Wetting of iron aluminide alloys by Ag, Au, and Cu1

Because successful integration of alloys into engineering structures often relies on joining technologies this study was done to learn about behavior relevant to brazing of iron aluminide alloys. Brazing processes are largely controlled by the wetting phenomenon, i.e. how well a liquid spreads over the surface of a solid. These experiments involved melting pure silver, copper and gold on the surfaces of Fe0.748Al0.252 and Fe0.589Al0.411 by induction heating in a vacuum chamber. The wetting contact angles were measured as a function of time. These FexAly alloys were wetted by Ag and Au (contact angles, θ<90°). The Ag and Au droplets both dissolved Al from the FexAly substrates. Silver melted near its reference temperature of 960°C and immediately formed a contact angle < 90°. Within minutes, the Ag droplets attained contact angles near 10°. Gold began melting below its reference temperature of 1063°C and this was attributed to Al diffusion into the solid Au. The Au alloy droplets formed contact angles of ˜ 10° in 1 min. Liquid from both Ag and Au droplets penetrated the grain boundaries of the FexAly alloys. A substantial reaction zone also formed under the Ag and Au droplets. In contrast, liquid Cu did not wet the FexAly alloys.