Interface reactions between TiAl alloys and diacetatozirconic acid–yttria molds differentiated by ammonium metatungstate addition

Two types of diacetatozirconic acid–yttria molds which were labeled as ZYW mold (diacetatozirconic acid–yttria mold with traces of ammonium metatungstate in the slurry) and ZY mold (diacetatozirconic acid–yttria mold without ammonium metatungstate) were prepared by traditional investment casting. The ZYW and ZY molds were sintered in a carbon-reducing atmosphere and in air, respectively, at 1550 °C for 4 h. Interactions between Ti–47Al–2Cr–2Nb (at%) alloys and the molds at 1650 °C for 30 min were studied. The microstructures of the metal–mold interfaces and the presence of inclusions and oxygen contamination in the TiAl bulk alloy were analyzed, and the influences of ammonium metatungstate were discussed. The results indicate that WO₃ releases O into the TiAl melt, introducing tungsten metal into the alloy matrix. The TiAl alloy ingots cast in the ZY molds had the fewest inclusions and the lowest oxygen contamination.