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The influences of Ca and Ce/La microalloying on the microstructure evolution and bio-corrosion resistances of extruded Mg-Zn alloys have been systematically investigated in the current study. Compared with single Ca or Ce/La addition, the Ca-Ce/La cooperative microalloying results in an outstanding grain refinement, because the fine secondary phase particles effectively hinder the recrystallized grain growth. The coarse Ca 2 Mg 6 Zn 3 phases promote the formation of Ca 3 (PO 4) 2 or hydroxyapatite particles during the immersion process and accelerate the dissolution of the corrosion product film, which destroys its integrity and results in the deterioration of anti-corrosive performance. The Ce/La elements can be dispersed within the conventional Mg 7 Zn 3 phases, which reduce the internal galvanic corrosion between Mg matrix and the secondary phases, leading to an obvious improvement of corrosion resistance. Therefore, the Ca-Ce/La cooperative microalloying achieves a homogenous fine-grained microstructure and improves the protective ability of surface film, which will pave a new avenue for the design of biomedical Mg alloys in the coming future. [ABSTRACT FROM AUTHOR]

Magnesium alloys are considered as good candidates for biomedical applications, the influence of Ce/La microalloying on the microstructure, mechanical property and corrosion performance of extruded Mg–5.3Zn – 0.6Ca (wt%) alloy has been investigated in the current study. After Ce/La addition, the conventional Ca 2 Mg 6 Zn 3 phases are gradually replaced by new Mg–Zn–Ce/La–(Ca) phases (T 1 ′), which can effectively divide the Ca 2 Mg 6 Zn 3 phase. The Ca 2 Mg 6 Zn 3 /T 1 ′ structure in Mg–Zn–Ca–0.5Ce/La alloy is favorably broken into small particles during the extrusion, resulting in an obvious refinement of secondary phase. The dynamic recrystallized grain size is dramatically decreased after 0.5Ce/La addition, and the tensile yield strength is improved, while further addition reverses the effect, due to the grain coarsening. However, the corrosion resistance of extruded Mg–Zn–Ca alloy deteriorates after Ce/La addition, because the diameter of secondary phase particle is remarkably decreased, which increases the amount of cathodic sites and accelerates the galvanic corrosion process. [ABSTRACT FROM AUTHOR]

Abstract: The current work presents the room-temperature mechanical properties and the corrosion resistance in 3.5% NaCl solution of conventional casting and rapidly solidified Mg6ZnMn (ZM61) magnesium alloys. It is found that the mechanical properties of rapidly solidified ZM61 alloy are dramatically enhanced, with the ultimate strength increased from 335MPa to 460MPa (37% increment), which can be attributed to the formation of the refined dendrite microstructure and the strengthening MgZn2 phase distributed within the matrix. Furthermore, the rapidly solidified ZM61 alloy performs better in corrosion resistance than the extruded ZK60 and pure Mg alloys, suggesting that the rapid-solidification technique is a promising way to improve the strength and corrosion resistance of magnesium alloy for the structural and corrosive media utilization. [Copyright &y& Elsevier]

Abstract: It is well recognized that amorphous alloys usually offer much higher resistance to corrosion over their conventional counterparts in most aqueous solutions. Whereas, in this work, we reported an anomalous corrosion resistance of an arc melting Zr62.3Cu22.5Fe4.9Al6.8Ag3.5 crystalline alloy, which was superior to that of the same composition in glassy state in simulated seawater. It was revealed that the easy formation of a highly protective Zr- and Al-enriched oxide layer at the surface of the crystalline alloy is responsible for the extremely high corrosion resistance. The current finding not only presents an excellent alloy candidate for potential application in seawater but provides a new insight into the understanding of corrosion behavior of amorphous/crystalline alloys in demanding corrosive media. [Copyright &y& Elsevier]

