Corrosion Fatigue Studies on a Bulk Glassy Zr-Based Alloy under Three-Point Bending

Abstract

Corrosion fatigue (CF) tests were carried out on bulk glassy Zr52.5Cu17.9Al10Ni14.6Ti5 (Vitreloy 105) samples under load-controlled three-point bending conditions with a load ratio of R = 0.1 in 0.01 M Na2SO4 + 0.01 M NaCl electrolyte. During cyclic testing, the bar-shaped specimens were polarized in situ at constant potentials and the current was monitored. Three different anodic potentials within the interval between the pitting potential EP and the repassivation potential ER and three different load amplitudes were applied. In some cases, in situ microscopic observations revealed the formation of black corrosion products in the vicinity of the crack tip during anodic polarization. Fractographic analysis revealed a clear distinction between two modes of crack growth characterized by smooth dissolution induced regions on the one hand and slim fast fracture areas on the other hand. Both alternating features contributed to a broad-striated CF fracture surface. Moreover, further fatigue tests were carried out under free corrosion conditions yielding additional information on crack initiation and crack propagation period by means of the open circuit potential (OCP) changes. Thereby, a slight increase in OCP was detected after rupture of the passive layer due to bare metal exposed to the electrolyte. The electrochemical response increased continuously according to stable crack propagation until fracture occurred. Finally, the fracture surfaces of the CF samples were investigated by energy dispersive X-ray with the objective of analyzing the elemental distribution after anodic dissolution. Interestingly, anodic polarization at a near repassivation potential of −50 mV vs. saturated calomel electrode (SCE), which commands a constant electric potential of E = 0.241 V vs. standard hydrogen electrode (SHE), led to favorable effects on the fatigue lifetime. In conclusion, all results are conflated to a CF model for bulk glassy Vitreloy 105 under anodic polarization in chloridecontaining electrolyte and compared to the previously proposed stress corrosion mechanisms under similar conditions.

Studies on Stress Corrosion Cracking of Vit 105 Bulk Metallic Glass

“…Altogether, our SEM investigations disclosed that cracks usually started at locally corroded zones. This was similarly observed in corrosion fatigue tests which were conducted in the present project employing the same sample type A of Vit 105 3PB samples (Grell et al, 2017). The randomness of the pitting process is one reason explaining the scattering of the final times to fracture.…”

Fatigue life prediction of gasoline storage tank considering varying current density and weld stress

“…As shown in the Figures 2 and 3, the corrosion rate tends to zero during the period from the formation of the passive film to the rupture, which can only be cracked by pure mechanical fatigue, and the fatigue acts on the passive film. 31–33…”

“…This requires pure mechanical fatigue to destroy the passivation film and crack it to expose the fresh metal surface that will continue to be corroded. 31 The corrosion rate is usually measured by Faraday's law 13,14 :…”

“…As shown in the Figures 2 and 3, the corrosion rate tends to zero during the period from the formation of the passive film to the rupture, which can only be cracked by pure mechanical fatigue, and the fatigue acts on the passive film. [31][32][33] The rate of this period is not a simple sum of the two, because the corrosion rate is 0, and the fatigue rate acts on another material, with the rate unknown, so the passive film will certainly produce a corrosion fatigue interaction rate da dN À Á co . The current density is the decisive factor, and the rest are constant.…”