材料期刊网

研究了相位角30o 、 60o 、90o和等效应变幅0.8%、0.6%、0.4%时双轴非比例加载下, 冷变形去应力状态Zr-4合金宏观响应和微观位错亚结构。结果表明: 应力矢量和应变增量矢量之间的滞迟角 在循环变形初期表现为较大的变化幅度，随着塑性变形的进行，变化幅度逐渐减小，并趋于稳定。滞迟角的变化幅度与加载路径曲率的变化有关。90°相位角时，变化幅度最小，30°时变化幅度最大。在椭圆和圆形加载路径下，随着应变路径弧长 的增大，等效应力的平均值升高，而变化幅度减小，并逐渐趋于稳定。随着相位角提高，等效应力响应的平均值升高。Zr-4合金在非比例加载过程中表现出初始硬化，随后持续软化的特征。随着相位角提高，循环软化程度加剧。非比例循环过程中Zr-4合金的等效应力高于相同等效应变幅下的比例加载, 表现出潜在强化特征。TEM观察表明：随着相位角的增加，Zr-4合金双轴疲劳位错亚结构由单个位错线向位错缠结及成熟的位错胞转化。材料内部各向同性强化机理加强是Zr-4合金非比例潜在强化的主要原因。

Macroscopic response and microscopic substructure have been studied for Zr-4 alloy in the cold-worked condition, which was subjected to biaxial out-of-phase loading with different phase angles of 30o 、60o 、90o and different equivalent strain amplitudes of 0.4%、0.6%、0.8%. The results show that the delay angle between stress deviation and strain increment tensor firstly exhibits a large variation range, and then drop to saturation as the plastic deformation processes. The variation range of delay angle depends on the curvature of loading path, it has the minimum value at 90o phase angle, and has the maximum one at 30o. The average value of equivalent stress increases, however, its variation range decreases to stable as the phase angle and equivalent strain amplitude increase. Zr-4 alloy displays an initial hardening followed by cyclic softening under out-of-phase loading. The Mises stress response curve of Zr-4 alloy under out-of-phase loading lies above that under both unaxial and in-phase loading. It indicates that cyclic additional hardening is displayed in Zr-4 under out-of-phase loading. TEM examination shows that the typical dislocation configuration changes from individual dislocation lines to tangles and embryonic dislocation cells as the phase angle and the equivalent strain amplitude increase. The isotropic hardening mechanism plays an important role in inducing cycle additional hardening.