Coloration of Stainless-Steel Surfaces using Magnetic Abrasive Finishing

Rapid advancement of materials and material-processing technologies has enabled fabrication of complex geometries on difficult-to-machine materials, and abrasive-finishing technology must in turn respond to those significant changes. An example of an advanced abrasive-finishing technique is the magnetic abrasive finishing (MAF) process. A magnetic abrasive comprises ferrous particles linked together along magnetic lines of force, when subjected to a magnetic field. These ferrous-particle chains offer configurational flexibility desired for the finishing process. Moreover, it is possible to influence the motion of a ferrous particle-even if the particle is not in direct contact with a magnet-by controlling the magnetic field. This impactful behavior of ferrous particles enables the application of the finishing operation not only to easily accessible surfaces but also to areas that are hard to reach by conventional mechanical techniques, such as freeform components and the interiors of flexible tubes. The obtained surface roughness ranges from the sub-nanometer to micrometer scales and alters light reflectivity, wettability by liquids, friction response, etc. Recent studies found that MAF leads to coloration of stainless-steel surfaces under certain finishing conditions through the formation of oxide layers. This presentation describes the fundamentals of MAF including some representative applications, the relationship between tool motion and the corresponding finished-surface structures, and characteristics of the observed coloration.