区域定向液相烧结原位合成无铅石墨黄铜基础研究

Lead-free graphite brass with easy-cutting properties,which non-toxic graphite substitute for lead element in brass, not only can meet the industrial needs but also can protect the ecological environment. During the traditional methods of cold-pressing sintering and melt stirring for graphite brass, there are some defects with obvious grapite segregation and high porosity,easy oxidation and serious zinc volatilization,so the new regional and directional liquid-phase sintering is proposed and adopted to prepare graphite brass. It is very important to further broaden the production and application of lead-free easy-cutting graphite brass. Based on theoretical analysis method of finite element,one-dimension temperature field equations can be resolved, and then the relationship among the solide ratio and temperture gradient of liquid-solid two phase zone and drawing velocities of billets was deduced. The ingredient,graphite particle morphology, porosity, instructure, crystal orientaion of grapite brass will be analyzed by metallographical, X-ray diffraction and scanning electron microscopic technologies, and then the crystal growth mechanism can be obtained during regional and directional liquid-phase sintering.The uniaxial tensile and turning experiments will be done for these billets with different instructure, and its deformation behaviour, crack formation and propagation law will be gained by scanning electron microscopic in situ tensile and transmission elcetron microscopic observation of dislocation. Thus, the relationship among alloy composition, structure, mechanical properties and cutting performance can be deduced and then the theoretical basis of lead-free and easy-cutting graphite brass prepared by regional and directional liquid-phase sintering can be obtained.

无铅石墨黄铜以无毒石墨代替铅黄铜中的铅元素，既环保又易切削，能极大的满足工业需求，保护生态环境。传统冷压烧结法和熔体搅拌法制备石墨黄铜存在石墨偏析严重、高孔隙度、易氧化和锌挥发严重的缺点，本项目采用定向液相烧结新技术制备石墨黄铜对于拓展无铅黄铜的生产和应用具有重要意义。采用有限元理论分析方法，求解区域定向烧结的一维温度场方程，获得区域定向烧结过程中液/固两相区固相率随温度梯度和拉坯速率的变化规律。应用X射线衍射仪和扫描电子显微镜对定向烧结石墨黄铜的成分、石墨颗粒形貌、孔隙率、晶体形貌和晶体取向进行分析，获得定向烧结石墨黄铜的组织演变规律。对不同组织形貌的铸坯分别进行单向拉伸和车削实验，并采用扫描电子显微镜原位拉伸和透射电镜技术研究石墨黄铜的变形行为和裂纹形成及扩展规律，获得合金成分和组织形貌与力学性能和切削性能的关系，为采用定向液相烧结技术制备无铅易切削石墨黄铜提供理论依据。

以石墨代替铅的无铅石墨黄铜复合材料具有优良的易切削、良好导电导热性和耐磨性，能极大满足工业需求，保护生态环境。传统冷压烧结法和熔体搅拌法制备石墨铜材料存在石墨偏析严重和高孔隙度等缺点，本项目采用定向液相烧结等技术制备石墨铜复合材料对于拓展其应用具有重要意义。采用有限元理论分析方法，求解了区域定向烧结的一维温度场方程，获得了区域定向烧结过程中液/固两相区固相率与温度梯度和拉坯速率的关系。采用定向烧结制备了直径12mm石墨黄铜线坯，石墨颗粒位于铜晶界并沿拉坯方向排列。研究了烧结工艺对石墨铜复合材料的力学性能和导电性能的影响。相对密度和电导率随球磨时间增加而减小，硬度呈现先减小后增大。随着烧结温度升高，铜晶粒逐渐长大，相对密度、电导率和硬度都呈现先升高后下降的趋势。当球磨8h时，石墨分散性最佳，材料硬度到高达61.4HV，电导率为87.7%IACS。研究了复合材料的成分、石墨颗粒形貌、孔隙率、晶体形貌和晶体取向变化规律。铜晶粒随石墨含量增加逐渐减小，改性石墨铜复合粉末粒径逐渐减小且石墨弥散分布在铜颗粒间，界面结合区域存在铜元素的成分扩散现象。石墨铜复合材料中随着变形量的增加，孔隙逐渐减少。石墨含量为1.0%时材料的相对密度和硬度分别为98.78%和63.9HV，电导率为89.7%IACS。材料的晶体取向在RD-ND面以轧制织构Goss、Brass织构为主，兼有剪切织构E、F和Rotated Cube。研究了石墨铜复合材料的变形行为、摩擦磨损行为、裂纹形成和切削性能规律。摩擦系数和磨损量随轧制变形量增加逐渐降低，磨损机理从疲劳磨损和磨粒磨损逐渐演变为粘着磨损，然后逐渐演变为疲劳磨损。当轧制循环低于4的变形量时，石墨颗粒周围存在明显的裂纹，材料的切削性能较差。随着变形量的增加，其切削性能逐渐提升。本项目探索了石墨颗粒与铜基体之间的界面结合过程及其控制方法，相关的研究结果对于推动新型的具有优良自润滑性、导电导热性和易切削铜基复合材料在航空航天、轨道交通和电子电器等领域的应用具有重要的理论参考价值。