Microstructural modification of pure Mg for improving mechanical and biocorrosion properties

Corrosion of carbon steel by Pseudomonas stutzeri CQ-Z5 in simulated oilfield water

Carbon steel, an important infrastructure material in the petroleum industry, experiences serious damage due to Microbially Influenced Corrosion (MIC) with untold economic impact. Pseudomonas stutzeri CQ-Z5 with solid biofilm formation and organic acid-producing ability was isolated from Changqing oilfield produced water. The corrosion behavior and mechanism of 20# carbon steel by P. stutzeri CQ-Z5 were explored in a simulated oilfield product water circulating device. Bacteria inoculation can hasten steel corrosion, the maximum corrosion rate reached 1.84 mm y-1. Pitting corrosion on rust layer was observed using SEM, and CLSM monitored the change in biofilm thickness. XRD displayed that oxides were the primary corrosion products, including Fe2O3, Fe3O4, and FeOOH. Analysis of contributions of corrosion types indicated that biofilm corrosion contributes 72 % to total corrosion, far higher than those of ion erosion and organic acid decay. Many genes involved in iron metabolism, biofilm synthesis, and organic acid production were annotated in the genome of P. stutzeri CQ-Z5. Accordingly, a hypothetical corrosion mechanism model of P. stutzeri CQ-Z5 for carbon steel involvement of initial ion erosion, then biofilm corrosion and organic acid decay was proposed. The work helped prevent carbon steel corrosion and improve corrosion mitigation strategies.

Data analysis of the influence of microstructure, composition, and loading conditions on stress corrosion cracking behavior of Mg alloys

Stress corrosion cracking (SCC) can be a crucial problem in applying rare earth (RE) Magnesium alloys in environments where mechanical loads and electrochemical driven degradation processes interact. It has been proven already that the SCC behavior is associated with microstructural features, compositions, loading conditions, and corrosive media, especially in-vivo. However, it is still unclear when and how mechanisms acting on multiple scales and respective system descriptors predictable contribute to SCC for the wide set of existing Mg alloys. In the present work, suitable literature data along SCC of Mg alloys has been analyzed to enable the development of a reliable SCC model for MgGd binary alloys. Pearson correlation coefficient and linear fitting are utilized to describe the contribution of selected parameters to corrosion and mechanical properties. Based on our data analysis, a parameter ranking is obtained, providing information on the SCC impact with regard to ultimate tensile strength (UTS) and fracture elongation of respective materials. According to the analyzed data, SCC susceptibility can be grouped and mapped onto Ashby type diagrams for UTS and elongation of respective base materials tested in air and in corrosive media. The analysis reveals the effect of secondary phase content as a crucial materials descriptor for our analyzed materials and enables better understanding towards SCC model development for Mg-5Gd alloy based implant.

Biodegradable shape memory alloys: Progress and prospects

Shape memory alloys (SMAs) have a wide range of potential novel medical applications due to their superelastic properties and ability to restore and retain a 'memorised' shape. However, most SMAs are permanent and do not degrade in the body when used in implantable devices. The use of non-degrading metals may lead to the requirement for secondary removal surgery and this in turn may introduce both short and long-term health risks, or additional waste disposal requirements. Biodegradable SMAs can effectively eliminate these issues by gradually degrading inside the human body while providing the necessary support for healing purposes, therefore significantly alleviating patient discomfort and improving healing efficiency. This paper reviews the current progress in biodegradable SMAs from the perspective of biodegradability, mechanical properties, and biocompatibility. By providing insights into the status of SMAs and biodegradation mechanisms, the prospects for Mg- and Fe-based biodegradable SMAs to advance biodegradable SMA-based medical devices are explored. Finally, the remaining challenges and potential solutions in the biodegradable SMAs area are discussed, providing suggestions and research frameworks for future studies on this topic.

In Vivo Corrosion Behavior of Biodegradable Magnesium Alloy by MAF Treatment

Coating treatment plays an irreplaceable role in propelling the clinical application of magnesium alloys. This experiment was designed in order to observe the anticorrosion behavior of magnesium fluoride coating in rats. The MgF₂ layer was prepared on the surface of AZ31 magnesium alloy in saturated NH₄HF₂ solution by microarc fluorination (MAF) at 190 V. The cross-sectional SEM, EDS, and XRD analysis indicated that the alloy surface was covered with MgF₂. Meanwhile, SEM observation was used to compare the magnesium alloy samples before and after treatment, and it was found that the samples after coating were flatter and smoother. Two sets of experiments were carried out with the subjects, 6-week-old male rats. So that the untreated AZ31 samples and the microarc fluorinated AZ31 samples could be buried under the muscle layer individually. The volume changes and surface morphology of the corroded samples were monitored dynamically using micro-CT over a 16-week period in vivo. Comparison of results between the two sets of samples presented that the corrosion of the microarc fluoridated samples was much slower than that of the untreated ones. The MAF coating was shown to be effective in controlling the corrosion rate and progression of the magnesium alloy.

Effect of high-pressure torsion on microstructure, mechanical properties and corrosion resistance of cast pure Mg

High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing.