高强导电Cu-Ni-Sn合金溶质偏析形成机制及控制的基础研究

Cu-Ni-Sn alloys are one of important elastic conductivity and engineering alloys, which possess excellent elastic performance, wear resistance, corrosion resistance, fatigue property and fracture toughness, and are widely used in the aerospace, navigation, mining, and low temperature environmental. However, the fundamental research and fabrication level of our country are far lower than the developed level of the world. The advanced alloys are manly depended on the import from America and Japan. The critical problem is that the inner mechanism of Sn microsegregration and inverse segregation is unclear and the corresponding control method is limited during Cu-Ni-Sn alloy solidification process. Hence, the project takes the high quality Cu-Ni-Sn alloy as the investigated object, and uses synchrotron radiation with high-energy ray to study the dendrite morphology evolution and solute transfer behavior. The critical role of forced flow field in the interdendritic region will be clarified. The formation of Sn segregation during ternary Cu-Ni-Sn alloys solidification will be revealed, and then establish the mathematical physical model of Sn segregation. Based on the above work, the project utilizes the imposed electromagnetic field and pressure field during alloy solidification to control the Sn inverse segregation, and uncovers the interaction mechanism between the physical fields, liquid flow, crystal growth, heat conduction, and alloy thermo-physical properties on the Sn transportation, finally preparing the high quality homogeneous Cu-Ni-Sn alloys. The project has an important scientific meaning and application value to the Cu-Ni-Sn alloy development of our country.

Cu-Ni-Sn合金是重要的弹性导电铜合金和工程合金，在航空航天、舰船、采矿及低温环境下获得广泛应用。然而我国Cu-Ni-Sn合金基础研究和制备技术远落后国际先进水平，高端产品基本依赖美国以及日本进口，其主要瓶颈是Cu-Ni-Sn合金凝固过程中Sn元素微观偏析及宏观反偏析形成机制不明及相应的控制手段匮乏。鉴于此，本项目采用高能射线同步辐射技术实时研究合金凝固过程中枝晶形貌演变及溶质传输迁移行为，把握影响及控制Sn元素偏析形成过程中枝晶间熔体对流的关键作用，建立两种Sn元素偏析类型形成机制的数学物理模型。在此基础上，本项目将采用外加电磁场及压力场来协同控制合金凝固过程中富Sn溶质对流，阐明该过程中外加电磁场/压力场、熔体对流、晶体生长及热传导等对Sn元素分布的耦合作用规律，最终制备出高品质均质Cu-Ni-Sn合金铸坯，该项目的顺利实施对提升我国Cu-Ni-Sn合金发展具有积极的科学意义。

u-Ni-Sn合金具有高的强度、硬度、弹性，优异的导电导热性、耐腐蚀性、耐磨性、抗应力松弛性能、抗高温氧化性能等，在精密仪器、电子电器、航空航天、天然气化工、机械制造等领域应用广泛。然而Cu-Ni-Sn合金的制备难点在于其液固区间比较大，采用传统的铸造法制备Cu-Ni-Sn合金极容易出现Sn元素的微观偏析和宏观反偏析。作为典型的时效析出强化型铜合金，Cu-Ni-Sn合金在时效后期发生不连续沉淀析出反应，形成的片层组织存在于晶界上引起晶界脆性，最终降低合金的性能。基于此，本项目以Cu-15Ni-8Sn合金为研究对象，通过高温淬火实验研究了Cu-15Ni-8Sn合金的凝固组织演变过程，设计单向凝固实验研究了不同冷却速度下Sn元素的宏观反偏析行为；然后采用垂直半连续铸造并同时施加机械振动和电磁场的方法制备出了组织成分均匀的Cu-15Ni-8Sn合金铸锭，并研究了合金的形变热处理工艺；最后通过加入高熔点的V元素使其在晶界和晶内形成高熔点的稳定第二相来抑制不连续沉淀的形核和生长，探究了V元素对Cu-15Ni-8Sn合金组织及性能的影响。基于以上研究内容，最终制备出高品质均质Cu-Ni-Sn合金铸坯，该项目的顺利实施对提升我国Cu-Ni-Sn合金发展具有积极的科学意义。