An alloy part is cast in a mold (280) having a part-forming cavity (292, 294, 296). The method comprises pouring a first alloy into the mold. The pouring causes: a surface (550) of the first alloy in the part-forming cavity to raise relative to the part-forming cavity; a branch flow of the poured first alloy to pass upwardly through a first portion (304) of a passageway; and the branch flow to pass downwardly through a second portion (310), of the passageway; solidifying some of the first alloy in the passageway to block the passageway while at least some of the first alloy in the part-forming cavity remains molten. A second alloy is poured into the mold atop the first alloy and solidified.