Effect of strain rate and corrosion products on pre-exposure stress corrosion cracking in the ZK60 magnesium alloy

Merson, Evgeniy; Poluyanov, Vitaliy; Myagkikh, Pavel; Мерсон, Д. Л.; Vinogradov, Alexei

doi:10.1016/j.msea.2021.142304

Cited by 11 publications

(22 citation statements)

References 47 publications

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“…Thus, it is apparent from the obtained results that the strain-hardening behaviour of the present alloy significantly depends on temperature but is just slightly affected by the other experimental conditions considered in the present study. Recently it was shown that the alloy used in the present study possesses extremely high strain-rate sensitivity [15], hence, indicating the pronounced thermally-activated nature of the mechanism governing the plastic deformation in this alloy. Thus, such a strong effect of even a slight change in the temperature on strainhardening behaviour observed in the present work is not surprising.…”

Section: Discussionmentioning

confidence: 74%

The effect of testing conditions on stress corrosion cracking of biodegradable magnesium alloy ZK60

et al. 2022

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The effect of the chemical composition, temperature, circulation and pH of the simulated body fluid (SBF) on the corrosion and stress corrosion cracking (SCC) susceptibility of the alloy ZK60 was studied through the immersion and slow-strain rate tensile (SSRT) testing respectively. It is found that both the corrosion and SCC susceptibility of the alloy is significantly affected by chemical composition and adjustment of pH level of SBF, while the temperature and circulation of the SBF exert a minor effect on these characteristics. The pH adjustment of 0.9 % NaCl solution to 7 ± 0.2 was done automatically and continuously during the SSRT testing by refreshment of the SBF. The control over pH decreased the corrosion rate and increased the SCC susceptibility of the ZK60 alloy. It is established that, in the considered SBFs (0.9 % NaCl, Ringer's and Hank's solutions), the alloy ZK60 possesses the highest SCC susceptibility and the least corrosion rate in Hank's solution, while in Ringer's solution, the SCC susceptibility and corrosion resistance are lowest. It is concluded that the experimental factors considered in the present study have to be accounted for in the reliable assessment of the corrosion and SCC resistance of the biomedical Mg alloys.

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Section: Discussionmentioning

confidence: 74%

The effect of testing conditions on stress corrosion cracking of biodegradable magnesium alloy ZK60

et al. 2022

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“…Nevertheless, one can notice that the flat, fibrous fracture surface topology bears a lot of similarity to that reported for magnesium alloys fractured in physiological solutions under stress corrosion cracking (SCC) conditions (e.g., AZ91D [103,104] or AZ31 and ZK60, as shown by some of the present authors in dedicated investigations [28,105,106]). Figure 13 illustrates some of the observed features, which are typical of SCC in many Mg alloys (including the same ZK60 [28,[105][106][107][108]) and are not seen in the specimens conventionally fatigued in air-there are visible signatures of intergranular brittle fracture (marked by red arrows) and multiple secondary cracks-and the characteristic fluted relief (marked by white arrows), which is indicative of SCC-induced plasticity ahead of the crack tip (flutes represent specific elongated dimples formed when voids are nucleated along slip-band intersections [109]). Of course, these features, which are sporadically observed on the fracture surface of the specimens fatigued in corrosive media, do not represent the predominant fracture mechanism, but rather, they indicate the plurality of the mechanisms involved in the fracture processes.…”

Section: Discussionmentioning

confidence: 99%

On the Corrosion Fatigue of Magnesium Alloys Aimed at Biomedical Applications: New Insights from the Influence of Testing Frequency and Surface Modification of the Alloy ZK60

et al. 2022

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Magnesium alloys are contemporary candidates for many structural applications of which medical applications, such as bioresorbable implants, are of significant interest to the community and a challenge to materials scientists. The generally poor resistance of magnesium alloys to environmentally assisted fracture, resulting, in particular, in faster-than-desired bio-corrosion degradation in body fluids, strongly impedes their broad uptake in clinical practice. Since temporary structures implanted to support osteosynthesis or healing tissues may experience variable loading, the resistance to bio-corrosion fatigue is a critical issue that has yet to be understood in order to maintain the structural integrity and to prevent the premature failure of implants. In the present communication, we address several aspects of the corrosion fatigue behaviour of magnesium alloys, using the popular commercial ZK60 Mg-Zn-Zr alloy as a representative example. Specifically, the effects of the testing frequency, surface roughness and metallic coatings are discussed in conjunction with the fatigue fractography after the testing of miniature specimens in air and simulated body fluid. It is demonstrated that accelerated environmentally assisted degradation under cyclic loading occurs due to a complicated interplay between corrosion damage, stress corrosion cracking and cyclic loads. The occurrence of corrosion fatigue in Mg alloys is exaggerated by the significant sensitivity to the testing frequency. The fatigue life or strength reduced remarkably with a decrease in the test frequency.

