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Method for Creating Porous Metal Structures by Particle Expansion

技术优势

This invention will simplify solid-state production of metal foams and allow it to be applied to a greater variety of metals. It can be used in standard powder metallurgy or applied to current solid-state foaming methods to increase the achievable porosity. There is no fundamental limit on scale, so the technology may be useful in a verity of applications ranging from small dental implants to the production of impact absorbing components in vehicles. This method offers the unique ability to tailor the type and amount of porosity on both the micron and bulk scales. Graded porosity can be achieved through varying the processing conditions as well as mixing powder feedstock which is able to be foamed with traditional, non-foaming feedstock.

技术应用

This technology can be applied to any application common to metal foams, including medical, aerospace, transportation, catalysis, filtration, etc. It offers new benefits in these applications by possessing smaller porosity and grain size and by introducing new materials and reducing the cost of other materials in the metallic foam market, such as ferrous alloys, copper-based alloys, nickel-based alloys, etc.

详细技术说明

Many metals are not feasible to be foamed in the liquid state, and solid state methods must be used. Solid state methods for foaming are much less efficient, resulting in lower porosity and with increased complexity. By utilizing the entrainment of oxide particles in a metal matrix, the particles can then be expanded at a later time using a suitable reducing agent (e.g., hydrogen) and elevated temperature (50% of melting temperature or less). A unique aspect of the process is that heat alone will not cause expansion as in many other methods. Furthermore, this method does not conflict with current practice in solid state foaming, making it possible to substitute this material for ΓÇ£plainΓÇØ metallic powder in order to achieve additional porosity (up to 40% more). Hence, the process is referred to as Additive Expansion by the Reduction of Oxides. The mechanical alloying process which can be utilized to create such materials is also capable of generating nonequilibrium metals and alloys, and therefore unique compositions for metal foams are possible. This new technology can easily create metal foams with porosity greater than 65%, using basic powder metallurgy concepts and no specialized equipment. The process is unique in that expansion occurs within the particles, not between them. Very small pores, less than a few microns in diameter, of controlled-size can be fabricated, and overall porosity can be controlled. It is anticipated that this technology may be applied to a variety of metals and alloys, possibly including titanium. Though not necessary, cryogenic processing can create extensive nano- to micron-sized porosity in relatively short times (a few hours for alloying and expansion). The creation of small bulk parts has been demonstrated, with no fundamental limits on scale. The material can be used for advanced filters, catalyst supports, energy-absorbing components, thermal and sound insulation, and heat transfer components.

*Abstract

Processes for creating metal foams can be complex and time consuming, often employing gas injection, decomposition of a blowing agent, or foaming of pre-cursor scaffolding. Current methods, such as gas entrapment, have limits to achievable porosity due to pore coalescence and percolation. The purpose of the invention is to create porous metals from a greater variety of metals and alloys while also uniquely controlling the location, size and morphology of the porosity. The principle advantage of this solid-state foaming method is that is can be applied using current processing technology at commercial scale. The process is versatile and can be included in other foaming methods to enhance their porosity as well. The mechanism for foaming is the reduction of oxides in the presence of hydrogen, the oxides being distributed throughout a metallic matrix. This unique mechanism allows the foaming step to be decoupled from temperature, and this can aid in sintering of the metal powder before expansion occurs.

*Principal Investigation

Name: Mark Atwater, Assistant Professor

Department: Applied Engineering

国家/地区

美国