engi
This can de ex. | age the surface by the indentor
Rp leads 1g 4 CL 2 Co diamond tip as in ordinary
Usher srg of Erg AFM. The lateral resolution in
al. This sudgep oe imaging is limited by the ra-
dius of curvature of the tip
DLC is the fü which is typically in the range
Derature Vacuum ; of 100nm. - ;
luna growth The indentation instrument
of 100300, (21) capacitively generates
(material break forces in the range of IHN to
I time, [can be 20mN with a resolution of
ome sow 100nN. The displacement of
Process, while AVN the indentor is continuously
ertain time ung = measured also capacitively,
umn interfaces yielding a resolution of 0.1
weal structure Figure 10: (a) SEM cross-section of nitrided steel with nitration zone in nm. When indenting the sur-
Wg the upper part ogf the image. (b, c) AFM image of nanoindentation at face, scanning of the tip is
> . chromium precipitations in the nitration zone and in the bulk material stopped, the tip is moved to
ycles N. at loads respectively. A .
metal content. I the desired position and a
Co 154 force-displacement curve is
hreshold of ie acquired. After indentation the surface impression can be imaged at minimum load to inspect e.g.
C Below this pile-up formation, etc.. For the evaluation of indentation data the model of Oliver and Pharr (22) is
etl concen: used, yielding hardness and Young's modulus of the sample.
os of tungsien The combination of nanoindentation and AFM is especially useful in metallography for the local
WEM DCHAWDG. investigation of small precipitations, grains, particles, etc.. As an example figure 10a shows a back-
=e fraction of scatter electron image of a steel cross-section where chromium precipitations are clearly visible.
oo The surface of the steel has been nitrided by a plasma diffusion process (upper part of the image).
wt i The small images of fig. 10 show AFM pictures of two precipitations, one within the diffusion
oe N zone, the other within the bulk material. Since precipitations are visible in the topographic image of
EEE the polished surface they should be harder than the surrounding matrix. A series of nanoindenta-
N tions, using maximum forces of 2 and 3 mN respectively, has been performed through both pre-
wed cubide cipitations along a line to determine the hardness profile of the particles and the matrix.
ne tree The results are presented in figure 11. Within the bulk material the iron matrix has a hardness of 7
Me SICHT 7 GPa which is in the expected range. The particles have a hardness of 24 GPa, indicating that they
material tage consist (at least partially) of chromium carbide, which was confirmed by X-ray spectroscopy
a thresbold, 16 (WDX). In the diffusion zone the particles have a higher hardness of 28 GPa, corresponding to
orystalline part! chromium nitride. The Fe-matrix, too, has a significantly higher hardness of 16 GPa, due to the ni-
tration process.
if structure and The lateral resolu-
cal properties of 30 30 tion of the hard-
ve description 0f - ness determination
520 5 is approximately
“ N 0.5 pm. On the
; i other hand the
I i 0 determination of
? z 4 6 8 10 0 2 4 9 : Young’s modulus
distance [micron] distance [micron] x
onction wich 0 (figure 12) has a
E mel Figure 11: hardness of precipitations in steel (a) Cr-carbid particle in the bulk material much lower reso-
a in. (b) Cr-nitrid particle within the nitration zone. lution due to the
mn he used!
9
