US2190237A - Method of making a composite metal structure - Google Patents

Description

I F: [WWW METHOD OF MAKING A COMPOSITE METAL STRUCTURE Filed Dec. 30, 1937 OOOOOOOO wvwO a 0N mm Mm v T P m m 5V IBM 0 H ratented Feb. 13, 1940 FATE OFl

METHOD OF MAKING A COMPOSITE METAL STRUCTURE Application December 30, 1937, Serial No. 182,411

7 Claims.

The present invention relates to metallic structures and more particularly to a method of fabricating porous metal structures that have a metallic ingredient dispersed within the interstitial pores thereof.

It is an object of the present invention to provide a method of fabricating a porous alloy structure from a porous metal matrix which comprises, impregnating a previously fiuxed porous metal matrix with a metal at such a temperature and for such a time as to prevent the impregnating metal from dissolving the porous metal matrix, and then subsequently heating the impregnated matrix and thereby causing at least a part of the impregnating metal to substantially uniformly diffuse into the metal of the matrix and form an alloy therewith without destroying the continuity of the porous metal matrix.

It is a further object, in some cases, to im- 2 0 pregnate the porous metal matrix with a mixture of two metals, one of which is readily alloyable with the metal of the matrix and the other of which is not readily alloyable with the metal of the matrix, the impregnated matrix being subsequently heated to cause the readily alloyable metal to uniformly diffuse intothe metal of the matrix and alloy therewith without destroying the continuity of the matrix and leave the less readily alloyab-le metal dispersed within the pores of the matrix.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

The single figure is a diagrammatic view, illustrating a method of applying loose uncompacted metal powder in a layer upon a strong metal back and sintering the loose layer in situ upon the metal back to form a porous metal matrix directly bonded to th bank by an alloy bond.

The present invention is directed to a low temperattu'e impregnating method whereby readily alloyable metals may be impregnated into a metal matrix or sponge at low temperatures and subsequently the impregnated sponge may be heated to cause uniform alloying of all or a part of the alloyable impregnating metal with the sponge without any harmful effects, such as destroying the continuity of the sponge.

In practicing such a method it is possible to substantially uniformly impregnate a copper sponge with pure tin and later heat the impregnated sponge and thereby cause the tin substantially uniformly diffuse into the copp of the matrix and alloy therewith to form bronze sponge in situ, having substantially tl same continuous structure as the original copp sponge. Likewise, a pure copper sponge may I impregnated with a mixtureeof -lead and ti: The impregnated sponge may be subsequent heated to cause the tin to uniformly dissolve int the copper to form an alloy therewith leavir the less alloyable lead uniformly dispersed withi the pores of the newly formed bronze sponge.

The present method can be advantageous carried out with any number of metallic sponge for example, copper, iron, nickel,,bronze sponge copper-nickel sponges. etc..,. together wit sponges which include a non-metallic disperse material therein, such -as'graphite. Imp'i'egnai ing metals such as tin, silver, aluminum, bismutl bismuth-lead alloys, tin-lead alloys, tin-silve alloys and many other metals and alloys there( can all be used to advantage.

While the following .description is directed t impregnating and subsequently alloying or par tially alloying the impregnated metal with sponge or matrix which is directly bonded to steel back, it should be understood that the meth od is not limited in this respect and may be use with equal success on sponges that have no sup porting backs.

Referring to the drawing a loose layer H] c the desired thickness of the finely divided matrix forming metal powder is applied onto a relativel strong metal strip H, such as steel, as the stri l l moves along under the hopper I2 at a suitabl; slow uniform speed. The loose matrix-formin metal powder I3 in hopper l2 runs out by th aid of gravity upon strip II and is preferabl; smoothed thereon by a suitable adjustabl smoothing device I4 to provide a smooth-sur faced uniform layer H] of loose metal powde upon the strip I I.

