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Magnesium alloys have narrow available slip result from close-packed hexagonal structure that limit their processing properties. In the recent work, the Mg-2Zn-0.46Y-0.5Nd, as materials for degradable stents, was applied to produce as-extruded micro-tube with an outer diameter of 3.0 mm and a wall thickness of 0.35 mm by hot extrusion with an extrusion ratio of 105:1 at 653 K and rapid cooling. The fine microstructure of the dynamic recrystallization of as-extruded micro-tube could be preserved by rapid cooling such as water-cooled, resulting in more excellent mechanical properties relative to air-cooled micro-tube. The addition of rare earth elements Y and Nd results in continuous dynamic recrystallization dominated the dynamic recrystallization mechanism. During the hot extrusion process, the activation of the non-basal slip system, especially the pyramidal 〈 c + a 〉 slip, could significantly weaken the texture strength, and the as-extruded micro-tube exhibits weak "RE" texture components 〈 01 1 ¯ 1 〉 ∥ ED and 〈 1 ¯ 2 1 ¯ 1 〉 ∥ ED. Hence, the magnesium alloy micro-tube prepared by the rapid cooling has fine microstructure and weak texture, which is favorable for further process and governance. [ABSTRACT FROM AUTHOR]

Abstract: Magnesium alloys are promising candidate materials for cardiovascular stents due to their good biocompatibility and degradation properties in the human body. However, in vivo tests also show that improvement in their mechanical properties and corrosion resistance is necessary before wide application. In this study, cyclic extrusion compression (CEC) was used to enhance the mechanical properties and corrosion resistance of Mg–Zn–Y–Nd alloy. The results show that the grain size was greatly refined to 1 m after CEC treatment. The second phase distributed along the grain boundaries with grid shape and nano-sized particles uniformly distributed in grains. The elongation (), ultimate tensile strength (UTS) and yield strength (YS) of the CEC treatment samples were 30.2%, 303 MPa and 185 MPa respectively. The CEC treated samples showed homogeneous corrosion because of the grain refinement and the homogeneous distribution of nano-sized second phase. The corrosion current density of the alloy decreased from 2.810 A/cm to 6.610 A/cm after CEC treatment. Therefore, improved mechanical properties, uniform corrosion and reduced corrosion rate could be achieved by CEC. [Copyright &y& Elsevier]

The hydration process of blended cementitious materials is primarily affected by the effect mechanism of supplementary cementitious materials. This study utilizes electrochemical impedance spectroscopy (EIS) method to investigate the hydration kinetics of cementitious materials incorporating metakaolin (MK), quartz (Q) and limestone powder (LS). The experimental results reveal the influence of MK+Q+LS on the hydration kinetics, phase assemblage, and microstructure of the blended systems. Besides, the electrochemical impedance response of blended cement materials exhibits variation based on the MK contents and the curing age. Furthermore, the resistance of the continuously connected micro-pores (R ccp) in the blended cementitious material progressively increases throughout the hydration process. The inclusion of MK reduces the R ccp values at early ages, while contributes to an increase in R ccp values from 7 days onward. Additionally, positive correlations are established between the R ccp value and compressive strength/heat release across different MK contents and curing ages. The combination of R ccp values and other characterization method can effectively reveal the microstructure evolution process. Therefore, as a nondestructive method, EIS can be effectively applied to predict the hydration of cementitious materials and the mechanical properties. • System with 40 % MK and 60 % quartz, simulated as low-grade calcined clay, exhibit comparable compressive strength to OPC. • The R ccp value, associated with the connected pores, exhibits a correlation with compressive strength and heat release. • R ccp values is related with the filler effect, carboaluminate formation effect and the pozzolanic reaction effect of MK. [ABSTRACT FROM AUTHOR]

Highlights: [•] Microstructure evolution of Ca-def HA coating was systematically investigated. [•] Poor crystalline Ca-def HA has been formed at the deposition time of 5min. [•] Reasons for direct formation of Ca-def HA coating on Mg–Zn–Ca alloy are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Besides common immersion tests, it''s essential to investigate biocorrosion of degradable magnesium alloys in physiological environment under stress that bone implants bear in vivo. Using self-designed immersion method simulating in vivo conditions and conventional immersion test, corrosion morphologies and pH variations of the coated samples with or without compressive stress and the substrate alloy were studied. Results showed that the applied stress can change the degradation mode of coated samples and promote corrosion process, causing peeling-off locations on the coating and continuous increase of pH value. Meanwhile, biocompatibility of the coated samples was not apparently affected by the compressive stress. [Copyright &y& Elsevier]

