在950 ℃, 30 min条件下, 采用含活性元素Ti的Sn0.3Ag0.7Cu-xTi (x=1.0, 1.2, 1.4, 1.6, 1.8, 质量分数, %)金属粉末对石墨进行反应金属化, 然后用Sn0.3Ag0.7Cu钎料在真空条件下实现了紫铜和石墨的间接钎焊. 钎焊接头的典型界面结构为: 紫铜/Cu₃Sn/Cu₆Sn₅/β-Sn/TiC/石墨. 在反应金属化过程中金属化粉末中的Ti起到重要作用, 而Ti含量对钎焊接头的界面组织和抗剪强度没有影响. 随着钎焊温度升高, 紫铜中越来越多的Cu溶解到液相钎料中反应生成Cu-Sn化合物, 接头的抗剪强度有一定程度的提高. 断口分析表明: 接头主要在β-Sn层中断裂, 并呈现韧性断裂. 当Cu-Sn化合物充满整个钎缝(600 ℃), 接头强度大幅提高, 达到30 MPa, 接头在石墨母材完全断裂.

Graphite and metal composite structures were widely used in aerospace, electrical engineering and electronics. Because of its conveniences and less cost, brazing was widely used to bond graphite and metals. Due to the differences in microstructure, graphite was difficult to be wetted by traditional braze alloys. To improve the wettability of traditional brazing alloys on graphite, active brazing process and indirect brazing process were developed to braze graphite to metals. As to active brazing process, active elements (such as Ti, Cr, Zr) were added into traditional brazing alloys, a high brazing temperature, was essential to guarantee the reaction of active elements with graphite. However, the mechanical properties of metals will degrade under high temperature. Electroplating and chemical plating were the general techniques for indirect brazing process. The covered coating had a mechanical combination which decreased the joint strength, rather than metallurgical bonding with graphite. Therefore, in this work, a new metallization method was proposed. On the one hand, a metallurgical bonding was formed between metallization layer and graphite substrate. On the other hand, graphite could be brazed to metal at a relatively low temperature. Firstly, graphite was metalized by Ti-containing Sn0.3Ag0.7Cu metallization powder at 950 ℃ for 30 min. Then metalized graphite was brazed with copper by Sn0.3Ag0.7Cu successfully. The typical interfacial structure of brazed joint was copper/Cu₃Sn/Cu₆Sn₅/β-Sn/TiC/graphite. Element Ti of metallization powder played an important role in metallization process for a reaction layer TiC was formed on the interface of graphite and metallization layer. Nevertheless, Ti contents had no effect on interfacial structure and shear strength of brazed joint. With the increase of brazing temperature, more and more element Cu dissolved into molten solder and formed Cu-Sn compounds by reacting with Sn. Furthermore, shear strength was improved slightly. Fracture analysis reveals that cracks extended along β-Sn layer and presented ductile fracture. When Cu-Sn compounds occupied the entire brazing seam (joint brazed at 600 ℃), shear strength improved remarkably and reached 30 MPa. Additionally, the joint was fractured in graphite entirely.