carbon-fullerene coating in air and nitro- gen atmospheres. Te thermogravimetry scans of coatings are shown in Fig. 6. In an air atmosphere, the carbon nano- fiber coating suddenly dropped in the temperature range of 752F (400C) and 1,112F (600C). It kept reducing until 50%wt. Tis is because cutting powder of the carbon nanofiber coating was used as a differential thermal analysis sample, and it contained the compound layer that was chemically combined with the test piece mold. Te weights of the fullerene and
3
carbon-fullerene coatings do not decrease until 752F (400C), but then show sharp declines. Te fuller- ene coating starts resolving at 752F (400C) and easily vaporizes into CO and CO2
. Compared to other types
Results and Conclusions
Differential thermal
analysis was conducted for carbon nanofiber, fullerene and
of carbon materials, fullerene oxidizes easily. However, based on the analysis results, at 752F (400C) or lower, the fullerene coating can control the high temperature degradation of the carbon nanofiber coating. In a nitrogen atmo- sphere, the fullerene coating remains stable and is not dissolved until 1,652F (900C). Te thermogravimetry scan of the carbon nanofiber coating in a nitrogen atmosphere shows a gradual decrease in weight as the temperature increases. Conversely, fullerene and carbon-fullerene coatings demonstrate lower weight decline ratios compared to that of the carbon nanofiber coating up to 1,202F (650C). It is possible that the fullerene coating has a protective effect on the carbon nanofiber coating as observed in an air atmosphere. During the diecasting process,
oxygen in the cavities is expected to be consumed by aluminum, which has a fast oxidization rate, and a nonoxi- dative atmosphere is created in the
cavities. Setting the temperature of molten metal at 1,202F (650C) or lower and the temperature of the mold surface during release at 752F (400C) or lower prevents the high temperature degradation of the coating. A diecasting test was conducted
by using molds with various carbon coatings. Te temperature of molten metal was 1,184F (640C). Te Scanning Electron Microscopy (SEM) micro- graphs of a core pin before and after 100 shots are shown in Fig. 6. Te before and after comparison of the pins shows the surface and cross section after use are denser than before use. Te density of the carbon nanofiber coating was low compared to that of
ONLINE RESOURCE
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Fig. 4. The setup of the mold release resistance test is shown. 58 | MODERN CASTING February 2014
Fig. 5. This graph shows the results of the mold release resistance test as a function of the pouring shot number.
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