluoride.