US2372203A - Sintered metal article and process of making - Google Patents

Description

March 27, 1945. F. R. HENSEL. E1-AL 2,372,203

SINTERED METAL ARTICLES .AND PROCESS 0F MAKING l Filed sept. e, 194s i INVENToRs f'a/zz Zijl/eiffel ?atented i0 Glaims. (CL75-22) -We have found that`a body can be produced This invention relates to copper base sintcred metal compositions and to. articles such as bearings, made therefrom.

I The present application is a continuation-iniied construction; and

Figure d is urea. i'

This invention contemplates an end view of thebearing of Figthe manufacture of metal powder articles, such as bearings from from copper powders which is of high strength and hardness by incorporating eithernicirel or cobalt and silicon in the powder mix to form part of our application Serial- No. 333,928, nl ed g nickel silicide or cobalt silicide, which is capable May 8, i940. Y of precipitation as a dispersed phase in the sin- An object of the invention is to improve the tei-ed copper body upon application oi a suitable physical. properties such as the soundness, 4 age hardening treatment. However, the process strength, hardness and wear resistance of such requires Very careful control of lsintering and compositions and articles. 11o heat Atreating conditions, rapid heating and de- Other objects of the invention will be apparent oxidizing atmospheres. Otherwise a soft shell is from the following description and accompanyfound to forno on the sintered article which ing drawing taken in connection with the apsometimes makes the article useless or maires it pended claims. necessary to machine away the shell.

In the drawing: A j llc 'We have now found that the addition of phos- Figure lis a longitudinal section through a phorus-to the powder mix enables the production bearing made from pressed metal powders ac-V oi metal bodies under ordinary conditions of sin` cording to one aspect of the present 'inventiomA tering and heat treatment without the forma- Figure 2 is an end view of said bearing; tion oi 'a soft shell. The phosphorus also has a Figure 3 is a section through a bearing of xnodi- 2c cleansing action upon the material and improves ductility and otherV physical properties.

The nickel or cobalt and silicon are added in the proportions in whichthey are capable of age hardening the copper. The phosphorus present at may also contribute to age hardening due to the copper powder, containingnickel or cobalt with i silicon and phosphorus. Such manufacture may involve the steps oi' pressing metal powders suitable dies and presses, sintering the compressed articles thus produced and subsequently 39 silicon peli cent beve" 0 1 to 1 applying an ageyhardening heat treatment. The PhDs-P11651; "f do 0 d5 m 1 present invention makes possible the fabrication Copper B'alan of articles of greater strength, hardness and Y wear-'resistance than has heretofore been possible is used Y Y Y while obtaining the @gommes incident to the so In some cases up to 10% ofa diluent metal,V

use of pressed powders es distinguished from c of molten metal and theolike.

Because of its high strength and low cost it is possible to produce a solid bearing by this invention, thereby avoiding the diiiicuties of prior art lined bearings such as poor -bond between lining and backing,"diierences in thermal expension coecients, and the like.

By using pressed powders, it is possible to thexnickel or cobalt. l

press the articles to the desired dimensions ande" -shape in a single operation by using a suitable "die and consequently extensive and time-consumingmachining and grinding operations are not required or are required only to a very ited extent. While bearings have heretofore been made from pressed metal powders it has'not heretofore been practicable toproduce pressed powdered bearings ofthe high strength and hardness which results from vthe application of the present invention.

formation oi nickel or cobalt phosphide. A powder Ve containing: v

Nickel; cobalt, or both Y 0.5 to 5 such as ziilc or tin may be added to the mixture.

it is preferred that the nickel or cobalt-and silicon be present in a ratio between 4:1 and 6:1. Where the higher proportions of phosphorus are used the silicon may be lower as part of the phosphorus will form intermetallic compounds with Some of the phosphorus may be lost during sintering and heat treatment so that the final composition may contain 0.01 to 1% phosphorus.

In the manufacture of bearings or other bodies of the composition the powdered elementsare thoroughly mlxedin the desired proportions land then pressed into a suitable shape using appropriate dies in a, hydraulic or automatic press.

Inasmuch as pure silicon readily oxidizes it is preferable to form a nickel or cobalt silicide, such as NizSi or Consi which may be lcomminuted to a fine powder and included inthe powder mixture instead of pure nickelor cobalt and silicon powder. Such a compound also is more amenable to diiusion alloying than are the uncombined elements. Some excess nickel or cobalt may also be added, within the proportions given, as well as the compounds.

