Process for making ceramic molds having a metal oxide barrier for casting and directional solidification of superalloys

A method for forming a barrier layer at the mold-metal interface in a mold suitable for the casting and directional solidification of superalloys therein including the process steps of:

• placing a mold made of a material comprising a first refractory oxide bonded together by silica within a furnace;
• introducing a controlled prevailing atmosphere into the furnace;
• heating the mold in the controlled prevailing atmosphere at an elevated temperature for a sufficient period of time to dissolve some of the first refractory oxide into the silica;
• casting a melt of superalloy metal into a cavity of the mold, and
• forming a barrier layer comprising a second refractory oxide by the oxidation of at least one constituent of the superalloy within the mold in integral contact with the first refractory oxide material, the barrier layer having a surface defining at least a portion of the interior wall surfaces of the cavity into which the superalloy melt is cast and comes into contact therewith, and having a thickness greater than 1 micron to substantially prevent the molten metal from penetrating into the mold structure and the microstructure of the mold in the vicinity of the cavity exhibiting a substantially porous free structure containing silica bearing phases therein in contact with the barrier layer.