US3791798A

US3791798A - Metal bonding with sintering

Info

Publication number: US3791798A
Application number: US00274433A
Authority: US
Inventors: J Joyce; Intire H Mc
Original assignee: National Standard Co
Current assignee: National Standard Co
Priority date: 1972-07-24
Filing date: 1972-07-24
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12
Also published as: AT322223B

Abstract

Heat bonding of a first metal component with a second metal component in which the holding is affected to the metal components being subjected to reduction and sintering in a favorable environment and in which the second metal component consisting of a reducible metal compound has contraction characteristics during reduction and sintering greater than that of the first metal component to effect bonding of two components.

Description

Unite States Fatet [19] Joyce et a1.

METAL BONDING WITH SINTERING Inventors: John F. Joyce; Hoy O. McIntire,

both of Columbus, Ohio National Standard Company, Niles, Mich.

Filed: July 24, 1972 Appl. No.: 274,433

Related US. Application Data Continuation-impart of Ser. No. 817,304, April 18, 1969, abandoned.

Assignee:

US. Cl 29/l82.2, 29/473.9, 29/494, 75/200, 75/208 R, 75/214, 75/224 Int. Cl. B221 7/02, B22f 3/00 Field of Search 75/200, 208 R, 214, 224; 29/473.9, 494, 182.2

References Cited UNITED STATES PATENTS 6/1972 Mclntire et al. 75/224 -[451 Feb. 12, 1974 2,992,172 7/1961 Blarney et al. 29/473.5 3,474,523 10/1969 Musso et a1 29/473.5 2,224,934 12/1940 Schuhmacker 75/200 FOREIGN PATENTS OR APPLICATIONS 628,679 9/1949 Great Britain 29/473.5 1,191,445 5/1970 Great Britain Primary Examiner-Benjamin R. Padgett Assistant Examiner-13. H. Hunt Attorney, Agent, or FirmWilliam J. Muse [57] ABSTRACT 24 Claims, N0 Drawings METAL BONDING WITH SINTERING CROSS REFERENCE To RELATED APPLICATIONS This is a Continuation-in-Part of our application Ser. No. 8l7,304, now abandoned, filed on Apr 18, 1969.

BRIEF SUMMARY OF THE INVENTION The present invention stems from a prior discovery that high density metal articles, such as wire and tubing, may be made by subjecting compacts ofthe configuration of wire or tubing characterized by being substantially composed of reducible metal compounds of fine particle size to a reducing environment at a temperature within a range of from the lowest temperature at which reduction will take place to a temperature at which sintering occurs, and then sintering the reduced compact. Typically a compact of the foregoing class may be composed of iron oxide and a binder in which the iron oxide in terms of the well-known Coulter Counter measurements is characterized by a mean particle size no greater than 6 microns, and at least 25 percent by weight being less than about 2.5 microns. All references herein with respect to particle size as measured in microns means as measured in terms of Coulter Counter measurements. A typical iron oxide powder within the foregoing range which has been successfully employed in the present invention was one in which 50 percent by weight of the particles were less than 0.8 microns, and 50 percent by weight in a range of from about 0.8 microns to 10 microns. Also compacts of iron oxide and a binder in which at least 35 percent by weight of the iron oxide particles are less than 10 microns are satisfactory for practicing the invention.

Other compacts of the class noted with which the invention has been practiced were composed of copper oxides and of materials disposed to yield upon reduction and sintering Type 304 stainless steel.

It is characteristic that reduced and sintered articles formed from compacts of the class noted shrink when reduced and sintered. For example Fe O compacts shrink up to 40 percent with there being some variation depending on the binder employed in the compact.

For purposes of disclosing and claiming the present invention it is to be understood that the expression metal component means a solid metallic member having been in the reduced metallic state throughout the subject process, unreduced metal component means a member consisting of compounds having a portion of the specific compound being a metal in the oxidized (as opposed to the reduced) state, and the expression reduced metal component means a solid metallic member having once been an unreduced metal compound component now reduced and sintered to form a metal component.

