P/M Porous Metal

(powder metallurgy porous metal), a metal or alloy whose interconnected porous structure is capable of transmitting a liquid, which exudes on the surface as drops or vapor (dew). This property permits the cooling of components subjected to high heat in aircraft, jet engines, and power units.

The high efficiency of this type of cooling—called transpiration cooling—using a liquid, such as distilled water, alkali metals, or liquefied gases, was announced in the USA as early as 1929. The first tests of a rocket-engine combustion chamber using transpiration cooling were carried out there in 1932. A liquid-propellant rocket engine using liquid hydrogen and oxygen has been constructed with a combustion chamber cooled by this method; the combustion chamber operates at temperatures up to 3320°C.

P/M porous metals are produced by a powder metallurgical process (distribution of powder, pressing or rolling, and sintering). Materials with the same properties are also produced by rolling two or more layers of woven metal gauze with subsequent sintering or by hot-rolling the layers without sintering.

The porosity of P/M porous metals ranges from 20 to 60 percent. The size of the pores varies from several to hundreds of microns, and the pore density may reach 7 × 10⁶ pores per sq cm.

P/M porous metals may be produced from practically any metal or alloy, including heat-resistant and refractory metals. They are supplied as sheets, tubes, bushings, rings, and shaped items.