DZ125鎳基合金的顯微組織與蠕變行為Microstructure and creep behavior of DZ125 nickel-based superalloy

通過蠕變性能測試及組織形貌觀察，研究DZ125合金的高溫蠕變行為。結果表明：經完全熱處理后，合金在枝晶干/間區域存在明顯的組織不均勻性，粗大γ′相存在于枝晶間，細小γ′相存在于枝晶干。蠕變初期合金中γ′相已轉變成筏狀結構，穩態蠕變期間合金的變形機制是位錯攀移越過γ′相，其中，位錯攀移期間，易形成位錯的割階，空位的形成和擴散是位錯攀移的控制環節。而蠕變后期合金的變形機制是位錯在基體中滑移和剪切進入筏狀γ′相。在高溫蠕變后期，合金中裂紋首先在晶界處萌生與擴展，且不同形態晶界具有不同的損傷特征，其中，沿應力軸成45°角晶界承受蠕變損傷的較大剪切應力可使其發生較大幾率的蠕變損傷；而加入的元素Hf促進細小粒狀相沿晶界的析出，可抑制晶界滑移，提高晶界強度，是合金蠕變斷裂后晶界呈現非光滑表面的主要原因。

By means of creep-property measurement and microstructure observation, the creep behavior of DZ125 superalloy at high temperatures was investigated. The results show that after full heat treatment, the unhomogeneous microstructure still appears in the dendritic/interdendritic regions of the alloy. Fine cuboidal γ′ precipitates locate in the dendrite arm regions, while coarse ones locate in the interdendritic regions. The cuboidal γ′ phase in the alloy transforms into the rafted structure along the direction vertical to the stress axis in the primary stage of creep. Dislocation climbing over the rafted γ′ phase is thought to be the deformation mechanism of the alloy during the steady creep stage. Thereinto, during the dislocation climbing, dislocation jogs are easy to form, and the formation and diffusion of vacancies are the controlling factors of dislocation climbing. In the latter stage of creep, the deformation mechanism of the alloy is dislocation sliding in γ matrix channels and shearing into the γ′ phase, and the microcracks firstly initiate and propagate along the grain boundaries. The grain boundaries with different configurations display various damage characters during creep. Thereinto, bigger shearing stress during creep damage of the alloy is applied on the boundaries at 45° angle relative to the stress axis, which increases the creep damage probability of them. However, the addition of the element Hf can promote the precipitation of the fine particle-like phase along the boundaries, which can inhibit the slipping of the grain boundaries to improve the strength of them. This is the main reason why the boundaries have non-smooth surfaces after creep rupture of the alloy.

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