Characteristics of Surface Layers Produced by Shot Peening

Author:  Schulze
Source:  Conf Proc: ICSP-8 Sept. 16-20, 2002 Garmisch-Partenkirchen, Germany
Doc ID:  2002021
Year of Publication:  2002
Abstract:  
Author Volker Schulze, Institut fur Werkstoffkunde I, Universitat Karlsruhe (TH), Karlsruhe, Germany Introduction Production processes, especially mechanical surface treatments like shot peening, lead to changes in the materials state close to the surface, which severely affect the success of the treatment, especially the resulting fatigue properties. Formerly these effects on fatigue life were controversely discussed as effects of mechanical workhardening, which first were postulated to be dominating by Foppl and his group [1,2], and effects of compressive residual stresses, which first were assumed to increase the fagitue properties by Thum and his group [3,4]. Additionally, effects of topography on fatigue properties were studied by Houdremont and Mailander [5] and Siebel and Gaier [6]. Today it is well known that most of the changes of surface characteristics induced by shot peening which are listed in Fig. 1 and the stability of these changes may affect the fatigue properties of components and that these effects can be described in the so called concept of local fatigue properties [7,8,9]. Therefore the influence of process parameters of the shot peening treatments listed in Fig. 2 on the surface characteristics has to be well known. Besides the parameters concerning the peening device or the shot, the parameters concerning the workpiece are of high interest. Especially the workpiece temperature and the prestress are altered in modifications of the peening process named arm peening and stress peening which will be discussed separately. In some cases additional annealing treatments are used to achieve further improvements of the material state close to the surface. In the present paper a systematic overview of up to date knowledge about the changes in the surface state due to shot peening is given by discussing characteristic examples concerning changes of the topography, residual stress state, workhardening state and microstructure of components due to shot peening. A special focus will be drawn to the previously mentioned modifications of the conventional shot peening process like stress peening, warm peening and peening plus subsequent annealing, which show improvements in the surface properties or at least improvements of the stability of the induced surface state.