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“…The cylindrical samples of 6 mm diameter and 30 mm length were machined from the hot-extruded bar of the commercial alloy ZK60, which is known to be strongly susceptible to PESCC. The chemical composition, microstructure and mechanical properties of this alloy as well as its susceptibility to SCC and PESCC at various conditions, were documented in detail in our previous reports [11][12][13][14][15][16]. The samples were immersed in the aqueous corrosive solution of 4 % NaCl + 4 % K 2 Cr 2 O 7 at the open-circuit potential and ambient temperature of 24°C.…”

Section: Methodsmentioning

confidence: 99%

“…Since the corrosive solution does not interact directly with the metal during mechanical testing, and, consequently, the effects associated with AD can be excluded, PESCC is commonly attributed to hydrogen being absorbed by the metal during pre-exposure to corrosive media [6 -10]. However, this interpretation of the origin of PESCC has been challenged by the present authors recently on the basis of several new experimental findings reported in [11][12][13]. Specifically, it was found that neither the loss in ductility nor the appreciable concentration of diffusible hydrogen is observed in Mg alloys pre-exposed to the corrosive solution if the corrosion products layer is removed from the specimens' surface prior to the subsequent tensile testing in air [12,13].…”

Section: Introductionmentioning

confidence: 94%

“…It was concluded that the role of diffusible hydrogen was minor because of insufficient penetration of this hydrogen into the Mg matrix during corrosion. Furthermore, it was suggested that PESCC could be caused by the retained corrosive solution, which was supposed to be sealed within the discontinuities in the corrosion products [11]. This was indirectly evidenced by the abundant presence of the corrosion products on the peripheral parts of the fracture surface as well as inside the secondary cracks in the pre-exposed specimens, which did not interact with external corrosive media during tensile testing in air.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for the presence of corrosive solution within corrosion products film in magnesium alloy ZK60

et al. 2022

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It has been recently suggested that it is the corrosion solution sealed within the corrosion products layer that can be the primary cause of pre-exposure stress corrosion cracking (PESCC) of Mg alloys. In the present study, we attempt to find additional evidence for the presence of the retained corrosive media in the corrosion products layer deposited on the surface of the ZK60 alloy. The samples of this alloy were pre-exposed to the corrosive solution for 1.5 h and then subjected to the thermal desorption analysis (TDA). The specimens were tested either immediately after pre-exposure or after the post-exposure immersion in CCl 4 or storing in desiccator for 24 h. During the immersion in CCl 4 , the volume of hydrogen desorbing from the samples was assessed. The main finding of the present study lies in that the corrosion reaction remains within ZK60 samples even after their extraction from the corrosive solution. This is evidenced by the extensive hydrogen desorption which continued and not ceased even after 24 hours after pre-exposure. It is established that the largest part of this hydrogen cannot be detected by short TDA of the sample right after pre-exposure to corrosive media, thus it should be produced in-situ during the immersion in CCl 4 . Considering that CCl 4 is inert with respect to Mg, it is concluded that the corrosion reaction producing hydrogen can be caused only by aggressive media retained within the corrosion products layer.

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Effect of strain rate and corrosion products on pre-exposure stress corrosion cracking in the ZK60 magnesium alloy

Cited by 11 publications

References 47 publications

The effect of testing conditions on stress corrosion cracking of biodegradable magnesium alloy ZK60

The effect of testing conditions on stress corrosion cracking of biodegradable magnesium alloy ZK60

On the Corrosion Fatigue of Magnesium Alloys Aimed at Biomedical Applications: New Insights from the Influence of Testing Frequency and Surface Modification of the Alloy ZK60

Evidence for the presence of corrosive solution within corrosion products film in magnesium alloy ZK60

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