By way of example and according to the present invention, vessels or reservoirs or cladded articles may be fabricated, for example, by inserting wire composed of a metal component into a hollow member, such as into an open end ofa piece of tubing, composed of an unreduced metal component, and then bonding the tubing and wire by subjecting the same to a predetermined temperature cycle. An important aspect of the present invention resides in the discovery that when the components of an assembly as noted are subjected to heating at elevated temperatures, for example, first a temperature at which the tubing is subjected to reducing and then a temperature to effect sintering, the tubing is shrunk forming a cladding around the wire plug and 5 producing an intimate bond between the inner surface of the tubing and the adjacent outer surface ofthe wire.

EXAMPLES OF THE PREFERRED EMBODIMENTS OF THE INVENTION Example I: The following is one example of how a final assembly, in accordance with the invention was produced. The by-produet iron oxide, from spent pickle recovery was milled in a conventional manner until 50 percent by weight of theiron oxide particles were less than eight-tenths microns and 50 percent by weight being in the range of eight-tenths microns to microns. A binder was then prepared by adding grams of corn starch to 100 milliliters of water and heating the solution to l60F until a gel was formed. 4.2 grams of this binder was then added to 22.7 grams of the milled iron oxide power and the combination was then mixed intimately in the mixmuller. The mixture of iron oxide and binder was then put into the cavity of an extrusion die having an opening of 0.1 15 inch in diameter and a pressure of 12,000 psi applied which formed an unreduced metal component in wire form. This unreduced metal component was then reduced in hydrogen at a temperature of about I,I00F for a period of five minutes, after which the temperature was raised to 2,l00F and remained at this temperature for five minutes during which time sintering was completed. The metallic iron wire was then drawn to 0.045 inch by pulling it through conventional wire drawing dies.

The tubing of the unreduced metal component was made from the identical formulation as the reduced metal component but extruded through a conventional tube forming die to form a tubular unreduced metal component having an outside diameter of 0.1 15 inch and an internal diameter of 0.065 inch. A section of the wire-like reduced metal component described above was put inside the tubular unreduced metal component and located so one of its ends was positioned at the end of the tubing. The wire was shorter in length than the tubing. This assembly was then bonded by placing it in hydrogen atmosphere at I,l0OF for eight minutes to effect reduction of the unreduced metal tubular component. The temperature was then raised to 2,l00F to effect sintering of the reduced tubular component and produced a bond between the sintered tubing and the sintered wire.

In other examples, a first assembly of a metal component defined by an iron wire of 0.057 inch in diameter was inserted into an open end of a tubular member of an unreduced metal component of the aforedescribed iron oxide compact having an outside diameter of 0.l 15 inch and an inside diameter of 0.064 inch. Similarly, in a second assembly of a wire of a reduced and sintered metal component produced as first above described of a diameter of 0.072 inch and drawn to a diameter of 0.047 inch was also plugged into an open end of a tubular member of an unreduced metal component as last described. Both such first and second assemblies were reduced and sintered within the parameters first above described. In both assemblies the tubular members thinned out but did not crack over the portions thereof plugged by the portions of the wires within the tubular members and formed satisfactory bonds. The unplugged portion of the tubular member of the first assembly shrunk to an outer diameter of 0.078 inch and the plugged portion to an outer diameter of 0.081 inch. in the second assembly the entire tubular member shrunk to an outer diameter of 0.072 inch.

In still another example an assembly of a metal wire of a reduced and sintered metal component produced as described in above Example 1 and drawn to a diameter of0.045 inch was inserted into a tubular member of one and one-half inches length of an unreduced metal component of Example 1 in a manner so that both ends projected outwardly of the tubular member. After sintering and reducing of the assembly within the parameters described in Example I, it was found that no cracks were formed in the outer'tu-bular member and a good bond was formed between the wire member and the tubular member.

