US3128177A

US3128177A - Copper-cobalt infiltrant for iron powder

Info

Publication number: US3128177A
Application number: US78211A
Authority: US
Inventors: Elliott H Rennhack
Original assignee: New Jersey Zinc Co
Current assignee: New Jersey Zinc Co
Priority date: 1960-12-27
Filing date: 1960-12-27
Publication date: 1964-04-07
Anticipated expiration: 1981-04-07

Description

United States Patent of New Jersey No Drawing. Filed Dec. 27, 1960, Ser. No. 78,211 3 Claims. (Cl. 75-153) This invention relates to powder metallurgy and, more particularly, to a novel infiltrant for iron powder compacts.

It is a well established practice to increase the strength of iron powder compacts by infiltrating the iron compact with another metal having a melting point lower than that of iron. This is generally done by placing an amount of'the infiltrant metal on the surface of the sintered iron compact sufiicient to fill the voids between the iron particles and by then bringing the compact up to a temperature sufficient to cause the infiltrant metal to become molten and infiltrate the iron compact. In some instances the infiltrant metal is applied to a green compact and then the resulting product is heated to a temperature sufficient to sinter the iron and in the meantime to cause the infiltrant to melt and impregnate the compact. Although the resulting infiltrated compact has a final strength greater than that of the non-infiltrated sintered compact, there is a frequent drawback to the infiltrated compact in that it needs machining or similar treatment to remove either a residue left from the infiltrant or a pitted surface produced by the erosive action of the molten infiltrant on the surface of the iron compact. These difiiculties are particularly displayed by copper and copper-base alloys which are favored infiltrants because of the high strength and ductility which they impart to iron powder compacts and because of their favorable wetting action for the iron and their suitbale melting points.

I have now found that the inclusion in cooper of a certain amount of cobalt imparts to the copper the ability to infiltrate an iron powder compact without leaving any residue on the surface of the compact and without pitting its surface. Thus, the novel infiltrant of the present invention consists essentially of copper containing between 1% and 4.5% by weight of cobalt.

The infiltrant may be applied to the iron compact either in the form of a green compact of the copper-cobalt alloy powder or in the form of a solid mass of the coppercobalt alloy. In each of these forms the proper amount of infiltrant for each iron powder compact can be readily determined and can be controlled by the shape and size of the mass of infiltrant pursuant to conventional infiltration technique.

The following examples of infiltrants both within and without the scope of the present invention will serve to demonstrate the merits of the infiltrants of the invention. In each instance, the infiltrant was used with an iron powder compact obtained by compacting iron powder, containing 0.75% by weight of zinc stearate as a lubricant, at a pressure of 20 t.s.i. into the form of standard tension bars of the Metal Powder Industries Federation. These bars were sintered in hydrogen for one hour at 1120 C. The resulting iron compacts had a representative tensile strength of 17,500 psi. with an elongation of 1 to 2% at fracture. The sintered bars had a pore volume of about 26% of the bar volume.

In testing the effectiveness of each infiltrant, an amount 3,128,177 Patented Apr. 7, 1964 "ice of the infiltrant was used which approximately 83% of the pore volume of the iron powder test bar pursuant to present commercial practice. In each instance the infiltrant was used in the form of a metal strip which was placed on the upper surface of the sintered iron powder test bar and the assembly was heated for 30 minutes at 1100 C. in a hydrogen atmosphere. The resulting infiltrated test bar was then cooled to room temperature at the rate of 37 C. per minute.

The following table summarizes the test data on the aforementioned iron powder test bars infiltrated as described with the specified infiltrant:

It will be observed from the foregoing data that pitting of or a residue on the surface of the iron powder test bar resulted from the use of conventional infiltrants (brass or copper) and from copper-cobalt alloys outside of the aforementioned eifective range of 1% to 4.5 by weight of cobalt. Within this cobalt range, the cuprous infiltrants impart high tensile strength and ductility to the iron powder compact without adversely affecting the surface of the compact by either pitting or a residue.

I claim:

1. An infiltrant for iron powder compacts having a melting point lower than that of iron and capable, when melted in contact with an iron powder compact, of infiltrating the compact without pitting the surface of the compact and without leaving a residue on the surface of the compact, said infiltrant comprising a copper-cobalt alloy consisting essentially of 1% to 4.5 by weight of cobalt and the balance copper.

2. An infiltrant for iron powder compacts having a melting point lower than that of iron and capable, when melted in contact with an iron powder compact, of infiltrating the compact without pitting the surface of the compact and without leaving a residue on the surface of the compact, said infiltrant comprising a copper-cobalt alloy powder the particles of which consist essentially of 1% to 4.5% by weight of cobalt and the balance copper.

3. An infiltrant for iron powder compacts having a melting point lower than that of iron and capable, when melted in contact with an iron powder compact, of infiltrating the compact without pitting the surface of the compact and without leaving a residue on the surface of the compact, said infiltrant comprising a solid mass of a copper-cobalt alloy consisting essentially of 1% to 4.5% by weight of cobalt and the balance copper.

References Cited in the file of this patent UNITED STATES PATENTS Evans et al. Jan. 6, 1959 OTHER REFERENCES

Claims

1. AN INFILTRANT FOR IRON POWDER COMPACTS HAVING A MELTING POINT LOWER THAN THAT OF IRON AND CAPABLE, WHEN MELTED IN CONTACT WITH AN IRON POWDER COMPACT, OF INFILTRATING THE COMPACT WITHOUT PITTING THE SURFACE OF THE COMPACT AND WITHOUT LEAVING A RESIDUE ON THE SURFACE OF THE COMPACT, SAID INFILTRANT COMPRISING A COPPER-COBALT ALLOY CONSISTING ESSENTIALLY OF 1% TO 4.5% BY WEIGHT OF COBALT AND THE BALANCE COPPER.