An experimental study of cryogenic machining on nanocrystalline surface layer generation

This paper presents an analysis of in-process liquid nitrogen cryogenic cooling on the generation of nanocrystalline workpiece (AISI4140) surface layer in machining. Samples from cryogenic machining demonstrate nanocrystalline grain refinement with beneficial properties, e.g., favorable wear characteristics. Correlations are established among process and geometry parameters, cooling conditions, cutting forces and surface layer states. Parameters studied are cooling state, depth of cut h and cutting edge radius r_β. Cutting forces are measured and a detailed analysis of micro/nano-structural surface layer conditions was carried out using Focused Ion Beam system, Atomic Force Microscopy and Nanoindentation. It is shown that the obtained micro/nanostructure strongly depends on the cooling conditions. In particular, the affected depth is influenced by the cooling state.