Interactions between Nb-Si based ultrahigh temperature alloy and yttria matrix mould shells

To find the best mould shells for investment casting of Nb-Si based ultrahigh temperature alloy, Y2O3 mould shells with zirconia face coat and yttria face coats doped without and with CaO + ZrO2, MgO + ZrO2, La2O3 + ZrO2 and CeO2 + ZrO2 were prepared and their interactions with the melt of the alloy at 1850 degrees C for 30 min were investigated. The results show that the interfaces between the alloy and the mould shells with yttria face coats doped with CaO + ZrO2, MgO + ZrO2 and La2O3 + ZrO2 during re -melting process all comprise two types of reaction layers, which are mainly composed of HfO2 + Y2O3 and TiO + HfO2. The interface between the alloy and the mould shell with yttria face coats doped with CeO2 + ZrO2 is also composed of two types of reaction layers, which consist of HfO2 + Y2O3 and cubic HfO2 respectively. A single reaction layer consisting of HfO2 + Y2O3 constitutes the interface between the alloy and the pure yttria mould shell, and the interface between the alloy and the mould shell with zirconia face coat is also composed of a single reaction layer but consisting of cubic HfO2. Both pure yttria and yttria doped with La2O3 + ZrO2 mould shells are more suitable for the investment casting of the alloy. (C) 2016 Elsevier Ltd. All rights reserved.