Mg2Si热电材料与Cu/Ni复合电极的接头界面及性能

Interface microstructure and properties between Mg2Si thermoelectric materials and Cu/Ni combined electrode

摘要:

为保证热连接过程中热电材料与导流电极之间实现良好连接，同时形成有效的阻隔界面防止界面元素扩散致使材料性能下降，本研究以Cu片作电极，引入中间层Ni箔作扩散阻挡层，采用电场激活压力辅助烧结(FAPAS)法，在合成高纯硅化镁(Mg2Si)热电材料的同时，同步制得Cu/Ni/Mg2Si热电接头。利用SEM、EDS以及XRD对接头界面的微观相组成、元素扩散特征以及新相生长规律进行了探讨，并且采用热震试验和四探针法对接头分别进行了力学性能和电传输性能的测试。结果表明，合成的Mg2Si纯度高，高温热膨胀性能稳定；Ni层能有效阻隔界面元素扩散，与Mg2Si实现良好的冶金结合，连接界面新相层的生成次序依次为Mg2SiNi3和Mg2Ni。Cu/Ni/Mg2Si具有较好的热膨胀匹配性能，连接界面在持续60次的热震循环后依然保持完整。随着时效时间延长，界面扩散层增厚，接触电阻有所增大，与 具有近线性关系，且700℃下未时效的接头获得最小接触电阻率112μΩ?cm2。

Abstract:

Elements diffusion across the interface will result in poor performance during service, so it’s important to put a barrier layer between thermoelectric materials and electrode, and get them bonded perfectly as well. In this work, with copper as electrode and nickel foil as barrier layer, Cu/Ni/Mg2Si thermoelectric joint was prepared by the field-activated pressure-assisted synthesis (FAPAS) method, in which the in situ synthesis of Mg2Si and bonding between different layers were accomplished in one step. SEM, EDS and XRD were used to observe the microstructure, determine phase component and forming process of new phases, and obtain element distribution across the interface; thermal shock test and four probe method were used to evaluate the mechanical properties and electrical resistivity of the joint. The results show that the synthesized Mg2Si has high purity and stable coefficient of thermal expansion (CTE) at high temperatures. The nickel layer blocks the mutual element diffusion effectively in interface and gets bonded well with copper and the synthesized Mg2Si, respectively, accompanied by the formation of new phase, Mg2SiNi3 and Mg2Ni, in turn in the former interface. Based on good match of CTE in Cu/Ni/Mg2Si interfaces, the joint stays intact even experiencing 60 thermal shock cycles. With the increase of aging time, the thickness of interfacial diffusion layer gets wider, and the contact resistance increases subsequently, which roughly fits the linear relation with . The minimum contact resistivity of the joint is 112 μΩ?cm2 when the bonding temperature is 700℃.