For bearings the density to which the powder mixture is pressed will depend upon the type of bearing intended to be made. Bearings can be made of varying porosity according to the service they are to perform;

(1) One type uses a dense material which after beat treatment approaches the theoretical density of the composition and which is used as a bearing without impregnation with a lubricant, i

relying on a surface iilm of oil or other lubricantl or on surface impregnation only. The final density of this bearing is between 8 and 8.5 grams per cc. This material has a high tensile strength after heat treatment and a fatigue strength in excess of 15,000 pounds per square inch.

The fatigue strength is determined by subjecting sample bars to repeated stress, reversal cycles under various loads. The fatigue strength is tlre maximum-loading stress at which the material will withstand an indeiinitely large number of stress reversals. In practice, if the test piece withstands 50 million reversal cycles under a given loading it is considered as capable of withstanding it indefinitely.

Hardness can be obtained between 70 and85 Rockwell B. The material is strong enough to be used as a solid bearing member which does not require integral bonding to a steel reinforcing backing. In some cases the solid bearing can be pressed into a steel sleeve. In the case of connecting rod bearings for internal combustion engines the connecting rod may be lined directly with the sintered bushing.

It is also possible to press tbe powders into a steel sleeve and sinter them together and to the steel in one operation. It is preferable that a steel be used which responds to the same heat treatment. Such steels include carbon steels, chromium-vanadium steels, and manganese-molybdenum steels.

After pressing the bearing blanks they are sintered at an elevated temperature. The sintering time will be inversely proportionalto the sintering temperature. At a higher temperature a shorter sintering time may be used. Moreover,

when pre-alloyed silicide powders are used the sintering time may be somewhat shorter than where the elements are mixed as powders since in the latter case sintering time must be allowed for proper diffusion of the elements into each other. It is preferable in this case to utilize metals which have a high diffusion rate and which are not unduly susceptible to oxidation.

The pre-alloying method has the advantage of requiring less sintering time and there is less danger of undue oxidation of the elements. Thus where the elements are diilcult to sinter and especially where they cannot be sintered with entire satisfaction even in an atmosphere of ccmmercial hydrogen the pre-alloying method should be used.

It is sometimes possible, however, to obtain sufllcient protection byutiiizing a. protective flux during the sintering operation. For example, certain hydrides, such as `calcium hydride, give pif nascent hydrogen which is an extremely powerful y reducing agent.

After the pressed metal'body has been sintered it is given an age-hardening treatment to eect precipitation of the intermetallic compound or a dispersed phase in the copper compounds as age-hardening treator copper alloy matrix. This ment may preferably, comprise quenching the sintered body from a temperature above 700 degrecs C. and subsequently aging the body at an elevated temperature within the range of 350 degrees C. to 700 degrees C. for an extended period of time, such as from one-half hour to several hours. The resulting aged body has much lfigher strength, hardness and wear resistance than a body of similar composition which has not been age-hardened.

It is sometimes desirable to introduce a repressing step after the sintering step to increase the density of the body.

As a specific example a mixture of the following composition is prepared:

Per cent by weight Nickel 2.5 Silicon 0.7 Phosphorus 0.3 Copper balance.

The nickel and silicon may be pre-alloyed or the elemental powders used. The mixed powders are ball milled for 18 hours and pressed at 35 tons per square inch into bearing blanks, such as rings, cylinders or half-cylinders in a lubricated die.

Tre pressed blanks are sintered in hydrogen at 1015 to l025 C. for about one hour.

They may then be repressed at tons per square inch in the original die.

A heat treatment is then given them by quenching from 800 C. in water and then aging for 5 hours at 450 C. in hydrogen. In one case bearings made as described had a density between 8.4 and 8.5 gms. cc., a hardness of '74 to 79 Rockwell B, a tensile strength of about 50,000 pounds per square inch and a fatigue limit of 17,500 p. s. i.

The high tensile strength obtained with these bearings is highly advantageous in heavy duty applications where extreme pressures and high speeds are encountered. Sintered bearings of the prior art ordinarily have extremely low tensile properties and the tensile strength seldom exceeds 25,000 pounds per square inch. Such bearings are apt to fail due to cracking during heavy duty operation. The bearings of the present invention have another advantage in having relatively high thermal conductivity. This material reduces the concentration of heat developed at localized bearing areas which has heretofore been one important cause of bearing failure due to the resulting expansion at the heated areas resulting in galling, scoring lor freezing of the bearing.

