Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Consolidation of powder prior to sintering
Reexamination Certificate
2000-04-18
2002-03-12
Mai, Ngoclan (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Consolidation of powder prior to sintering
C419S044000, C419S049000
Reexamination Certificate
active
06355209
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to the field of consolidating hard metallic bodies, and also to rapid and efficient and heating and handling of granular media employed in such consolidation, as well as rapid and efficient heating and handling of pre-form powdered metal or metal bodies to be consolidated, where such bodies consist essentially of tungsten, nickel and iron, and/or cobalt.
The technique of employing carbonaceous particulate or grain at high temperature as pressure transmitting media for-producing high density metallic objects is discussed at length in U.S. Pat. Nos. 4,140,711, 4,933,140 and 4,539,175, the disclosures of which are incorporated herein, by reference.
The present invention provides improvements in such techniques, and particularly improvements in such techniques, and particularly improvements leading to consolidation of bodies consisting of tungsten, nickel and iron, and/or cobalt, and functionally gradient material (FGM) compositions thereof. Such bodies may contain minor amounts of cobalt, manganese, and/or titanium, as minor compositional elements.
SUMMARY OF THE INVENTION
It is a major object of the invention to provide for consolidation of metallic powder consisting of tungsten, nickel and iron, as may be employed in target penetration, drilling, and related impact activities. Such powder may contain minor amounts of cobalt, manganese, and/or titanium, as minor compositional elements.
It is another object of the invention to provide rapid and efficient heating of carbonaceous and/or ceramic particles used as pressure transmitting media, and also transfer of heat generated in the particles to the work, i.e. the hard metal pre-form to be consolidated. Basic steps of the method of consolidating the preform metallic body in any of initially powdered, sintered, fibrous, sponge, or other form capable of compaction, or densification (to reduce porosity) then include the steps:
a) providing flowable particles having carbonaceous and ceramic composition or compositions,
b) heating the particles to elevated temperature,
c) locating the heated particles in a bed,
d) positioning the preform body at the bed, to receive pressure transmission,
e) effecting pressurization of said bed to cause pressure transmission via said particles to the body, thereby to compact the body into desired shape, as for example cylindrical shape, increasing its density; and
f) the body to be consolidated consisting essentially of the metals tungsten, nickel and iron. The body may optimally contain minor amounts of cobalt, manganese, and/or titanium, as minor compositional elements.
Another object is to achieve rapid or almost instantaneous densification of composite metal alloy system, the resultant material being fine grained, isotropic, and maintaining original metastable microstructures. In the case of tungsten powder, coated with nickel and iron, or with other metals or ceramics, densification occurs so rapidly and at such a low temperature, that tungsten-tungsten contiguity is virtually non-existent.
A further object is to produce a functionally gradient material (FGM) for use as a shaped, heavy metal penetrator, a particular FGM material powder system used being comprised of a tungsten-nickel-iron-cobalt heavy metal powdered alloy (WHMA) nose section, such as a tungsten composite, high strength steel and tungsten coated powder and transitioning to a high strength steel based powder. It may include an intermediate layer of metal matrix composite of the WHMA, and low alloy steel powder (LAS), and a monolithic LAS base section. The powdered material system employs tungsten particles coated with prealloyed binder composition but other elementally blend, mixed or otherwise combined particles are applicable. The total binder typically consists of elemental nickel (Ni) and iron (Fe) and cobalt (Co) of approximately 16 weight percent of the total composition; but other compositions may be employed.
The ability to fabricate a functionally gradient heavy metal penetrator in one single forging operation has several advantages. The first is the ability to design and engineer a penetrator with specific and predictable dynamic performance criteria. The second advantage is that of reduced manufacturing costs directly related to fewer hot forging steps. Additional cost reductions are realized in the area of raw material usage by eliminating forging trim and scrappage resulting from the use of a powder metallurgy, near net shape forging preform.
By the use of the methodology of the present invention, substantially improved structural articles of manufacture can be made having minimal distortion, as particularly enabled by the use of carbonaceous, or ceramic, or carbonaceous/ceramic particulate in flowable form.
An additional object includes provision of a method for consolidating hard metal and/or ceramic powder, and/or composite material with or without polymeric powder, to form an object, that includes
a) pressing the FGM into a preform, and preheating the preform to elevated temperature,
b) providing flowable pressure transmitting particles and heating said particles, and providing a bed of said flowable and heated pressure transmitting particles,
c) positioning the FGM preform in such relation to the bed that the particles substantially encompass the preform,
d) and pressurizing the bed to compress said particles and cause pressure transmission via the particles to the preform, thereby to consolidate the preform into a desired object shape, having final density.
The preform typically consists of a tungsten, nickel iron complex, which may contain minor amounts of Co, Mn and/or Ti.
An additional object is to provide a body to be consolidated having varying metallic composition along a body dimension. That varying composition may be characterized by a series of zones, extending either axially or radially for example along the article's axis each zone having a characteristic composition which differs from that of an adjacent zone or zones. The metal in successive zones may consist of at least two of the metals tungsten, nickel, iron, and cobalt, and may consist of all three of tungsten, nickel, and iron, or all four, but in varying proportions in successive zones. For a projectile having great penetration capability, a tapered nose zone may consist primarily of tungsten, and successive zones to the rear may contain less and less tungsten, WHMA and more and more steel.
For a three metal body, the metals being M
1
, M
2
and M
3
, the weights W
1
, W
2
and W
3
per unit volume of the respective metals M
1
, M
2
and M
3
are related and selected, to be as follows:
W
1
>W
2
>W
3
The novel features which are believed to be characteristic of this invention, both as to its organization and method of operation, together with further objectives and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purposes of illustration and description only and are not intended as a definition of the limits of the invention.
REFERENCES:
patent: 4140711 (1979-02-01), Convers
patent: 4539175 (1985-09-01), Lichti et al.
patent: 4933140 (1990-06-01), Oslin
Dilmore Morris F.
Fleming Marc S.
Meeks, III Henry S.
Ceracon, Inc.
Haefliger William W.
Mai Ngoclan
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