CA1292630C

CA1292630C - Microcrystalline alloys prepared from solid state reaction amorphous or disordered metal alloy powders

Info

Publication number: CA1292630C
Application number: CA000523435A
Authority: CA
Inventors: Richard S. Henderson; Michael A. Tenhover; Robert K. Grasselli
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1985-12-31
Filing date: 1986-11-20
Publication date: 1991-12-03
Anticipated expiration: 2008-12-03
Also published as: EP0229478A3; JPS62170401A; IN165517B; AU6676986A; EP0229478A2; BR8606422A

Abstract

MICROCRYSTALLINE ALLOYS PREPARED FROM SOLID STATE
REACTION AMORPHOUS OR DISORDERED METAL ALLOY POWDERS

ABSTRACT

Microcrystalline alloys are synthesized by heat-treating amorphous or disordered metal alloy powder precursors which have been prepared under solid state reaction conditions. The resultant microcrystalline alloys retain the same wide range of compositions present in the amorphous metal alloy powders. These microcrystalline alloys can be formed into solid shapes prior or subsequent to microcrystallization.

Description

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1 (SEM-P-7454) MICROCRYSTALLINE ALLOYS PREPARED FROM SOLID STATE
REACTION AMORPHOUS OR DISORDERED METAL ALLOY POWDERS

FIELD OF THE INVENTION

This invention relates to the preparation of microcrystalline alloys from amorphous or disordered metal alloy powder precursors. Nore specifically, this invention relates to the synthesis of microcrystalline alloys from amorphous or disordered metal alloy powders prepared by the interdiffusion of intimately mixed precursor materials during solid state reaction processes and novel microcrystalline compositions obtained therefrom.

~ACXGROUND OF THE INVENTION

Microcrystalline alloys have become of interest in the area of structural and engineered materials due to their mechanical, physical, wear and corrosion resistant properties. These alloys are characterized by many random nucleation sites, each havinq separate cry~tallinity, but whose growth has been inhibited, due to ~he growth of adjacent nucleation sites. This is different from true crystalline materials, which result from the continued growth of one nucleation site, forming a longer range, continuous ordered structure. The fine grained structure resulting from the numerous small nucleation sites is responsible for the impro~ed mechanlcal and wear resistant properties of mlcrocry~talline alloys, compared to polycrystalline materials. Microcrystalline alloys may possess high tensile strength, high thermal &tability, and high ductility depending on the prevalent characteristics of the elemental components o~ the individual microcrystalline alloy. These materials are of special .~ ~.~ .

1;2~1Z63~

l(a) interest for use as tool steel alloys, such as cutting tools, dies, and other s;milar metal products, which require high strength properties, as well as high temperature performance and oxidation resistance.

3~

2 (SEM-P-7454) Microcrystalline alloys can be formed by heat-treating amorphous metal alloy powders at a temperature above the crystallization temperature of the powder. This is done for a period of time sufficient to produce the microcrystalline material but not so long as to form a substantially crystalline material. The compositional range of the amorphous alloy material is retained during the microcrystallization heat-treatment and present in the microcrystalline material formed. The composition and homogeneity of the amorphous or disordered metal alloy powder precursor therefore determine the degree to which various desired microcrystalline alloy characteristics such as hardness ductility and heat performance will exist in the resultant microcrystalline alloy.

The majority of amorphous metal alloy materials are prepared by rapid solidification processing (RSP) from a molten precursor phase. The amorphous metal alloy material is then heat-treated at a temperature above the cryst~llization temperature of the material for a time necessary to form its microcrystalline counterpart.

The RSP technique to form amorphous metal alloys has found great commercial success as a variety of known alloys can be manufactured by thls technique in various forms such as thin films ribbons and wires.
The technique involves sub~ecting a melt of the amorphous metal alloy composition to be made to rapid cooling rates on the order of 105-107C/sec. One e~ample of this method is taught by United States Patent No. 3 856 513 to Chen et al. which discloses directing a stream of the molten metal into the nip of rotating double rolls maintained at room temperature which quenchs the metal in the form of an amorphous ribbon thin film wire or platelet. To obta~n an amorphous or disordered metal alloy powder from an RSP-prepared material requires mechanically reduclng the amorphous metal alloy material as by ch~pping crushing grinding or ball milling. The resultant powder is then heat-treated at a temperature above the crystallization temperature of the amorphous metal alloy for a period of time necessary to cause microcrystallization to occur.

