Forming metal foam structures

Details Forming metal foam structures Forming metal foam structures

2000-06-29

2002-10-15

Mai, Ngoclan (Department: 1742)

Powder metallurgy processes

Powder metallurgy processes with heating or sintering

Making porous product

C419S009000, C427S247000, C427S427000, C427S455000

Reexamination Certificate

active

06464933

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to the technology of making light-weight metal cellular structures and particularly to the use of cold-gas spraying techniques for achieving such metallic cellular structures.
2. Discussion of the Prior Art
Foamed metals have been heretofore made by essentially adding a gas-evolving compound to molten metal and thereafter heating the mixture to decompose the compound causing the gas evolved to expand and foam the molten metal (see U.S. Pat. Nos. 3,940,262; 5,281,251; 5,622,542). To avoid adding the gas-evolving compound to a molten body of metal, solid particles of the metal, mixed with a gas-evolving compound, can be hot pressed or compacted and then subsequently heated near the melting temperature of the metal, or into the solidus-liquidus range of the metal, to create foaming for a cellular structure (see U.S. Pat. No. 5,151,246). Casting molten metal around granules which are then leached out leaving a porous structure is another method of providing metals with cellular structures.
None of the above techniques are compatible with providing a preformed substrate with a foamed metal coating. Among the techniques used to obtain thick coatings on metal members, are thermal-spray depositions, such as plasma jet or electric-arc metal spraying which presents several drawbacks: unfavorable high thermal and dynamic effects on the substrate; unfavorable changing of the physical properties of the coating during spraying; unfavorable phase transformation of the deposited particles; overheating of the substrate; and erosion or jamming of the spraying equipment.
What is needed is a relatively low temperature spraying technique that achieves compacting of the sprayed metal particles and yet has a composition that promotes foaming to achieve a cellular deposit. “Cold-gas” dynamic spraying of metals was initiated in Russia relatively recently as evidenced by their U.S. Pat. No. 5,302,414. However, the disclosure of such Patent did not teach how to achieve a foamed structure nor did it teach suitable parameters to obtain metal particle welding commensurate with the need for metal foaming.
SUMMARY OF THE INVENTION
The invention herein creates a cellular, venticular or foamed metal structure by first depositing a coating of cold-compacted metal particles, containing a foaming agent, onto a suitable substrate as a result of at least sonic-velocity projection of such particles, and, secondly, thermally treating the coating to gasify the foaming agent and thermally transform the welded metal particles to a plastic-like condition, such as a result of the temperature being slightly above the softening temperature for the metal or above the eutectic temperature of the metal if it is such an alloy.
In a more definitive aspect, the invention is a method of fabricating a foamed metal structure using a supply of metal particles, comprising: (a) introducing a supply of powder metal particles and foaming agent particles into a propellant gas to form a gas/particle mixture; (b) projecting the mixture at or above a critical velocity of at least sonic velocity onto a metallic substrate to create a deposit of pressure-compacted metal particles containing the admixed foaming agent; and (c) subjecting at least the coating on said substrate to a thermal excursion effective to activate expansion of the foaming agent while softening the metal particles for plastic deformation under the influence of the expanding gases.


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