Manufacturing processes lead to a modification of a component’s surface layer that may result in a change of the surface properties. The influence is caused by a change e.g. of residual stresses or hardness in the surface layer, which can increase or decrease the functional performance of engineering parts. Therefore the Collaborative Research Center (CRC) SFB/TRR 136 “Process Signatures” aims to describe manufacturing processes by generated surface material modifications. For this approach it is assumed that there are process independent correlations, the so called “Process Signature” and its components, between the loads within the workpiece material and the resulting material modification.
The investigation focuses on the mechanisms working in the modified surface layers. Consequently specimens with defined surface modifications were loaded with either mechanical and / or thermal loads to investigate the impact of these loads on the modification. During the first phase of the CRC residual stresses were recognized as important and measurable material modification. Furthermore the full width at half maximum of a peak (FWHM) is an indicator of the deformation of the material. Mainly the FWHM is determined by the distribution of the randomly oriented lattice plane distances. As these distances change with the deformation of the material the FWHM gives information of the microstrains and the dislocation quantity. Therefore the residual stresses and the FWHM on the surface and to some extent in depth of these specimens were measured. The results underline the difference between the input material states used in this investigation, ferrite/pearlite annealed and quenched and tempered AISI 4140, on the possible modification and alteration of the preceding surface modification. Furthermore the changes in FWHM hint at dislocation density and formation of dislocation structures in the material. For the further development and applicability of the approach of the “Process Signatures” it is essential to understand the mechanisms leading to stable dislocation structures and residual stress states and how to value the stability of these states.