S. Zan; Z. Liao; J.A.R. Linares; K. Winter; D. Axinte
International Journal of Machine Tools & Manufacture 215 (2026) 104363
Micrometric cutting has attracted great research interest both in academic and industrial areas due to its vital
role in microfabrication. Different from macro-cutting where many grains are involved in the process that av
erages/minimises the crystallographic effects, in micrometric cutting localised crystallographic deformation
mechanisms can highly affect the machining results. However, experimental challenges of micrometric level
cutting have confined most investigations to simulations or less-ideal tests (e.g. micro-scratching and single-point
diamond turning), leaving the detailed interplay between chip flow and microstructure largely unexplored. In an
apparent paradox, in orthogonal micrometric level cutting conditions, expected to yield forward (2D) chip flow,
can produce pronounced sideway (3D) chip flow when grain-orientation anisotropy and boundary-induced ki
nematic constraints dominate; such aspects cannot be captured in macro-cutting. Based on these, when cutting at
micrometric level it is important to understand how the slip system of the grains will be activated, what will
happen when the grain boundary is encountered, as well as why the specific chip form and flow direction is
generated under different conditions of these. To resolve this, grain orientations and boundaries were pre-
characterised on a Ni-based superalloy sample, on which micrometric boss features were subsequently fabri
cated. Orthogonal grain-level cutting tests were then conducted on these structures, effectively isolating the
deformation region, eliminating constraints from adjacent material, and allowing the chip to flow freely on both
sides. Chip morphology, flow direction, and local deformation mechanisms were examined via advanced ma
terial characterisation technologies. Key findings that are specifically manifested at micro level include: The
formation of serrated chips is influenced by the Schmid factor, resulting in variations in segment morphology
across different crystallographic orientations. Sideway chip flow can be generated in micrometric orthogonal
cutting process due to the selective activation of the slip-systems and inclined grain boundary guided sliding.
Furthermore, when twin boundary exists, periodic extrusion-shear dominated material deformation cycle can
happen in chip formation process due to the alternated stress. Therefore, we reveal for the first time that when
cutting at grain levels, although geometrically defined orthogonal cutting was performed, the chip follows
crystallographic rules imposed by slip planes and grain boundary conditions. These insights provide a new
mechanistic framework for understanding micrometric level cutting anisotropy and the boundary-driven paradox
of sideways chips, offering guidelines to optimise micrometric machining strategies in microfabrication
applications.