【作者】 沈孝芹；

【导师】 李亚江；

【作者基本信息】 山东大学 ， 材料加工工程， 2010， 博士

【摘要】 Al2O3-TiC复合陶瓷由于在Al2O3基体上添加了TiC增强颗粒,使其具有更高的硬度、强度和断裂韧性,被广泛应用于切削刀具的制备。将Al2O3-TiC复合陶瓷与W18Cr4V高速钢用扩散焊方法连接起来制成复合构件,对于改善结构件内部应力分布状态、拓宽Al2O3-TiC复合陶瓷的使用范围具有重要意义。本文采用真空扩散连接工艺,对Al2O3-TiC复合陶瓷和W18Cr4V高速钢的连接进行了试验研究。通过控制真空度1.33×10-4～1.33×10-5Pa,连接温度1080℃～1160℃,保温时间30～60min,压力10～20MPa,可获得界面结合良好的Al2O3-TiC/W18Cr4V扩散连接接头。当连接温度1130℃、保温时间45min、连接压力15MPa时,Al2O3-TiC/W18Cr4V扩散连接接头的剪切强度达154MPa。用金相显微镜和扫描电镜(SEM)分析了Al2O3-TiC/W18Cr4V扩散界面组织结构,研究了工艺参数对界面结合状态和组织结构的影响。结果表明,升高连接温度和延长保温时间,界面过渡区的宽度增加,显微硬度增加,但没有硬度高于Al2O3-TiC陶瓷的脆性相生成。用X射线衍射仪(XRD)分析了Al2O3-TiC/W18Cr4V扩散接头剪切断口相组成,结果表明,断口靠近Al2O3-TiC侧主要存在着A12O3、TiC、TiO和Ti3Al等相,断口靠近W18Cr4V侧主要有A12O3、TiC、Cu、CuTi、CuTi2、Fe3W3C、FeTi等相。本文提出Al2O3-TiC／W18Cr4V扩散界面过渡区主要由Al2O3-TiC/Ti界面反应层、Cu-Ti固溶体层、Ti/W18Cr4V界面Ti侧反应层和W18Cr4V钢侧反应层组成。电子探针(EPMA)分析表明,Al2O3-TiC/Ti界面反应层主要含Ti、Al、O; Cu-Ti固溶体层含Ti、Cu和少量Fe; Ti/W18Cr4V界面Ti侧反应层含Ti和C; W18Cr4V钢侧反应层主要含Ti、Fe、W、C、Cr等。Ti存在于Al2O3-TiC/W18Cr4V界面过渡区的多个反应层中,与多种元素有共存区,表明Ti与多种元素发生了反应,Ti是控制Al2O3-TiC/W18Cr4V扩散连接接头界面反应的主要元素。Al2O3-TiC/W18Cr4V扩散界面形成过程分四个阶段：首先Ti-Cu-Ti中间层熔化形成Cu-Ti液相,填充Al2O3-TiC/W18Cr4整个界面；其次Cu-Ti液相中的Ti向Al2O3-TiC和W18Cr4V两侧扩散并发生反应,使液相区进一步增宽和成分均匀化；然后液相逐渐凝固,各界面间反应生成多种化合物；最后是固相成分均匀化阶段。对Al2O3-TiC/W18Cr4V扩散连接过程的非对称性进行分析,提出Al2O3-TiC/W18Cr4V扩散连接液相凝固过程的非对称模型。对Al2O3-TiC/W18Cr4V扩散连接界面反应机理研究表明,扩散界面反应形成了Al2O3-TiC/TiC+Tl3Al+TiO/CuTi+CuTi2+TiC/TiC+FeTi/Fe3W3C+a-Fe/W18Cr4V的界面结构。对Al2O3-TiC/W18Cr4V扩散连接接头应力分布进行有限元计算,研究了工艺参数、中间层、试样尺寸及形状对接头应力分布的影响。结果表明,接头边缘界面附近应力变化幅度很大,靠近接头中心应力分布很均匀。接头最大轴向拉应力位于接头边缘附近的陶瓷侧,最大剪切应力位于接头边缘Ti/W18Cr4V界面处。降低加热温度和增大连接压力会降低接头轴向残余拉应力。使用Ti-Cu-Ti复合中间层比使用纯Ti中间层可以降低界面轴向应力和剪切应力。增大试样直径和减小W18Cr4V钢厚度可以减小轴向拉应力。方形截面试样四角的应力值比同截面积圆形试样的轴向拉应力要大。对Al2O3-TiC/W18Cr4V扩散界面剪切断裂进行分析,界面裂纹扩展路径可分为界面断裂和混合断裂,其中混合断裂的接头强度高于界面断裂。通过控制扩散工艺参数可以控制界面断裂的形式。界面剪切断口形貌呈解理脆性断裂特征,有明显的解理台阶,也有少量的韧性断裂特征。界面断裂主要发生在靠近Al2O3-TiC陶瓷一侧的界面处,主要是穿晶断裂,也有少量的沿晶断裂。本文对Al2O3-TiC复合陶瓷和W18Cr4V高速钢扩散连接界面结构、界面反应机理、应力分布和界面断裂等进行了研究,该研究工作为Al2O3-TiC复合陶瓷的推广应用提供了试验依据和理论基础,为Al2O3-TiC复合陶瓷与其他金属的连接提供了研究思路。更多还原

