[en] Plasma electrolytic oxidation coating was carried out in phosphate-based electrolyte embedded with different amounts of lanthanum nitrate (LN) on AZ31 magnesium alloy substrate in order to characterize the microstructure and protective properties of the prepared coatings. The SEM/elemental map results show that the additive lanthanum is positioning homogeneous within coating structure. Also, according to the obtained results and mechanism of PEO coating formation, the amount of additive replacement within the external porous layer was more than the replacement occurred within the internal dense structure. Results of potentiodynamic polarization (PDS) and electrochemical impedance spectroscopy (EIS) tests show that the corrosion resistance properties of PEO coatings in the presence of LN additives are greatly improved. Formation a structure with a higher density coupled with the barrier role of deposited lanthanum hydroxide due to the penetration of corrosion agents improves the corrosion resistance of the oxide coating. Finally, thermodynamic calculations prove that lanthanum hydroxide sediments were formed in respective immersion condition and also shows their stability and insolubility. - Highlights: • Lanthanum nitrate reduces coating's pores density. • Lanthanum nitrate increases PEO coating's corrosion resistance. • Insoluble La(OH)₃ has barrier effect against corrosive agents penetration. • Formation of La(OH)₃ is possible thermodynamically.

[en] Fretting wear is a potentially significant degradation mechanism in nuclear steam generators and other shell and tube heat transfer equipment as well. This paper presents an overview of the recently developed code FIVDYNA which is used for the non-linear flow-induced vibration and fretting wear analysis for operating steam generators (OTSG and RSG) and shell-and-tube heat exchangers. FIVDYNA is a non-linear time-history Flow-Induced Vibration (FIV) analysis computer program that has been developed by Babcock and Wilcox Canada to advance the understanding of tube vibration and tube to tube-support interaction. In addition to the dynamic fluid induced forces the program takes into account other tube static forces due to axial and lateral tube preload and thermal interaction loads. The program is capable of predicting the location where the fretting wear is most likely to occur and its magnitude taking into account the support geometry including gaps. FIVDYNA uses the general purpose finite element computer code ABAQUS as its solver. Using ABAQUS gives the user the flexibility to add additional forces to the tube ranging from tube preloads and the support offsets to thermal loads. The forces currently being modeled in FIVDYNA are the random turbulence, steady drag force, fluid-elastic forces, support offset and pre-strain force (axial loads). This program models the vibration of tubes and calculates the structural dynamic characteristics, and interaction forces between the tube and the tube supports. These interaction forces are then used to calculate the work rate at the support and eventually the predicted depth of wear scar on the tube. A very good agreement is found with experiments and also other computer codes. (author)

[en] Highlights: • Improving structural properties and corrosion resistance of ZrCC by adding ZnSO₄. • Increasing epoxy coating’s anti-corrosion properties with ZrCC as a pretreatment. • Lowest cathodic disbondment rate for duplex coating with 2.4 mM ZnSO₄ in ZrCC. • Introduce an acceptable new parameter using EIS to evaluate cathodic disbondment. -- Abstract: The protective performance of zirconium-pretreated epoxy films with and without zinc sulfate additive in 3.5 wt% NaCl solution was investigated. A new parameter with a reasonable relation based on EIS tests for the scratched samples was introduced to determine the amount of corrosive electrolyte diffusing into the coating/substrate interface, and it was attributed to cathodic disbondment resistance. It was revealed that coating segregation was reduced via surface pretreating by zirconium with additives.

[en] The present study is to investigate the effect of free surface motion of the fluid on the dynamic behavior of the thin-walled cylindrical shells. This paper outlines a semi-analytical approach to dynamic analysis of the fluid-filled horizontal cylindrical shell taking into account the free surface motion effect. The aim of the method is to provide a general approach that can be used for both analysis and synthesis of fluid structure interaction problems in the horizontal cylindrical shells where the dynamic interaction of a flexible structure and incompressible and inviscid flow is in focus. The approach is very general and allows for dynamic analysis of both uniform and non-uniform cylindrical shell considering the fluid forces including the sloshing effect exerted on the structure. The hybrid method developed in this work is on the basis of a combination of the classical finite element approach and the thin shell theory to determine the specific displacement functions. Mass and stiffness matrices of the shell are determined by precise analytical integration. A potential function is considered to develop the dynamic pressure due to the fluid. The kinetic and potential energies are evaluated for a range of fluid height to find the influence of the fluid on the dynamic responses of the structure. The influence of the physical and geometrical parameters on the fluid-structure system has been considered in the numerical solutions. When these results are compared with corresponding results available in the literature, both theory and experiment, very good agreement is obtained. (authors)

[en] We investigated the effect of cerium oxide (Ceria) nanoparticles existing in the external porous structure of microarc oxidation (MAO) coating on the protective behavior and adhesion strength of MAO/epoxy duplex coating implemented on AZ31 Mg alloy. MAO coating was considered as the pretreatment for applying the epoxy layer. The presence of ceria particles affected the morphology of the surface and cross-section of the MAO coating and its corrosion resistance. Embedding ceria nanoparticles in the external porous structure of the MAO layer showed that the MAO structure, in addition to its pretreatment role, acts as the container of ceria particles. The results of the electrochemical impedance spectroscopy (EIS) test on duplex coatings with and without defects and the pull-off test in dry and wet conditions revealed that the presence of ceria at an optimal concentration (3 g/l) improves the protective behavior of the epoxy layer and its adhesion strength. Moreover, ceria nanoparticles with the barrier effect and active protection improved the protective behavior of the dual-layered coating.

[en] Highlights: • PEO/Silane containing inhibitors as pretreatment of epoxy layer. • Studying active corrosion protection of inhibitors by EIS and EN tests. • Best protective properties for three-layer coating with Ce and 8-HQ inhibitors. • Improvement of wet adhesion strength of three-layer coating with Ce and 8-HQ. PEO/Silane/Epoxy coating system with inorganic inhibitor (Ce(NO₃)₃) in the plasma electrolytic oxidation (PEO) layer as well as organic inhibitors in the silane layer was investigated in terms of active corrosion protection properties and adhesion strength. The results of electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) and pull-off tests indicated that the presence of the 8-Hydroxyquinoline (8-HQ) organic inhibitor provides the optimal performance for coating systems. The formation of Ce(OH)₃ in the PEO coating structure and the complex chelate of Mg(HQ)₂ in the silane layer lead to the creation of active corrosion protection properties for the coating systems.