US2884687A - Wear-resistant sintered powdered metal - Google Patents

Description

United States Patent Ofiice Patented May 5, 1959 WEAR-RESISTANT SINTERED POWDERED METAL Robert F. Thomson, Grosse Pointe Woods, and Eric W. Weinman, Birmingham, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application July 19, 1954 Serial No. 444,403

9 Claims. (Cl. 29-182) cations has been limited because of their relatively low wear resistance. Accordingly, a principal object of the present invention is to provide a novel sintered powdered metal having a high degree of wear resistance due to the presence of titanium-aluminum particles. A funther object of this invention is to provide a simple and inexpensive process for forming a sintered powdered metal article containing such particles and having close dimensional tolerances.

These and other objects are attained in accordance with the present invention by the inclusion of a powdered alloy of titanium and aluminum in a powdered metal mix. The resultant product, when sintered, or when sintered and worked to a controlled degree of porosity, possesses excellent wear resistance properties due to the presence of dispersed titanium-aluminum particles. These particles also contribute a substantial degree of score resistance to the sintered powdered metal material. The titanium-aluminum is preferably introduced in the form of a pulverized intermediate alloy, as hereinafter more fully explained.

Moreover, sintered and forged powdered metal parts formed in accordance with our invention, when compared withwear-resistant parts made by conventional manufacturing methods, do not require the expensive machining operations otherwise often necessary to provide the required tolerances.

Since little or no machining isnecessary, scrap or waste is reduced to a minimum. Such a wear-resistant sintered powdered metal may be used to form piston rings, tappets, gears, valve stem guides, bearings and bearing surfaces, including camshaft thrust bearing plates, etc.

Recently sintered powdered metals have been provided with increased wear resistance by [the inclusion of powdered nickel-titanium alloys in the powdered metal mix. This development is disclosed in co-pending patent application S.N. 317,361 filed October 28, 1952, now abandoned, in the name of.Alfred L. Boegehold and owned by the assigneeof the present invention. ever, the use of titanium-aluminum particles in the mix, "in-accordance with the present invention,'affords further advantages over the use of nickel titanium particles.

How-

Titanium-aluminum particles are preferable from an eco 4nomic.standpoint since the average titanium-aluminum alloy, on a weight basis, costs approximately only onehalf as much as the typical nickel-titanium alloy. Furthermore, titanium-aluminum has a considerably larger volume than nickel-titanium for the same amount of weight. Of course, titanium-aluminum also does not :contain any relatively critical nickel.

Onwintering, moreover, titanium-aluminum. particles alloy with the powdered metal mix to which they are added to a considerably lesser extent than nickel-containing compounds and rtend to remain in substantially the same form in which they are introduced. Maximum wear resistance cannot normally be obtained if these particles alloy to an excessive extent with the base metal of the powdered mix. Another advantage of a sintered powdered metal containing titanium-aluminum particles is that this metal is more susceptible to beneficial cold working and heat treatment.

Other objects and advantages will more fully appear from the following detailed description of a preferred embodiment of our invention.

The part to be manufactured is made by initially thoroughly mixing a finely pulverized alloy of titaniumaluminum with the powdered base metal. Even a relatively minute amount of this alloy powder improves wear and score resistance of the sintered powdered material to an appreciable extent, and the range of this constituent may vary from a small but efiective amount to a quantity constituting approximately 25 by weight of the final mix. However, in order to provide the desired combination of economy and strength, particularly impact strength and shock resistance, the titanium-aluminum content preferably should be maintained between about 0.5% and 15% by weight. When more than 25% titanium-aluminum is used, the strength and ductility of the resultant sintered powdered metal article are appreciably reduced. The excessive brittleness of such an article, which reduces its utility for many applications, is evidenced by chipping or cracking of wear test speciments when they are being ground. Optimum properties are usually obtained when the powdered metal mix contains approximately 1% to 10% of the pulverized titanium-aluminum alloy.

Finely divided graphite, preferably mesh or finer, may be mixed with the metal powder and normally improves the quality of the part if it is present in small amounts. Quantities not in excess of approximately 6.5% by weight are generally satisfactory, while a graphite content between about 0.3% and 4% provides superior results in most instances. The inclusion of carbon is especially desirable in powdered iron mixes, but may be omitted for some applications when certain other base metals constitute the predominant constituent in the powdered metal mix.

In view of [the above considerations, we have found that a sintered powdered metal article having optimum score and wear resistance properties in accordance with the present invention comprises approximately 1% to 10% by weight of pulverized titanium-aluminum alloy, 0.3% to 4% by weight of carbon, and the balance substantially all powdered iron or other base metal.