The moving metal strip H with the loose laye ill thereon passes into the sintering chamber 2 and is there heated in a non-oxidizing or reduc ing atmosphere to such a temperature and f0 such a time as will cause the loose or only slight]; compacted metal particles to molecularly 1001 together and form a strong highly porous matri: lining l5 and at the same time to molecularl: bond to the metal strip I I. During this sintering process the thickness of the loose powder laye: I0 is materially reduced due to shrinkage s that the porous metal lining l5 emerging at 2 from the sintering chamber 20 is about one d less than the loose powder layer II) which :rs chamber 20. Hence, the original thickof the powder layer I is made such as will the desired thickness and density of the sind porous metal matrix lining ID. This can eadily determined by trial for any given inlients in the matrix-forming metal powder l3. trip H is of steel it is preferably, but not zssarily, first copper plated before the loose 'der layer I0 is applied thereon since it has 1 found that the sintered porous lining l5 will d somewhat more strongly to a copper surface a it will to a steel surface. However, the )us matrix lining l5 will bond successfully to uncoated clean steel surface. The temperaof the sintering chamber is accurately conled by suitable means and is preferably heaty electric heating elements 25. be highly porous matrix lining [5 preferably ;es from the sintering chamber 20 into the er jacketed cooling chamber 22 where it is ed under non-oxidizing or reducing condis to substantially prevent oxidation of the )us metal matrix. The reducing or nonlizing gas is admitted to the sintering chamber hrough an inlet 23 and then escapes through outlet 24 of the cooling chamber 22. In manner the non-oxidizing atmosphere is ;ent in both chambers 20 and 22 and at a ;sure slightly in excess of atmospheric presa to assure that no atmospheric gases enter aforementioned chambers. 'he density or porosity of porous matrix lining :an be accurately controlled, if desired, by subiently sizing the lining by a pressure opera- 1, for example, by passing strip II with the ous lining l5 bonded thereto between pressure 5 30 and 3| illustrated in the drawing. These s 30 and 3| may be set any desired distance .rt so as to compress the lining l5 to any ired thickness, thereby reducing the porosity reof. .fter the porous metal lining I5 has been lded to strip II the lined strip is preferably into short lengths which may then be imrsed in a fluxing bath either under vacuum inder atmospheric conditions, or the strip may painted with the fluxing material, such as amnium or zinc chloride, rosin and alcohol, borax ition etc., or exposed to an atmosphere of a (ing gas. The fluxed strip is then immersed a molten bath of the desired impregnating tal. It is preferable to utilize a vacuum durimpregnation to draw the occluded air and Les from the pores of the matrix prior to imrsing the same in the impregnating metal bath 1 then apply pressure to the bath by increasthe pressure thereover to force the impreg- ;ing metal into the pores of the immersed metal vnge. The impregnated metal sponge is then moved from the impregnating bath and pref- ,bly cooled, although the cooling step is not :essary to the success of the steps that follow. bsequently the sponge may be heated under o-oxidizing or reducing conditions to a temrature well above the impregnating temperae, to cause the impregnated metal to alloy or rtially alloy with the metal of the matrix. In trying out the aforementioned steps it has an discovered that the fluxing step may be minated if the sintered metal matrix is imagnated before exposure to atmospheric air ice the surfaces therein are substantially free m oxidation or other surface films. A. specific example of the fabrication of a copper sponge impregnated with tin by such procedure is as follows: Uncompacted copper powder on a steel strip is preferably sintered at a temperature of approximately 1900" F. for from to minutes, which causes the copper particles to sinter together to form a strong sponge having a continuous metallic network which is alloyed by an alloy bond to the supporting back. This copper sponge is then fiuxed by immersion in ammonium chloride solution or any other suitable flux disclosed herein and is subsequently immersed in a bath of molten tin which is preferably maintained at a temperature of approximately 450 to 500 F., the melting point of tin being 449.4 F. Prior to the immersion of the sponge in the impregnating bath the aforementioned vacuum is applied and then under evacuated conditions the sponge is immersed and pressure applied for a period of immersion approximately from 1 to 2 minutes, which is sufficient to cause complete and uniform impregnation of the tin into the sponge. The tin impregnated copper sponge, if desired, may next be cooled to set the impregnated metal although this step is not necessary. The impregnated sponge is then heated under nonoxidizing or reducing conditions to a temperature well above 500 F., for example 1000 to 1900 F. for a period up to 10 minutes. During this heating period the tin, which readily dissolves copper, at these higher temperatures uniformly diffuses into the copper matrix thereby forming a uniform and homogeneous bronze without destroying the continuity of the matrix. The period of heating, the temperature of the heating step, or both, may be varied to accomplish partial alloying of the tin.

