Abstract
Anisotropic creep at different temperature and different stress in a nickel-base single crystal superalloy has been researched in this dissertation. The creep properties of [001], [011] and [111] orientations under different aging treatment conditions, the influence to creep property of small deviated [001] orientation, and the creep performance of transverse [001] orientation have been investigated. The conclusions can be drawn as following:
During low temperature aging heat treatment, the sizes and uniformity of γ' particles increase with the extension of aging time. The cubicity of γ' particles increase after two-step aging treatment. They have a mean size of about 0.4µm that are well aligned along <0 0 1> in γ matrix after aging for 4h at 1080℃+24h at 870℃. During high temperature aging heat treatment, the sizes of primary γ' particles increase with the extension of aging temperature and time. The cubicity of γ' particles decreases and the secondary γ' phase appears in the broad γ matrix channel. The sizes of secondary γ' precipitates are less than 0.15µm in irregular shape. The high temperature aging heat treatment is 4h at 1200℃+24h at 870℃。
The anisotropy of creep properties along [001], [011] and [111] oriented single crystals are obvious at 750℃/750MPa. After low temperature aging heat treatment, the creep rupture life decrease in the order of [001], [111] and [011] oriented alloys; but the creep rupture life decrease in the order of [111], [001] and [011] oriented alloys after high temperature aging heat treatment. The difference of creep performance among different oriented alloys decreases greatly under the test condition of 982℃/248MPa. The creep life decreases in the order of [111], [001] and [011] oriented alloys at both aging heat treatment method. The existence of secondary γ' phase makes the creep performance at high temperature aging heat treatment better than low temperature aging heat treatment. The longest creep life increases above 30% in all the oriented alloys. The specimens of deviated [001] orientation gain longer creep lives and lower elongations under the condition of low temperature and high stress. The primary creep strain of different specimens is different, but the difference does not influence the creep property obviously. The creep performance of perpendicular to [001] oriented alloy is lower under the condition of low temperature and high stress, which is different from [001] oriented alloys that gain longer creep life. When the test temperature increases the creep life of transverse [001] oriented alloy is similar to [001] oriented alloy.
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