Preparation of nanotwinned cBN cutting edge by combining mechanical lapping and ion beam polishing

Abstract Nanotwinned cubic boron nitride (nt-cBN) is a promising tool material for ultra-precision cutting of ferrous metals. However, high hardness and excellent thermal stability make it difficult to obtain sharp cutting edge by using conventional methods. In this study, the factors influencing the material removal modes and edge sharpness in mechanical lapping process have been investigated, and a novel method combining mechanical lapping and ion beam polishing is proposed for achieving the sharp nt-cBN cutting edge. The results show that the material removal in mechanical lapping is mainly contributed by the transgranular ductile failure at the nanometer scale. Besides, high material hardness with a low Poisson's ratio and small impact force on the cutting edge are beneficial for obtaining sharp cutting edge. Therefore, the ion beam polishing process is adopted to sharpen the mechanically lapped cutting edge. By using a steel baffle plate with straight profile and eliminating the clearance between the baffle plate and rake/flank face with resin filler, the edge radius is observed to decrease from micrometre scale to about 60 nm. The proposed method represents a promising strategy for the preparation of ultra-sharp cutting edge with low cost and high accuracy.