Shot Peening of Ceramics: Damage or Benefit?

Author:  Frey, Pfeiffer
Source:  Conf Proc: ICSP-8 Sept. 16-20, 2002 Garmisch-Partenkirchen, Germany
Doc ID:  2002026
Year of Publication:  2002
Abstract:  
Authors Tobias Frey, Wulf Pfeiffer, Fraunhofer Institute for Mechanics of Materials, Freiburg, Germany Abstract Non-transformation toughened ceramics show the typical brittle material behavior of failure before deformation at room temperature. Thus, strengthening of ceramics due to deformation induced compressive residual stresses has been thought to be not possible. Nevertheless, preliminary investigations had shown that, using ceramic-specific parameters, shot peening can introduce high compressive residual stresses into the near-surface of silicon nitride and improve the load capacity. The aim of the presented investigation was to improve the shot peening conditions in order to extend the increase of load capacity while maintaining the surface integrity. The materials investigated where alumina and silicon nitride, the properties determined where residual stresses, load capacity and topography. For the assessment of the surface strengthening the X-Ray diffraction analysis (XRD) and the ball-on-plate strength test were used. Due to the low penetration depth of X-rays XRD allows to evaluate the peening-induced residual stresses. In the ball-on-plate test, the sample is loaded with a spherical silicon nitride indenter up to failure of the sample which is detected by a high frequency ultrasonic detector. The results show that high compressive residual stresses in the GPa-range can be introduced in silicon nitride and alumina which may boost the load capacity of the near surface layers by a factor of up to 9. Only little effect on the surface integrity could be obtained.