Surfacing beads are prepared by a direct current tungsten inert gas arc nickel-aluminum (Ni-Al) powder surfacing process.
With the aim of controlling the dilution rate and obtaining surfacing beads rich in intermetallic compounds, the effects of
surfacing parameters on geometric parameters, dilution rate, composition, and microstructure of the bead are investigated.
An assistant cooler, which can potentially reduce the temperature of the base metal, is used in the surfacing process and
its effect on dilution rate and microstructure is studied. The result indicates that with the surfacing parameter combination
of low current and speed, the width and penetration of the bead decrease, reinforcement increases, and dilution rate drops
markedly. With the reduction of the parameter combination, the intergranular phase γ-(Fe, Ni) is formed in the grain boundaries
of Ni-Al intermetallic matrix instead of the intergranular phase α-Fe, and large amount of intermetallics are obtained. With
the use of an assistant cooler on a selected operation condition during the surfacing process, the reinforcement of the bead
increases, penetration decreases, and dilution rate declines. The use of an assistant cooler helps obtain a surfacing bead
composed of only intermetallics.
Keywords dilution rate - microstructure - Ni-Al powder surfacing - tungsten inert gas arc - assistant cooler