iy Fundamental Investigations for Residual Stress Measurements in the
x Micrometer Range by means of the Correlation of Magnetic Quantities to
b Experimentally Determined Stress-Strain Fields
i [. Altpeter, S. Kühn, M. Kopp, W. Arnold, M. Kréning, Fraunhofer-Institute IZFP, Saarbruecken,
a Germany; M. Zehetbauer, Institute for Material Physics, Vienna, Austria
1
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un ff I. Abstract
ron
Hessen und hy Increasing miniaturization of micromechanic and microelectronic components has directed
Dri intensified attention to residual stress measurements with high lateral resolutions. The fundamentals
prt, 4 for a quantitative method to measure residual stresses in the micrometer range, which is less time-
os consuming and less expensive than X-ray methods, was developed within the framework of a DFG
Cir research program. For the first time, the Barkhausen Noise Eddy Current Microscope (BEMI) offers
ehtun ir Kono a powerful testing technique that can be used (adequate calibration provided) for non-contact, high-
pasty li resolution residual stress measurements in the micrometer (Lum) range.
ehfisch, Einrie
onoskopie, Hi
She 2. Objective and Solution
Vestn, dio
Biron} The objective of the research work was the establishment of fundamentals for quantitative residual
1 Brechushimessm stress measurements in the micrometer (um) range that takes less time and cost less than
conventional X-ray methods. The investigations for this research project were performed using the
Barkhausen Noise Eddy Current Microscope (BEMI, developed by IZFP) that detects magnetic
material properties in the micrometer range (see Chapter 3.3 below). Nickel specimens, coarse-
grain annealed to enlarge the grain and to reduce residual stresses, were used for the experiments.
To apply a defined residual stress state to the material in the elastic range, the specimens were
subjected to a tensile testing machine. The amount of residual stresses was verified with
electromagnetic methods and the X-ray Bragg Peak Profile Analysis technique for each specimen.
Despite the long times required for data acquisition, and the X-ray analysis to determine stress
fields inside the grain and local dislocation density, the line-profile analysis was still indispensable
as a reference method.
3. Investigation Methods
3.1 Back-Scatter Electron Diffraction
The location of individual grains, which is relative to the tension axis and corresponds to the
magnetization direction and to the surface normal, effects Barkhausen Noise and eddy current
signals. The grain orientation characteristic, which yields the easy direction of the spontaneous
magnetization (111 for nickel), is a very important factor for the interpretation of micromagnetic
measurements. Also, the assignment of the reflections recorded by the X-ray Bragg Peak Profile
Analysis (XPA) technique to individual crystallites would not be possible without metallurgic
reproductions. The orientation of the grains was determined by Electron Back Scatter Diffraction
(EBSD) and Orientation Imaging Microscopy (OIM) techniques. The EBSD indicates the
diffraction of back-scattered electrons from the primary electron-beam on a heavily tilted sample.
High lateral resolution (approximately 200nm) and high orientation accuracy (+2° for absolute
measurements) are the most important advantages. References [2] and [3] refer to detailed
information about data acquisition operations.
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