低层错能铜合金的强韧化研究

The purpose of our research is mainly about the design of copper alloys, studying the influence of different alloying element upon stacking fault energy, in order to fabricate copper alloys with low stacking fault energy. Ultrafine grains can be introduced using severe plastic deformation in liquid nitrogen condition, with deformation nano-twins in the grains at the same time. Annealing treatment has been carried out after severe plastic deformation of copper alloys to form annealing twins during the annealing process. By this process, copper alloys can simultaneously have high strength and good ductility, stable microstructure and great electrical conductivity as well. We are going to solve problems as follows: (1) What is the relationship among the formation mechanism of deformation twins in nano scale and annealing twins and stacking fault energy, and also the influence of stacking fault energy upon the space of twin lamellae? (2) During the plastic deformation process, what are the influences of conditions like deformation temperature and strain rate upon the evolution of microstructure such as grain size and the size of deformation twins? The influence of annealing process upon microstructure after deformation will also be investigated, especially the formation mechanism of annealing twin, which will require deep discussion. (3) The interactions between twin boundaries and dislocations will also be studied, explaining the influence of twin on the strength and ductility of the materials. The quantitative relationships between the microstructure and mechanical properties and electrical conductivity will be built.

本项目首先进行铜合金的成分设计，研究加入不同合金元素对铜层错能的影响，得到低层错能铜合金。其次在液氮冷却的条件下对铜合金进行大塑性加工变形，得到超细晶粒，同时在超细晶粒内部产生纳米变形孪晶。最后将经过大塑性变形后的铜合金进行退火热处理，使合金在退火过程中形成纳米退火孪晶。通过这种方法制备的纳米孪晶铜合金将具有较稳定的微观组织、较高的强度、一定的塑性及良好的导电性能。拟解决如下问题：（1）纳米尺度的变形孪晶和退火孪晶形成机理与层错能的关系，层错能对孪晶层间距大小的影响；（2）塑性变形过程中，变形温度和应变速率等条件对晶粒大小、变形孪晶的尺寸等组织结构演变的影响；退火工艺对变形后材料的微观组织（主要是晶粒大小、变形孪晶）的影响，特别是对退火孪晶的形成规律进行深入研究；（3）研究孪晶界与位错之间的交互作用，从理论上解释孪晶对材料强度和塑性的影响，建立微观组织和力学性能、导电性能的定量关系。

纯铜拥有良好的延展性，但强度较低。传统的材料强化方式在提高强度的同时会导致塑性急剧降低。通过设计显微组织和加工工艺，在提高材料强度的同时，仍然保留良好的塑性。本项目进行铜合金的成分设计，研究加入不同合金元素对铜层错能的影响，得到低层错能铜合金。采用低温和高应变速率条件下对铜合金进行塑性变形，可以引入纳米孪晶来改善塑性。对纯铜及低层错能铜锗合金进行塑性加工得到纳米结构材料，研究合金含量、层错能、应变量等参数对晶粒尺寸、位错密度、孪晶密度等微观组织的影响，阐明了形变诱导的硬化和软化机理。在纳米结构铜合金中发现了反常的退火硬化现象，研究了退火工艺对微观组织稳定性和退火孪晶的影响，揭示了纳米结构低层错能材料退火硬化及软化的机理。晶粒尺寸均匀分布的纳米结构金属材料的塑性仍然较低，设计微观组织不均匀的异质结构材料，有望打破强度-塑性的倒置关系。用表面机械研磨处理（SMAT）制备了梯度结构纯铜、铜合金及镁合金，阐明了加工时间和温度对梯度结构纯铜组织和性能的影响，系统研究了不同层错能的铜合金经过不同时间SMAT处理后的微观组织和力学行为的变化规律，研究了镁合金中梯度层的体积百分比对力学性能的影响。我们的研究揭示了梯度结构材料的微观组织变化规律及协调变形机制，为使低层错能铜合金获得优异性能提供了参考。