【作者】 陈哲；

【导师】 曹健；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2015， 硕士

【摘要】 针对Si C陶瓷钎焊过程中母材与金属基钎料显著的物理性质差异会引发较大的残余应力问题,本文从调节钎缝热膨胀系数的角度出发,配制了可实现原位合成Ti B晶须与Ti C颗粒的Ag Cu Ti/B4C复合钎料,并将其应用到Si C/Si C与Si C/Nb的连接体系中,提升了相应的钎焊接头的可靠性。通过试验结果与理论分析得到了复合钎料钎焊Si C陶瓷接头的强化机制与形成机理。在Si C/Si C体系中,分别利用含B4C质量分数为0%,1%,1.5%,2%四种成分的Ag Cu Ti复合钎料对Si C/Si C实现钎焊连接。研究了工艺参数对Si C/Si C接头组织与力学性能的影响,分析了接头的断裂位置与裂纹扩展路径,建立了工艺、接头组织与力学性能的联系。一定范围内提升钎焊温度、延长保温时间均有利于钎缝原位合成Ti B与Ti C反应的充分进行,从而缓解接头物理性质的错配,缓解残余应力,提升接头强度。此时对应的Si C/Si C弯曲试件断裂路径与钎缝呈45°夹角,断裂主要发生在两侧的陶瓷母材上。而参数过高会导致界面反应过于剧烈,从而恶化接头性能,此时接头主要断裂在反应层上。在相同钎焊条件下,含1.5wt.%B4C成分的复合钎料对应接头性能最佳,优化工艺参数为950℃,保温10min时,接头平均强度达到140MPa,比纯Ag Cu Ti钎料能达到的最高接头强度高出52%。利用复合钎料对Si C/Nb母材体系实现了可靠的钎焊连接。由钎焊工艺对接头组织与性能影响的研究可知,Nb侧界面为固溶体组织,故塑韧性较好。接头质量主要由Si C侧界面反应与钎缝中心区反应共同决定。当Si C侧形成良好冶金结合,同时钎缝中原位合成大量弥散的Ti B与Ti C时,接头剪切强度最高可达98MPa,对应的工艺参数为890℃,保温10min。利用纯Ag Cu Ti钎料与不同成分的复合钎料钎焊Si C/Nb,相同工艺参数下最佳成分复合钎料对应接头强度比纯金属钎料对应强度提高了近60%。纯金属钎料与含1wt.%B4C复合钎料对应钎缝热膨胀系数较大,试件在高水平残余应力作用下以圆弧形路径完全断裂于陶瓷母材;含1.5wt.%B4C钎料对应钎缝热膨胀系数显著降低,同时钎缝还保持较好的塑性,此时接头呈复合式断裂,裂纹由Si C扩展至钎缝,钎缝的塑性变形与晶须颗粒的联合作用会阻碍裂纹扩展;含2wt.%B4C成分的钎料虽然对应钎缝的热膨胀系数很低,但钎缝的弹性模量显著提高,且塑性变差不利于应力释放,最终接头在界面处断裂。更多还原

【Abstract】 Residual stress of high level usually exists in the Si C brazing joints due to the mismatch of physical properties between ceramics and filler metals. Given this,homemade Ag Cu Ti/B4 C composite filler metals were employed in Si C/Si C and Si C/Nb systems for the in situ synthesis of Ti B whiskers and Ti C particles in seam, and thereby adjusting the coefficient of thermal expansion(CTE) of braze and lowering the residual stress. The strength of Si C brazing joints was, therefore, improved. Also, the strengthening and formation mechanism of brazing joints with composite filler metal was studied by experimental results and analytical work.In Si C/Si C joining system, Ag Cu Ti filler metals containing 0wt.%, 1wt.%, 1.5wt.%,2wt.% B4 C were employed to achieve the joining of Si C. The effects of brazing process parameters on the microstructure and mechanical properties of joints were studied.Besides, fracture location and crack propagation path were analyzed, and thereby establishing the connection among process, microstructure and mechanical properties. It was found that the increase of brazing temperature or holding time, to some extent,exerted positive effects on the in situ synthesis of Ti B and Ti C, which helped to lower the mismatch of properties between ceramics and braze, thus released the residual stress and raised the strength. In this situation, the angle between crack path and brazing seam reached 45°, and fracture mainly occurred on the ceramics. However, improperly high parameters resulted in violent interfacial reaction and deteriorating brazing joints, and fracture mainly occurred on reaction layer. When under same brazing process, the joints corresponding to composite filler metal containing 1.5wt.% B4 C showed the most satisfactory performance. The optimal processing parameters were determined as 950℃,10 min, and the average strength reached 140 MPa in this situation, which was 52%higher than the maximum strength of joints corresponding to pure Ag Cu Ti filler metal.Ag Cu Ti/B4 C composite filler metals were also employed in Si C/Nb joining system and achieved reliable brazing joints. According to the effects of processing parameters on microstructures and mechanical properties of Si C/Nb joints, it was found that there existed Nb-based solid solution at Nb/braze interface, and therefore showed excellent toughness. So the quality of brazing joints were mainly determined by the reaction at Si C interface and the in situ synthesis in brazing seam. When dependable metallurgical bonding was achieved at Si C interface and there existed dispersive and multiple in situ synthesized Ti B and Ti C, the shear strength of Si C/Nb joints reached 98 MPa,corresponding to the optimal parameters 890℃, 10 min.In addition, Si C/Nb joints were studied corresponding to composite filler metals with different compositions. Under the same brazing processing parameters, the strength of joints corresponding to 1.5wt.% B4 C filler metal was 60% higher than that corresponding to pure Ag Cu Ti filler metal. The CTE of brazing seam for pure Ag Cu Ti filler metal and filler metal containing 1wt.% B4 C was still very high, and thus the fracture occurred on ceramics completely with arc path under high residual stress.While the composite filler metal containing 1.5wt.% B4 C significantly reduced the CTE of brazing seam, the plasticity and toughness of seam stayed fine. In this situation, the joints showed composite fracture, and the crack propagated from Si C to brazing seam.Obviously the plastic deformation and combination effects of Ti B whiskers and Ti C particles would hinder the cracks’ propagation. When it came to composite filler metal containing 2wt.% B4 C, the CTE of brazing seam was extremely low, but the elastic modulus was significantly enhanced. The plasticity also deteriorated and thus had negative influence on the release of residual stress, and the fracture ultimately occurred at the interface completely.更多还原