【作者】 黄利；

【导师】 盛光敏；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2011， 硕士

【摘要】 在异种金属材料的固态扩散连接过程中,由于材料之间存在较大的物理、化学和力学性能差异,使得在连接界面处易生成金属间化合物并在接头处晶粒粗化、接头内应力增大,从而很难获得较好的接头综合性能。针对这些问题,本文在前期研究基础上,利用表面纳米晶所提供的大量非平衡缺陷作为短程扩散通道,同时借助于脉冲压力减小原子扩散过程中的势垒并利用镍中间层阻隔铁-钛间的直接扩散,以期尽量减少Fe-Ti金属间化合物的形成,降低焊接温度,缩短焊接时间,进一步提高焊接接头的性能。本试验采用厚度为12.5μm的镍箔作为中间层对表面自纳米化后的钛合金与不锈钢进行了脉冲加压扩散连接。本文通过调整工艺参数（温度、脉冲加压次数）进行了多次扩散连接试验,借助金相观察、显微硬度测试、扫描电镜观察、能谱分析和X射线衍射等分析手段,研究了钛合金与不锈钢接头界面组织结构,得出温度和脉冲加压次数对接头质量的影响规律,并得出最佳连接工艺参数。结合界面结构形成机制对连接界面结构进行了系统分析,发现连接界面形成了α-Ti/β-Ti/Ni在β-Ti中固溶体/ Ni₃Ti/NiTi/NiTi₂/镍层/Fe-Ni固溶体/γ-Fe的连续过渡的层状结构。试验结果表明,表面自纳米化后TA17钛合金与0Cr18Ni9Ti不锈钢加镍箔中间层脉冲加压扩散连接的最佳连接工艺参数为:连接温度T=850℃、脉冲压力P=8～50MPa、脉冲次数N=40次、脉冲频率f=0.5Hz、脉冲前保温时间t1=0s、脉冲后保温时间t2=120s。在此工艺下得到的接头强度达到322.7MPa,连接用时仅为180s。由于考虑到接头金属间化合物层和压缩率的影响,脉冲加压次数增加,接头综合性能降低。通过断裂机制的微观分析,拉伸断裂发生在Ni-Ti金属间化合物层与镍层之间,镍箔有效地阻止了Fe、Ti间的相互扩散和迁移,避免界面上更多的脆性金属间化合物产生,在镍与钛合金连接界面处形成了Ni₃Ti/NiTi/NiTi₂等新相。对表面自纳米化试样中原子扩散动力学进行了计算,计算结果与常规粗晶试样中对应的结果对比表明,Ni原子在纳米化后钛合金中的扩散系数提高。用5% HCL溶液作为电解质分别对连接试样的焊缝、两侧母材金属进行电化学腐蚀试验,得到同一区域金属在不同电解质溶液中抗腐蚀性能不同,在5%HCL电解质溶液中连接接头其抗腐蚀能力大小为:焊缝>不锈钢>钛合金;通过本试验研究表明,将表面自纳米化和加中间层技术应用于钛合金与不锈钢的扩散连接中,实现了钛合金与不锈钢在短时间和低温连接,提高了异种材料接头性能,为异种金属的连接提供了一种新的方法。更多还原

【Abstract】 Due to tremendous differences of physical, chemical and mechanical property, thicker intermetallic compounds is yielded easily on the bonding interface, grains grow significantly in the diffusion layer, and residual stress is developed during the diffusion bonding of dissimilar metal, which deteriorated badly mechanical character of joint. To solve these problem, surface self-nanocrystallization （SSNC） was apllied to synthesize nanostructured layer on the bonded surfaces of 0Cr18Ni9Ti stainless steel and TA17 titanium alloy bars, and then pulse-pressuring diffusion bonding （PPDB） with nickel interlayer was carried out on these bars which based on the previous studies.PPDB of titanium alloy to stainless steel was carried out with nickel interlayer with a thickness of 12.5μm after samples SSNCed. Diffusion experiments were processed by adjusting the technical parameters of diffusion bonding （bonding temperature and impulse cyclic times）. Microstructure observation, micro-hardness testing, SEM observation, EDS determination and XRD analysis were employed to investigate the structure of the joint. And the potimal technical parameters of the diffusion bonding were obtained. Based on the formation-mechanism of interface-structure and the test results it was found thatα-Ti/β-Ti / Ni₃Ti/NiTi/NiTi₂/ Fe-Ni solid solution/γ-Fe layered structure were formed on the bonding interface.Under conditions of bonding temperature 850℃, pulse pressure 8～50MPa, pulse pressuring cycles 30 cycles, frequency 0.5Hz, preserved temperature for 0s before pulsing and 120s after pulsing, the time for bonding was only 180s under the optimum situation, and the joint strength reached 322.7MPa. Considering the effects of compressibility and the intermetallic, with the impulse cyclic times increase, the joints’property decreased. Base on the test of fracture’s breadcrust and the micromechanics of rupture, PPDB joints ruptured around the interface between Ni-Ti inter-metallic compounds layers and nickel interlayer in the tension test.At the same time, nickel interlayer blocked the interdiffusion of Fe and Ti effectually and form the Ni₃Ti/NiTi/NiTi₂ intermatallic phase.Researches showed that application SSNC to diffusion bonding of titanium alloy and stainless steel may increase atoms diffusion coefficient.The jiont and base metal were taken to do electrochemical corrosion test with 5% HCL corrosive liquid, respectively. The results indicated that the corrosion beharvior magnitude jiont > Stainless steel > Ti alloy, and the joint’s corrosion beharvior were better than TA17 alloy and 0Cr18Ni9Ti stainless steel.With SSNC treatment before bonding and adding Ni interlayer, the temperature and time of diffusion bond is lowered, the performance of joint of is improved, and the negative effects of intermetallic compounds was reduced as small as possible. Through this research, a improved technology for the bonding of dissimilar materials was developed.更多还原