| Summary: | 博士 === 國立清華大學 === 材料科學(工程)研究所 === 83 === The slow strain rate tension (SSRT) technique was used to study
the effect of strain rate on the susceptibility to stress
corrosion cracking (SCC) and crack velocity of 67/33 brass in
0.1M sodium halide solutions (pH=6.8) at 25C. The results
indicate that F- ions induce a significant suscept- ibility to
intergranular stress corrosion cracking (IGSCC) and that
susceptibility increases with decreasing strain rate. In
contrast, in 0.1M Cl-, Br-, or I- solutions, no SCC
susceptibility was observed, regardless of the strain rates
used. Pitting potentials, Ep, and protection poten- tials,Epp,
have been determined for brass (33% Zn) using a cyclic
polarization method.The pitting potentials, Ep, and protection
potentials, Epp, depend on the logarithmic concentration of F-
ions according to the equations: Ep=a+blog[F-] and Epp= a+
blog[F-]. The minimum concentration of NaF solu- tions that
caused intergranular stress corrosion cracking (IGSCC) was
1x10-4M. This concentration, was also the critical level for
repassivation, ob- served in cyclic polarization tests. In the
presence of 10-1M NaF the potential range for IGSCC was -150 to
-50mV(SCE). In aerated solutions, a minimum fluoride con-
centration of for producing IGSCC was found to be 1x10-4M,
whereas the threshold concentration shif- ted to 1x10-2M in
both nitrogen- and oxygen-satur- ated solutions. There exist a
critical fluoride concentration of 10-1M as solution exposed to
air or saturated with air, showing the most serious IGSCC
susceptibility and corrosion rate of 67/33 brass. BTA was a
favorable inhibitor of IGSCC and electrochemical dissolution of
67/33 brass as dis- solved oxygen increases.
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