Ni-Cr合金真空单层钎焊金刚石砂轮

摘要

单层高温钎焊超硬磨料砂轮具有传统电镀砂轮无法比拟的优异磨削性能，国内应及早研制开发应用此种砂轮。本文利用真空炉中钎焊的方法，用Ni-Cr合金钎料，适当控制钎焊温度、保温时间和冷却速度，实现了金刚石与钢基体间的高强度连接。扫描电镜X射线能谱，结合金相及试样逐层的X射线结构分析，剖析了Ni-Cr合金与金刚石和钢基体钎焊界面的微区组织结构；揭示了Ni-Cr合金对金刚石和钢基体表面的浸润和钎焊机理。即在钎焊过程中会在金刚石界面形成富Cr层并与金刚石表面的C元素反应生成Cr7C3，在钢基体结合界面上Ni-Cr合金和钢基体中的元素相互扩散形成冶金结合，这是实现合金层与金刚石和钢基体都有高结合强度的主要因素。最后重负荷磨削试验表明金刚石为正常磨损，没有整颗金刚石脱落，说明金刚石确有高的把持强度。%The brazing of a monolayer diamond grinding wheel with active filler metals can show distinct advantages over conventional electroplated diamond grinding wheel in terms of faster cutting and longer life.The present study has shown that a commercially available Ni-Cr alloy can be used as an active filler material for brazing diamond grit.Furnace brazing is carried out in a current of vacuum.SEM-EDS microanalyses have shown that during brazing the chromium present in the alloy segregated preferentially to the surface of the diamond to form a chromium-rich reaction product.X-ray diffraction reveals that the wetting and bonding behaviour on diamond surface by Ni-Cr alloy melt is realized through Cr7C3 which is produced by interaction between Cr atoms of Ni-Cr alloy and C atoms of diamond surface at elevated temperatures.The analyses also indicate that the bond between the alloy and the steel substrate is established through a cross-difusion of iron and chromium.Finally,a grinding test shows that the wear modes of such a brazed grinding wheel are mainly grit fracture and attrition rather than grit dislodgement from the bond.