1~?26~1~

3 (SEM-P-7454) United States Patents Nos. 4,400,212 and 4,410,490 to Ray disclose the production of cobalt-chromium-carbon and cobalt-nickel-tungsten-carbon microcrystalline alloys, respectively, by the RSP method described above. United States Patent No. 4,473,402, also to Ray, discloses the consolidation, as by hot extrusion or cold pressing and sintering, of amorphous powder cobalt-chromium-carbide compositions prepared by the RSP technlque to produce microcrystalline alloys. Ray reports a range of microcrystalline alloy material compositions which is wlder than previously achieved composition ranges. This is due to the use of the RSP-rapld quench technlque, which allows the direct stabillzation of a hlgh temperature phase, in this case an amorphous phase, from the melt state, to form the amorphous alloy. Stabilization by slower temperature reductlon would yield a total or nearly total equllibrlum state and may also cause crystallization to occur. Ray prepares his alloys, in all three patents, by melt spinning techniques.
The resultant alloy is chemically homogeneous and in ribbon form, and must be commlnuted to powder form prior to heat-treatment to produce the mlcrocrystalllne alloy. The comminution results in some loss of homogenelty ln the resulting amorphous metal alloy powder, this decrease ln homogenelty becomlng a characterlstic of the microcrystalllne phase of the composltlon formed by this process.

The Journal of Materlals Science, 16, 1981, at pages 2924-2930, contalns two articles by Ray, Hlgh Strength Mlcrocrystalllne Alloys Prepared by Devltrification of Metallic Glass, and Devitrlfication/Hot Consolldation of Metalllc Glass: A New Materlals Technology via Rapid Solldlflcatlon Processlng. These articles dlsclose a process for crushlng the amorphous metal alloy melt spun-RSP ribbons to powders and hot presslng the powders to the desired microcrystalline form.
Microcrystalllzation occurs during the hot pressing process, combining a bulk forming process with the heat treating necessary to form the mlcrocrystalllne alloy.

12~

4 (SEM-P-7454 The RSP process for making amorphous metal alloys, which has been discussed herein above, suffers from the disadvantage that the so-formed amorphous alloy is produced in a limited shape, that is as a thin-film such as a ribbon, wire or platelet. While there are a few direct uses for amorphous metal ribbons, most often a comminution step is required to obtain a more readily usable amorphous alloy powder, as is required to prepare microcrystallin2 alloys. The comminution step often results, to some extent, in a loss of homogeneity between the ribbon and powder stages. Further, comminution of the amorphous alloy, and subsequent recombination ln a desired bulk shape, is a difficult process when it is realized that most amorphous metal alloys have high mechanical strengths and also possess high hardnesses.

While RSP technlques do somewhat lncrease the range of microcrystalline alloy compositions obtainable over that of a total equlllbrium state system, the range remalns rather narrow, as the melt phase of the amorphous alloy precursor material is not far removed from the equ~llbrlum phase.

An alternative method to RSP techniques is the use of solid state reactlon processes to produce amorphous or disordered metal alloy powders. Such a process ls dlsclosed ln Internatlonal Appl~cation Number PCT/US84J00035, publlshed under the Patent Cooperatlon Treaty, to Johnson et al. The process disclosed therein relates to the productlon of amorphous or flne crystalllne materlals by solld state reactlons. This process comprises contactlng two or more materials such that they undergo chemlcal reaction resulting ln the diffusion of the materlals into one another, and heatlng the materials at a temperature which permlts the chem~cal reactlon to occur, thus forming a metastable solid. Reacting at a temperature near the crystallization temperature may form a fine crystalline alloy. Thls process further requires that the phase formed have a lower free energy than the sum of the free energies of the startlng components.

3~

(SEM-P-7454) What is lacking in the area of mlcrocrystalline alloy preparatlon from powders is a simple process for the direct formation of a large variety of microcrystalline alloy composltions from amorphous or disordered metal alloy powders. Especially lacking is a simple process that would synthesize amorphous metal alloy materials directly as powders which may undergo lmmediate heat treatment to produce microcrystalline alloys without loss of homogeneity.

Hence it is one object of the present inventlon to provide novel microcrystalline alloy compositions.

It is another object of the present invention to provide a simple process for the preparation of a large variety of homogeneous microcrystalline alloy compositions.

These and additional objects of the present inventlon will become apparent in the descriptlon of the invention and examples that follow.

SUMMARY OF THE INVENTION

The present lnventlon relates to a process for the synthesls of a mlcrocrystalllne alloy comprising heat treating a substantially amorphous or dlsordered metal alloy powder prepared by the lnterdiffuslon of lntimately mlxed precursor materials during a solld state reaction process at a temperature sufflciently above the crystalllzation temperature to form the mlcrocrystalline alloy.