The invention may also be practiced with compacts of other than iron oxide. In this regard reagent grade copper oxide was ball milled for eight hours to a fine particle size. A copper oxide compact was then formed by mixing the milled copper oxide with a binder in the following proportions: 22.7 grams of the copper oxide, 0.8 gram potato starch, 2.0 ml water, 2.0 ml glycerin and two drops NaOH. The copper oxide was then extruded through a conventional tubing die to provide tubing of an unreduced metal component having an internal diameter of 0.065 inch and an outside diameter of 0.113 inch. With tubing thus formed, piano wires ofv diameters of 0.049 inch, and of 0.055 inch were inserted into individual tubes of the aforementioned unreduced metal component and then reduced in hydrogen at about 700F and sintered at 1800F. After sintering the tubing assembled with the wire of 0.049 inch in diameter had an outside diameter of 0.102 inch and the tubing assembled with the wire of 0.055 inch had an outside diameter of 0.107 inch. ln both cases a mechanical bond was effected.

In another example of the invention, Type 304 stainless steel from 366.0 grams, Fe O 51.2 grams NiO, and 111.6 grams of ferrochromium (1.96% Si, 68.1% Cr. 42% C, 0.29 N balance Fe) was ball milled for 64 hours and by Coulter Counter measurement it was determined the maximum particle size was microns, the mean particle size 0.8 micron, and 90 percent by weight of the particles were less than 2.5 microns. The milled material was combined with a binder consisting of 25 grams metal oxides, 3 grams water, and 0.44 grams pregelatinized (dry) starch forming an unreduced metal component compact which was then extruded to form a tubing of an unreduced metal compo nent having an internal diameter of 0.067 inch and an outside diameter of 0.112 inch. A piano wire of a diameter of 0.049 inch was inserted into the tubing and the assembly was then reduced and sintered. The heating of the assembly was carried out in a hydrogen atmosphere beginning at a temperature of about 1,100F which was gradually increased to a temperature of about 2,200F over a period of approximately 3 /2 hours. After reduction and sintering the tubing was well secured to the wire with intermittent metallurgical bonds existing between the wire and the tubing. The rather long reducing time was for the purpose oflowering the carbon content of the stainless steel to about 0.03 percent.

that is both (a) of a particle size having at least 35 weight percent less than 10 microns in diameter and (b) that is reducible in a gaseous environment at reasonable reduction temperatures. U.S. Pat. No. 3,671,228 teaches a quantitative criterion for the en ergy required for reduction of the metal compound that adequately defines those metal compounds operable with the present invention. That criterion is that the metal compound of compounds should have a standard free energy of reaction with hydrogen at the reaction temperature of less than +15 Kilocalories per gram .atom of hydrogen. if such a metal compound is of the proper particle size as disclosed in the present specification, its behavior during reduction and sintering will conform to the relations as hereinafter disclosed.

Articles produced by the subject process are unique in that the component formed from the metal compound has a uniform porosity of from 0.1 to 5 percent by volume and a mean grain size of less than 20 microns in diameter. Such a structure is not readily pro duced by conventional prior art techniques in powder metallurgy since the present invention uses metal compounds ofa particle size less than would be used in conventional powder metallurgy techniques.

It is possible to calculate the approximate linear shrinkage of any unreduced metal compound compact and thus determine the approximate minimum diameter of wire for a given unreduced tube diameter. To do this, one must first know the initial density (Di) of the metal compound-binder-air mixture. The initial density (Di) of the metal compound-binder-air mixture may be measured directly. For example, this parameter can be determined by the measured volume. (Di) may also be calculated providing there is substantially no reaction between the metal compound, the binder and/or the air (as is the case with starch, water, and Fe O or may be calculated where any such reactions are known and understood. Where there is substantially no reaction, (Di) maybe determined as followsz where,

W weight V Volume c metal compound I; binder at air (or voids) in initial compact One must also know the approximate final density (Df) of the sintered tube. This may be measured directly or determined by the formula:

where 1 defines the operation of addition of theexpression that follows for each of the individual compounds (the general designations of which are represented by j) Wem may be zero or any weight (preferably equivalent to up to about 50 percent by volume of the unreduced mix). in a completed assembly of a wire and tubing the mating portions of the wire and the inside of the tubing after sintering are the same to assure intimate metal bonding between the wire and the tubing. It is characteristics of the invention that tubing of an unreduced metal component when reduced and sintered without the presence ofa wire will be ofa diameter less than the inside diameter of such a reduced and sintered component assembled with a wire.

