α-Case formation in Ti-6Al-4V investment casting using ZrSiO4 and Al2O3 moulds

Ti-6Al-4V turbine blade-like geometries were cast in ZrSiO4 and Al2O3 based investment shells at different preheating temperatures to identify the least reactive conditions. The Cold Crucible Induction Melting method was employed to prevent unexpected melt reactions. The resulting sample α-case composition and characteristics of each sample were extensively analysed and the effect of mould stability and preheating temperature were evaluated. This work highlights the diffusion barrier effect that mould-metal reaction products provoke in the detrimental element transport. Interestingly, the results demonstrate that in the less stable preheated ZrSiO4 mould the diffusion layer thickness was 50 μm less than that of the more stable Al2O3. This likely occurred because the reaction products present in the outer reaction layer hindered the detrimental element transport and a thinner diffusion layer was obtained.