The lnventlon further relates to a microcrystalllne alloy prepared by heat-treating a substantially amorphous or dlsordered metal alloy powder prepared by the lnterdlffuslon of lntimately mlxed precursor materlals during a solld state reactlon process at a temperature sufficlently above the crystallization temperature to form the mlcrocrystalline alloy.

~Z630 6 (SEM-P-7454) Also the invention relates to a microcrystalline alloy characterlzed in that the free energy of the alloy is greater than that of a rapidly solidified material of about the same composition and a process for producing the same.

DETAILED DESCRIP~ION

In accordance with this invention there are provided novel compositions of microcrystalline alloys synthes~zed from substantially amorphous or disordered metal alloy powder precursors prepared by solid state reaction methods. The phrase microcrystalline alloy as used herein refers to an alloy material character~zed by a crystalline grain size of about 0.01 microns to about 1.0 microns. The phrase amorphous metal alloy connotes amorphous metal-containing alloys that may also comprise nonmetallic elements The term substantially with respect to the amorphous metal alloy powder means that the powders used to prepare the microcrystalline alloys are at least 50 percent amorphous preferably at least 80 percent amorphous and most preferably about 100 percent amorphous.

The processes disclosed herein provide for the formation of m~crocrystalline alloys from amorphous or disordered metal alloy powder precursors prepared by solid state reaction methods. Solid state reaction preparation of the amorphous alloy produces the alloy in powder form thus avoid~ng the need for comminut~on and increasing retention of the chemical homogeneity of the amorphous material ~n the subsequently produced microcrystalline alloy. These solid state reaction methods yield d~rect synthesis of amorphous or disordered metal alloy composit~ons in powder form far from the equilibrium composition. This hlghly non-equllibrium state ~nfluences the transformation from amorphous metal alloy powder to microcrystalline alloy in such a manner that these processes yield a microcrystalllne alloy with increased composit~onal dlverslty and commensurate diversity with respect to physlcal properties.

12~263V

7 (SEM-P-7454) The same processes which are disclosed herein to yield an atomic sca1e dispersement of atoms in a highly non-equilibrium state are amenable to the production of microcrystalline alloys or alloy compositions which are inaccessible by RSP technique due to the liquid immiscibility of the molten precursor state. A homogeneous and well-dispersed arrangement of the alloying atoms is obtainable in this type of solid state reaction synthesis which cannot be obtained by RSP
processing of immiscible molten metals. This is indicative of the expanded compositional variety of microcrystalline alloys that are feas~ble from amorphous metal alloy powder precursors prepared by the solid state reaction processes described herein.

The solid state reaction employed can vary depending on the des~red alloy composition and properties. Some adaptable solid state react~on methods include chem~cal reduction react~ons and thermal decomposltion reactlons. Each reaction method y~elds a powder alloy composition which ls formed by the interdiffusion of the initial components absent the necessity of chemically reacting those initial components. This composition may be amorphous or be made amorphous by heat-treating at a temperature and pressure below that necessary for crystallization. The resultant amorphous or disordered powder as taught herein ~s su~table to undergo heat-treatment to the microcrystalline phase.

Solid state chemical reduction for the synthesis of amorphous or disordered metal alloy powder precursors is disclosed in United States Patent No. 4 537 625 entitled Amorphous Metal Alloy Powders and Synthesls of Same by Solid State Chemical Reduction Reactions. This process comprises disposing a precursor compound in a liquid medium and reduc~ng this compound to obtain a substantially amorphous metal alloy.
More spec~fically the process as disclosed involves dissolving the precursor compound in a solvent to form a solution and reducing the compound which causes formation of a precipitate. Th1s precipitate is an ~ntlmate m~xture of the components of the amorphous metal alloy to be 63~

8 (SEM-P-7454) synthesized. The reduction which preferably occurs in the absence of oxygen and at a temperature below crystallization temperature can be accomplished by addition of a reducing agent to the solution or by other reducing methods such as electrochemical reduction or photocatalytic reduction. Subsequent heat-treatment at a temperature below the crystallization temperature of the amorphous metal alloy to be formed causes transition to the amorphous phase.

Solid state thermal decomposition is another method by which amorphous metal alloys may be formed. United States Patent No.
4 537 624 entitled Amorphous Metal Alloy Powders and Synthesis of Same by Solid State Decomposition Reactions teaches such a process. This process includes the step of thermally decomposing a precursor compound at a temperature below the crystallization temperature of the amorphous metal alloy to be formed. The decomposition of the precursor material may occur ln a partial or full vacuum or under an inert reducing or reactive atmosphere. The precursor components may alloy during the decompos~tion step if the temperature and timing are conducive to alloylng of the given components. When alloying does not take place durlng the decomposition step a powder which is an intimate mixture of the components of the alloy to be formed ls obtained. This is then subsequently heat-treated at a temperature sufficiently below the crystallization temperature of the alloy components to form the amorphous phase.