【Abstract】 ceramic matrix composites composed of Al2O3 matrix and TiC reinforcing particles have been widely used as cutting tools because of their high strength, hardness and fracture toughness. If the diffusion joining of Al2O3-TiC ceramic matrix composites and W18Cr4V high speed steel can be realized, it will be have important significance to perfect the stress distribution in the components and enhance the use range of Al2O3-TiC composites.In this paper, Al2O3-TiC ceramic and W18Cr4V steel was bonded together by vacuum diffusion bonding technology. Al2O3-TiC/W18Cr4V diffusion bonding joint with sufficient combination interface can be obtained by controlling heating temperature 1080℃～1l60℃, holding time 30-60min, bonding pressure 10-15MPa and vacuum degree 1.33x10-4～1.33x10-5 Pa.The microstructure feature of the Al2O3-TiC/W18Cr4V interface was investigated by optical microscope and scanning electron microscopy (JXA-840). The influence of diffusion bonding parameters on interface combining state and microstructure of Al2O3-TiC/W18Cr4V interface was studied. With the increase of heating temperature and prolong of holding time, the transition zone width of the Al2O3-TiC/W18Cr4V interface broadened and the microhardness in transition zone improved. The phase components in shear fracture surface of Al2O3-TiC/W18Cr4V joint were determined and analyzed by XRD. The results indicated that the phases near Al2O3-TiC interface were Al2O3, TiC, TiO and Ti3Al. And Al2O3, TiC, Cu, CuTi, CuTi2, Fe3W3C and FeTi phases were near W18Cr4V interface.The division on the transition zone of Al2O3-TiC/W18Cr4V diffusion bonding interface was put forward to include Al2O3-TiC/Ti interface reaction layer, Cu-Ti solid solution layer, Ti/W18Cr4V interface reaction layer near Ti side and reaction layer near W18Cr4V side. The elements in the Al2O3-TiC/Ti interface reaction layer are Ti, Al and O. The elements in the Cu-Ti solid solution layer are Cu and Ti. The elements in the Ti/W18Cr4V interface reaction layer near Ti side are Ti and C. The elements in the reaction layer near W18Cr4V side are Ti, Fe, W and C. Ti exists in almost of all the reaction layers of Al2O3-TiC/W18Cr4V transition zone and coexists with many kinds of elements. It indicates that Ti was the main controlling element of interface reaction in Al2O3-TiC/W18Cr4V interface.The formation of Al2O3-TiC/W18Cr4V interface includes four stages. Firstly, Ti-Cu-Ti multi-interlayer melted into Cu-Ti eutectic liquid and spread throughout Al2O3-TiC/W18Cr4V interface. Secondly, Ti in the Cu-Ti eutectic liquid diffused into Al2O3-TiC and W18Cr4V and the width of Cu-Ti liquid broaden. Thirdly, the Cu-Ti liquid solidified and reaction layers in Al2O3-TiC and W18Cr4V interface formed. Lastly, the components in all reaction layers homogenized. The non-symmetry for the process of Al2O3-TiC/W18Cr4V diffusion bonding was studied. The reaction mechanism of Al2O3-TiC/W18Cr4V interface was studied and the results indicated that phase structures in the interface are Al2O3-TiC/TiC+Tl3Al+TiO/CuTi+CuTi2+TiC/TiC+FeTi/Fe3W3C+a-Fe/W 18Cr4V.The distribution of axial stress and shear stress in Al2O3-TiC/W18Cr4V diffusion bonding joint was studied using finite element method (FEM).The influences of bonding parameters, interlayer, sample size and shape on stress distribution were investigated. The calculated results indicated that the gradient of the axial stress and shear stress are great near the joint edge and are flat near the center. The maximum axial tensile stress located in Al2O3-TiC side near the joint edge. The maximum shear stress located in Ti/W18Cr4V interface near the joint edge. With the decrease of the bonding temperature and the improvement of bonding pressure, the axial tensile stresses decrease. With Ti-Cu-Ti interlayer instead of Ti interlayer, the axial stress and the shear stress both decrease. Improving the diameter of the sample and decreasing the thickness of W18Cr4V can decrease the axial tensile stress in the joint. The axial tensile stress in square sample is higher than that in round sample with equal area.The propagation paths of interface cracks in Al2O3-TiC/W18Cr4V joint include interface fracture and mixed fracture which had higher strength than interface fracture. The fracture mode can be controlled by controlling diffusion bonding parameters. The shear fracture of Al2O3-TiC/W18Cr4V joint was mostly cleavage fracture with obvious cleavage step. The fracture position mainly located at the interface near Al2O3-TiC. The fracture was mostly transgranular cleavage.The microstructure, interface formation mechanism, stress distribution and interface fracture of Al2O3-TiC/W18Cr4V diffusion bonding joint were studied in this paper. The studies can provide experimental basis and theory foundation for the wide application of Al2O3-TiC ceramic and research method for joining of Al2O3 and other metals.更多还原