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novel type of multilayered thin film in the present study.
Because their unit cell dimensions are very close to one
another, good atomic coherence and hence good me-
chanical hardness can be easily maintained at the sur-
face when one of them is grown on top of the other
using magnetron sputtering techniques. The hardness
varies from 4.3 to 4.8 GPa over the three synthesized
Ni/Ni Al multilayered films, which is high enough to be
3
comparable with that of Ni Al hard films. The hard
3
and tough multilayered films are expected to be used
as hard coatings and miniaturized sensors in micro-
electromechanical systems.
FIG. 4. The fracture cross-section profile of Film 1 by SEM. It can be
clearly seen that the fractured striations are continuous, layer through
layer, and no delamination appears within the multilayered film.
ACKNOWLEDGMENTS
good adhesion to one another, should be the primary reason
for the high hardness of the films. Multilayers fabricated
We gratefully acknowledge W.R. Thiele for SEM ex-
periments, M. Kempf for assistance on hardness meas-
urements, and M. Goeken and W.H. Xu for help in
preparing the manuscript. X.K.M. also wishes to ac-
knowledge Alexander von Humboldt Foundation of Ger-
many for a research fellowship. This work was
financially supported by Natural Science Foundation of
China under Contract No. 59981003.
from Ni and Ni Al are expected to exhibit grain-to-grain
3
eptaxy between the layers because both the constituents
have a fcc structure with a low lattice mismatch (1.3%).
Dislocation movement across the coherent interfaces is
therefore estimated to be difficult because, for instance,
two unit dislocations in the fcc Ni phase will have to be
paired up to form a superdislocation upon penetrating
into the neighboring fcc (L1 ) Ni Al or else an antiphase
2
3
domain boundary will result in the wake of a single dis-
location. This is the so-called order/disorder strengthen-
ing effect, and so the order/disorder multilayered films
become surprisingly hard and strong. One of the reasons
why Film 3 was harder than Film 1 and 2 should be that
Film 3 contained more order/disorder layers.
Figure 4 shows the fracture cross-section morphology
of Film 1 by scanning electron microscopy (SEM). The
continuous fracture striations of layer through layer show
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1
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3
J. Mater. Res., Vol. 15, No. 12, Dec 2000
2597
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