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The effects were confirmed by Cheng and Zheng [21]. They
prepared a TiN layer on NiTi by nitrogen PIII and found that the
negative pulsed voltage applied during PIII significantly influenced
the microstructure of the TiN coatings. As shown in Fig. 6.4, the 15
kV sample showed the smallest roughness of 4.591 nm [root mean
square (RMS)], but the surface roughness of the 5 kV sample was
larger by a factor of 2.45. Generally, the RMS roughness values
were observed to increase with increase in bias voltage. Further,
investigation showed that either a very small bias (5 kV) or large (30
kV) bias did not favour the formation of smooth and uniform TiN
coatings [21].
Figure 6.4
Surface roughness of TiN coatings as a function of negative
pulsed bias voltages. Reprinted from Ref. [21], Copyright 2006,
with permission from Elsevier.
PIII&D [22-27].
By changing the bias voltage, two kinds of coatings were fabricated
[22]. At a voltage of
A biomimetic structure was produced by C
H
2
2
30 kV, an ion-mixed amorphous carbon coating
with a thickness of about 160 nm was produced on NiTi, but PII&D
conducted at
−
40 kV resulted in direct carbon ion implantation and
formation of hard titanium carbide at the interface between the
carbon coating and NiTi substrate. This structure was observed to
enhance the surface mechanical properties such as Young's modulus
and hardness [22]. Both the deposited amorphous carbon film and
carbon-implanted layer favored-cell proliferation (Fig. 6.5 [22])
and the surface of all the samples was generally tolerated by the
−
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