Process for porous materials and property improvement methods for the same

Abstract

A powder metallurgy method of forming a lightweight porous material body that includes mixing matrix material powder with one or more types of high volatility material powder having tendency to vaporize when heated to its vaporization temperature; hot consolidating the mixture under sufficient pressure and at a temperature below vaporization temperature of high volatility material powder to form a substantially consolidated body consisting of dispersions of high volatility material powder particles in the matrix material; heating the consolidated body to a temperature sufficient to vaporize the high volatility material powder particles and to create a vapor pressure sufficiently high to cause yielding of surrounding matrix material, thus forming pores, cooling the compact body after pore formation.

Description

BACKGROUND OF THE INVENTION [0001] The present application claims priority to U.S. Provisional Patent Application No. 60 / 685,519, filed May 31, 2005, and U.S. Provisional Patent Application No. 60 / 697,932, filed Jul. 11, 2005, each of which are specifically herein incorporated by reference in their entirety. [0002] The present invention is directed to a process of forming lightweight, and high strength and lightweight porous materials. In one embodiment, the present invention offers a process to dispersion harden materials by forming nano and micrometer sized pores with thermally stable compounds formed on pore surfaces. Pores thus formed are small and spaced in short proximity to each other sufficiently to act as barriers to dislocation movement, strengthening the material, while lowering its density. In another embodiment, the invention provides a method of manufacturing parts with internal cavities, parts being shaped by vapor pressure from within. [0003] This invention relates t...

AI Technical Summary

Benefits of technology

[0020] Yet, another object of this invention is to provide increased ductility to brittle materials, such as metals, ceramics and glasses, by providing pores that act as dislocation sinks.

[0023] Another object of this invention is to provide substantially uniform size pores in materials in sizes and with mean separation distances less than 10 μ to cause strengthening of the matrix material within which they are formed.

[0024] A further object of this invention is to provide a simple manufacturing process for objects having at least one internal cavity. The simplified process eliminates the need to join two or more pieces to manufacture a hollow part.

[0030] In one embodiment of the invention, the decomposing high volatility material particles create stable compound forming agents that can react with the matrix material to form thermally stable oxides, carbides, nitrides, or borides. For example, oxide-forming agents may be oxygen atoms and oxygen containing molecules, or oxidizing molecular compounds, which react with matrix material constituents to form stable oxides on and near pore surfaces. The pores are small enough (smaller than 100 μm) and in close proximity (closer than 10 μm) of each other to create stable barriers to dislocations within the matrix material, thus causing strengthening of the matrix material. In brittle materials, such as ceramics and glasses, and some metals, pores can act as dislocation sinks, rendering the material more ductile.

Problems solved by technology

There are no directly comparable prior art that dispersion strengthens materials by creating oxidized pores.

However, a number of patented processes refer to creation of metal foams, containing pores typically too large and too uncontrollable to be useful in material strengthening.

This approach, therefore, is not very suitable for creation of pores with uniform size and distribution, such as the pores that can be used in strengthening the matrix material.

The bubble formation is too uncontrollable, and pore sizes created can only be too large to be effective in dispersion strengthening.

Additionally, working with molten metals is very corrosive to the containers, and apparatus that are used to blow or to rotate the melt.

However, heating rate has to be very high to generate the foaming action.

This is extremely fast heating and is impractical for creating pores of substantially uniform size in any rod material having a thickness that is meaningful in industry.

Such fast heating rates eliminate typical industrial furnaces from being used in the process, and require expensive heating equipment, such as laser, electron beam, or induction heating, thus making the process expensive.

Thus, is unnecessarily expensive.

This process is impractical, expensive, and is limited to lower melting point metals.

This adds to the cost of the process.

Additionally, times required for the diffusion bonding of powder particles are by necessity too long, and as a consequence processing costs would be high.

A further unwanted consequence of diffusion bonding involves the potential degradation of the material properties due to a small inclusion, a foreign substance, which can affect properties by diffusing long distances within the solid structure of the matrix material, and creating a large volume of weakness in the material.

Another deficiency of this prior art process is its use of propellant materials that have decomposition temperatures below the hot compaction temperature.

This approach limits the process to propellants too difficult to control due to their tendency to create excessive gas pressures at foaming temperatures, and hydrogen containing propellants are frequently corrosive to many types of matrix metal.

Excessive gas pressures can be generated if the temperature difference between the decomposition temperature and the foaming temperature is too large.

A further difficulty with this prior art patent involves its impracticality.

If the hot compaction were carried out in air, metal particle surfaces would heavily oxidize, which would render the powder nearly impossible to bond to each other.

Rolling process under protective atmosphere or in vacuum would especially be very expensive.

Also, when hot compacting the powder mixture, or during rolling, creation of any significant temperature gradient within the powder mass would render colder portions of the powder to remain unbonded, causing the subsequent foaming treatment useless in those regions.

Because of these reasons, the process as described in U.S. Pat. No. 5,151,246 would not economically produce a usable product.

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