Bearing tests made by an independent research agency on the bearings of'the composition and properties described in a General Motors bearing test machine which simulates automotive connectingv rod service showed remarkable results for so hard and strong a material. With 50% overloading, so that the test conditions were midway betweenthe loads for automotive and aircraft service the bearings ran without showing distress of any kind in a 50 hour test and were in excellent condition at the end. There was no galling, scoring or freezing. The co-operating shaft showed n0 excessive wear, These results are truly remarkable for so hard a material, first because it could be run at such high speeds and loads. and second because the shaft showed no excessive wear.

(2) Another type of bearing is pressed at a lower pressure to produce a final density after asraaos (3) A third type of bearing is pressed at a still'V lower pressure to give a still more porous product, the nal density of which is between 5 and '7.5 grams per cc., the fatigue strength of which is below 10,000 p.' s. i. and the hardness of which is below 35 Rokwell lB before impregnation. This bearing is most suitable for impregnation with lead, thallium or other lubricant meta-l which penetrates through the porous body, or with oils or waxes. It is generally necessary to bond this material to a reinforcing backing unless the serv- 'ice conditions are light.

We have attempted to produce bearings of the compositions described herein by casting the met: als in the form desired. In this case where a.

soft lower melting metal is incorporated, as is often required for bearings, it has been impossible to produce castings which commre favorably with the sintered product herein described. Where lead is used, for example, the cast members were found to be extremelyweak and unsound with low tensile strength and having numerous flaws and dirt inclusions. It is also gen vally recognized that silicon is detrimental to the making of copper-lead alloy bearings by casting. The present-invention eliminates these diiculties.

The nickel or cobalt aids in protecting the cop- Aper from corrosive attack from the acid content .in or produced from the lubricating oils present at the bearing.. surfaces. They materially increase the resistance to attack from such acids.

It is sometimes preferred to apply a slow quenching procedure rather than theV rapid quenching in water oroil. One procedure is to sinter the bearing at apprommately 1000 dee5 since these tend to decrease the thermal conductivity. Itis possible, however. to add elements to copper which do not substantially reducethe thermal conductivity but which add corrosion ref -sis`tance to the alloy and improve its qualities as bearing. For example, cadmium added in prc portions ranging from.05 to about 5% of the total compdsitionis helpful.. Y Y

The agehardened copper p0wder composition has an ideal ,microscopic structure i'or bearing purposes. The hardened intennetallic compounds mixture prior to pressing and sintering. For example, a small amount of graphite may be added to the mixture. It is also possible to add the low melting point metals and alloys such as lead, zinc, cadmium, tin, thallium and babbitt at this stage.

In most cases, however, where lubricant metals Y are used, it is preferred to impregnato the sintered and age-hardenedvbearing,.which ordinarily has `a porous structure, with the llubricant after the age-hardening step has been applied. For example, the bearing can be impregnated with one of the lower melting point and softer metals mentioned by immersing the bearing in a. bath of the molten soft metal for a suiiicient period of time. This impregnation may also in some cases be lcombined with 'the age-hardening step by maintaining the bath at the desired temperature for age-hardening purposes and keeping the bearing immersed for a suicient period of time.

Referring to the drawing, Figures 1 and 2 i'lustrate a cylindrical bearing lil made from pressed copper powders, thebearing being sintered and age-hardened as described herein. Figures 3 and 4 illustrate a modiiled form of bearing whpren the bearing surface l l is formed of the pressed, sintered and age-hardened metal powders, the powders being pressed against a backing support i2 of a strong alloy such as iron or steelorthe like. and sintered thereto.

While the present invention, as to its objects and advantages, has been described herein as carried but in spec'ilc embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and g5 scope of the appended claims.

what is claimed is: 1. A sintered metal composition iormed from 0.5 to 5% of metal selected from the group con- Y 0.01 to 1% phosphorus, and the balance substantially allcopp'er, said metal composition containing a silicide of 'said nickel or cobalt present as a dispersedphase therein imparting strength and hardness thereto.

