Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Heat and pressure simultaneously to effect sintering
Reexamination Certificate
1999-10-05
2001-02-06
Jenkins, Daniel J. (Department: 1742)
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Heat and pressure simultaneously to effect sintering
C075S228000, C264S603000
Reexamination Certificate
active
06183690
ABSTRACT:
FIELD AND HISTORICAL BACKGROUND OF THE INVENTION
The present invention is directed to bonding particle materials, and more particularly to reactive or nonreactive synthesis, consolidation, or joining of metallic, ceramic, intermetallic, or composite materials to near-net shapes by application of high shear, high current (1-20 kA), and high pressure (about 1 to 2,000 MPa).
Pressure-assisted consolidation or sintering generally involves heating a particle powder compact, while applying pressure simultaneously. The powder compacts are typically heated externally using graphite or molybdenum heating elements and the pressure is applied hydraulically, pneumatically or isostatically depending on the type of the process. Conventional pressure assisted consolidation techniques include hot pressing, hot isostatic pressing, hot forging, and hot extrusion. The conventional techniques require long processing time and high chamber temperature in order to produce high-density parts. In addition, several preparatory steps are required, such as powder heat treatment, precompaction, canning, welding, and machining.
The field of powder consolidation includes powder particles with average particle sizes ranging from about 100 microns to less than 0.01 microns. In any powder consolidation process, the objective is to have minimum grain boundary contamination, maximum density and minimum grain growth. However, powder particles with large surface area, due to their surface charge distribution, readily react with the atmosphere and form a stable oxide phase, which significantly affects the consolidation process. The presence of these oxides, moisture and other contaminants on the surface of the particles, limits the final density that can be achieved and degrades the mechanical properties of the consolidated parts. Thus, it is important to reduce the surface impurities, such as oxygen and other contaminants present on the particle surfaces.
The consolidation of powders to near theoretical density, without significant grain growth has been a difficult task because of the tendency for the grains to coarsen at elevated temperature. Attempts have been made to consolidate powders with average particle size less than 0.01 microns by many techniques, such as furnace sintering, hot pressing, and hot isostatic pressing. However, the drawback is that the total time required for consolidation at the elevated temperature, is very long (several hours) which leads to significant grain growth, and poor mechanical and thermal properties.
Most refractory metals, ceramics, intermetallics and certain composite materials, are extremely hard and require diamond-tipped tools to machine them to final dimensions. In order to minimize expensive machining, the powder densification process must be capable of near-net shaping. The development of a novel process that consolidates the difficult-to-sinter materials into near-net shaped parts has been the goal of many powder metallurgy industries.
As application opportunities continue to emerge that require materials to perform at higher temperatures for sustained periods of time, joining of ceramic and intermetallic materials becomes necessary to enable advanced structure to be produced. Sinter bonding, sinter-HIP bonding, diffusion bonding are typically employed to join these advanced materials. However, long preparation and processing times are required in the conventional techniques that result in high manufacturing cost.
Ultrafine particle materials (with average particle size less than 0.01 micron) have great potential in structural, electronic, thermal management and optical applications since these materials exhibit superior performance characteristics.
Various techniques relating to compacting or sintering of powder materials are disclosed in U.S. Pat. Nos. 3,250,892; 3,340,052; 3,598,566; 3,670,137; 4,005,956; 5,084,088; 5,427,660; and 5,529,746; and in publications—F. V. Lenel, “Resistance Sintering Under Pressure”, Journal of Metal, Vol. 7, No. 1, pp 158-167 (1955), and M. J. Tracey et al., “Consolidation of Nanocrystalline Nb—Al Powders by Plasma Activated Sintering”, NanoStructured Materials, Vol. 2, pp. 441-449 (1993).
The prior art techniques are also not considered effective at least for the reasons that they: are limited to producing smaller size parts, result in nonuniform distribution of temperature throughout the powder compact, result in lower than near theoretical densities, result in undesirable grain growth, do not reactively consolidate or join the materials, do not consolidate or join precursor particle materials, require pretreatment or presynthesis of the particle material, do not apply to ultrafine particles (<1 micron), etc.
In view of the above, there is a need in the industry for a technique that can rapidly consolidate, bond or join precursor or elemental particle material to near theoretical density without requiring complicated preparatory steps.
OBJECTS AND SUMMARY OF THE INVENTION
The principal object of the present invention is to provide a method of rapidly bonding a particle material to near theoretical density with minimum grain growth and to join or bond with high interface integrity and minimum microstructural distortion in the bulk material.
An object of the present invention is to provide a method of bonding a particle material to near theoretical density and near net shape using pulsed plasma, pressure and current.
Another object of the present invention is to provide a method in which a particle material can be reactively or nonreactively consolidated or joined to near-net shape and near theoretical density in a short period of time (less than 10 minutes) with minimum grain growth.
Yet another object of the present invention is to provide a method of bonding a particle material to near theoretical density in which oxygen and other contaminants are removed during the bonding step without any additional preparatory steps.
Still yet another object of the present invention is to provide a method of bonding particle material to near theoretical density which produces bonded material or desired articles economically at reduced processing temperature and time while maintaining nanometer dimensions.
An additional object of the present invention is to provide a method of bonding a particle material to near theoretical density which produces dense near-net shape parts or articles without expensive machining.
Yet an additional object of the present invention is to provide a rapid bonding technique that can join ceramic, intermetallic, and other dissimilar materials in a short period of time without any complicated preparation.
Still yet an additional object of the present invention is to provide a method of bonding a particle material to near theoretical density which can produce near-net shape parts or articles directly from precursors or elemental particle material without the complicated synthesis steps.
Another object of the present invention is to provide a method of bonding a particle material to near theoretical density by simultaneously applying high shear or high pressure, and high current directly to the particle material resulting in: high heating rate (less than 100° C.-1,500° C. per minute), improved particle surface activation, enhanced densification, uniform distribution of heat, and strong bonding.
Yet another object of the present invention is to provide a method of bonding a particle material to near theoretical density which can be used to bond powders with average particle size ranging from 100 microns to 0.01 microns, without significant grain growth, by rapidly processing at lower temperature and duration.
Still yet another object of the present invention is to provide a method of bonding a particle material to near theoretical density which does not require the use of any binders or additives for producing desired shapes.
An additional object of the present invention is to provide a method of bonding a particle material to near theoretical density which produces near-net shape, high density ceramic or other material p
Sethuram Krupashankara M.
Sudarshan Tirumalai S.
Yoo Sang H.
Agarwal, P.C. Dinesh
Jenkins Daniel J.
Materials Modification Inc.
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