To avoid excessive porosity in the case or cladding the gauge of the wire should preferably be 0.95 to 1 ratio or less than the diameter of the unreduced and/or unsintered metal component tube. Photomicrographic examination of the bond between the outer surface of the wire and the inner surface of the tubing showed that in many instances grain growth occurred across the inner faces of the wire and tubing indicating that a sound metallurgical bond is obtained. In other instances strong bonds are obtained by physical forces. importantly a high satisfactory bond is achieved without the assistance of externally applied mechanical forces.

The invention thus comprehends the cladding of one metal with another as exemplified by the aforedescribed assemblies including a first component wholly or partially encased in a second member with the second member cladding the first member.

I claim:

1. The method of forming an assembly of metal components which comprises: placing a first metal component within a cavity in a second unreduced metal component with said second component consisting essentially of a particulate metal compound with said metal compound having a free energy of reaction with hydrogen of less than Kilocalories per gram atom of hydrogen at the reduction temperature and with said metal compound having at least 35 weight percent of the particles in the second component less than 10 microns in diameter, subjecting the assembly to a gaseous reducing environment at a temperature and for a period of time to effect reduction of the metal compounds reducible in said environmentthereby shrinking the second component until the maximum inside diameter of said cavity is substantially equal to the outside diameter of the first component thereby effecting a bond therebetween and then subjecting the assembly to a temperature sufficient to effect sintering of the reduced metal component.

2. The method of claim 1 where the metal compounds are selected from the group consisting of: the oxides of Fe, Co, Cr, Ni, Cu, and W.

3. The method of claim 1 where the metal compounds are selected from the group consisting of W5 CuCl, and H WO,

4. The method of claim i in which said first metal component is a wire, said unreduced metal component is a tube, said wire being of smaller diameter than the inner diameter of said tube before reduction and sintering and of the same diameter as the diameter of said tube after reduction and sintering, and in which said wire is inserted into said tube.

5. The method of claim l in which said first metal component is a substantially solid metal body, said unreduced metal component is a hollow body, said solid metal body being smaller than thehollow area of said unreduced metal component before sintering and the same as said hollow area after sintering, and in which said solid metal body is inserted into the hollow area of said hollow body. I

6. The method of claim 1 wherein the minimum diameter of the wire is larger than the final diameter (df) of the tube as determined by the formula:

rs DfXc(Wc+ Wb) where ,JJJZ L L Vc--l- Vb+ Var Df= Wm/Vm Vafand W weight V volume c metal compounds b binder or plasticizer ai air (or voids) in initial compact af= air (or voids) in final sintered tube Di initial density Df= final density af= final internal diameter di initial internal diameter X molecular or atomic weight x number of metallic atoms per molecule of metal compounds m metal and the maximum diameter of the wire is not greater than 0.90 of di.

7. The method of Clairn i in which said first metal component is a wire, said unreduced metal component is a tube, said wire being of smaller'diameter than the inner diameter of said tube, and in which said wire is inserted into said tube.

8. The method of claim 4 in which said wire extends through said tube.

9. The method of claim 1 wherein said unreduced metal component consists essentially of iron oxide.

10. The method of claim 4 in which said unreduced metal component consists essentially of iron oxide.

11. The method of claim ll wherein said metal component and said unreduced metal component are formed from compacts consisting essentially of particles of iron oxide and a binder in which at least 35 percent by the weight of the iron oxide particles have a major dimension less than 10 microns.

