DZ125镍基合金的显微组织与蠕变行为Microstructure and creep behavior of DZ125 nickel-based superalloy

通过蠕变性能测试及组织形貌观察，研究DZ125合金的高温蠕变行为。结果表明：经完全热处理后，合金在枝晶干/间区域存在明显的组织不均匀性，粗大γ′相存在于枝晶间，细小γ′相存在于枝晶干。蠕变初期合金中γ′相已转变成筏状结构，稳态蠕变期间合金的变形机制是位错攀移越过γ′相，其中，位错攀移期间，易形成位错的割阶，空位的形成和扩散是位错攀移的控制环节。而蠕变后期合金的变形机制是位错在基体中滑移和剪切进入筏状γ′相。在高温蠕变后期，合金中裂纹首先在晶界处萌生与扩展，且不同形态晶界具有不同的损伤特征，其中，沿应力轴成45°角晶界承受蠕变损伤的较大剪切应力可使其发生较大几率的蠕变损伤；而加入的元素Hf促进细小粒状相沿晶界的析出，可抑制晶界滑移，提高晶界强度，是合金蠕变断裂后晶界呈现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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