Process control of GASAR porous metals

Abstract

GASAR porous metals are produced by melting under a partial pressure of hydrogen and then casting into a mold that ensures directional solidification. Hydrogen is driven out of solution and grows as cylindrical pores normal to the solidification front. Experiments have been performed to produce GASARs from pure Ni and Inconel 718, a nickel-base superalloy. The processing variables studied in these experiments included the pressure of H₂(g), total pressure, superheat, and solidification rate. An analysis that considers heterogeneous bubble nucleation was developed that identifies processing conditions in which H₂(g) bubbles are stable in the liquid before solidification. It is hypothesized that these conditions lead to low porosity because the bubbles float out of the melt and are not incorporated into the final porosity. Experimental data are shown to support this hypothesis.