【作者】 孙元；

【导师】 张杰；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2011， 博士

【摘要】 氮化硅陶瓷以其优异的高温力学性能被广泛应用于航空航天等领域,为了扩展Si₃N₄陶瓷的应用范围,Si₃N₄陶瓷的连接成为急待解决的问题。本文利用Au-Ni-V钎料对Si₃N₄陶瓷进行钎焊,研究钎料成分和工艺参数变化对接头显微组织和性能的影响;深入探讨接头的显微组织与力学性能之间的关系;揭示含V活性钎料连接Si₃N₄陶瓷的界面反应机理;并在Au-Ni-V钎料中加入第四组元Pd或者Mo,讨论第四组元的加入对接头显微组织,力学性能以及连接机理的影响。研究发现,利用Au-Ni-V钎料连接得到的Si₃N₄/Si₃N₄陶瓷接头主要由三部分组成:Si₃N₄陶瓷母材,由Au[Ni]固溶体和富Ni相构成的焊缝合金区,以及陶瓷母材和焊缝合金区之间的VN界面反应层。当钎焊条件为1373K/30min时,钎料合金中V含量在一定范围内增加,VN界面反应层增厚,使得界面结合强度增加,对接头的力学性能有利,但V含量超过15 at.%时,焊缝合金区中的脆性相Ni₂SiV₃不断增多,这种脆性化合物的形成导致接头中的残余应力增大,接头的力学性能下降。当钎焊条件为1423K/30min时,在一定范围内增加V含量,界面反应层增厚,焊缝合金区由Au[Ni]和均匀分布的颗粒状Ni[Si,V,Au]固溶体构成,接头的抗弯曲性能提高,V含量达到20 at.%,Ni基固溶体中将析出Ni₃Si相,对接头的性能不利。通过对钎焊工艺的探索发现,在一定范围内提高钎焊温度或者延长保温时间,VN界面反应层增厚,对接头的性能有利。可是当钎焊温度过高（1473K）或保温时间过长（90min）,焊缝合金区中的Ni[Si,V,Au]固溶体转变为大块的金属间化合物Ni₃Si,Ni₃Si的形成对接头的力学性能不利。采用Au58.7Ni₃6.5V4.8 at.%钎料在1423K保温60min连接得到的Si₃N₄/Si₃N₄陶瓷获得了最高接头性能,其平均三点弯曲强度为249MPa。接头具有良好的高温性能,当试验温度达到973K,接头的抗弯曲性能仍保持在200MPa以上,在973K的大气氛围下保温100h后,接头的室温抗弯曲性能为269MPa。在Au-Ni-V钎料中加入第四组元Pd,随着添加的Pd含量增加,接头的界面反应层增厚,Ni基固溶体中的Si含量不断增加,最终形成多种Ni-Si化合物。利用Au54.1Ni₃6.1V4.8Pd5钎料在1423K保温60min连接得到的Si₃N₄/Si₃N₄陶瓷接头性能最高,室温强度为264.4MPa,试验温度提高到1073K,接头的平均抗弯曲强度仍保持在221MPa。在Au-Ni-V钎料中添加1 at.%的Mo颗粒,Mo颗粒与Ni、V和Si发生了反应,形成四元化合物Ni₂Si（VMo）₃,该化合物的生成对接头性能不利。本文阐明了利用含V的活性钎料连接Si₃N₄陶瓷的界面连接机理:在钎焊加热过程中,钎料合金熔化,Si₃N₄陶瓷母材/液相钎料界面处的V与Si₃N₄发生反应,生成反应产物VN,Si从界面反应中释放出来,熔入液相钎料合金中。随着钎焊温度增加或者保温时间的延长,界面处形成的VN晶粒长大并互相连接,VN与Si₃N₄晶粒之间没有特定的位相关系。界面反应层的厚度变化与保温时间满足线性定律,说明反应层的生长速率是由V与Si₃N₄之间的反应速率控制的。通过动力学计算可知,利用Au58.7Ni₃6.5V4.8钎料连接Si₃N₄陶瓷,VN界面反应的活化能为329.5 kJ/mol,在该钎料合金中添加了5 at.%的Pd之后,活化能降低至255.9 kJ/mol,证明Pd的加入不仅可以提高钎料合金的熔点,还可以改变界面反应活化能,有效促进界面反应。更多还原