Magnesium alloys are considered to be one of the most promising stent materials due to their good biological compatibility and biodegradable properties. However, the poor workability at room temperature restricts the processing of high-precision micro-tubes for the application as stent materials. In this study, Mg–Zn–Y–Nd alloy tube blank was firstly produced through hot extrusion. By multi-pass cold drawing combining with interpass annealing, the extruded tube blank can be processed into high-precision micro-tube with an outer diameter of about 2.0 mm and a wall thickness of about 0.15 mm. The drawn micro-tube after annealing exhibits improved mechanical properties with an ultimate tensile strength of about 298 MPa and a large breaking elongation of up to 20%. Meanwhile, the micro-tube shows good corrosion resistance with a trend of uniform corrosion in simulated body fluid solution. The investigation revealed that a significant improvement in the mechanical properties is mainly attributed to grain refinement and texture weaken, while the good biodegradable properties is related with the low density of crystallographic defects as well as fine and homogeneous microstructure. As a result, the successful processing of magnesium alloy micro-tube provides the precursor for laser engraving stents. [ABSTRACT FROM AUTHOR]

• PL additive had a diminishing retarding effect on cement hydration. • Appropriate dosage of PL had positive effects on the work performance of cement-based materials. • PL could increase the dispersion of cement system. The application of lignin dispersants in cementitious materials has been limited due to its strong retarding effect on cement hydration. In this study, polyaniline modified lignin (PL) was prepared to be as a new lignin additive to increase the dispersion of cement system and maintain good mechanical properties of cementitious materials. This investigation systematically revealed that different contents of PL (0%, 0.5%, 1.0%, 2.0%) had various effects on the early hydration, the work performance and the microstructure of cement paste and mortar. Appropriate dosage of PL was beneficial to achieve better dispersion and improve the fluidity of cement system. The retarding effect on cement hydration was significantly reduced by PL, compared to unmodified lignin. When the content of PL was 0.5% and 1.0%, the mechanical properties of the mortar was maintained as well as mortar without PL. However, excessive content of PL (2.0%) decreased the flexural strength and compressive strength significantly. XRD and TG tests exhibited that no new hydration products were generated and the formation of calcium hydroxide was inhibited after the addition of PL. Besides, SEM and MIP results showed that low dosage of PL could decrease the porosity due to the filling effect. When the dosage of PL in cement exceeds 2.0%, the structure was more loose and porous, attributed to the delayed hydration and air entertainment. The dispersion mechanism was also discussed and ascribed to electrostatic repulsion caused by PL adsorbed on the surface of cement particles and the steric effect due to the branched chains of PL. This study provides a new idea for high-value application of lignin and the promotion of low-carbon building materials by using renewable resources. [ABSTRACT FROM AUTHOR]

Abstract: The microstructures, mechanical and corrosion properties of three extruded Mg–2Zn–0.46Y–xNd alloys (x =0.0, 0.5, 1.0wt%) were studied by optical microscopy, scanning electronic microscopy (SEM), electrochemical measurements and tensile tests. Microstructural observations indicated that Nd led to the uniformity and the variation of morphology of major second phase; tensile tests showed that Nd can improve the ductility at moderate amount (0.5wt%) and will be detrimental up to 1.0%; Mg–2Zn–0.46Y–0.5Nd alloy exhibited excellent mechanical properties (σ b , 269.0MPa, σ 0.2, 165.6MPa and elongation, 24%); electrochemical tests revealed that Nd can enhance the corrosion resistance and Mg–2Zn–0.46Y–1.0Nd alloy had lowest corrosion current density, which was reasoned that the line-shape and rodlike NdZn2 phase might serve as corrosion barriers and the dissolved Nd can raise the electrode potential of the matrix. [Copyright &y& Elsevier]

Abstract: Magnesium alloys have been widely investigated in the field of biomaterials due to their moderate mechanical properties close to human bone and gradual degradation in human physiological environment without second surgeries. But results from clinical studies showed that magnesium implants suffered from too rapid degradation in human physiological environment. To reduce the degradation rate of magnesium alloys, surface modification is essential and effective besides element alloying. In this study, TiO2 films were deposited on Mg–Zn alloy by direct current reactive magnetron sputtering. The morphology and structure of the films were characterized by atomic force microscopy (AFM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The corrosion resistance in simulated body fluid (SBF) at 37°C was evaluated by potentiodynamic polarization and hydrogen evolution tests. The corrosion behavior of the samples was investigated by SEM with energy dispersive spectroscopy (EDS) after immersion for different periods. The results showed that the compact films were composed of particles with the size of about 100nm and could effectively improve the corrosion resistance in SBF. After immersion for 10 days, the corrosion rates of the substrates and samples with TiO2 films were 4.13mm/y and 1.95mm/y, respectively. During the immersion, the TiO2 films could induce the growth of hydroxyapatite (HAp) to improve the bioactivity of the samples. [ABSTRACT FROM AUTHOR]