超低温ECAP定向凝固高导电铜铬/锆合金的强韧化调控机制

For eliminate the crosswise grain boundaries, the directional solidification pure copper has more outstanding conductive then the polycrystal copper. But for it’s relative low strength, severly restrict the copper use in some important fields. Equal channel angler pressing can promote the middle and lower stacking fault energy (SFE) single crystal materials continuous orientation twining. In reaction to the phenomenon, this application based on the ECAP directional solidification pure copper, study on the directional solidification copper-chromium/zirconium alloy wire at the liquidnitrogen cooling, using XRD, TEM, DSC and EBSD technology, through solid solution, deformation and precipitation strengthening regulate and control, detect the directional twining effection and the evolution of precipitate phase of continuous columnar grains of Cu-Cr/Zr alloy by ultra-low temperature ECAP. clear the evolution of the material structure and investigate its thermal stability during the deformation and heat treatment. Analyze the correlation effect between the geometric physical parameters of deformation and the critical grain size. Establish a theoretical model for the transformation of microstructure to explore the synergistic mechanism of material's strength and plasticity, thermal stability and electrical conductivity by low-temperature ECAP and heat treatment. Clear the regulation mechanism of strengthening and toughening. The solution of these problems is of great significance for regulating the dislocation configuration, twinning and grain boundary evolution, grain boundary design and interface stability of FCC metals during low temperature cyclic loading and heat treatment.

定向凝固纯铜由于消除了横向晶界，具有比多晶铜更加优异的导电性能，但是较低的强度严重限制了它在重要领域的应用。等通道角挤压能够促使中低层错能的单晶组织发生连续定向孪生，针对这一现象，本申请在对ECAP关键技术的研究基础上,对液氮冷却ECAP定向凝固Cu-Cr/Zr合金进行研究。采用XRD、TEM、EBSD和DSC等技术,通过固溶、形变和沉淀强化联合调控，探索连续柱状晶Cu-Cr/Zr合金在超低温ECAP中的定向孪生效应及析出相的演变规律，明确变形及热处理过程中材料组织的演变并考察其热稳定性，分析变形几何物理参数与极限晶粒尺寸的关联效应，建立微观组织转变的理论模型，探明低温ECAP及热处理与材料强塑性、热稳定性和导电性能的协同作用机制，明确材料的强韧化调控机制。这些问题的解决为揭示FCC金属在低温循环加载和热处理过程中的位错组态、孪晶和晶界的演变、晶界设计和界面稳定性的利用与调控具有重要意义

定向凝固纯铜较低的强度严重限制了该材料在重要领域的应用。等通道角挤压能够促使中低层错能的单晶组织发生连续定向孪生，针对这一现象，本项目对液氮冷却超低温ECAP多种成分Cu-Cr/Zr典型合金的强韧化调控机制进行系统深入的研究。采用XRD、TEM、EBSD和DSC等技术,通过固溶、ECAP+轧制和沉淀强化联合调控，分析不同成分和组织的Cu-Cr/Zr合金在超低温ECAP定向加载过程中的组织演变、特征织构转变规律及析出相的分布及其对力学性能的影响，以及变形及热处理过程中材料组织的演变并考察材料热稳定性，分析变形几何物理参数与形变组织极限晶粒尺寸的关联效应，建立微观组织转变的物理模型，明确超低温ECAP及热处理与材料强塑性、热稳定性和导电性能的影响规律并揭示材料的强韧化调控机制。. 结果表明，不同成分及初始组织的铜及铜合金在超低温ECAP后其力学性能大幅度提升，导电性能均维持在较高水平。超低温ECAP后，单晶铜组织中形成密集分布的平行剪切带使定向孪生应力不断降低，多路径变形后其导电率保持在98%IACS以上。变形几何物理条件和应变状态严重影响ECAP过程中材料组织的剪切模式，并且从根本上影响变形后的极限晶粒尺寸及其分布，从而对材料性能产生直接影响。超低温ECAP能够加剧Cu-Cr/Zr合金的晶粒细化，出现低温退火强化；不同初始组织的纯铜及Cu-Cr/Zr合金在ECAP中低应变量下，轴向剪切主导材料的应变方式，材料组织主要沿ECAP通道发生轴向滑移，位错滑移占主导地位，在ECAP无转向（A路径）变形中主要形成亚微米纤维结构；随着屈服强度的提高，剪切模式向通道交截面方向发生转变，孪晶分割逐渐成为主导细化方式，促使材料组织形成纳米结构。超低温ECAP不仅能够大幅度降低材料组织的温升效应，弱化再结晶，而且能够促进形变孪生，加剧材料晶粒的细化过程，使变形后的极限晶粒尺寸达到纳米级，从而为大尺寸纳米结构金属的连续制备提供了良好的基础。优化时效参数能够促使材料力学性能和导电性能的良好匹配。