Likewise, in order to eliminate the necessity of coating the dies with a lubricant during the briquetting operation, a small but effective amount of zinc stearate powder not in excess of about 2.5% may also be beneficially included in the powdered metal mix. In general, we have found that best results are obtained with a mix having a zinc stearate content between approximately 0.3% and 2%. Other die lubricants, such as stearic acid in powder form, can also be used in place of the zinc stearate. The use of such die lubricants is especially desirable in forming sintered copper base metal articles, for example, while it is not necessary to include a die lubricant in aluminum base powder mixes.

Among the pulverized titanium-aluminum intermediate alloys which may be used, those containing approximately 30% to titanium and 10% to 70% aluminum result in the production of a sintered powdered metal part having satisfactory wear resistance. For best results,

final sintered product.

excellent results.

and 60% aluminum and 40% to 70% titanium is preferred. If the aluminum content of the titanium-aluminum alloy is excessive, the aluminum becomes molten at the sintering temperature, and partial loss of the titanium: aluminum alloy results. Approximately l' to 400 mesh titanium-aluminum powder is conveniently and preferably employed. Titanium-aluminum particles which are too coarse are somewhat prone to cause scoring.

It will be noted that it is necessary to form particles of titanium-aluminum in order to obtain high wear and score resistance in accordance with the invention. Merely adding titanium and aluminum separately, even if these constituents are added in the aforementionedpreferred proportions, normally does not form these particles. It is the alloy of titanium and aluminum, rather than the individual elements, which contributes the desirable properties of wear and score resistance to the sintered powdered metal article.

We have found that the intermediate titanium-aluminum alloy may be formed by preparing a charge of the desired percentages of titanium sponge and aluminum v 4 ployed. Moreover, both electrolytic iron and Swedish sponge iron powders are satisfactory base materials for many powdered iron parts. The size of the base metal powder particles may vary from about 50 to 325 mesh, depending on the material used and the application for which it is designed.

The wear-resistant sintered powdered metal part may be produced by various processes. One highly satisfac tory method involves briquetting a mixture of the pulformed. A briquetting pressure between approximately .pig, such as commercially available 28 aluminum, the

Pro-alloy then being pulverized and added to thepowdered ferrous base metal. The intermediate alloy mix may also contain small amounts of other metals, such as iron, manganese, silicon, chromium, magnesium and nickel. these metals will not exceed approximately 6% manganese, 3% iron, 2% silicon, 1% chromium, 1% magnesium and 0.5% nickel. When converted to percentages of the final sintered powdered metal product, the above silicon and manganese contents, for example, constitute .on the average only about 0.3% and 0.9%, respectively. The above percentages of the minor constituents are not critical in most instances, however, and are listed as examples only.

The titanium and aluminum are preferably placed in a graphite crucible, covered, and heated to a temperature between approximately 2700 F. and 2950 F. has much as titanium is a readily oxidiza'ble and nitrida'ble element, it is desirable to use an inert atmosphere, such .as argon, as the melting atmosphere.

The formed titanium-aluminum alloy, which solidifies at about 2450 vF., may be cooled to room temperature in the crucible.

If the titanium-aluminum is to be poured from the crucible, this is preferably done while the temperature of the alloy is between approximately 2500 F. and 2700 F.

Cooling and pouring also should take place under an inert atmosphere, the metal preferably being cast under an argon atmosphere as pigs in chilled molds.

Intermetallic compounds, such as TiAl and TiAl are thus formed, and when pulverized and added to the base metal powder, greatly improve the wear resistance of the Mixtures of these titanium-aluminum compounds frequently result, and some of the Normally the approximate maximum quantity of titanium and aluminum may also be present in the form I of a solid solution of titanium and aluminum. Regardless of the exact form in which the titanium-aluminum particles are present in the powdered metal, their presence greatly improves the Wear and score resistance of the resultant sintered powdered metal part.

Among the powdered base metals which may be used in practicing the present invention are ferrous metals, zinc, alununum, magnesium, nickel, copper and lead.

Various powdered alloys of these elements, of course, likewise may have their score and wear resistance improved by the inclusion of dispersed titanium-aluminum particles.