【Abstract】 Silicon nitride ceramics with excellent mechanical properties at high temperature have been widely used in aerospace and other fields. It is extremely necessary to join the Si₃N₄ ceramics for extending the application of Si₃N₄. In this research, Au-Ni-V filler alloy was used to braze Si₃N₄ ceramics. The effect of filler alloy content and brazing parameters on microstructure and mechnical properties of joint has been studied and the effect of microstructure on mechanical properties was analyzed in detail. The mechanism of interfacial reaction between active filler metal of V and Si₃N₄ ceramics was studied deeply. Furthermore, the fourth element of Pd or Mo was added into Au-Ni-V filler alloy to reveal the effect of addition of fourth element on the microstructure, mechanical properties and the mechanism of the joint formation.The results show that the Si₃N₄/Si₃N₄ joint brazed with Au-Ni-V filler alloy consists of three parts: Si₃N₄ ceramic substrates, filler alloy seam composed of Au[Ni] solid solution and Ni-rich phases, and VN reaction layer between substrates and filler alloy seam. Under brazing parameter of 1373K/30min, with V content in filler alloy increasing in a certain range, the thickness of VN reaction layer increases, resulting in the improvement of bonding strength and mechanical properties of the joints. However, when V content exceeds 15 at.% , the brittle alloy phase Ni₂SiV₃ increases, leading to the rise of residual stress in the joint and decrease of mechanical properties of joint. Under brazing condition of 1423K/30min, with the increase of V content in a certain range, reaction layer thickness increases and the filler alloy seam is composed of Au[Ni] solid solution and granular Ni[Si,V,Au] solid solution distributed uniformly. The mechanical properties of joint can be improved. However, Ni₃Si phases precipitated from Ni-base solid solution, and the properties of joint decreased when V content is too high.According to the study of brazing parameters, it can be found that the VN reaction layer was thickened and the mechanical properties of joint was improved with brazing temperature or holding time increasing in certain ranges. However, when the brazing temperature is too high （1473K） or the holding time is too long （90min）, Ni[Si,V,Au] solid solution transformed to an intermetallic compound of Ni₃Si in the filler alloy seam, which leads to the decrease of mechanical properties of joints. Therefore, the average three-point bending strength of Si₃N₄/Si₃N₄ joint brazed using Au58.7Ni₃6.5V4.8 at.% at 1423K for 60min reaches the maximum value of 249MPa at room temperature. The joint has good high-temperature performance. When testing temperature increased to 973K, the bending strength of joint is more than 200MPa and when the joint was annealed in air at 973K for 100h, bending strength of joint increases to 269MPa.In this research, the fourth element of Pd was added into Au-Ni-V filler alloy to improve the mechanical properties of joint. The results show that with increasing Pd content, the thinckness of VN reaction layer increases and the Ni-based solid solution grows because the Si content increases continuously. Finally, Ni-Si compounds are formed in the joint. Therefore, the average three-point bending strength of Si₃N₄/Si₃N₄ joint brazed using Au54.1Ni₃6.1V4.8Pd5 at 1423K for 60min reaches the maximum value of 264MPa at room temperature. When testing temperature increases to 1073K, the average bending strength of joint is 221MPa. As 1 at.% Mo particles is added into Au-Ni-V filler alloy, Ni, Si and V react with Mo to form tetradic compound of Ni₂Si（VMo）₃. The formation of Ni2Si（VMo）3 phase leads to a sharp decrease of the bending strength of joint.This paper illustrates the formation mechanism of Si₃N₄ ceramics joint brazed with filler alloy containing activity of V. During heating process, the filler alloy melted and V at the interface at Si₃N₄ ceramic/liquid filler alloy reacted with Si₃N₄ and formed the VN compound. Si atoms were produced by decomposition from Si₃N₄ and dissolved continuously into the molten brazing alloy. With increasing the brazing temperature or holding time, the VN grain grew and connected with each other. There is no specific crystal orientation relationship between VN and Si₃N₄. The increase of the VN reaction layer with holding time obeys the linear law, indicating that the growth rate of the reaction layer is controlled by the reaction between V and Si₃N₄. Based on the dynamics calculation, the activation energy of VN reaction layer formation of joint brazed using Au58.7Ni₃6.5V4.8 is 329.5 kJ/mol. But when 5 at.% Pd is added into this filler alloy, the activation energy of reaction layer formation reduces to 255.9 kJ /mol, which indicates that the addition of Pd not only improve the melting point of filler alloy, but also change the activation energy of interfacial reaction between V and Si₃N₄, which leads to the effective promotion of interfacial reaction.更多还原