添加石墨对Ni-Cr合金保护气氛钎焊金刚石磨粒界面组织的影响

Effect on Microstructure for Adding Graphite to Ni-Cr Alloy when Brazing Diamond Abrasive in Controlled Atmosphere

钎焊单层金刚石工具磨粒具有高的出刃和把持力,但在高温钎焊过程中易造成金刚石较大的热损伤,利用在Ni-Cr合金中添加适量的石墨,期望能够阻止金刚石石墨化,降低金刚石焊后热应力和过度反应。采用添加质量分数为0%、1%、2%石墨的Ni-Cr合金作为钎料对金刚石进行保护气氛钎焊试验,钎焊温度1 050℃保温5 min,利用扫描电镜对焊后金刚石的形貌和焊缝组织进行分析,测试钎缝的显微硬度。结果表明,添加1%石墨的钎料对金刚石润湿性较好,添加的C元素能够与Cr元素反应后形成碳化物,其中部分Cr3C2在金刚石表面形核长大,并与金刚石有一定位向关系,Cr7C3的形貌由实心转变为空心,钎缝中形成簇状共晶石墨,显微硬度由630 HV0.2下降到580 HV0.2,有利于金刚石磨粒的后期出露和降低热应力。

Brazing diamond tools has high protrude and strong bonding, while brazing process may cause much thermal damage to the diamond. Adding an appropriate amount of graphite into the Ni-Cr alloy is expected to prevent diamond graphitizing, and reduce the thermal stress of the diamond after brazing. The diamond is brazed at 1 050 °C using Ni-Cr alloy added 1%, 2%, 3%（wt） graphite separately in controlled atmosphere and held temperature for 5 minutes, then the surface micrographs and the interface microstructures of the samples are observed by scanning electron microscope and energy dispersive spectrometer. The result shows that the filler added 1% graphite has wettability, and the element of C from the graphite can react with the element of Cr to form the carbide, in which part of CraC2 can grow in nucleus on the diamond surface, and the growth direction of Cr3C2 has a certain orientation relationship with the crystal plane of diamond. The micrographs of Cr7C3 changes from solid into hollow and cluster graphite is formed in filler. The microhardness of the filler descends from 630 HV0.2 to 580HV0.2, which makes the diamond protrude easily when used.