' The usable powdered ferrous metals include iron, steel and powdered alloyed irons. If ferrous base materials are used, commercial iron powders, such 'as those made by duced by atomizing very hard steel, grinding and reducing the carbon content of the powder, can also be cm- A steel powder, which may be pro 20,000 and 120,000 pounds per square inch may be employed, depending on the composition of the part and the purpose for which it is to be used. Before briquetting, it is important that the powdered metal constituents -be thoroughly mixed in order to provide uniformity of structure and propertiesto the finished article. 7

The green briquette is then sintered under suitable conditions of time, temperature and atmosphere into a structure having a controlled degree of porosity. Sintering temperatures between 1900 F. and 2300 F. and sintering times between one-half hour and one hour have proved to be highly satisfactory for powdered ferrous base metal briquettes. These sintering times are not crit ical, however, and sintering periods as short as four minutes and as long as two hours are satisfactory for various applications. For non-ferrous base powders, such as lead base alloys, for example, the sintering temperature may be as low as about 500 F. Among the non-oxidiz ing furnace atmospheres which may be employed, dry Drycolene gas or a gaseous mixture of fNeutralene and a small amount of natural gas are satisfactory. For some non-ferrous base powders, such as copper or bronze powders, a dissociated ammonium atmosphere is particularly effective.

\ It is convenient to prepare Drycolene by burning one part of natural gas with approximately ten parts of air, condensing the Water vapors, passing the gas through hot charcoal and drying it in activated alumina. The dry Drycolene gas thus is composed of approximately 20% carbon monoxide, 3% hydrogen and 77% nitrogen. The Neutralene atmosphere mentioned above is a closely related gaseous mixture which usually consists of approximately 1.5% carbon monoxide, 1.5 hydrogen-and 97% nitrogen. It has proved advantageous to mix about 100 parts of Neutralene with one part of natural gas. Of course, other furnace atmospheres, such as hydrogen, mixtures of nitrogen or hydrogen and methane, etc., can be used, but Drycolene and Neutralene are readily available and each provides a highly effective protective atmosphere.

Following the sintering step, the density and strength of the formed powdered metal part maybe increased by hot or cold working, including forging and multiple pressing operations. The forging operation is preferably one of'hot forging, and it usually is expedient to forge the briquette before it has cooled after the sintering step. If desired, the sintered briquette may be permitted to cool and then be reheated to a temperature appropriate for forging. Forging temperatures approaching those used for sintering are generally suitable for use in the present invention. Alternatively, desirable physical properties may be obtained by multiple cold pressing of the briquette. The forging or pressing operations, whether hot or cold, increase the tensile strength of the sintered material, especially as the porosity approaches zero. Inasmuch as a very dense structure may permit scoring under severe operating conditions, it is desirable to carefully control the forging so as to provide the formed part with proper porosity. More specifically, therefore, we have usually found it advisable to control forging so as to form "a powdered metal "article having between approximately assess? 2% and 20% porosity, thereby improving resistance to score.

Following the forging or pressing operation,'whichever isernployed, the sintered blank may be subjected to anjappropriate heat treatment. In the case of a ferrous base metal part, for example, tempering for approzu'mate- 1y 30.1060 minutes at a temperature between about 800 F. and 1100 F. reduces stresses introduced by 'coldpressing'and tempers the martensite formed during rapid cooling after forging. If hot forging has been employed, coolingis preferably accomplished in a die or between plates. In the case of a ferrous base article, the finished productmay be advantageously surface treated with an iron-manganese-phosphate coating, such as that provided by the Lubrite treatment. Other appropriate surface treatments can be used, of course.

It will be understood that a sintered powdered metal article containing dispersed particles of titanium-aluminum in accordance with this invention may be manufactured under the usual porous metal techniques as disclosed in a number of patents, such as Patents Nos. 1,738,163, 2,097,671, 2,075,444, etc. Also, instead of briquetting the metal powder as hereinbefore explained, itmay be molded to shape prior to sintering as suggeste in Koehring Patent No. 2,198,702.

f Likewise, the powdered metal mix may be merely spread on or otherwise placed in contact with a-supporting surface and subsequently sintered. This supporting surface may be a non-porous metal backing strip, such as a steel strip, and the powdered metal may be bonded to the back on sintering. When this latter procedure is used, it may be desirable to first electrodeposit a suitable metalfiplate on the surface of the back to improve the strength of the bond. This type of process is disclosed in Koehring Patents Nos. 2,187,086 and 2,198,253. After sintering, the composite of spongy powdered metal on the back may be rolled to increase the density of the powdered metal article and then resintered or annealed. Additional rolling and annealing treatments can be employed to further increase the density of the formed artitle. "In this manner a highly'wear-resistant sintered powdered metal layer may be formed on a steel back.

All of the above modifications are understood to be within the scope of the present invention, which broadly comprehends the provision of a sintered powdered metal part containing particles of a titanium-aluminum alloy.

