Fatigue strength of in situ processed Cu-Nb composite wires

为了研究多股和单股原位Cu-Nb复合丝的疲劳强度，进行了常温和低温疲劳试验和断口观察。随着Nb含量和拉拔应变的增加，0.2%的抗拉应力和UTS增大。杨氏模量不随拉伸应变变化，而随Nb含量的增加而减小。当温度降低到77K时，0.2%的抗压应力和UTS增加了5~10%，而杨氏模量几乎保持不变。尽管高拉应变钢丝在高应力幅区的疲劳强度较高，但无论拉拔应变大小，在低应力区的疲劳强度几乎相同。疲劳初期塑性应变范围急剧减小。在77K时，疲劳强度提高了2倍。高Nb含量的线材在高应力区疲劳强度较高，而在低应力区疲劳强度较低。这是由于高和低Nb含量的线材在高和低应力区的杨氏模数和加工硬化相关的塑性应变范围的大小。铜丝鞘内的滑移面、退粘面和夹杂物是裂纹萌生的可能场所。低温下疲劳裂纹扩展区域的微小不规则性较小。获得了Nb丝起到阻挡裂纹扩展的作用的证据。平均应力对疲劳强度的影响较小。在4.2K和14T下的剩余电阻率为0.10μΩcm，应变为1.8%时增加了0.02μΩcm。

In order to investigate the fatigue strength of multi- and mono-strand in-situ Cu-Nb composite wires, fatigue tests at room and cryogenic temperatures and fractographic observations were carried out.1. The 0.2% proof stress and the UTS increased with the Nb content and drawing strain. The Young's modulus did not change with the drawing strain, while it decreased with the Nb content. With decrease in the temperature to 77K, the 0.2% proof stress and the UTS increased by 5 to 10%, while the Young's modulus was almost constant.2. Although the fatigue strength at high stress amplitude region was high in the wire with high drawing strain, it was almost the same in low stress region regardless of the drawing strain. A drastic decrease in the plastic strain range in the initial stage was observed in the fatigue. At 77K, the fatigue strength increased by a factor of 2.The fatigue strength in the wire with high Nb content was high at high stress region, while it was rather low at low sterss region. This is explained by the magnitude of plastic strain range associated with the Young's modulus and work hardening in the wires with high and low Nb content in the high and low stress regions.4. The slip plane decohesion facets and inclusions within the Cu wire sheath were possible sites for the crack initiation. Te magnitude of small irregularity in the fatigue crack propagation region was smaller at low temperature.5. Evidence on the roles of the Nb filaments acting as barriers against crack propagation was obtained.6. The effect of mean stress on the fatigue strength was small.7. The residual resistivity at 4.2K and 14T was 0.10μΩcm and it increased by 0.02μΩ cm with straining by 1.8%.