Synthesis of open-cell metal foams by templated directed vapor deposition
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Low-density, open-cell nickel base superalloy foams have been synthesized by a high-rate, electron beam-directed vapor deposition process and their mechanical properties evaluated. The deposition process uses an open-cell polymer foam template upon which is deposited a metal alloy coating. The electron beam evaporated flux was entrained in a rarefied transonic gas jet and propagated along the flow stream lines through the polymer structure. After vapor deposition, the polymer template was removed by low-temperature thermal decomposition. The resultant ultralightweight metal foams consisted of a three-dimensional open cell, reticulated structure possessing hollow triangular ligaments with relative densities of 99 wt% Ni) metal foams manufactured by © 2001 Materials Research Society IP address: 132.177.228.65
D.T. Queheillalt et al.: Synthesis of open-cell metal foams by templated directed vapor deposition
thermal decomposition of Ni(CO4) gas are produced by Inco Limited (Toronto, Ontario, Canada) under the trade name Incofoam. It is increasingly used for the nickel electrode of rechargeable batteries. Refractory metal foams (i.e., Zr, Nb, Hf, Ta, W, and Re) produced by chemical vapor infiltration (CVI) are also manufactured by Ultramet Advanced Materials (Pacoima, CA) and Recemat International (The Netherlands) under the trade names Ultrametal and Recemat. Potential applications include thermal insulation, lightweight nozzle flaps for advanced turbine engines, aerobraking structures, aircraft wing and fuselage structures, molten metal, and catalytic filtration devices. Advantages of the CVD and CVI processes include high throwing power resulting in high deposition rates, non-line-of-sight deposition, relatively inexpensive capital equipment costs (because it is a lowvacuum process) and the ability to deposit both elemental metals and some alloys. However, vapor decomposition of the least expensive chemical precursors occurs at high temperatures where the thermal stability of the polymer template must be taken into consideration. The need to use toxic, low decomposition temperature chemical precursors results in a costly process that is difficult to implement in an environmentally satisfactory manner. Physical vapor deposition (PVD) techniques including metal spray deposition, thermal evaporation, reactive sputtering, and arc-vapor deposition have also been used to manufacture metal foams.22–24 The arc-vapor deposition process developed by Vapor Technologies, Inc. (Boulder, CO), and other conventional PVD processes investigated by Montedison (Milan, Italy) have been patented in recent years. However, PVD processes such as these offer a number of potential advantages including the ability to deposit most metal elements and many of their alloys and to even create foams with multilayered or functionally graded metal ligaments. However, because these processes operate in high vacuum (10−5–10−9 torr), they coat only the surfaces that are in the line-of-sight of the vapor source. This is likely to result in uneven coati
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