Refractory coatings for containment of molten reactive metals and their alloys

The primary difficulty with continuous casting of reactive metals, specially titanium and its alloys, is the inability of current crucible materials to withstand the rigors of prolonged exposure to the high temperatures and reactive environment necessary to process reactive metals. Crucible material selection and crucible fabrication will be critical to successful continuous cast technology of reactive metals. Thermodynamic analysis was employed to choose the potential crucible compounds for molten reactive metals and to explain the experimental results. Plasma spraying technology was used to build multi-layer crucibles. Resistive and induction melting techniques were used to investigate the actual high temperature thermodynamics and interface reactions between molten reactive metals (titanium and titanium aluminide) and crucible coatings.; Experimental results and thermodynamic analysis showed that {dollar}rm Ysb2Osb3{dollar} has the highest stability and lowest oxygen contamination for contact with molten titanium, which confirmed the importance of {dollar}rm Ysb2Osb3{dollar} as a containment material. Its disadvantage was a low thermal shock resistance. The complex oxide, SrZrO{dollar}sb3{dollar}, was identified as another potential candidate that showed real potential for containment of molten titanium. At 1760{dollar}spcirc{dollar}C for 30 minutes, a low zirconium content but no detectable strontium was found in titanium, and titanium oxygen contamination was the second lowest.; CaO-stabilized ZrO{dollar}sb2{dollar}, {dollar}rm Ysb2Osb3{dollar}-stabilized ZrO{dollar}sb2{dollar}, CaTiO{dollar}sb3{dollar}, and CaZrO{dollar}sb3{dollar} crucibles were eliminated for containment of molten titanium because these compounds severely contaminated titanium. Of three degradation mechanisms of the ceramic coating: dissolution, reaction and erosion, dissolution was the main mechanism observed. A general thermodynamic procedure was developed to choose the potential crucible compounds for molten reactive metals using the compound free energy and the oxide solubility in molten reactive metals as the most primary factors for selection.