12. The method of claim ii in which 50 percent by weight of the iron oxide particles are each less than .8 microns, and 50 percent by weight of the iron oxide particles each being in a range of from about 0.8 microns to l0 microns.

13. The method of claim 7 in which said unreduced metal component consists essentially of compacted particles composed predominantly of iron oxide particles, and the diameter of the wire is in the ratio of 0.95 to l with respect to the inner diameter of the tube.

H4. The method of claim 4i wherein the diameter of the wire is the same as the diameter (df) of a tube of a sintered reduced metal component initially composed 3,791 ,798 6 where, (1f 0.041 inch m metal 11f air (or voids) in final sintered tube ().04l inch and the minimum diameter of wire to unre- Once Di and Df have been determined, the linear 5 duccd bore diameter is about 0.60 to L0. shrinkage (FLS) may be calculated from the formula: Where it is desired to combine metal compounds as FLS 1 where the unreduced tube reduces and sinters to form (3) a metal alloy (for example, combining Fe O and Cr O where to form stainless steel), the determination of shrinkage FLS fractional linear Shrinkage (Equations (5) and are modified as follows:

FVS fractional volume shrinkage FL 3 Di(z:c1 W01 X02 Xml-l- Z W 1 g where shrinkage is substantially uniform in all dlw t X61 Xc2DfU/VC1+WC2+Wb) Thus, the minimum acceptable wire gage is about rections. (5a) Fractional volume shrinkage is determined by: l5 and .3 Di(x01 W01 X02 Xml+x02 W02X01 Xm2) V"+Vb+Vi)(Vm+Vaf) dfflh X61 x021) W01- W Wb V0+Vb+Vai 4 f( if c (6a) FLS may also be expressed Where ml first metal (forexample, Fe) 3 x WcXmDi m2 second metal (for example, Cr) I'L'S:1 DfX0(W0+Wb) (5) cl first metal compound (for example, Fe O c2 second metal compound (for eample, (B 0 where, Where three metal compounds are combined in the x number of metal atoms per molecule of metal green tube (for example, combining Fcg g, CrO and compound M0 to form stainless steel), Equations (5) and (6) are X molecular or atomic weight further modified as follows:

FLS-1 3 Di(xc1 W01 Xc2Xc3Xm1-l-xc2 W02X 01 X03Xm2+rc03Wc3Xcl X02Xm3) X01Xc2Xc3Df(Wc1+W02+W03+Wb+Wa) (5b) and f 3 Di(a:01 W01 X02 X03Xm1+x02 WcxXcl X03Xm2+x03Wc3X01 XcZXmS) X01Xc2Xc3Df(W01+Wc2+Wc3|-Wbl-Wa) Since the reason for determining the fractional linear where 03 a third metal compound (for example, NiO) shrinkage is to determine the final internal diameter m3 a third metal (for example, Ni) (df) of a sintered tube in terms of its original (unre- In many instances it may be desirable to include eleduced) internal diameter (di) and since the fractional mental or alloy metal powder (for example, elemental linear shrinkage is the difference between di and df di- F find/0f Cf F6 alloy P in the um'educed vided by di, the final internal diameter (df) is deter- 4O tu metal P d m u u h tal p wders mined as follows: will reduce the shrinkage characteristics of the unre- 3 xWcXmDi duced tube so that preferably the metal powders will df=dtw {m not exceed about 95 percent, by volume, of the powder V.M u r mixture. Where metal powders are included, Equation For example, to determine the final diameter of the L and (,6) l "lid fi i l? 9 tube of Example I: where W0 22.7 grams Fe o em elemental or alloy metal powder Wb 4.2 grams binder The general formulas which may be derived from Wa=negligible Equations (3) and (4) above are expressed below.

