10
A. Patil et al.
5 μm
2 μm
2 μm
2 μm
Pure Ni
Ni-10Ti-10C
Ni-5Ti-10C
Ni-5Ti-20C
Graphite
Graphite
Graphite
TiC
TiC
TiC
Fig. 3 SEM images of pure nickel and Ni-Ti-C at 25 K× magnification. (Color figure online)
SEM micrographs reveal the presence of nanoscopic spherical titanium carbide
precipitates uniformly distributed within the nickel matrix. The crystallite size of
titanium carbide precipitates in the nickel matrix remained nanoscopic even after
SPS processing. Microstructure indicates that pure nickel exhibits coarser grains as
compared to that of Ni-Ti-C composites, as no second phase precipitates such as
titanium carbide and graphite are present to limit the grain growth during sintering.
Ni-10Ti-10C exhibited a higher volume fraction of uniformly distributed nanoscopic
in situ titanium carbide precipitates within the nickel matrix as compared to other
Ni-Ti-C composites. The titanium carbide precipitates bordering the graphite phase
have also been observed since in situ titanium carbide forms near the graphite source.
The highest volume fraction of acicular graphite is observed in Ni-5Ti-20C composites, primarily due to the existence of unreacted carbon left after in situ titanium
carbide formation. This unreacted graphite phase available in the matrix expectedly
increased the wear resistance of the composite due to solid lubrication of graphite.
Additionally, to quantify the amount of in situ titanium carbide reinforcement formed
in the nickel matrix, the approximate area fraction of the titanium carbide precipitates in the Ni-Ti-C composites was obtained by analyzing several SEM micrographs
using image analysis software. Approximately, 9.1%, 4.3%, 4.8% of titanium carbide
A. Patil et al.
5 μm
2 μm
2 μm
2 μm
Pure Ni
Ni-10Ti-10C
Ni-5Ti-10C
Ni-5Ti-20C
Graphite
Graphite
Graphite
TiC
TiC
TiC
Fig. 3 SEM images of pure nickel and Ni-Ti-C at 25 K× magnification. (Color figure online)
SEM micrographs reveal the presence of nanoscopic spherical titanium carbide
precipitates uniformly distributed within the nickel matrix. The crystallite size of
titanium carbide precipitates in the nickel matrix remained nanoscopic even after
SPS processing. Microstructure indicates that pure nickel exhibits coarser grains as
compared to that of Ni-Ti-C composites, as no second phase precipitates such as
titanium carbide and graphite are present to limit the grain growth during sintering.
Ni-10Ti-10C exhibited a higher volume fraction of uniformly distributed nanoscopic
in situ titanium carbide precipitates within the nickel matrix as compared to other
Ni-Ti-C composites. The titanium carbide precipitates bordering the graphite phase
have also been observed since in situ titanium carbide forms near the graphite source.
The highest volume fraction of acicular graphite is observed in Ni-5Ti-20C composites, primarily due to the existence of unreacted carbon left after in situ titanium
carbide formation. This unreacted graphite phase available in the matrix expectedly
increased the wear resistance of the composite due to solid lubrication of graphite.
Additionally, to quantify the amount of in situ titanium carbide reinforcement formed
in the nickel matrix, the approximate area fraction of the titanium carbide precipitates in the Ni-Ti-C composites was obtained by analyzing several SEM micrographs
using image analysis software. Approximately, 9.1%, 4.3%, 4.8% of titanium carbide