Changes in surface layer after Piezo Peening of quenched and tempered AISI 4140

Author:  F. Lienert, J. Hoffmeister and V. Schulze
Source:  Conf Proc 2014: ICSP-12 Goslar, Germany (pgs.511-516)
Doc ID:  2014129
Year of Publication:  2014
Abstract:  
Piezo-Peening is a new alternative mechanical surface treatment process which may be addressed as a machine hammer peening treatment. Thereby a piezo actuator with an indenter is causing mechanical deformation of the surface area by multiple impacts in a previously defined pattern. Using this approach, advantages of shot peening and deep rolling can be combined. In order to get a process understanding and an idea of influence of the process parameters, different parameters like hardness and size of the indenter are changed. After the mechanical surface treatments the residual stress and full width at half maximum (FWHM) depth distributions were measured using X-ray diffraction technique. The surface topography was investigated with confocal white light microscopy. By changing these parameters systematically a wide range of compressive residual stress depth distributions can be generated. This goes from medium surface residual stresses of about -600 MPa and low penetration depths like induced by shot peening to large surface residual stresses of -1200 MPa and penetration depths comparable to deep rolling. Furthermore, surface roughness can be reduced. The dependency of surface residual stresses, penetration depths, FWHMs and surface roughnesses on the process parameters is analysed in order to determine their effects on the resulting surface layer. In addition, the variety of adjustable surface layer states can be shown. They reach from states comparable to shot peening to states comparable to deep rolling and even beyond that. By means of the knowledge of the parameter influence, the possibility of finding the best set of parameters to increase the fatigue strength for a certain load case is given.