3. A bearing formed of a compact body of copper powder sintered together and containing a precipitation hardening ingredient selected from the group consisting ofV nickel silicide and cobalt silicide as a dispersed phase therein imparting thereto greater hardnessand strength'than leaded bronze, said bearing nevertheless having freedom from galline, scoring and freezing under automotive engine service conditions and freedom from- Y a tendency-to wear the co-operating shaft excesare presentes microscopic particles throughout the copper bas which is .itself soft in comparison thereto.' The intermetallic com- .pounds'being in extremely ,line forniV and embedded in a softer base have no the surface of the co-operating bearing. Y

In some cases it maybe desiredfto add a material having lubricating properties'tothe tendency to score sively,sai d bearing being composed of 0.5 to 5% nickel, 0.1-t0 1% silic, 0.01 to'l phosphorus,

and the balance substantially all copper.

' 4. A bearing formed of a compact body of copper powder sintered together and containing a precipitation' hardening ingredient selected from Y the group consisting of nickel sillcide and cobalt silicide as a dispersed phase therein imparting thereto greater. hardness and strength than- 'leaded bronze, bearmg nevertheless having freedom from galline. scoring and freezing under automotive ensine serviceconditions and freedom from a tendency to wear the ao-operating shaft excessively, said bearing being composed ot 0.5 to 5% nickel, 0.1 to 1% silicon, 0.01 to 1% phosphorus and the balance substantially all copper, and having a density between 8 and 8.5,grams per cc. and a .fatiguevstrength in excess of 15,000 pounds per square inch.

5. A bearing formed of per powder sintered together and containing a precipitation hardening ingredient selected from the group consisting of nickel silicide and cobalt silicide as a dispersed phase therein imparting thereto greater hardness and strength than leaded bronze, said bearing nevertheless having freedom from galling, scoring and freezing under Y automotive engine service conditions and freedom from a tendency to wear the co-operating shaft excessively, said bearing being composed of 0.5-

to 5% nickel, 0.1v to 1% silicon, 0.01 to 1% phosphorus and the balance substantially all copper, and having a density. between 7.5 and 8 grams tinuous network of voids.

6. A bearing formed oi a. compact body of copper powder sintered together and containing a precipitation hardening ingredient selected cobalt silicide as a dispersed phase therein imparting thereto greater hardness and strength a compact body or cop- A per cc. and a porosity characterized by a disconfrom the group consisting of nickel silicide and than leaded bronze, said bearing neverthelessl having freedom from galling, scoring and freezing under automotive engine service conditions and freedom from a tendency to wear the cooperating shaft excessively, said bearing being composed of 0.5 to 5% nickel, 0.1 to 1% silicon, 0.01 to 1% phosphorus, and the balance substantially all copper, and having a density, exclusive `of any impregnant, of 5 to '1.5 grams per cc. and

characterized by a. continuous network of voids. '7. A bearing formed .of a compact body .of copper powder sintered together and containing a precipitation hardening ingredient selected from the group consisting of nickel silicide and cobalt silicide as a dispersed phase therein imparting thereto greater hardness and strength than leaded bronze, said bearing nevertheless having freedom from galling, scoring and freezing under automotive engine servlceconditions operating shaft excessively, said bearing being composed of 0,5 to 5% nickel, 0.1 to 1% silicon,

. 0.01 to 1% phosphorus and the balance substantially all copper. and having a density, exclusive of impregnant, oi 5 to '1.5 grams per cc. and characterized by a continuous network o! voids and a lubricant impregnating said voids.

8. A bearing formed of a compact body ot copper powder sintered together and containing a precipitation hardening ingredient selecd from the group consisting o! nickel silicide and cobalt silicide as a dispersed phase therein imparting thereto greater hardness and strength than leaded bronze, said bearing nevertheless having `freedom from galling. and freezing under automotive engine service conditions and freedom from a tendency to wear the eooperating' shaft excessively, said bearing being composed of 0.5 to 5% nickel, 0.1 to 1% silicon, 0.01 to 1% phosphorus and the-balance substantially all copper, and having a density, exclusive of impregnant, o! 5 to '1.5 grams per cc. and characterized by a. continuous network of voids and a lubricant metal selected from the group consisting of lead and thallium imliregnating said voids.

9. The method of making a sintered copper powder body age hardened with nickel or cobalt silicide without forming a sott shell thereon, which comprises mixing with copper base metal powders suilicient nickel or cobalt and silicon to eiifectiage hardening thereof by heat treatment and adding phosphorus to said mixture, pressing, sintering and age hardening said mixture.

10. The method of making a sintered copper powder body age hardened with nickel or cobaltsilicide without forming a soft shell thereon, which comprises mixing with copper base metal powders suiilcient nickel or cobalt and silicon to effect age hardening thereof by heat treatment and adding 0.05 to 1% phosphorus to said-

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