Biomedical Engineering Reference
In-Depth Information
15.3.3.3 Effects of Substrate Preparation on Diamond Deposition
The effects of the Murakami/acid chemical etching can clearly be seen on the WC-Co substrate sur-
faces.
Figure 15.15
shows that cobalt etching was successfully achieved because no cobalt peaks could
be detected in the EDX spectrum. In addition, the etching process produced a roughened surface.
Diamond layers were deposited on pretreated WC-Co dental burs. Adherent diamonds on WC-Co
dental burs consisting of mainly (111) faceted diamond crystals were deposited as shown in
Figure
15.16
. Micrographs of the burs show that the diamond film is uniformly coated onto the complex 3D
substrate surface. The modified filament arrangement produced a uniform and dense diamond coating
even though the substrate is nonplanar with a complex geometry. The morphology of the diamond sur-
face of the dental bur is rough making the bur extremely desirable for dental machining applications.
The coated dental bur was cut in order to study the cross section of the tool as can be seen in
Figure 15.17
. It was found that the coating is thicker at the cutting teeth with average thickness of
about 23 μm (growth rate of ∼1.5 μm h
1
) due to the slightly higher temperature at the bur tip because
cutting teeth is closer to the filament coil. At the base of the bur, the heat is carried away faster and
therefore it is at a lower temperature giving rise to lower growth rates and hence thinner films, at
about 8 μm in thickness. The thicker coating at the tip is expected to give the tool longer life.
15.4
BUR PERFORMANCE INVESTIGATIONS
CVD diamond films have attracted considerable interest for cutting tool applications, including rotary
tools and inserts due to their excellent physical and chemical properties.
In this chapter, we report an investigation of diamond film deposited on etched and un-etched
WC-Co dental burs, and subsequent machining results on human teeth, borosilicate glass, and acrylic
teeth are presented
[66,67]
.
15.4.1
Tool Preparation
Two sets of laboratory tungsten carbide (WC-Co) dental burs (AT23 LR) with fine WC grain sizes
(1 μm) 20-30 mm in length and 1.0-1.5 mm in diameter (supplied by Metrodent Ltd, UK), were used
as substrates. SEM and EDX were used to characterize the etched surfaces of substrates.
15.4.2
CVD Diamond Deposition on the Dental Burs
Diamond films were deposited onto the cutting edge of the burs. The coiled tantalum filament (0.5 mm
diameter) was held vertically within the vacuum deposition chamber, and the dental burs were posi-
tioned centrally and coaxially within the coils of the filament such that the cutting edges were 5 mm
from the filament coils. Prior to deposition, the tantalum filament was carburized for 30 min with 3%
CH
4
with excess hydrogen. Standard deposition conditions described in Section 3.3 were used. The
deposition time and pressure in the vacuum chamber were 5-15 h and 20 Torr, respectively.
15.4.3
Dental Bur Machining: Drilling Experiments
In order to examine the cutting performance of the diamond-coated dental burs, a variety of clini-
cal and laboratory materials such as borosilicate glass, acrylic teeth, and natural human teeth were
