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黝铜矿系热电材料的钎焊工艺及机理研究

发布时间:2019-02-11 21:39
【摘要】:热电材料是一种利用固体中载流子(电子和空穴)运动实现热能和电能直接相互转换的功能材料,主要应用于温差发电和热电制冷。热电材料的能量转化效率高低采用一个无量纲的热电优值ZT进行衡量,ZT值越大,材料热电性能越优异。含铜的硫化物系列热电材料具有较高的ZT值,其中黝铜矿晶体结构复杂且高度对称,本身具有较低的晶格热导率及稳定性。因此本课题选取黝铜矿系热电材料作为主要研究对象,从材料制备和连接两方面进行研究,提升材料的热电性能并实现与电极间的高可靠性连接。采用熔炼+退火+热压烧结制备黝铜矿系热电材料,对制备过程中各阶段得到的材料进行晶体结构测试及微观组织分析,发现Cu12Sb4S13热电材料中存在第二相,影响材料整体的热电性能。通过掺杂Ni元素等电位取代Cu12Sb4S13中的Cu,抑制第二相的析出,最终获得单一相组成的Cu10.4Ni1.6Sb4S13热电材料。对掺杂元素前后的材料进行热电性能测试及各项参数对比,发现掺杂后的材料热电性能有所提升。在温度为427℃时,Cu12Sb4S13热电材料ZT值为0.54,Cu10.4Ni1.6Sb4S13热电材料ZT值为0.85。Cu10.4Ni1.6Sb4S13热电材料熔点为604℃,使用温度为420℃,为保证热电材料服役温度和稳定性,选择熔点在420℃-604℃之间的钎料体系。本课题首先采用Al-Si-Cu钎料和Zn-Al钎料对Cu10.4Ni1.6Sb4S13热电材料与Cu电极进行钎焊连接,得到的接头界面出现贯穿裂纹和溶蚀等缺陷,通过调节工艺参数仍无法消除,需更换钎料种类;采用Ag-Cu-Sn钎料对Cu10.4Ni1.6Sb4S13热电材料与Cu电极进行钎焊连接,在钎焊温度为500℃,保温时间为5min时,所得接头的界面结构为:Cu10.4Ni1.6Sb4S13/Cu2S3Sn/Sn S+Ag3Sn/Cu3Sn/Cu。在钎焊连接过程中,热电材料中的S元素发生较为严重的扩散且扩散距离较远,导致钎缝中生成大量硫化物。随着钎焊温度升高,S元素扩散程度加大,扩散到电极侧的S元素与Cu结合生成Cu2S化合物层而使母材产生溶蚀现象,溶蚀程度逐渐变大,溶蚀宽度呈指数性增长,最高接头强度只有3.1MPa。为了减缓接头扩散反应,采用Ag-Cu-Sn钎料并添加Ni扩散阻隔层对Cu10.4Ni1.6Sb4S13热电材料与Cu电极进行钎焊连接,钎焊温度为480℃,保温时间为2.5min,所得接头的界面结构为:Cu10.4Ni1.6Sb4S13/Ni Sb+Ni Sb S+Cu2S3Sn/Sn S+Ag3Sn/Ni3Sn2/Ni/(Cu,Ni)3Sn2/Ag3Sn+Cu3Sn/Cu3Sn,发现Ni扩散阻隔层能够有效地阻碍热电材料中S元素的扩散。钎焊工艺参数对接头界面组织和力学性能具有重要影响,在钎焊温度为480℃,保温时间为5min时,热电材料侧反应层清晰明显且厚度适中,界面各区域形成了良好的冶金结合,接头平整且无明显缺陷,界面结构最优,此时接头抗剪强度可达9.3MPa,相较无扩散阻隔层提升200%。对接头断口进行分析,得到Cu10.4Ni1.6Sb4S13/Cu接头断裂机制为沿晶脆性断裂,断裂位置出现在热电材料侧反应层及热电材料上。
[Abstract]:Thermoelectric material is a kind of functional material which uses the motion of carrier (electron and hole) in solid to realize the direct conversion between heat energy and electric energy. It is mainly used in thermoelectric power generation and thermoelectric refrigeration. The energy conversion efficiency of thermoelectric materials is measured by a dimensionless thermoelectric excellence value (ZT). The larger the ZT value is, the better the thermoelectric properties of the materials are. The copper sulfide series of thermoelectric materials have a high ZT value, among which tetrahedrite has a complex crystal structure and a high symmetry, and has low lattice thermal conductivity and stability. Therefore, this paper selects tetrahedrite series thermoelectric material as the main research object, from the material preparation and the connection two aspects carries on the research, enhances the material thermoelectric performance and realizes the high reliability connection with the electrode. Tetrahedrite series thermoelectric materials were prepared by melting annealing and hot pressing sintering. The second phase was found in Cu12Sb4S13 thermoelectric materials by crystal structure test and microstructure analysis. The thermoelectric properties of the whole material are affected. The second phase precipitation was inhibited by doping Ni element instead of Cu, in Cu12Sb4S13, and the mono-phase Cu10.4Ni1.6Sb4S13 thermoelectric material was obtained. The thermoelectric properties of the materials before and after doping were tested and compared with each other, and it was found that the thermoelectric properties of the doped materials were improved. When the temperature is 427 鈩,

本文编号:2420133


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