The Preparation And Characterization Of Ni-base Superalloy Single Crystal

Ni-base superalloy single crystals have been grown by the modified vertical Bridgman method.Using Al₂O₃ ceramics crucible and<001>-orientated seed,single crystals up to 30-40mm in diameter and 260 mm in length were obtained;during the process of growth of crystal,the heated temperature was 1480℃to melt uniformly and the growth rate was 2cm/h.The morphology demonstrated the typical microstructure of the Ni-base superalloy single crystal with a minor ofγ′/γeutectic in the interdendritic region.The average first dendrite arm space was 367μm,second dendrite arm space was 60μm and theγ’phase was cubical and distributed uniformly.The elements of Mo,Ta,Co,Ru distrbuted in theγ′/γeutectic;the superalloy single crystal was mainly consisted ofγ’andγphase;according to the formula,the lattice at room and high temperature wereδ_25℃=-0.087%,δ_982℃=-0.5641%,respectively.The heat treatment was 1310℃,4h,A.C+1050℃,4h,A.C+870℃,24h,A.C;withing temperature and time increasing,TCP and carbide precipitated,short aging after 1050℃for50h and 70h,carbides phase precipitated;the aging time and temperature had an influence on mirohardness.The oxidation behavior was investigated at 900 and 1000℃for 200h,and the weight gain reached nearly a constant value when oxidized for 120h at two temperatures,the kinetic curve was parabolic;the oxidation morphology at 900℃for 200h was spherical,however,the oxidation particle was anomalous at 1000℃for 200h,the size became bigger,the oxidation production contained NiO,Cr₂O₃,Al₂O₃,spinels（Ni,Co）Al₂O₄,NiCr₂O₄,NiTa₂O₄andW₂₀O₅₈;the thickness of oxide layer was about 10μm.