1 - Erich Schmid Institute

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C A New Cantilever Technique Reveals Spatial Distributions of Residual Stresses
Figure C.5: Depth profiles of residual stresses in sections B and A1 to A10. The maximum of compressive
stresses between A8 and A9 indicates the center of the scratch as it was suggested
by SEM images. The stress distribution in section B, which is located far away from the
scratch, was determined in a separate ILR experiment. The length of each section is written
beside the denomination of the section.
C.3 Discussion and Concluding Remarks
The depth profiles of residual stresses in the vicinity of the scratched Ni film obtained with
the 3D-ILR method show two main characteristics. First, the mean stress drops from
initially 460 ± 60MP a in section B to a minimum value of −478 ± 91MP a in section
A8, which corresponds well to the SEM images that show the center of the scratch
lying between sections A8 and A9. The radius of the plastic zone is therefore about 30
microns, considering the change from tensile to compressive stress between the sections
A3 and A4. Secondly, the stress gradient vanishes towards the center of the scratch. The
unexpected compressive stress determined in section A1, about 45 microns away from
the center, could originate from the imperfect shape of the indenter, which would lead
to a shallow imprint parallel to the scratch in this section. Owing to the indenter radius
of 300 microns, micron size bumps on the indenter lead to peripheral contact, as it was
also discovered in similar experiments. To assure that the compressive stress is limited
to section A1, the thin film was removed in a few microns wide part of section B next
to section A1. This resulted in a pronounced decrease in the deflection which leads to
the conclusion that the thin film material removed on the left side of A1 was definitely
subjected to tensile stresses.
The mean depth resolution of 200nm and the average lateral resolution of a few microns
obtained in this experiment demonstrate the possibility for high spatial resolution.
Further improvement can be achieved by removing thin sublayers with thicknesses below
100nm 11 and designing the cantilever appropriately, which involves an adequate choice
of the substrate thickness, the lengths of the sections Ai and the indicator section B.
Another advantage of the 3D-ILR method is that information can be obtained directly
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