The solld state reaction methods recited above yield amorphous or dlsordered metal alloy powders in a high non-equilibrium state. This hlgh free energy state is characterized by higher molecular disorder than the melt phase employed with RSP for compounds having similar compositions. Solld state reactions produce stable amorphous or dlsordered alloy materials having much greater compositional diversity than can be obtalned using RSP techniques which produce materials that generally conslst of equilibrium phase compounds.

12~26~) 9 (SEM-P~7454) The resultant amorphous or disordered alloy powder, embodying variations in compos~tion due to the high free energy of this material, is then heat-treated, in accordance with this disclosure, to form the microcrystalline alloy. Solid state reaction processes, such as those discussed above, lncrease the range of compositions that will exist in any given microcrystalline alloy. By increasing the range of compositions, a commensurate increase in the range of properties, characteristic to different compositions, is achieved, thus making solid state reactions desirable for microcrystalline alloy production.

The amorphous metal alloy powders, produced by the solid state reactions discussed above, or any other solid state reaction methods, can be compacted to a desired shape, or left in the powder form, and heat-treated to a temperature between about 0.6 and 0.95 of the solidus temperature of the amorphous or disordered metal alloy powder to produce the microcrystalline alloy. The heat-treatment process to the m~crocrystalline phase occurs over a period of from about 1 hour to about 1,000 hours, depending on the amorphous or disordered metal alloy composition used and the treatment temperature.

SPECIFIC EXAMPLES

The following examples are presented to more thoroughly explain the instant inventlon, but are not intended to be limitative thereof.
The examples demonstrate the use of amorphous or disordered metal alloy powder precursors, prepared by solid state reaction methods, to produce microcrystall~ne alloys which have the desired properties characteristic of the amorphous or disordered metal alloy powder precursors.

Example 1 This example illustrates the formation of a microcrystalline alloy composition of iron-nickel-boron from an amorphous or disordered metal alloy powder prepared under solid state reduction conditions.

63~

(SEM-P-7454) About 4 mmol of nickel chloride NlC12 6H20 and about 16 mmol of iron chlorlde FeC12 4H20 were dlssolved in about 100 ml of distilled water to form a reaction solution and then filtered into a 500 ml flask. The reaction solution was degassed with argon. An argon-degassed solution of about 50 mmol of NaBH4 dlssolved in about 100 ml of dlstilled water was then added over about a one and one-quarter hour period. Immediately upon addition of the sodium borohydride solution hydrogen gas was evolved from the solution and a black magnetic preclpitate was formed. After the addition was completed the reaction solutlon was stlrred for about 16 hours to insure that the reaction had gone to completion. The solution was cannulated away from the preclpitate and the preclpitate was then washed with two 50 ml portions of dlstilled water. The precipitate was then dr~ed under a vacuum at about 60C for about four hours. In this condition the black preclpltate powder reacts vlgorously upon exposure to oxygen and so should be maintalned ln the absence of oxygen.

The powder was then transferred under inert condltions to a quartz tube whlch was sealed under vacuum and was heat-treated at about 290C for 264 hours. Thls produced a powder consistlng substantially of amorphous material.

A portlon of the powder was further heat-treated at about 900C
for one hour to produce a sllver coheslve agglomeration whlch reacted sllghtly upon exposure to oxygen.

X-ray diffractlon data of the material lndlcated a microcrystalllne alloy of the approxlmate composltlon Fe8Ni2B
conslstlng of multlple phases.

The procedure descrlbed ln Example 1 was repeated w~th the `exceptlon that the heat-treatment of the amorphous or dlsordered metal alloy-powder to form the mlcrocrystalllne alloy was carrled out at about t~3t~

11 (SEM-P-7454) 600C for about one hour. The resultant alloy was determined to be microcrystalline and to have about the same composition, Fe8Ni2B, as in Example 1. This illustrates that the temperature of this heat-treatment need only be sufficiently above the crystallization temperature, and that a broad range of temperatures beyond the crystallization temperature may be employed. This temperature range will vary, of course, depending on the elemental components of a given amorphous metal alloy powder precursor.