Voids, helium bubbles and stacking fault tetrahedra (SFTs) are common irradiation-induced defects in face-centered cubic (FCC) metals and their alloys that have detrimental effects on their deformation behavior and lifetime. The formation mechanisms of voids and SFTs have been investigated in single crystals but the potential augmentation of these mechanisms by a heterophase interface has not been well studied. Here, using transmission electron microscopy (TEM), we report on the stability of both SFTs and voids at interfaces in an irradiated Cu/Ag nanolayered composite. With atomistic simulations, we show that the heterophase interface can promote the transformation of voids (<2 nm diameter) directly into SFTs. The interfacial misfit dislocations generate an atomically varying stress field that substantially reduces the activation barrier for the transformation at an interface compared to that in a single crystal or coherent interface. The transformation mechanism involves the sequential hopping of vacancies, starting at the interface and then later progressing to the nearest and next nearest atomic layers. The calculations further show that just a few helium atoms can hinder this mechanism and stabilize interfacial voids, explaining the coexistence of voids and SFTs near the interface observed experimentally. Last, the effect of stabilized defects at the interface on dislocation nucleation is studied via atomistic calculations employing quasi-static loading schemes. The results indicate that both voids and SFTs promote interfacial dislocation nucleation, which, in turn, damages the SFTs. These findings can provide the insight needed to design strategies for healing irradiation defects by interface engineering. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Inconel 718 was subjected to various heat treatments, i.e., solution heat treatment, standard ageing treatment and standard ageing plus 700 °C thermal exposure. The mechanical properties of the alloys were determined using tensile tests and Charpy pendulum impact tests at 650 °C and room temperature, respectively. The highest yield strength of 988 MPa was attained in the standard aged specimen, whereas a maximum impact toughness of 217 J cm −2 was attained in the solution-treated specimen. After thermal exposure, the mechanical properties of the specimens degrade. Both the yield strength and impact toughness decreased monotonically with increasing thermal exposure time. Subjected to a 10000-h long-term thermal exposure, the yield strength dramatically decreased to 475 MPa (almost 50% of the maximum strength), and the impact toughness reduced to only 18 J cm −2 . The microstructures of the specimens were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Coarsening of γ′ and γ″ and the transformation of γ″ to δ-Ni 3 Nb was observed after thermal exposure. However, a complete transformation from metastable γ″ to δ-Ni 3 Nb was never accomplished, even after the 10000-h long-term thermal exposure. Based on the obtained experimental results, the effects of the microstructural evolution on the mechanical properties are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Li can significantly decrease the degradation rate for Mg-based and Zn-based alloys. • Both tensile and compressive strain would promote the anode dissolution rate of both Mg-based and Zn-based alloys. • Tensile and compressive strain can increase the strain energy and decrease the energy barrier of reaction. • Electron polarization between solute atoms and solvent atoms are the main causes of the change of surface properties. Using density functional theory and an improved Butler-Volmer model, we comparatively investigate the underlining mechanisms of solute alloying and mechanical straining on the electrochemical polarization and degradation behaviors of both Mg-based and Zn-based alloys. Our results suggest that some elements such as Li can potentially decrease the degradation rates for both alloys, while others like Fe, Ni, Cu, and Al, will play an opposite effect. By introducing the scaled strain energy to study the strain effect on the degradation kinetics of both alloys, we further reveal that both tensile and compressive strain would promote the degradation rate by decreasing the activation energy barrier. [ABSTRACT FROM AUTHOR]

The industrial applications of Mg and its alloys are restricted by their poor corrosion resistances, owing to the rapid dissolution and hydrogen evolution behaviors. In this study, a sequentially bridged reduced graphene oxide (RGO)/bistriethoxysilylethane (BTSE) coating is successfully grafted on the surface of Mg alloy substrate, to simultaneously inhibit the corrosion and wear behaviors. It exhibits well-aligned biomimetic nacre-like "bricks and mortar" structure connected by covalent bonding networks, consisting of the Si-O-C bonds between the RGO sheets and the Si-O-Si bonds derived from BTSE self-crosslinking reactions. The reduced porosity and defects lead to a high continuity and integrity of the RGO/BTSE coating, which decreases the corrosion rate by an order of magnitude compared with bare Mg substrate and RGO coated sample, owing to the enhanced barrier effect and weakened galvanic corrosion. In addition, the hybrid coating also performs well anti-wear property due to the intrinsic lubrication of RGO sheets, which can protect the substrate from friction and wear. The wear rate decreases from 3.5 × 10−3 mm3N-1 m-1 of bare Mg alloy to 5.13 × 10-5 mm3N-1 m-1 of RGO/BTSE coated sample. The interlayer slipping between the RGO sheets effectively decreases friction resistance, although the incorporation of BTSE slightly increases their shear resistance. [ABSTRACT FROM AUTHOR]

In order to expand the applied range of Mg alloy, a variety of coatings have been designed to improve their corrosion and wear resistance. Here, we report a 3-aminopropyl triethoxysilane (APTES) modified Mg(OH) 2 /reduced graphene oxide (RGO) hybrid coating with integrated anti-corrosion/wear property on Mg alloy, which is prepared by in-situ crystallization using a facile hydrothermal method. The ultra-thin Mg(OH) 2 /RGO layer with 250 nm exhibits a dual-structure, in which the inner layer is composed of Mg(OH) 2 , and then RGO sheets hybrid with Mg(OH) 2 via the hydrogen bond to form the outer layer. The lubrication of RGO sheets and the high hardness of dense Mg(OH) 2 give rise to the significant decrease of wear rate, which is two orders of magnitude less than that in Mg substrate. Next, the APTES layer effectively fills the pores and defects on the surface of Mg(OH) 2 /RGO via the Si-O-Mg and amide bond, and it forms a barrier film enriched with Si-O-Si bond via the self-crosslinking reaction. The effective combination of inorganic and organic layer contributes to the improved anti-corrosion property. Unlabelled Image • Ultra-thin Mg(OH) 2 /RGO-APTES film is constructed by a hydrothermal method. • The composite coating shows an integrated anti-corrosion/wear performance. • The enhanced barrier effect is ascribed to the cross-linking effect of APTES agent. • A dual-structure contributes to the decreased friction coefficient and wear rate. [ABSTRACT FROM AUTHOR]