Wear and score test apparatus were employed to compare sintered powdered metals formed in accordance with our invention with the same materials devoid of titaniumaluminum particles. In the case of sintered powdered iron, for example, each sample to be tested was machined to prepare a inch by 1% inch rubbing surface. The specimens were next successively locked in a fixture of the wear test machine and placed in contact with a rotating smooth-surfaced cast iron wheel having a face width of one inch. Increased wear resistance was measured by decreased weight loss in grams and in decreased volume loss in cubic inches, while score resistance was indicated by the load required to cause scoring under prescribed test conditions.

A wear test using this apparatus was conducted in which the specimen load was increased during the 18 hour period from zero load and automatically adjusted to produce a constant frictional load of 64 pounds. At the end of this test period the sintered and forged specimens formed from a conventional mixture of powdered iron and approximately 2% graphite showed an average weight loss of 0.028 gram. On the other hand, the sintered and forged powdered metal specimens of similar composition but containing the aforementioned preferred amounts of titanium-aluminum particles lost an average of only approximately 0.0053 gram. Likewise, while the conventional powdered iron samples underwent a weight loss averaging about 238 lcubic inches, the specimens formed in accordance with the present inven- 6 tion changed on'the average only ISXIO- 'cubic: inches. Theresultsof'lthis test show how greatly the presence of dispersed titanium-aluminum particles increases'the wear resistance of sintered powdered metal articles.

"Tests also indicate that the presence 'of the titaniumaluminumparticles appreciably increases the anti-friction properties of sintered powdered metals. This property was measured by means of the specimen load required to produce a 64 pound frictional load.' Samples formed of sintered powdered iron containing titanium-aluminum particles required an average of about 804 pouunds specimen load to produce the 64 pound frictional load as compared with an average of'only approximately 568 pounds specimen load when the samples without these particles were tested, thus indicating that the coefficient of friction 'of such a material is substantially reduced by the presence of the titanium-aluminum particles.

The aforementioned specimens 'werealso subjected to a score test in'which thetest samples were placed against the aforementionedrota'ting wheel for'60 minutes under a 502 pound specimen load, andthis load was then increased until' scoring occurred. The ordinary sintered powdered iron specimens required a load averaging only 502 pounds to produce scoring, but an average load of approximately 801 pounds was required to cause any indication of scoring of the sintered'powdered iron containing the titanium-aluminum particles. Hence, the results of this test; indicate that the-presence 'of these particles also materially increases the score resistance of sintered powdered metals.

' Similar=favorable results were obtained by the addition of a pulverized titanium-aluminum alloy to other powdered metals. 'For example, when this alloy was added to sintered powdered 'bronze, the beneficial results provided by titanium-aluminum were also evident. .In the case-of sintered powdered bronze, the samples were prep'aredkas tensile bars briquetted at a pressurecf 60,000 pounds per square'inch. .They were then .sintered for 25rminutes 'in a dissociated' ammonia 'atmosphere at a temperature of .1575 F. and subsequently cooled. in this atmosphere. None of the samples were forged.: -As before',-eachspecimento betested'was machined to prepare a A; inch by 1% inch rubbing surface and the specimens successively subjected to the aforementioned wear test.

A wear test using the above-described apparatus was conducted in which the specimen load was increased to 512 pounds and retained at this figure for a total test period of five hours. At the end of this time the sintered copper base test specimens which did not contain titanium-aluminum particles lost an average of 0.341 gram, While the copper base samples of similar composition but containing the titanium-aluminum particles showed an average weight reduction of only 0.0155 gram. Also, while the latter specimens underwent a volume loss averaging only 2X10" cubic inches, the average volume of the test specimens not containing titaniumaluminum particles was reduced on the average about 269 10- cubic inches.

When the various sintered powdered bronze samples were also subjected to the score test and compared, the samples which did not contain titanium-aluminum required a load of only about 590 pounds to produce scoring, but an average load of approximately 791 pounds 'was required to cause any indication of scoring of the samples containing titanium-aluminum particles.

While the present invention has been described by means of certain specific examples, it is to be understood that other forms may be adopted and are contemplated as being within the scope of the present invention, as defined in the following claims.

