纳米孪晶立方氮化硼机械研磨机理研究

Mechanical Lapping Mechanism of Nanotwinned Cubic Boron Nitride

为了将新型超硬纳米孪晶立方氮化硼(nt-c BN)材料制备成能够实现铁基金属材料,特别是硬度较高材料的精密及超精密切削刀具,针对机械研磨方法,从理论和试验角度分别对纳米孪晶立方氮化硼材料的机械研磨机理进行了研究。对纳米孪晶立方氮化硼材料动态脆塑转变临界研磨深度进行了理论分析及试验验证;基于临界研磨深度,实现了对该材料的塑性域精细研磨;利用理论计算及原子力显微镜表面检测结果,针对研磨后塑性沟槽深度及宽度,分析了研磨过程中塑性沟槽形成机理。研究结果表明,纳米孪晶立方氮化硼材料动态脆塑转变临界研磨深度为23.9 nm;使用0.5μm金刚石研磨颗粒研磨材料表面粗糙度达到1.99 nm,PV值77.05 nm;研磨塑性沟槽深度理论最小值2.25 nm,与试验结果相吻合;研磨塑性沟槽宽度为固定、游离研磨颗粒共同作用的结果,宽度保持在亚微米级。因此,纳米孪晶立方氮化硼材料具有较好的可加工性,采用机械研磨方法能够实现较高精度表面的高效率加工。

In order to manufacture a nanotwinned cubic boron nitride（nt-c BN） cutting tool which is promising to cutting ferrous metal, especially for hardened steel, lapping mechanism is investigated with both theoretical and experimental methods. The dynamic critical lapping depth of nt-c BN is first calculated by theoretical analysis, and then proved through lapping experiments. Based on the critical depth, nt-c BN bulk is lapped in ductile regime and fine surface can be achieved. Moreover, aiming to reveal generation mechanism of the plastic grooves on lapped surface, both depth and width of the grooves are studied according to theoretical calculation and experimental results. It indicates that the dynamic critical lapping depth of nt-c BN is 23.9 nm, and surface roughness of lapped nt-c BN with 0.5 μm diamond grits is 1.99 nm and PV value is 77.05 nm. Additionally, the theoretical minimum groove depth on fine finished nt-c BN surface is 2.25 nm which was proved by experimental results, as well as the grooves＇ width in sub-micron scale is generated under the complicated reaction of free grits and fixed grits. Therefore, nt-c BN material has excellent machinability as compared to diamond, and can be machined by mechanical lapping with high efficiency and high precision.