A new approach for studying mechanical properties of thin surface layers affected by manufacturing processes

solids at small length scales, ever since its formulation as a technique in the early 1980s.* The small size of an indentation, typically one micrometer or less in surface extent, makes it a potentially attractive tool also for the quantitative study of the characteristics of surface layers in monolithic solids. Here, we report results from a study in which nano-indentation has been combined with taper-sectioning to analyze the mechanical properties of thin surface layers affected by manufacturing processes. The so-called white etching layer (WL) produced in steel surfaces by machining and abrasion is characterized The WL is found to have a hardness in the range of 11.5-16.2 GPa, which is significantly greater than that of untempered martensite produced by heat treatment processes. These hardness values are close to those measured on steel piano wires. The so-called burn-layer produced on ground surfaces of steels is found to have a hardness distribution very similar to that of a white layer suggesting that the two layers are of the same type. Localized hardening and softening of surface layers, over spatial extents of a few micrometers, caused by material removal processes are accurately resolved by the combined use of nano-indentation and taper-sectioning. The taper-sectioning/nano-indentation approach is also shown to be a good procedure for characterizing the hardness of PVD-TiN films deposited onto hard metal substrates.