Vc We 5.24 (theoretical density of Fe O 4. 32 These formulas encompass the subject matter of Equa- Vb V/b 1.07 (measured binder density) 3.92 tions (5) and (6); (5a) and (6a); (5b) and (6b); and

Va determined to be negligible (5c) and(pcLand are as follo vsg 7 therefore, H i i n i Di 2 2 ,Z t .z[ 4.32 3.92 3.26 gins/em (1) wem g figfi I f: 2 DJ Wem+Wb+E W0;

Df= 7.46 percent of theoretical) Xc 159.7 I M'WCDXm. di 0.065 inch W +z 1 if h V D; Ac,-

f (7.46)159.7(22.7+4t.2) H

of two reducible and sinterable metal compounds to form a metal alloy as determined by the formula:

(1 f= at 16. The method of claim 4 wherein the minimum diwhere df=di Wc-l-Wb+Wai Vc+ Vb+ Vai Df= (Wm/Vm Vaj) and W weight V volume c metal compounds b binder or plasticizer 1i air (or voids) in initial compact af= air (or voids) in final sintered tube Di initial density Df= final density df= final internal diameter di initial internal diameter X molecular or atomic weight x number of metallic atoms per molecule of metal compounds m metals ml first metal m2 second metal cl first metal compound 02 second metal compound and the maximum diameter of the wire is not greater than about 0.96 of di 15. The method of claim 4 wherein the minimum diameter of the wire is no larger than the final diameter (df) of a tube of a sintered reduced metal component initially composed of three reducible and sinterable metal compounds to form a metal alloy as determined by the formula:

where Wc-l- Wem+ Wb-l- Wai I. V w+j miV +sY L A Df= (Wm/Vm Vaf) and W weight V 9mi c metal compounds b binder or plasticizer ai air (or voids) in initial compact af= air (or voids) in final sintered tube Di initial density Df= final density df= final internal diameter di initial internal diameter X molecular or atomic weight x number of metallic atoms per molecule of metal compounds m metals ml first metal m2 second metal cl first metal compound c2 second metal compound em elemental metal or alloy and the maximum diameter of the wire is not greater than 0.95 of di.

17. The method of claim 4 wherein the minimum diameter of the wire is the same as the final diameter (df) of a tube of reduced metal composed as determined by the formula:

af= (Wm/Vrii Vaf) and W weight Df= final density a'f= final internal diameter dz initial internal diameter X molecular or atomic weight x number of metallic atoms per molecule of metal compounds m metals m1 a first metal m2 a second metal m3 a third metal c1 a first metal compound 02 a second metal compound 03 a third metal compound and the maximum diameter of the wire is not greater than 0.95 of di.

V volume 0 metal compounds b binder or plasticizer em elemental metal or alloy ai air (or voids) in initial compact af= air (or voids) in final sintered tube Di initial density Df= final density df= final internal diameter di initial internal diameter X molecular or atomic weight x number of metallic atoms per molecule of meta compounds m metals 19. The method of claim 1 wherein said unreduced metal component consists essentially of materials disposed to yield stainless steel upon reduction and sintering.

20. The method of claim 1 wherein said unreduced metal component is formed from a compact consisting essentially of particles of copper oxide and a binder.

21. The method of claim 1 wherein said unreduced metal component is formed from a compact consisting essentially of particles not exceeding 10 microns in size disposed to yield stainless steel upon reduction and sintering.

22. The method of claim 21 wherein the mean size of said particles is .8 micron, in which percent by weight of said particles are less than 2.5 microns.

23. An assembly of meta] components comprising a soli solid inner body, and a solid outer body intimately bonded over their contiguous surfaces, wherein the outer body has the following characteristics:

a uniform porosity of about 0.1 to 5 percent by volume, and a mean grain size of less than about 20 microns.

