Corrosion of Titanium Matrix Composites Page: 5 of 7
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Potentiodynamic polarization curves were determined for all of the composites at all three
temperatures. An example of those for unalloyed Ti, Ti + 20 vol% TiC, and Ti + 20 vol%
TiB2 are shown in Fig. 3. All of the curves show active-passive behavior and no transpassive
region. The unalloyed Ti shows very little effect of temperature except for a positive shift in
the corrosion potential at 90 C.
Polarization curves for the Ti + TiC composites show increased currents due to higher
temperatures and higher particulate concentrations. All curves also show what appears to be
a secondary passivation reaction at approximately 0.4 V vs S.C.E. A comparison of these
curves to those for unalloyed Ti suggests that the secondary passivation peak may be related
to another phase. Since analyses of the composites showed the presence of no other phases
except the Ti matrix and the TiC reinforcement, it is most likely due to the corrosion and
passivation of TiC. An examination of the polarization curves in Fig. 4 for four Ti + TiC
composites tested at 90 C helps support the interpretation that the secondary passivation peak
is related to TiC. The maximum current density of this peak increases with reinforcement
.E-05 2.5 TiC 10 TiC 5 TiC
-1 -0.5 0 0.5 1 1.5 2
Potential, V vs S.C.E.
Fig. 4: Effect of composite composition on the potentiodynamic polarization behavior of
Ti + TiC composites.
Polarization curves for the Ti + TiB2 composites also show increased currents for higher
temperatures and higher particulate concentrations. The curves for the Ti + TiB2 composites
are, however, very similar to those for unalloyed Ti. The addition of the TiB2 increased the
primary passivation and the passive currents but did not appreciably affect the corrosion
potential. This is in contrast to the Ti + TiC composites and suggests that the Ti + TiB2
composites corrode more rapidly than but in a manner similar to unalloyed Ti. Earlier
research  on the corrosion of pressed and sintered TiB2 showed that it did not passivate in
deaerated HCl, that the corrosion potential was similar to the -0.5 V vs S.C.E. shown in Fig.
3 for unalloyed Ti and for the Ti + TiB2 composites, and that current densities in the
"passive" region were approximately 1 X 10-2 A/cm2. This helps explain the similarities and
the differences between the polarization cures for unalloyed Ti and those for the Ti + TiB2
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Covino, B.S., Jr. & Alman, D.E. Corrosion of Titanium Matrix Composites, article, September 22, 2002; (digital.library.unt.edu/ark:/67531/metadc780332/m1/5/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.