Herein the tensile creep behavior and microstructure evolution of an as‐cast Mg–9.82Gd–0.38Zr alloy under different stresses at 250 °C are investigated. The results of creep test show that the creep strain and steady creep rate increase with the creep stress at 250 °C. The fitted stress exponent n value (4.4) and transmission electron microscopy analysis suggest that the steady creep is dominated by the dislocation climb and glide mechanisms together. At the primary stage, due to the segregation of the Gd content, a fine‐strengthening β′ phase precipitates near the α‐Mg grain boundary. Then the transformation of β′ precipitates to a needle‐like β phase, coarsening, and growth of the β phase toward the intragranular direction gradually deteriorate the creep resistance of the experimental alloy. Moreover, two kinds of precipitate‐free zones (PFZs) appear at the end of the secondary creep stage and the PFZs nearly perpendicular to the applied stress direction widen gradually because of the directional diffusion. The nucleation and propagation of creep crack along the cracked eutectic phase and PFZs lead to the greatly rising creep rate at the end of the tertiary creep stage, which eventually results in the intergranular creep fracture of the experimental alloy.

中文翻译：

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铸态Mg–9.82Gd–0.38Zr合金在250°C时的拉伸蠕变行为和组织演变

在此研究了在250°C下不同应力下铸态Mg–9.82Gd–0.38Zr合金的拉伸蠕变行为和组织演变。蠕变试验的结果表明，在250°C时，蠕变应变和稳态蠕变速率随蠕变应力而增加。拟合应力指数n值（4.4）和透射电镜分析表明，稳定蠕变主要由位错爬升和滑移机制共同控制。在初始阶段，由于Gd含量的偏析，在α-Mg晶界附近析出了一个细化的β'相。然后，β'的析出沉淀为针状β相，变粗大，β相向晶内方向的生长逐渐降低了实验合金的抗蠕变性。此外，在二次蠕变阶段的末尾出现两种无沉淀区（PFZs），并且由于方向扩散，几乎垂直于外加应力方向的PFZs逐渐变宽。