We claim:

1. A sintered powdered metal consisting essentially of a titanium-aluminum alloy and at least one base metal selected from the group consisting of iron, zinc, aluminum, magnesium, nickel, copper,-- lead and alloys oiisaid metals, said titanium-aluminum alloy being present in, a quantity ranging from a small amount efiective to, materially increase the wear resistance of the base metal toan amount not in excess of approximately 25%, said titanium-aluminum alloy comprising about 30% to 90% titanium and 10% to 70% aluminum. 1

2. A highly wear-resistant sintered article made from a powdered metal mix consisting essentially of about 0.5% to by weight of dispersed particles of an alloy of titanium and aluminum, and the balance substantially all at least one metal selected from the group consisting of iron, zinc, aluminum, magnesium, nickel, copper, lead and alloys of said metals, said titanium and aluminum constituting about to 90% and 10% :31 70%, respectively, of the titanium and aluminum 3. A sintered and worked powdered metal characterized by outstanding wear and score resistance, said powdered metal consisting essentially of approximately 0.5% to: 1 5% of a titanium-aluminum alloy and the balance substantially all at least one metal powder selected fiom thev group consisting of iron, zinc, aluminum, magnesium, nickel, copper, lead and alloys of said metals, the titanium and aluminum in said titanium-aluminum alloy constitutingabout to 70% and 30% to respectively, of said alloy.

4, A highly wear-resistant sintered powdered metal consisting essentially of about 0.5% to 15% dispersed particles of an alloy of titaniumand aluminum, carbon not in excess of 6.5%, and. the balance substantially all ferrous base metal, said titanium and aluminum constituting about 30% to 90% and 10% to respectively, of the titanium and aluminum alloy. H 1

5. ,A highly wear and score-resistant sintered powdered metal consisting essentially of about 1% to.-10% dispersed particles of titanium-aluminum, carbon not in excess of 6.5%, and the balance substantially all copper base metal, said titanium-aluminum comprising 30%. to %titanium and 10% to 70% aluminum. J

6. A sintered powdered metal article characterized by outstanding wear and score resistance, said article being formed .from afipowdered mix consisting essentiallyofi. about 1% to 10% by weight of powdered"titaniun1'-; aluminum,; intermetallic compound containing between 30% and90% titanium, 0.3% to 4% by w'eight'lof finely divided graphite, a small but effective amount of die. lubricant not in excess of 2.5%,. by eight, untrue balance substantially all at least one powdered metalselected from the group consisting, of iron,zinc, aluminum, magnesium, nickel, copper, lead and'alloys of said}, metals. 7. A highly wear and score-resistant sintered metal, article formed from a powdered mix consisting essentially of about 0.3% to 4% finely divide'dgraphite, 0.5% to: 15%.,of titanium-aluminum alloy'in the form of par}, tides-dispersed throughout said mix, and thenbalance substantially all powdered ferrous base metal, saidtiiQ- tanium-aluminum' alloy consisting essentially! of ,30%' to 90% titanium-and 10% to 7.0%a1umin'um.

claim 7 8. The sintered metal article set forth in whichthe titanium-aluminum alloy in the powdered has a mesh size between and 400.

9 A highly wear-resistant sintered powdered metal 'conf sisting essentially of about 1% to 10% titanium-alumi num alloy in the form ofdispersed particles in which titanium constitutes between 30% and 90% by weight of the titanium-aluminum alloy, and the balancesub stantially all at least one metal powder selected from the class consisting of iron, zinc, aluminum, magnesium, nickel, copper, lead and alloys of said metals.' v

References Cited in the file of this patent I UNITED STATES PATENTS 1,551,333 Schroter a a1 Aug. 25, 1923 1,684,131 Franks et a1 ..'Sept. 1l', 192s 2,160,659 Hensel May 30, 1939 2,418,881 Hensel et al. ..1 Apr. 15, 1947 2,612,443 Goetzel et a1. Sept. 30, 1952 2,741,827 Koehler Apr. 17,1956 OTHER REFERENCES l Schwarzkopf: Powder Metallurgy," publ. 1947 pp;

Claims (1)

1. A SINTERED POWDERED METAL CONSISTING ESSENTIALLY OF A TITANIUM-ALUMINUM ALLOY AND AT LEAST ONE BASE METAL SELECTED FROM THE GROUP CONSISTING OF IRON, ZINC, ALUMINUM, MAGNESIUM, NICKEL, COPPER, LEAD AND ALLOYS OF SAID METALS, SAID TITANIUM-ALUMINUM ALLOY BEING PRESENT IN A QUANTITY RANGING FROM A SMALL AMOUNT EFFECTIVE TO MATERIALLY INCREASE THE WEAR RESISTANCE OF THE BASE METAL TO AN AMOUNT NOT IN EXCESS OF APPROXIMATELY 25%, SAID TITANIUM-ALUMINUM ALLOY COMPRISING ABOUT 30% TO 90% TITANIUM AND 10% TO 70% ALUMINUM.