In a like manner a tin-lead mixture can be used as the impregnating alloy for a copper matrix in which instance the impregnating bath is maintained up to fifty degrees above the melting point of the tin lead alloy. In this case, the subsequent heating of the impregnated sponge, which has a uniform dispersion of the lead alloy therethrough, causes the tin to diffuse into the copper matrix and leave the lead, which is not readily alloyable with either copper or bronze, in a finely divided state within the pores of the bronze matrix.

In a similar manner a bronze sponge can be utilized in which case, as the tin diffuses therein, the tin content of the bronze, is changed to a higher percentage than was present in the origi nal sponge.

In place of tin such aforementioned metals as bismuth, cadmium, bismuth-lead or silver-tin etc. can be used as impregnating metals for copper or bronze sponges, in each case the impregnating temperature being just above the melting point of the impregnating metal or alloy and the subsequent heating step being slightly below the melting point of the porous metal sponge when a pure metal sponge is used, and preferably below the melting point of the highest melting constituent metal when an alloy sponge is used. Likewise, iron sponge can be readily impregnated and subsequently alloyed with aluminum and similarly nickel sponge can be transformed into Monel sponge by impregnating with copper etc.

The present method is decidedly advantageous when it is desired to impregnate and subsequently alloy a sponge with a readily alloyable metal since such a method as herein described prevents any substantial dissolving action by the impregnating metal on the sponge whereby the structure of the sponge in its final form is substantially similar to the structure of the'sponge prior to the tmprtghhtthg thh hhhhthh tttht.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. The steps in the method of making a metallic structure comprising: providing a porous metal matrix of copper which has intercommunicating voids therein by sintering together finely divided non-compacted copper powder, fiuxing said matrix with a suitable flux so that the flux penetrates within the intercommunieating voids of the matrix, immersing the fiuxed matrix in a molten bath of tin at a temperature only slightly above the melting point of tin and for such a short period of time that the tin While flowing within the intercommunicating voids of the matrix has no substantial dissolving action upon the metallic structure of the matrix, removing the impregnated matrix from the bath, and then heating the impregnated copper matrix to a temperature well above the melting point of tin whereby the tin difiuses into the copper and simultaneously progressively raises the melting point of the alloy formed by the copper and the tin and thereby prevents the continuity of the resultant matrix from being destroyed to form a bronze matrix with intercommunicating voids therein.

2. The steps in the method of making a porous metal structure having a metal held within the pores thereof comprising: providing a porous metal matrix having intercommunicating voids therein by sintering together finely divided noncompacted metal powder, fluxing said matrix with a suitable flux so that the flux penetrates within the intercommunicating voids of the matrix, impregnating the matrix with the mixture of metals, one of which readily alloys with the metal of the matrix and the other of which does not readily alloy with the metal of the matrix by immersing the porous metal matrix in a molten bath of an alloy of the two impregnating metals which bath is maintained at a temperature slightly above the melting point of said alloy for a short time only and thereby preventing any substantial dissolving action by the readily alloying impregnating metal upon the matrix, then subsequently heating the impregnated metal matrix to a temperature sufiiciently high to cause the readily alloyable metal to uniformly diffuse into the matrix to form an alloy therewith, and leave the remainder of the impregnating metal dispersed within the pores of the metal matrix, and then cooling the alloyed matrix.