24. An assembly made by the method of claim 21.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,791,798 Dated February 12, 1974 fl fl John F. Joyce and Hov O. McIntire It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, line 17, Equation (6a) change "dfjdi 3 to read df di Column 9, line 4, in the formula, "d di under the \V symbo; in the denominator delete "Wc" and insert Wc Wc same line,

second occurrence of "Xcl" and insert Xc2 Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR, C. MARStIALL DANN Attesting Officer Commissioner of Patents F ORM PO-105O (10-69)

Claims

2. The method of claim 1 where the metal compounds are selected from the group consisting of: the oxides of Fe, Co, Cr, Ni, Cu, and W.
3. The method of claim 1 where the metal compounds are selected from the group consisting of WS2, CuCl, and H2WO4.
4. The method of claim 1 in which said first metal component is a wire, said unreduced metal component is a tube, said wire being of smaller diameter than the inner diameter of said tube before reduction and sintering and of the same diameter as the diameter of said tube after reduction and sintering, and in which said wire is inserted into said tube.
5. The method of claim 1 in which said first metal component is a substantially solid metal body, said unreduced metal component is a hollow body, said solid metal body being smaller than the hollow area of said unreduced metal component before sintering and the same as said hollow area after sintering, and in which said solid metal body is inserted into the hollow area of said hollow body.
6. The method of claim 4 wherein the minimum diameter of the wire is larger than the final diameter (df) of the tube as determined by the formula:
7. The method of claim 1 in which said first metal component is a wire, said unreduced metal component is a tube, said wire being of smaller diameter than the inner diameter of said tube, and in which said wire is inserted into said tube.
8. The method of claim 4 in which said wire extends through said tube.
9. The method of claim 1 wherein said unreduced metal component consists essentially of iron oxide.
10. The method of claim 4 in which said unreduced metal component consists essentially of iron oxide.
11. The method of claim 1 wherein said metal component and said unreduced metal component are formed from compacts consisting essentially of particles of iron oxide and a binder in which at least 35 percent by the weight of the iron oxide particles have a major dimension less than 10 microns.
12. The method of claim 11 in which 50 percent by weight of the iron oxide particles are each less than .8 microns, and 50 percent by weight of the iron oxide particles each being in a range of from about 0.8 microns to 10 microns.
13. The method of claim 7 in which said unreduced metal component consists essentially of compacted particles composed predominantly of iron oxide particles, and the diameter of the wire is in the ratio of 0.95 to 1 with respect to the inner diameter of the tube.
14. The method of claim 4 wherein the diameter of the wire is the same as the diameter (df) of a tube of a sintered reduced metal component initially composed of two reducible and sinterable metal compounds to form a metal alloy as determined by the formula:
15. The method of claim 4 wherein the minimum diameter of the wire is no larger than the final diameter (df) of a tube of a sintered reduced metal component initially composed of three reducible and sinterable metal compounds to form a metal alloy as determined by the formula:
16. The method of claim 4 wherein the minimum diameter of the wire is the same as the final diameter (df) of a tube of a sintered reduced metal component initially composed of two reducible and sinterable metal compounds and an alloy metal or alloy to form another alloy as determined by the formula:
17. The method of claim 4 wherein the minimum diameter of the wire is the same as the final diameter (df) of a tube of reduced metal composed as determined by the formula:
18. The method of claim 1 wherein said unreduced metal component consists essentially of copper oxide.
19. The method of claim 1 wherein said unreduced metal component consists essentially of materials disposed to yield stainless steel upon reduction and sintering.
20. The method of claim 1 wherein said unreduced metal component is formed from a compact consisting essentially of particles of copper oxide and a binder.
21. The method of claim 1 wherein said unreduced metal component is formed from a compact consisting essentially of particles not exceeding 10 microns in size disposed to yield stainless steel upon reduction and sintering.
22. The method of claim 21 wherein the mean size of said particles is .8 micron, in which 90 percent by weight of said particles are less than 2.5 microns.
23. An assembly of metal components comprising a soli solid inner body, and a solid outer body intimately bonded over their contiguous surfaces, wherein the outer body has the following characteristics: a uniform porosity of about 0.1 to 5 percent by volume, and a mean grain size of less than about 20 microns.
24. An assembly made by the method of claim 21.