Example 3 About 9.109 (45.75 mmol) of FeC12 4H20 and 2.8569 ~12 mmol) of CoC12 6H20 were dissolved in 300 ml of distilled water. This solution was filtered into a 1 liter Schlenk flask and degassed with argon. Against a counterflow of argon, 1.6239 of neodymium powder (11.25 mmol) was added. To this rapidly stirred suspension a degassed solution of 5.499 (144 mmol) of NaBH4, in 200 ml of distilled water, was added dropwise over a 1 hour period. After stirring overnight, the solution was cannulated away from a black neodymium-containing precipitate mlxture. This mixture was then washed with two 100 ml portions of distilled water and dried under vacuum at 60C for 4 hours. Under vacuum, this material was heated to 200C for 20.5 hours to remove any H2 from the powder. the material was then sealed in a quartz tube and heat-treated at 840C to produce a microcrystalline material of the composition NdlsFe61C16B8 Exam~le 4 ~ n an argon filled dry box, 6.3069 of a copper powder precipitate of high surface area, prepared by the reaction of CuC12.2H20 and NaBH4 in water at room temperature under inert condltlons, was added to a tetrahydrogenation solution of 0.2469 of ~'C'6 while stirring rapidly. The solvent was removed, and the resultant dry powder mixture was sealed under vacuum in a quartz tube.

Z~30 12 (SEM-P-7454) The material was heat treated at 200C for two hours followed by heating for 22 hours at 300C. Elemental analysis indicated that the resultant powder which had an atomic percent of Cugg 3~0 7 contained about 2.7 weight percent tungsten (calculated 2.0 weight percent tungsten).
Only copper lines were observed by x-ray analysis. Subsequent heat-treatment of this disordered metal powder at elevated temperatures above the crystallization temperature of the powder produced a microcrystalline alloy of the same composition.

The above-described examples demonstrate the formation of microcrystalline alloy compositions from amorphous or disordered metal alloy powder precursors prepared by solid state reaction methods. This novel application of solid state reaction methods to form particulate precursor compounds as amorphous or disordered metal alloy powders existing in a high free energy state followed by microcrystallization heat-treatment processing may facilitate retention of some of the highly disordered state of the system in the resultant microcrystalline alloy material. This increases compositional variation over prior known methods of microcrystalline alloy preparation and is a si~pler method than those previously utilized. Further these materials and processing techniques may also make resultant materials useful as strengthening aids. Materials which could be altered to produce novel composites may include crystalline metal powders ceramics and plastics.

The scope of this invention is intended to include modifications and variations commensurate with the scope of the appended claims. The parameters herein presented such as temperatures above and below crystallization temperature and time periods appropriate to amorphous alloy and microcrystalline alloy formation as well as the identified solid state reaction methods are not intended to be limitative.

Claims

1. A process for the synthesis of a microcrystalline alloy comprising heat-treating a substantially amorphous or disordered metal alloy powder prepared by a solid state reaction process at a temperature sufficiently above the crystallization temperature to form said microcrystalline alloy.

2. The process as in claim 1 wherein said solid state reaction is a chemical reduction reaction.

3. The process as in claim 1 wherein said solid state reaction is a thermal decomposition reaction.

4. The process as in claim 1 wherein said amorphous metal alloy powder is heat-treated at a temperature between about 0.6 and about 0.95 of the solidus temperature of said amorphous metal alloy powder.

5. A microcrystalline alloy prepared by heat-treating a substantially amorphous or disordered metal alloy powder prepared by a solid state reaction process at a temperature sufficiently above the crystallization temperature to form said microcrystalline alloy.

14 (SEM-P-7454)

6. The microcrystalline alloy as in claim 5 wherein the grain size of said microcrystalline alloy range from about 0.01 microns to about 1.0 microns.

7. A process for the synthesis of a microcrystalline alloy comprising heat-treating a substantially amorphous metal alloy powder prepared by a solid state reaction process and having a high non-equilibrium state at a temperature sufficiently above the crystallization temperature to transform said powder to said microcrystalline alloy said microcrystalline alloy being characterized in that the highly non-equilibrium state of said amorphous metal alloy powder is retained in said microcrystalline alloy.

8. The process as in claim 7 wherein sald solid state reaction is a chemical reduction reaction.

9. The process as in claim 7 wherein said solid state reaction is a thermal decomposition reaction.

10. The process as in claim 7 wherein said amorphous metal alloy powder is heat-treated at a temperature between about 0.6 and about 0.95 of the solidus temperature of said amorphous metal alloy powder.

(SEM-P-7454)

11. A microcrystalline alloy, characterized in that the free energy of the alloy is greater than that of a rapidly solidified material of about the same composition, synthesized by heat-treating a substantially amorphous metal alloy powder prepared by a solid state reaction process at a temperature sufficiently above the crystallization temperature to form said microcrystalline alloy.