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Abstract
The yield point phenomenon observed in nanoindentation of metallic materials has been ascribed to the nucleation of dislocations or multiplication and the film fracture on the surface of the metals. The current study has been undertaken to examine the properties of passivating films on Type 316 austenitic stainless steel. A complementary set of ex situ and in situ experiments showed the presence of deformation prior to a discontinuity in loading with both load-depth sensing techniques and imaging the surface topography. The results of nanoindentation experiments showed that the yield point is dependent on the presence of surface passive film. If the materials, which exhibit permanent deformation prior to a discontinuity in loading, and after the surface films are removed by nanowear and depassivated, Type 316 stainless steel shows no sign of yield point effect; the occurrence of excursions is shown in this material to be dependent on surface passive film. It is more likely that the phenomenon is indeed controlled by film fracture and not the rapid generation of dislocation.
ACKNOWLEDGMENTS
This work was supported by a special fund for the National State Basic Research projects (Grant No. G19990650), and the National Natural Science Foundation of China (Grant No. 50171013).
Presented at the STLE/ASME Tribology Conference in Ponte Vedra Beach, Florida October 26-29, 2003
Final manuscript approved September 19, 2003
Review led by Jacqueline Krim