Origin of ductility of intermetallic compounds CoZr and Co39Ni11Zr50 at low temperatures

CoZr属于少数金属间化合物，其在多晶形式下在室温下具有极强的延展性。用Ni代替少量的Co可以提高塑性。虽然已经对这类材料进行了许多研究，但高延性的起源仍然不清楚。高塑性的原因是在二次滑移系上容易滑移和马氏体相变。为了解决这一技术上的重要问题，将首次在低温（300 K - 4 K）下进行机械测试。一方面，拉伸试验用于确定屈服应力、加工硬化、断裂应力和断裂应变的温度依赖性。基于应力松弛试验的热活化分析将用于确定活化参数，作为应力和温度的函数，从而得出变形机制的结论。另一方面，将在室温和液氮温度下进行高压扭转实验，并测量所形成的局部剪切织构作为剪切应变的函数。纹理模拟激活滑移系的信息，其贡献可以通过与合适的多晶模型模拟进行比较来获得。此外，一位有经验的中国合作伙伴将用透射电子显微镜进行位错分析，以获得有关位错类型、排列和密度的信息，但不包括它们对塑性应变的贡献。还将特别注意（Co，Ni）Zr中的马氏体相变对延展性的影响（也可能是低温下CoZr中的应力诱导）。这些研究是基于在韧性稀土金属间化合物YCu和YAg上获得的大量经验。他们应该把金属间化合物延展性的原因放在更广泛的基础上，从而在未来更有针对性地寻找结构应用的延展性金属间化合物。由于（Co，Ni）Zr具有较好的抗氧化性能，是一种合适的模型材料。

CoZr belongs to the few intermetallic compounds, which in polycrystalline form are extremely ductile at room temperature. The ductility can be increased by substituting a small amount of Co by Ni. Although there have been made many investigations on this material class, the origin of the high ductility is still not clear. Reasons favored for the high ductility are easy slip on secondary slip systems and martensitic transformation. To solve this technologically important problem, for the first time mechanical tests will be performed at low temperatures (300 K – 4 K). On the one hand tensile tests are used to determine the temperature dependence of the yield stress, work-hardening, fracture stress and fracture strain. Thermal activation analysis based on stress relaxation tests will be used to determine the activation parameters as a function of stress and temperature allowing conclusions on the deformation mechanisms. On the other hand high pressure torsion experiments will be performed at room and liquid nitrogen temperature and the local shear texture formed will be measured as a function of shear strain. Textures accummulate the information on the activated slip systems, the contribution of which can be obtained from comparison with suitable polycrystal model simulations. In addition, dislocation analyses with transmission electron microscopy will be done by an experienced chinese partner to get information on type, arrangement and density of the dislocations, but not on their contribution to plastic strain. Special attention will be also paid to the influence of the martensitic transformation in (Co,Ni)Zr on the ductility (possibly also stress-induced in CoZr at low temperatures). The investigations are based on much experience gained on the ductile rare earth intermetallic compounds YCu and YAg. They should put the reasons for ductility of intermetallic compounds on a broader basis giving rise in the future to a more targeted search of ductile intermetallic compounds for structural applications. Because of the better oxidation resistance, (Co,Ni)Zr is a suitable model material.