黄銅の応力腐食割れに関する研究-4-腐食液のpHと温度の影響

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Effects of pH and temperature of corrosive solution on the stress corrosion cracking in Cu-30wt%Zn alloy have been investigated by the Weibull distribution method. All test pieces were full annealed and their average grain sizes were controlled in　20 μm. And then, the test pieces have been stress corrosion tested at various solution temperatures of 14, 19, 24, 29, 34 and 39℃ under the constant applied stress of 80% of the yield stress in Mattsson's corrosive solution of pH 6.5, 7.0 and 8.0　The results of pH 7.5 reported before have been added to their results and are discussed statistically. The failure time(tf), crack initiation time(ti) and crack propagation period(te) obey the single Weibull distributions with high values of shape parameter(m) that evaluated from 6.44 to 16.65 in tf, from 4.63 to 13.04 in ti and from 3.78 to 10.65 in te. But, the ffects of pH and temperature on the parameter m of the Weibull distribution are not found. The Weibull distributions with two parameters of m and η of failure times have been confirmed to be right by comparisons with histograms of 19　actual failure times and the cumulative failure distribution functions F(t) vs time curves or plots of calculated failure probability densities fe. By illustrating the cumulative failure distribution function F(t) and the failure probability density function f(t) vs time curves at every temperature, it is found that the solution temperature dependence on failure time is very remarkable. Effects of pH and temperature on scale parameter (η) of the Weibull distribution are very remarkable in tf, ti and te. In pH 7.0, the parameter takes the smallest value in the pH range from 6.5 to 8.0 at every temperature which corresponds to the result by Mattsson and the result of Cu-35wt%Zn alloy reported before. Apparent activation energies of Qtf in tf, Qti in ti and Qte in te are evaluated from Arrhenius plots of reciprocals of scale parameters. In pH 7.0, Qte takes the highest value of 20 kcal/mol in the pH range from 6.5 to 8.0. In the pH range from 6.5 to 7.5 the crack propagation seems to be the type of intergranular cracking. And, Qtf in pH 8.0 is equall to Qti and Qte that takes the lowest value of 11 kcal/mol in the pH range from 6.5 to 8.0. It seems to be the type of both intergraular cracking and transgranular cracking.
奈良教育大学の論文

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岡敏博
奈良教育大学技術教室

黄銅の応力腐食割れに関する研究-4-腐食液のpHと温度の影響

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