Surface Porous Structure and Microhardness of Intermetallic NiAl Compound

A porous structure on the surface of the intermetallic NiAl compound was obtained after the fibrous tungsten phase of directionally solidified NiAl-W eutectic alloys was selectively removed by pulsed polarization. Pore shape, diameter, and spacing were dependent on growth rate during directional solidification. Pore diameter and spacing decreased with increasing growth rate. Nanopores with a diameter of 220 nm and an etching depth of 45.56 μm were produced at a pulsed potential of 0.5 V and an etching duration of 72 hours. With prolonged etching, pore diameter remained unchanged and etching depth increased. The Vickers microhardness of the porous intermetallic NiAl compound (0.325 to 0.351 GPa) was lower than that of the directionally solidified NiAl-W eutectic alloys. The microhardness of the porous intermetallic NiAl compound decreased with increasing pore diameter, pore spacing, or etching depth.