黄銅の応力腐食割れに関する研究-3-腐食液温度の影響

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Effects of corrosive solution temperature on the failure time in stress corrosion cracking of Cu-30wt%Zn alloy have been investigateted by the Weibull distribution method. All test pieces were full annealed and their average grain sizes were controlled in 20μm. 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 80% of the yield stress in Mattsson's solution of pH 7.5. The failure time(tf), crack initiation time(ti) and crack propagation period(tc) obey the single Weibull distributions with high values of shape parameter(m) that are from 9.3 to 13.3 in tf, from 4.8 to 10.1 in ti and from 3.8 to 10.7 in tc. The Weibull distributions with estimated location parameters (γ) of failure times have been confirmed to be right by comparison with histograms of actual failure times and the cumulative failure distribution function vs time curves or plots of calculated failure probability densities. By illustrating the cumulative failure distribution function F(t), the failure probability density function f(t) and the failure rate　λ(t) vs time curves at every temperature, it is found that solution temperature dependence on failure time is very remarkable. Apparent activation energies evaluated from Arrhenius plots of reciprocals of median values(M) are 16.1 kcal/mol in tf, 14.1 kcal/mol in ti and 18.1 kcal/mol in tc.
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