Research on the localized Corrosion of Brass and Special

• Main Authors: Lee, Cheng Kuo, 李正國
• Other Authors: Shih Han Chang
• Format: Others
• Language: en_US
• Published: 1994
• Online Access: http://ndltd.ncl.edu.tw/handle/81207793223159068704

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.