Performance of nanolayer CrN/Ag coated cutting tools

Abstract

A nanolayer CrN/Ag coating comprising a lamination of hard transition metal and soft metal was synthesised using an industrial scale four target dc closed field unbalanced magnetron sputtering ion plating system (CFUBMSIPS). For comparison, a monolayer CrN coating was also grown on the same deposition system. Characterisation was conducted using SEM, TEM, XRD and Vickers microhardness and scratch testers. Wear behaviour was studied on an SRV wear tester. Performance of coated cutting tools was evaluated via two kinds of machining tests: one was using the coated microdrills to continuously make through thickness holes on FR4 printed circuit boards and the other using the coated turning cutters to machine S45C steel bars. The structural analysis showed that the nanolayer CrN/Ag coating with bilayer thickness λ 30 nm was composed of alternative stacking layers of pure Ag and CrN phases. The nanolayer CrN/Ag coating, in spite of having lower hardness than the monolayer CrN coating, showed great improvements in the wear resistance and microdrilling and turning performance, which could be attributed to the combination of multilayer structure and lubricating function of Ag.