3. The steps in the method of making a porous bronze structure having lead dispersed in the pores thereof comprising: providing a copper matrix having intercommunicating voids therein by sintering together finely divided non-compacted copper powder, fluxing said matrix with a suitable flux so that the flux penetrates within the interstitial pores of the matrix, impregnating the copper matrix with lead and tin by immersing the copper matrix in a molten bath of lead and tin for a short time only, which bath is maintained at a temperature only slightly above the melting point of the lead-tin alloy then subsequently heating the impregnated metal matrix to a temperature well above the melting point of the lead-tin alloy and thereby causing the tin to uniformly difiuse into the copper matrix ant hhht t hthhth thththhh hhththt hthttththt th continuous structure of the matrix, and leavin the lead dispersed within the interstitial pore of the bronze matrix.

4. The steps in the method of making a metal lic structure comprising: providing a DOIOlJ metal matrix of homogeneous character by sin tering together finely divided non-compacte metal powder, fluxing said matrix with a suit able flux so that the flux penetrates the inter stltial pores of the matrix, impregnating th fluxed porous metal matrix with a mixture c metals which includes one metal that is readil alloyable with the metal in the matrix and. an other metal which is not readily alloyable wit the metal of the matrix, at a temperature onl slightly above the melting point of the impreg nating alloy and for such a time as to preven any substantial dissolving action by the readil alloyable metal upon the matrix, then subse quently heating the impregnated porous mete matrix at a temperature well above the impreg nating temperature and thereby causing th readily alloyable metal to diffuse into the mete of the matrix and form an alloy therewith with out destroying the continuous structure of th matrix and leaving the less alloyable metal dis persed within the pores of the matrix.

5. The steps in the method of making a com posite metal structure comprising: uniforml distributing a loose layer of uncompacted meta powder upon a relatively strong non-porou metal supporting back, subjecting the loose layei in situ upon said back, to such a temperature an for such a time as will cause the loose metal par ticles to molecularly bond together and form relatively highly porous matrix having inter communicating voids therein and simultaneousl cause said matrix to molecularly bond to sai metal back, impregnating the porous meta matrix with a metal which is readily alloyabl with the metal of the matrix at a tempera ture only slightly above the melting point of th impregnating metal and for such a time as t prevent the impregnating metal from having substantial dissolving effect on said matrix, an then subsequently heating the impregnate matrix to a temperature sufficiently high to caus substantially uniform difiusion of at least a por tion of the impregnating metal into the porou metal matrix and thereby form an alloy in sit with the matrix without destroying the con tinuity of the matrix.

6. The steps in the method of making a com posite metal structure comprising: uniforml; distributing a loose layer of uncompacted meta powder upon a relatively strong non-porous sup porting back, subjecting the loose layer, in sit upon said back, to such a temperature and fo such a time as Will cause the loose metal particle to molecularly bond together and form a rela tively highly porous matrix having inter-com municating voids therein and simultaneousl; cause said matrix to molecularly bond to sai metal back, impregnating the porous meta matrix with a mixture of metals one of whic] readily alloys with the metal of the matrix am the other of which does not readily alloy with th metal of the matrix at a temperature slightl; above the melting point of the metal mixture am for such a time as to prevent any substantial dis solving action by the readily alloyable impreg nating metal upon the matrix, then subsequentl; heating the impregnating metal matrix to a tem :rature sufficiently high to cause at least a porm of the readily alloyable metal to uniformly lfuse into the matrix to form an alloy there- 'Lth, and leave the remainder of the impreglted metal dispersed within the pores of the etal matrix.

'7. The steps in the method of making a metallic ructure comprising: sintering together finely vided, non-compacted metal powders, to form porous metal matrix, impregnating the matrix formed with a mixture of metal including at ast one metal which is readily alloyable with ,e metal of the matrix and' another metal which not readily alloyable with the metal of the atrix at a temperature only slightly above the melting point of the impregnating alloy and for

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