【作者】 谢凤春；

【导师】 冯吉才； 何鹏；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 博士

【摘要】 由于石墨具有优越的抗热震性、高熔点、高热导率和抗热疲劳性,因此石墨材料具有广阔的应用领域,如碳换向器不仅可以应用在所有的直流电机上,还可以在航空、航天、军工等领域中得到推广与应用。本文采用商用钎料和自己研制的新型钎料对石墨与铜进行钎焊,分析了钎料制备原理和界面反应机理。本文研究结果不仅填补了我国碳换向器生产的技术空白,且为碳基材料与异种金属的连接提供了技术储备。本文选择Ag、Cu、Ti、Sn四种元素作为机械合金化(MA)制备钎料的主要成分。其中,Ag元素的添加方式为Ag单质粉末或者AgCu共晶粉。研究了球磨时间、球料比、元素添加方式等工艺参数对粉末形貌、粒度、合金化程度、钎料熔点的影响。建立了MA的工艺模型,提出了一种点蚀状剥落的局部模型。通过数学模型、动力学模型和热力学模型分析表明,球速越大,Pmax越大,粉末被破碎的程度大;颗粒越小粉末的稳定程度也越大,粉末的温升不足以使粉末融化。本文在机械合金化转速为260r/min,球磨时间为7h时,球磨后的粉末平均直径低于20μm。采用非晶态TiZrNiCu钎料钎焊时,接头的界面结构为石墨/TiC/Ti-Cu、Cu-Zr、Ni-Ti系金属间化合物/Cu基固溶体/Cu,TiC是实现钎料与石墨冶金连接的主要因素。钎焊工艺参数对接头界面组织和性能产生一定的影响。当钎焊温度为1193K、保温时间为900s时,接头获得最佳抗剪强度26MPa;在1223K/900s和1173K/600s参数下获得接头的平均电阻为3.3 m?和3.2 m?,均满足使用要求。但是从电阻极差、相邻叶片电阻差、方差等因素分析,在1223K/900s试验条件下,接头电阻具有最高的稳定性。石墨/AgCuTiSn/Cu钎焊接头的界面结构为石墨/TiC/Ti3Sn+Ag(s.s)+Cu-Sn化合物+Cu(s.s)/Cu(s.s)/Cu。随着钎焊工艺参数的增加,白色Ag(s.s)的尺寸和分布面积减少,钎料向Cu母材侧的晶间渗入增强,黑色的金属间化合物相明显长大。石墨侧发现了“须”状组织,其随着钎焊工艺参数的提高先增多、增长、增大,然后减少,直至消失,这种变化将对接头的力学性能带来一定的影响。结果表明:当钎焊温度为1093K,保温时间为900s时,接头获得最大的抗剪强度24MPa。另外,接头的断裂位置与钎焊工艺参数有关。在最佳的工艺参数下,断裂几乎全部发生在石墨母材处,接头的抗剪强度最高。采用AgCuTiSn钎料对石墨/Cu进行连接时,Sn元素熔化形成了液相通道,加速了其它元素的扩散、反应,使得钎料熔化,达到了降熔的作用;同时,为钎焊过程提供了活泼的Ti原子。采用AgCuTi和AgCuTiSn钎料对实际件进行焊接,并试车运行。结果表明,换向器工作状态稳定,该产品的使用寿命达到15000h以上,可以达到传统换向器使用寿命的5倍。本文建立了石墨/TiZrNiCu/Cu接头界面反应层成长动力学方程,并分析了石墨/AgCuTiSn/Cu钎焊界面的反应机理。通过研究钎料与碳基材料的反应机理可知,Ti基钎料实现连接主要是利用Ti与C反应生成TiC;Cr基钎料实现连接主要是在界面反应层处产生一定厚度的CrmCn相反应层,其种类受到钎焊温度、保温时间和钎料中含有的其它元素来决定。更多还原

【Abstract】 With excellent thermal shock and heat fatigue resistance as well as high melting point and heat conductivity, graphite has wide application field. For example, graphite commutators can be used in not only all direct current engine, but also aviation, space and army fields. In this paper, commercial and self-developed brazing alloy were used to join graphite and copper. Interface reaction mechanism of the brazed joints and preparation principle of braze alloy were analyzed. The investigation not only fills up the technique blank of producing graphite commutators in our country, but also supplies technique reservation for joining carbon-based materials with dissimilar alloys.Ag, Cu, Ti, Sn powder were selected to make braze alloy by mechanical alloying, in which Ag powder was added by two ways (pure Ag powder or AgCu eutectic powder). The effects of ball milling time, ratio of grinding media and adding way of element on pattern of powder, grain size, degree of alloying and melting point of braze alloy were studied. The model of mechanical alloying was built and a local model of pitting flaking was also introduced. It can be known from mathematical, kinetic and thermodynamic models that when the milling speed increases, Pmax is large and the alloy powder is crushed heavily. If the powder grain is small, the stability of powder is good and the powder is not be melted during ball milling. When the rotary speed is 260r/min and the ball milling time is 7h, the average diameter of powder is below 20μm after ball milling.When TiZrNiCu filler was used to braze graphite with copper, the interface structure is graphite/TiC/Ti-Cu, Cu-Zr, Ni-Ti intermetallic compound/Cu-based solid solution/Cu, in which TiC is the key factor for bonding braze alloy and graphite successfully. Brazing parameters have effects on the microstructure and property of joint interface. The maximum joint strength 26MPa can be obtained when the brazing temperature is 1193K and holding time is 900s. The average resistance of joint brazed at 1223K/900s and 1173K/600s is 3.3 m? and 3.2 m?, respectively, which can meet the requirements of application. The resistance stability of joint is optimum when the parameter is 1223K/900s, considering the resistance extreme difference, resistance difference and variance between adjacent blades.The interface structure of graphite/AgCuTiSn/Cu joint is graphite /TiC/Ti3Sn+Ag(s. s)+Cu-Sn compound+Cu(s. s)/Cu(s. s)/Cu. As the brazing parameters increase, the size and area of white Ag(s. s) decrease and the intergranular infiltration of braze alloy into Cu base metal intensifies. Meanwhile, black intermetallic compound grows up obviously. Whisker microstructure is found at graphite side, which becomes much, long, large and then decreases, even disappears as the brazing parameters increase. The change of microstructure leads to the corresponding variety of joint property. The results show that the maximum joint strength 24MPa is obtained when the brazing temperature is 1093K and holding time is 900s. On this situation, the joint fractures near graphite side. During joining graphite and copper by AgCuTiSn braze alloy, Sn becomes liquid and accelerates the diffusion and reaction among other elements as well as the melting of braze alloy, the result of which decreases the melting point of braze alloy and supplies active Ti atoms during brazing. By using AgCuTi and AgCuTiSn braze alloys, graphite/copper commutators were brazed. After trial test, the work state of the brazed commutators is stable and their service life is over 15000h, which is 5 times longer than the service life of traditional commutators.Kinetic equation of reaction layer growth of the brazed graphite/TiZrNiCu/Cu joint was built. Interface reaction mechanism during brazing graphite/AgCuTiSn/Cu is analyzed in detail. By studying the reaction mechanism of braze alloy and carbon-based materials systematically, Ti and C reacts and forms TiC when using Ti-based braze alloy. There is a CrmCn reaction layer on the interface when using Cr-based braze alloy. The kind of CrmCn is affected by brazing temperature, holding time and other elements in the braze alloy.更多还原