Biomedical Engineering Reference
In-Depth Information
13.5
The percentage of densification of WC-Co as a function of the
continuous heating temperature for various initial particle sizes.
quantitative, the starting temperature is often used for comparison.
However, because sintering is a continuous kinetic processes, rigorously
speaking, a single point of demarcation for the starting temperature of
sintering does not exist. Based on typical experimental behavior, the starting
temperature can be defined as the temperature at which the rapid
densification stage initiates, as marked on Fig. 13.4. In general, the
densification versus temperature plot shifts to the left (lower temperature)
when nanosized powders are used rather than micron-sized powders.
For example, several studies on the sintering of nano yttrium stabilized
zirconia (YSZ) have shown that the sintering temperature of nanocrystalline
ZrO
2
initiates at a temperature 200
C lower than that of the micro-
crystalline powders.
12-14
An even greater temperature difference of sintering
8
C - was reported by Mayo
15
for nanosized titania compared to
commercial TiO
2
powders. Similar results were observed when sintering
nano ceria
16
and nano titanium nitride powders.
17
A comprehensive study on the sintering of nano tungsten carbide and
cobalt (WC-Co) powders was conducted by Maheshwari et al.
18
Figure 13.5
shows the percentage of densification as a function of the continuous
heating temperature for various initial particle sizes. Clearly, the entire
sintering temperature decreases steadily as the initial average particle size
decreases from 30 microns to 10 nanometers. It seems, however, that there is
little difference between the onset temperatures of the sintering of particles
greater than one micron.
400
8
