Abstract
Mo/Nb/γ-TiAl functionally graded materials (FGMs) were prepared using a spark plasma sintering (SPS) method, and the MoSi2/Mo/Nb/γ-TiAl FGMs were then siliconized in molten salts. The MoSi2/Mo/Nb/γ-TiAl FGMs before and after oxidation at 1323 K in air were evaluated using optical microcopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The Mo/Nb/γ-TiAl FGMs were obtained by joining at 1373 K for 5 min using SPS. The Nb foil was firmly joined to the γ-TiAl surface and the Mo foil was firmly joined to the Nb foil. The ΔαNb-MoΔT and Δαγ-TiAl-MoΔT values were consistent with the criterion for stable FGMs without interlayer cracking of ΔαΔT less than 4.3×10-3, where ΔαNb-Mo and Δαγ-TiAl-Mo are the differences between the coefficients of thermal expansions of Nb and Mo, and between those of γ-TiAl and Nb, and ΔT is the difference between the SPS temperature and room temperature. The Mo/Nb/γ-TiAl FGMs were siliconized by dipping in a molten-salts mixture before heating in a mullite crucible at 1173 K for 40 h. The MoSi2Mo/Nb/γ-TiAl FGMs were dense and had neither cracks nor voids. The thickness of the MoSi2 layer was approximately 50 μm. The thickness loss of the MoSi2/Mo/Nb/γ-TiAl FGMs was 11 μm after the 200 h exposure to air at 1323 K. The thickness loss of the MoSi2/Mo/Nb/γ-TiAl FGMs was approximately 20 % less than that of NbSi2/Nb/γ-TiAl FGMs.
