Improvement on sintering property of the face coat of yttria mould shells for investment casting

Abstract

In order to explore methods for improving the sintering property of yttria face coat to prevent the thermal spalling phenomenon during investment casting, without significantly increasing the cost，the effects of electrode types in the vacuum furnace and the doping of oxides on the sintering character of yttria face coat at high temperature have been investigated. By contrast with the results of traditionally sintered pure yttria face coat at 1700 ℃, the promotion in densification of the yttria face coat of the mould shells by doping La2O3 + ZrO2 is the most efficacious, whereas doping CeO2 + ZrO2 can impede the densification of the yttria face coat. After sintering at 2000 ℃ in a vacuum furnace with graphite electrodes, the yttria face coat can get complete densification, while the yttria face coat shows incomplete densification in a furnace with tungsten electrodes, whatever doped or undoped. But yttria grains in the face coats doped with oxides are larger than those in the un-doped one. Both CaO + ZrO2 doping and MgO + ZrO2 doping can make greater acceleration of the yttria grain growth than La2O3 + ZrO2 doping and CeO2 + ZrO2 doping.