A study of low cycle fatigue properties of low activation materials for fusion reactors

为了研究低活性铁素体钢(9Cr-2W钢，JLF-1)的疲劳性能，在完全推拉的轴向应变控制条件下，进行了室温空气中的低周疲劳试验。应变率为0.4%/S，在最初的20次循环内观察到循环应变硬化，然后逐渐发生循环应变软化，直到最终破坏，但塑性应变范围变化不大。在破坏循环次数的一半左右测得的拉伸滞后曲线中的峰值应力取决于总应变范围，在较小的总应变范围内循环应变软化导致的峰值应力的下降幅度大于较大应变范围内的峰值应力。利用Manson-Coffin方程建立了总应变范围与疲劳寿命的回归曲线，并与8Cr2W钢的疲劳寿命进行了比较。结果表明，JLF-1具有比8C…更好的疲劳性能更多的R-2W钢(F82H)。采用电子束熔炼和真空电弧重熔工艺制备了高纯钒合金V-4Cr-4Ti，NIFS-HEAT-2。通过尽可能地减少杂质，成功地制作出26 mm厚的板材。将正常尺寸的试件从板材中加工出来，以研究其力学性能。拉伸试验和断裂韧性试验是在室温下的空气和真空(约104Pa)环境中进行的。该合金具有较高的塑性，延伸率均在80%以上，且两种环境下均出现明显的韧窝断裂。在断裂韧性试验中没有观察到韧性裂纹的扩展。抗裂性曲线呈直线上升，与斜率为2×σ流的钝化线基本一致，钝化持续时间在数百J/m~2以上。这意味着材料非常坚韧，在室温下无法获得有效的J。这些结果有助于加深对低活性候选材料的疲劳和断裂性能以及疲劳和断裂韧性评估实验中的尺寸效应的了解。较少

To investigate fatigue property of a low activation ferritic steel (9Cr-2W steel, JLF-1), low cycle fatigue tests were performed in air at room temperature under an axial strain control of a complete push-pull condition. The strain rate was 0.4 %/s. Cyclic strain-hardening was observed within initial 20 cycles, and then cyclic strainsoftening occurred gradually until the final failure, though the plastic strain range did not change remarkably. Tensile peak stresses in hysteresis curves measured at around a half of number of cycles to failure depended on the total strain range, and the decrease of the peak stress by the cyclic strain-softening in the smaller total strain range was larger than that in the larger strain range. The regression curve of the total strain range against the fatigue life was formulated using Manson-Coffin's equation and the fatigue life ofJLF-1 steel was compared with that of 8Cr2W steel. It was shown that JLF-1 has a superior fatigue properties to those of a 8C … More r-2W steel (F82H). A high purity vanadium alloy, V-4Cr-4Ti, NIFS-HEAT-2, was produced using electron beam melting and vacuum arc re-melting process. The impurity was tried to reduce as little as possible and a 26 mm thick plate was fabricated successfully. The normal size specimens were machined out of the plate to investigate the mechanical properties. Tensile tests and fracture toughness tests were conducted in air and in vacuum (about 10〜4 Pa) environment at room temperature. The alloy showed high ductility and elongated over 80 %, and clear dimple fracture occurred in both environments. A ductile crack growth was not observed during the fracture toughness tests. The crack resistance curve went up straightly, and it was almost same as the blunting line of which slope was 2 x σflow The blunting continued over several hundreds of J value in MJ/m2. It means that the material is very tough and the valid J cannot be obtained at room temperature. The present results contributed to enhancing understanding on fatigue and fracture properties of the low activation candidate materials and on the size effects in the fatigue and the fracture toughness evaluation experiments. Less