Formation of porous intermetallic thick film by Ni-Al microscopic reactive infiltration

Abstract

Microporous structures of nickel-aluminide thick films lining the inner wall of microchannels have been investigated. The microchannels were produced in metal bodies by a powder metallurgical process utilizing microscopic reactive infiltration. In the experiment, a nickel-powder compact containing shaped aluminum wires was sintered at a temperature between the melting points of nickel and aluminum. Infiltration and diffusion of aluminum into the surrounding nickel powder, accompanied by the reaction between the metals, occurred during the sintering and brought about the formation of microchannels lined with a NiAl intermetallic layer. In this process, nickel powder composed the device body, and the aluminum wires gave the shape of the microchannels. The intermetallic layer had a microporous structure when the diameter of the aluminum wire was 500 μm and the porosity of the compact specimen was 23.6-31.5% within the porosity range examined. When the porosity was 36.0%, such a structure, the porous thick film, was not observed. On the other hand, the porous NiAl thick film was produced in all specimens with an aluminum wire of 200 μm in diameter. The voidage of the porous thick film was maximized when the porosity of the compact specimen was 29.8%, and it reached to 53.8% in the case the diameter of the aluminum wire was 500 μm, and 60.2% in the case that was 200 μm. © 2008 The Japan Institute of Metals.